Discussion:
OT: Vertical doublets (was: Home made Sigma-GT5 & KRC2 or SGC?)
(too old to reply)
JAKidz
2004-03-23 15:46:01 UTC
Permalink
Greetings:

Any suggestions on the optimum dimensions of a ladderline-fed
Sigma-GT5-like hatted vertical doublet that the KAT100 will tune
efficiently between 10 and 40 m? A Sigma-GT5-like design posted on
Usenet by AB6SJ takes advantage of the availability of aluminum tubing
in 6 foot lengths so it is a bit bigger than the GT-5.

W4RNL suggests a 44 foot horizontal doublet fed by ladderline is
an optimal doublet length for 10-40m. It's tempting to turn this doublet
vertical and shorten it with bar hats like the GT-5 if it is efficient.
But at least one antenna guru (whose call I can't find at the moment)
has stated repeatedly that W4RNL's doublet design is very inefficient
because of tuner losses. Who is right? What are the tuner efficiency
tradeoffs of having the structure resonance low, high or mid-frequency?

73,
John, K7JG
Don Wilhelm" (Don Wilhelm)
2004-03-23 16:35:02 UTC
Permalink
John,
The answer to your question does not have a simple answer.
If you know the antenna feedpoint impedance, you can use a program like TLW
(I believe you can download it from the ARRL site) to try different feedline
lengths that will be practical for your installation and see if you can find
a length that will be within the range of your tuner.

L B Cebik's 44 foot length is chosen because of the single lobe radiation
pattern for all bands 40 through 10 - LB assumes (correctly) that any
impedance can be matched by some method. Longer lengths will develop lobes
on the higher bands - and for a vertical that should translate to a
(desirable) low angle of radiation, but ground reflection will determine
just how low that angle really will be. Your proposed capacity hatted
dipole would have different feedpoint impedance than LB's 44 foot wire
dipole, but the radiation pattern (meaning = no extra lobes) should be
similar.

As far as tuner loss is concerned, that depends on the tuner characteristics
and how it is used. Commonly used T match tuners can have multiple settings
that will provide a match, and some of those settings are quite lossy. If
properly used, the tuner loss can be kept to a minimum. A properly
configured L network usually has a lower loss than the T match tuners, so
perhaps a KAT2 or KAT100 would be a better choice than a T match tuner.

A 44 ft dipole is not resonant on any ham band, so your question about high,
low resonance does not compute - it is in the class of a non-resonant
antenna.

73,
Don W3FPR

----- Original Message -----
Post by JAKidz
Any suggestions on the optimum dimensions of a ladderline-fed
Sigma-GT5-like hatted vertical doublet that the KAT100 will tune
efficiently between 10 and 40 m? A Sigma-GT5-like design posted on
Usenet by AB6SJ takes advantage of the availability of aluminum tubing
in 6 foot lengths so it is a bit bigger than the GT-5.
W4RNL suggests a 44 foot horizontal doublet fed by ladderline is
an optimal doublet length for 10-40m. It's tempting to turn this doublet
vertical and shorten it with bar hats like the GT-5 if it is efficient.
But at least one antenna guru (whose call I can't find at the moment)
has stated repeatedly that W4RNL's doublet design is very inefficient
because of tuner losses. Who is right? What are the tuner efficiency
tradeoffs of having the structure resonance low, high or mid-frequency?
Stuart Rohre
2004-03-23 22:28:00 UTC
Permalink
A lot easier than worrying and computing the exact impedance at the end of
the parallel feeder at the rig is to have handy 5 and 10 foot extensions of
line to add in to correct the impedance presented to the antenna tuner, IF
it has a problem.
-Stuart
K5KVH
JAKidz
2004-03-23 17:15:01 UTC
Permalink
Post by Don Wilhelm" (Don Wilhelm)
The answer to your question does not have a simple answer.
Dang.
Post by Don Wilhelm" (Don Wilhelm)
L B Cebik's 44 foot length is chosen because of the single lobe
radiation
Post by Don Wilhelm" (Don Wilhelm)
pattern for all bands 40 through 10 - LB assumes (correctly) that any
impedance can be matched by some method.
Understood. I'm aware of other arguments that this design is very
inefficient because of tuner loss. Translating from feedpoint impedance
calculated by a program such as Multinec to a tuner and what is
matchable and what isn't with the KAT100 is an area I don't understand
(yet).
Post by Don Wilhelm" (Don Wilhelm)
A 44 ft dipole is not resonant on any ham band, so your question about
high,
low resonance does not compute - it is in the class of a non-resonant
antenna.
Sorry for not being clear. I meant that given the effect of size on
feedpoint impedance and ultimately the tuner, how should the structure
be sized, the reasonance point for a smaller structure being higher
frequency and a larger lower frequency. Playing with Multinec, it looks
like the higher angle lobe that appears on 10 m with a 44' foot vertical
doublet is reduced with a shorter hatted doublet. It looks like the
physical structure of the Sigma 5 is resonant toward the higher
frequency size with matching done at the antenna feedpoint. Is this
still the design goal if ladderline is used and matching is by the
KAT100 at the transceiver feedpoint?

73,
John K7JG.
Don Wilhelm" (Don Wilhelm)
2004-03-23 18:50:01 UTC
Permalink
John,

I think we are mixing too many things together here - and that results in
more variables than my brain can handle!!! It is not really possible to
answer your question directly without a LOT of work, but I can give you some
pointers.

Firstly, a length of transmission line CAN be a tuner all in itself, it will
behave that way anytime there is SWR present on the transmission line - it
will transform impedance from its input to its output. That is one big
reason that one length line will work in a particular installation while
another will not. The half wavelength (or multiple) feedline case is easy -
that is the only time a feedline with SWR will have the same impedance at
the input and output ends. If one does not understand that, he (she) will
continually scratch their head wondering why a particular antenna fed with
ladder line works and another one doesn't - it depends very greatly on the
feedline length, and the characteristic impedance of the feedline is NOT the
impedance that is to be matched - these are quite different things.

First consider the antenna for its radiation pattern, then next for its
feedppoint impedance. (Or just the feedpoint impedance alone if the pattern
is not important to you.) Then separately consider the length of feedline
sufficient to reach from the antenna to the shack (this is the minimum
length, you can always add, but not subtract from this). That (after a few
calculations) will tell you what impedance you must feed in the shack. Then
finally, ask the question 'What kind of network do I need to transform that
impedance to the 50 ohms resistive that my transmitter needs?'. If you want
to avoid the calculations, you can put it up and make measurements with an
antenna analyzer and proceed with 'cut and try' methods.

I don't know of any other method to do it right. As for tuners, some tuners
are more efficient than others. It all depends on the Q of the components
and the magnitude of the circulating current - primary losses result from
the current through the inductor(s). Folks who want to generalize this by
saying that all tuners are lossy are technically correct, there is no free
lunch, but there are things that can be done to minimize the loss. We all
have to figure out just how much is tolerable for our installation and
budget - lower losses usually translate to increased cost - larger wire in
the coils to reduce the series resistance, better quality capacitors, lower
loss transmission line, and the list can go on and on.

One just has to 'make your choices' and do the best with what we have based
on those choices. There are no 'magic' answers.

73,
Don W3FPR

----- Original Message -----
Post by Don Wilhelm" (Don Wilhelm)
Post by Don Wilhelm" (Don Wilhelm)
L B Cebik's 44 foot length is chosen because of the single lobe
radiation
Post by Don Wilhelm" (Don Wilhelm)
pattern for all bands 40 through 10 - LB assumes (correctly) that any
impedance can be matched by some method.
Understood. I'm aware of other arguments that this design is very
inefficient because of tuner loss. Translating from feedpoint impedance
calculated by a program such as Multinec to a tuner and what is
matchable and what isn't with the KAT100 is an area I don't understand
(yet).
Post by Don Wilhelm" (Don Wilhelm)
A 44 ft dipole is not resonant on any ham band, so your question about
high,
low resonance does not compute - it is in the class of a non-resonant
antenna.
Sorry for not being clear. I meant that given the effect of size on
feedpoint impedance and ultimately the tuner, how should the structure
be sized, the reasonance point for a smaller structure being higher
frequency and a larger lower frequency. Playing with Multinec, it looks
like the higher angle lobe that appears on 10 m with a 44' foot vertical
doublet is reduced with a shorter hatted doublet. It looks like the
physical structure of the Sigma 5 is resonant toward the higher
frequency size with matching done at the antenna feedpoint. Is this
still the design goal if ladderline is used and matching is by the
KAT100 at the transceiver feedpoint?
73,
John K7JG.
Stuart Rohre
2004-03-23 21:59:01 UTC
Permalink
If you use ladderline feed to any antenna vertical or horizontal, you do not
need to match at the center feed point in Theory. Your Antenna Matching
Unit will tune both the line and the antenna to a match. You operate a
balanced (ladderline) at high SWR normally, and because of the higher
impedance of such lines and limited dielectric construction of them you
still have very low losses compared to coax feeds (even with SWR line loss).
The Sigma 5 of Force 12 only needs coils at the center feedpoint to match it
to coax without use of a perfect tuner. IF it were fed with balanced line,
the coils could go away, except for their effect in moving the length toward
resonance on the lowest bands, and easing the job of matching thereby.

Tuners have been widely mesured and have much lower losses in proper
adjustment than many hams believe as has been cited in the work of Witt and
others. What is rarely mentioned, is losses are related to having several
lossy components rather than fewer.

Typically, capacitors are lower loss than inductors. Having more inductors
gives somewhat higher loss. Thus, a tuner with only one capacitor and one
inductor is about the most practical minimum parts count, and this "L
network", has lowest tuner loss over Tees and Pis. A little studied area
is using the unbalanced L network to load a balanced line without use of a
balun. It can work. It would be interesting for someone to do a study on
it.
-Stuart
K5KVH
Stuart Rohre
2004-03-23 22:12:01 UTC
Permalink
But, with any reasonable commercial tuner out there on the market, You will
not have excess tuner loss nor inefficiency with the 44 foot doublet.

Experiments have not shown ANY heating in use of Dentron Super (high power)
or Junior (100 watt or less) tuners in several tests using a variety of
doublets or loops.

One has big coils and caps, the other minimal caps and coils to fit a QRP
sized case. Additional experiments with the 300 watt rated, but compact,
B&W tuner also did not show any heating. Transceivers were at 100 watts for
the tests. It was found that a Dentron or B&W did tune up with a more
readily found (higher Q) setting when the internal balun was bypassed and
the tuner was hooked by one foot of coax to an external 4:1 balun made by
Van Gorden. There was only one foot of coax from tuner coax output to the
balun input. At the time, the high impedance side of the balun was hooked
to ladder line feed of a 1149 foot circumference loop being tuned to 20m.
The Van Gorden device is obviously a larger inductor than either tuner's
internal balun, and most internal baluns of commercial tuners of that
vintage were voltage baluns. A current balun is preferred by the literature
on choosing baluns.

Don't let fear of tuner loss keep you from putting up the convenient 44 foot
antenna.
-Stuart
K5KVH
Ron D'Eau Claire
2004-03-23 17:50:01 UTC
Permalink
True, but keep in mind that ground losses (unless you live at the =
seashore)
pretty much wipe out any radiation below about 15 degrees in a vertical. =
The
44 foot vertical has maximum gain at about 15 degrees elevation, so it
actually represents probably the most efficient combination.=20

However, almost all verticals show maximum radiation at 0 degrees, and =
the
losses of any significant radiation below about 15 degrees are simply
accepted as part of the cost of not being in the middle of a huge, =
efficient
ground plane.

The "guru" who insists repeatedly that the losses in an ATU (or any =
matching
network) are significant is proof that saying something over and over =
again
doesn't make it so. The ATU easily can be the most efficient part of a
typical antenna system. As Don said, some ATU's are more efficient than
others. The L-match used in the Elecraft ATU's is, overall, the most
efficient system we have. But even the much-maligned "T" match networks =
can
be very efficient, if used correctly.=20

Ron AC7AC

-----Original Message-----
...Playing with Multinec, it looks like the higher angle lobe that =
appears
on 10 m with a 44' foot vertical doublet is reduced with a shorter =
hatted
doublet. It looks like the physical structure of the Sigma 5 is resonant
toward the higher frequency size with matching done at the antenna
feedpoint. Is this still the design goal if ladderline is used and =
matching
is by the KAT100 at the transceiver feedpoint?

73,
John K7JG.

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George, W5YR
2004-03-23 19:56:06 UTC
Permalink
Just a comment re tuner loss:

Frank Witt, AI1H, has written in QEX an excellent article on measuring tuner
loss using an impedance meter such as the MFJ 259B. I and several others
have performed numerous tests on various types of tuners and have yet to
find one with an inherent loss exceeding one dB. Most come in the range of
0.5 to 0.75 dB on 20 meters. One KW tuner was measured at 0.11 dB!

As a rule, and according to theory, L networks tend to show less loss than T
or PI networks.

Any tuner will exhibit larger losses when "mistuned" or when one attempts to
tune a load that is outside the envelope for the tuner.

There are excellent computer programs available for tuner analysis that
include calculation of losses in real components with finite Q values. They
confirm the minimal power loss in a well designed and adjusted tuner.

73, George W5YR
Fairview, TX
***@att.net
http://www.w5yr.com


----- Original Message -----
From: "Ron D'Eau Claire" <***@easystreet.com>
To: <***@mailman.qth.net>
Sent: Tuesday, March 23, 2004 10:48 AM
Subject: RE: [Elecraft] OT: Vertical doublets (was: Home made Sigma-GT5 &
KRC2 or SGC?)


The "guru" who insists repeatedly that the losses in an ATU (or any matching
network) are significant is proof that saying something over and over again
doesn't make it so. The ATU easily can be the most efficient part of a
typical antenna system. As Don said, some ATU's are more efficient than
others. The L-match used in the Elecraft ATU's is, overall, the most
efficient system we have. But even the much-maligned "T" match networks can
be very efficient, if used correctly.
Bob Tellefsen
2004-03-23 22:05:00 UTC
Permalink
Hi John
I'll swing at your questions.
First, you have to look at a nonresonant dipole along with its feedline
as a system. You can't take each part separately.

Let's talk about 40m for an example. With different combinations of
antenna length and feedline length, you can have a current maximum
(lowest impedance), a voltage maximum (maximum impedance), or
something in between at the shack end of the feeder.
I try to adjust such an antenna system for the current maximum at the
feedpoint. That makes a resistive load for the ATU, and allows use
of a simple 1:1 balun.

The rub is when you go multiband. Let's talk 20m now. Suddenly that
nice, tame low Z feedpoint is now a high Z feedpoint with lots of rf
voltage.
Very tough for an ATU to match. Also, not a good place for a balun.

On 15m, the third harmonic of 7 MHz, the feedpoint will again be low,
but it may not be exactly at a resonant point, meaning lowest reactance.
Ten meters again will be a high Z feedpoint. And so on. The WARC bands
fall in between these points.

Here I use a 60 ft fat non-resonant dipole on all bands, 10m down to 80m.
Since I'm out in the garage, it is easy for me to loop some additional
feedline
through the rafters to bring a middle-of-the-road impedance on all bands
to the feedpoint at the rig. This is not a perfect solution, as almost
every band
has some reactance along with the resistance. However, if it is not
extreme,
a good antenna tuner can cancel it during the matching process.

For contests, where I'm jumping from band to band, I find my 50 ohm:12.5 ohm
balun gives the best overall results. However, if I expect to spend a lot
of
time on one band, say 40m for ragchewing, I will pick my 1:1 balun, as it
works
best with this antenna/line combination in my situation. If 20m, I might
wind up
with my 50 ohm:200 ohm balun.

Since these nonresonant systems are all different, you have to figure out
what
antenna length you will have, how long a feeder you can run, and then in the
shack adjust for the best match under these conditions.

One way to do this, rather than run extra line through the rafters, is to
use extension sectons connected with banana plugs and jacks. This way, you
can have the shortest possible feedline coming to the shack, and then insert
correcting lengths as needed to
match any given band. This is an easy fix, especially if you have a band
decoder to control relays which can do the switching for you.

I hope this gives you some ideas, John.
Good luck and 73
Bob N6WG
Ron D'Eau Claire
2004-03-23 22:24:01 UTC
Permalink
I found that article useful too, George.=20

Having a several tuners handy, I took a slightly more "nuts and bolts"
approach to evaluating losses and hooked up two identical T-Match tuners
back-to-back. Measure the power in at the 50 ohm input and measure the =
power
out at the 50 ohm "output" with the second tuner running "backwards". I =
knew
what settings my antenna used on each band, so I set the ATU on the xmtr
accordingly and adjusted the second ATU for a 1:1 match at the rig with =
a 50
ohm dummy load and wattmeter attached.=20

I found attenuations of less than 2 dB across the band PROVIDED the =
T-match
ATU's were adjusted for the highest inductance at which a match could be
found. It is very easy to make it 'match' at much smaller inductance
settings in many cases, but sometimes the losses of the two tuners was =
in
excess of 8 dB in that state!=20

I suspect that's why some ops find that the inductor melts in their =
T-match
circuits.=20

One of the very nice T-network simulators that I like is W9CF's version =
at:
http://fermi.la.asu.edu/w9cf/tuner/tuner.html

I had another relevant experience using a commercial ATU that had nylon
"banana plug" connectors for wire antennas. I was loading a voltage-fed =
wire
and it worked just fine. But shortly after commencing a transmission I
smelled something and the SWR jumped off the scale. I was running 15 =
watts
output at the time.

Following the hot smell I discovered that the banana connector had =
melted
until the hot lead for the antenna shorted to the case. Inexpensive =
plastic
connectors are NOT good high-voltage RF insulators. There was a very =
good
reason why the "ancient ones" always used good-quality ceramic =
insulators
wherever high RF voltages might be present. Keep in mind that I melted =
that
connector in short order running ONLY 15 WATTS output!=20

Ron AC7AC

-----Original Message-----
...Frank Witt, AI1H, has written in QEX an excellent article on =
measuring
tuner loss using an impedance meter such as the MFJ 259B. I and several
others have performed numerous tests on various types of tuners and have =
yet
to find one with an inherent loss exceeding one dB. Most come in the =
range
of 0.5 to 0.75 dB on 20 meters. One KW tuner was measured at 0.11 dB!

As a rule, and according to theory, L networks tend to show less loss =
than T
or PI networks.

Any tuner will exhibit larger losses when "mistuned" or when one =
attempts to
tune a load that is outside the envelope for the tuner.

There are excellent computer programs available for tuner analysis that
include calculation of losses in real components with finite Q values. =
They
confirm the minimal power loss in a well designed and adjusted tuner.

73, George W5YR
Fairview, TX
***@att.net
http://www.w5yr.com
George, W5YR
2004-03-24 01:22:01 UTC
Permalink
Interesting finding, Ron . . .

Conventional wisdom holds that the loss in a tuner is predominately in the
inductor since even modest quality variable caps have very high Q and low
loss. So, the general idea when tuning a T-network or a PI-network - either
of which will have multiple combinations of L and C that appear to "match" -
is to find the tuning that uses the least possible amount of inductance.
I believe you will find that Witt has made that statement also.

I have verified this experimentally with my MFJ 989C tuners by using r-f
ammeters in the balanced line output and finding the tuning that gives
maximum line current. Invariably that tuning is the one that has minimum
inductance.

Another verification is the W9CF simulator you mentioned. Try different
values of Q for the inductance and then different values of L and C and the
optimum value will have the least inductance.

I have also investigated this using Reg Edward's tuner design program and
find the same result: least loss in the tuner with least inductance.

So, I find your conclusion and result that you seem to measure minimum loss
with maximum inductance difficult to understand or explain. Perhaps you can
shed some light for me.

Interesting . . .

73, George W5YR
Fairview, TX
***@att.net
http://www.w5yr.com


----- Original Message -----
From: "Ron D'Eau Claire" <***@easystreet.com>
To: <***@mailman.qth.net>
Sent: Tuesday, March 23, 2004 3:22 PM
Subject: RE: [Elecraft] OT: Vertical doublets (was: Home made Sigma-GT5 &
KRC2 or SGC?)


I found that article useful too, George.

Having a several tuners handy, I took a slightly more "nuts and bolts"
approach to evaluating losses and hooked up two identical T-Match tuners
back-to-back. Measure the power in at the 50 ohm input and measure the power
out at the 50 ohm "output" with the second tuner running "backwards". I knew
what settings my antenna used on each band, so I set the ATU on the xmtr
accordingly and adjusted the second ATU for a 1:1 match at the rig with a 50
ohm dummy load and wattmeter attached.

I found attenuations of less than 2 dB across the band PROVIDED the T-match
ATU's were adjusted for the highest inductance at which a match could be
found. It is very easy to make it 'match' at much smaller inductance
settings in many cases, but sometimes the losses of the two tuners was in
excess of 8 dB in that state!

I suspect that's why some ops find that the inductor melts in their T-match
circuits.

One of the very nice T-network simulators that I like is W9CF's version at:
http://fermi.la.asu.edu/w9cf/tuner/tuner.html

I had another relevant experience using a commercial ATU that had nylon
"banana plug" connectors for wire antennas. I was loading a voltage-fed wire
and it worked just fine. But shortly after commencing a transmission I
smelled something and the SWR jumped off the scale. I was running 15 watts
output at the time.

Following the hot smell I discovered that the banana connector had melted
until the hot lead for the antenna shorted to the case. Inexpensive plastic
connectors are NOT good high-voltage RF insulators. There was a very good
reason why the "ancient ones" always used good-quality ceramic insulators
wherever high RF voltages might be present. Keep in mind that I melted that
connector in short order running ONLY 15 WATTS output!

Ron AC7AC
Darrell Bellerive
2004-03-24 01:41:00 UTC
Permalink
Interesting discussion!

Anyone have any references to the efficiency of baluns with respect to
mismatched impedances? For instance the non-resonant doublet used on 40
through 10 metres.

I have always believed that baluns were only useful at the design
impedance and that losses would dramatically increase as the impedance
changed from the design value. Not to mention harmonic generation.

So if the loss due to a tuner is typically less than 1 dB over it's
matching range, what would the losses of a balun be over a similar range
of impedances?

Darrell VE7CLA K2 #1973
Post by George, W5YR
So, I find your conclusion and result that you seem to measure minimum loss
with maximum inductance difficult to understand or explain. Perhaps you can
shed some light for me.
Interesting . . .
Don Wilhelm" (Don Wilhelm)
2004-03-24 03:20:01 UTC
Permalink
Darrell,

Baluns differ in design, but the ferrite bead baluns are normally quite
low-loss (others are too). Charles Green has made several balun
measurements with mismatched loading and has not found any major problem
that I an aware of. Sorry, but I cannot recall where his results were
published. If he is still monitoring this reflector, perhaps we will hear
from him.

The main problem with using a balun on a non-resonant antenna/feedline
system is that the balun can be rendered ineffective when the feedpoint
impedance is high.
For good balun operation, a common rule of thumb is that the reactance
across the balun (from input ot output) be 10 times the impedance at the
output. If the impedance at the feedpoint is very high - say 3000 ohms at a
voltage feed point - then the input to output impedance of the balun should
be 30,000 ohms!!! That would take MANY beads - so many that it is not
practical.

The better solution is to use a length of balanced feedline that produces a
reasonable feedpoint impedance (somewhere between 20 and 600 ohms). Finding
a single length that will keep the feed impedance within that range for all
bands of interest is the real challenge - two bands is easy, three is a bit
harder, but 4 or more can produce hair pulling and other acts of
despairation <G>.

As an added point, I fail to see how a balun (or any other passive
component) can generate harmonics unless the core is driven into hard
saturation (a result of using a too small core). It takes a lot of power to
saturate the core in a properly designed balun.

73,
Don W3FPR

----- Original Message -----
Post by Darrell Bellerive
Anyone have any references to the efficiency of baluns with respect to
mismatched impedances? For instance the non-resonant doublet used on 40
through 10 metres.
I have always believed that baluns were only useful at the design
impedance and that losses would dramatically increase as the impedance
changed from the design value. Not to mention harmonic generation.
George, W5YR
2004-03-24 03:48:00 UTC
Permalink
Just a comment about balun material generating harmonics, Don:

Bead baluns are subject only to the common-mode current flowing on the outer
braid of the coax or the "parallel" current on a balanced line. The
differential-mode current does not affect the beads directly, unlike the
older voltage baluns in which the windings carried differential-mode
current. In those, the core material had to stand up to the full load
current.

While bead baluns can become hot at maximum legal power (or beyond!), they
are far less likely to saturate and have any effect on the differential mode
operation of the line.

In the case of a balun placed at a point of high differential-mode impedance
on the line, the core balun is much to be preferred over the bead balun for
the reason you cite: it takes a lot of beads to deal with several thousand
ohms of load impedance. With the core balun, the effectiveness improves as
the sq2uare of the number of turns while with a bead balun each bead adds
only its own incremental effect. But even the core balun itself in a current
balun configuration deals only with the common-mode current, not the load
current, and is relatively immune to saturation.

Incidentally, I transition my ladderlines to coax with five-bead baluns on
RG-8X. The measured loss of these baluns is about 0.1 dB on 20 meters using
the method developed by Frank Witt.


Good summary of balun operation - thanks for posting it.

73, George W5YR
Fairview, TX
***@att.net
http://www.w5yr.com


----- Original Message -----
From: "Don Wilhelm" <***@isp.com>
To: "Darrell Bellerive" <***@shaw.ca>; "Elecraft Email List"
<***@mailman.qth.net>
Sent: Tuesday, March 23, 2004 8:14 PM
Subject: Re: [Elecraft] OT: Now Balun effectiveness
Post by Don Wilhelm" (Don Wilhelm)
Darrell,
Baluns differ in design, but the ferrite bead baluns are normally quite
low-loss (others are too). Charles Green has made several balun
measurements with mismatched loading and has not found any major problem
that I an aware of. Sorry, but I cannot recall where his results were
published. If he is still monitoring this reflector, perhaps we will hear
from him.
The main problem with using a balun on a non-resonant antenna/feedline
system is that the balun can be rendered ineffective when the feedpoint
impedance is high.
For good balun operation, a common rule of thumb is that the reactance
across the balun (from input ot output) be 10 times the impedance at the
output. If the impedance at the feedpoint is very high - say 3000 ohms at a
voltage feed point - then the input to output impedance of the balun should
be 30,000 ohms!!! That would take MANY beads - so many that it is not
practical.
The better solution is to use a length of balanced feedline that produces a
reasonable feedpoint impedance (somewhere between 20 and 600 ohms).
Finding
Post by Don Wilhelm" (Don Wilhelm)
a single length that will keep the feed impedance within that range for all
bands of interest is the real challenge - two bands is easy, three is a bit
harder, but 4 or more can produce hair pulling and other acts of
despairation <G>.
As an added point, I fail to see how a balun (or any other passive
component) can generate harmonics unless the core is driven into hard
saturation (a result of using a too small core). It takes a lot of power to
saturate the core in a properly designed balun.
73,
Don W3FPR
Darrell Bellerive
2004-03-24 04:38:07 UTC
Permalink
Don,

Thanks very much for your detailed replies! I would really like to
understand this much better than I do.

Choke baluns seem to be the favoured solution, but I can't help but
wonder about the losses in the coax cable due to the impedance mismatch.
I can see where a choke balun of ferrite beads or from a coil of coax
will keep the RF off the shield of coax feedline when used with a
resonant dipole, but in multiband operation, I would expect the vast
differences in reactance and impedance would create vast differences in
losses. Particularly with long runs of coax.

As you have stated a doublet with open wire feeders can be built to have
a finite and manageable impedance range over two or three bands, but
getting a manageable impedance range on all 9 bands from 160 to 10
metres is almost impossible to achieve.

Therefore I would believe that a non-resonant doublet connected at the
feed point to a remote balanced-balanced tuner either directly or via
ladder line would have less loss across all 9 bands from 160 to 10
metres than would a coax fed doublet with a choke balun or current
balun.

Certainly, from a practical standpoint using the KAT2 or KAT100 and a
coax feedline to a choke balun or current balun fed doublet would be
easier to design and construct than coax feedline and control cable to a
remote tuner, however, I can't help but wonder what one looses in
efficiency for the sake of convenience. Does the decrease in loss
justify the complexity of the remote tuner? How much loss are we really
dealing with?

And finally yes, it is at saturation of a toroidal balun that harmonics
are generated. The source of my understanding about harmonic generation
is from an article by Richard L. Measures, AG6K where he states:
"More turns means more ampere-turns of magnetic flux in the balun's
core, and high magnetic flux densities can cause the ferrite-core to
saturate. This distorts the RF waveform and creates harmonics. These
harmonics extend well into the UHF TV band."

Darrell VE7CLA K2 #1973
Post by Don Wilhelm" (Don Wilhelm)
Darrell,
Baluns differ in design, but the ferrite bead baluns are normally quite
low-loss (others are too). Charles Green has made several balun
measurements with mismatched loading and has not found any major problem
that I an aware of. Sorry, but I cannot recall where his results were
published. If he is still monitoring this reflector, perhaps we will hear
from him.
The main problem with using a balun on a non-resonant antenna/feedline
system is that the balun can be rendered ineffective when the feedpoint
impedance is high.
For good balun operation, a common rule of thumb is that the reactance
across the balun (from input ot output) be 10 times the impedance at the
output. If the impedance at the feedpoint is very high - say 3000 ohms at a
voltage feed point - then the input to output impedance of the balun should
be 30,000 ohms!!! That would take MANY beads - so many that it is not
practical.
The better solution is to use a length of balanced feedline that produces a
reasonable feedpoint impedance (somewhere between 20 and 600 ohms). Finding
a single length that will keep the feed impedance within that range for all
bands of interest is the real challenge - two bands is easy, three is a bit
harder, but 4 or more can produce hair pulling and other acts of
despairation <G>.
As an added point, I fail to see how a balun (or any other passive
component) can generate harmonics unless the core is driven into hard
saturation (a result of using a too small core). It takes a lot of power to
saturate the core in a properly designed balun.
73,
Don W3FPR
Don Wilhelm" (Don Wilhelm)
2004-03-24 06:45:01 UTC
Permalink
Darrell,

See comments below:

----- Original Message -----
From: "Darrell Bellerive" <***@shaw.ca>
To: "Don Wilhelm" <***@arrl.net>
Cc: "Elecraft Email List" <***@mailman.qth.net>
Sent: Tuesday, March 23, 2004 10:35 PM
Subject: Re: [Elecraft] OT: Now Balun effectiveness
Post by Darrell Bellerive
Don,
Thanks very much for your detailed replies! I would really like to
understand this much better than I do.
-----------------------------------------
One just must 'hit the books' - the theory oriented sections of the ARRL
Handbook and the ARRL Antenna Book are good starting places - that was MY
initial education into a career in electronics. It is confusing at first,
but gets better with detailed study - beware, this is not an easy subject -
as one instructor put it, the study of electromagnetic fields is one area
where one must handle 4 dimensions to place a point - the 3 dimensions
describing the point in space and the time of the occurance of that point -
the only other discipline requiring similar analysis is 3 phase AC motors.
---------------------------------------------
Post by Darrell Bellerive
Choke baluns seem to be the favoured solution, but I can't help but
wonder about the losses in the coax cable due to the impedance mismatch.
I can see where a choke balun of ferrite beads or from a coil of coax
will keep the RF off the shield of coax feedline when used with a
resonant dipole, but in multiband operation, I would expect the vast
differences in reactance and impedance would create vast differences in
losses. Particularly with long runs of coax.
----------------------
The input to output impedance of the balun is what keeps the RF off the
outer coax shield - imagine that single parameter as an RF choke on the
outer side of the shield. The length of coax does not enter the picture
except when considering the loss of the coax due to its length and SWR.
Keep separate things separate - it makes understanding the system easier.
-------------------------
Post by Darrell Bellerive
As you have stated a doublet with open wire feeders can be built to have
a finite and manageable impedance range over two or three bands, but
getting a manageable impedance range on all 9 bands from 160 to 10
metres is almost impossible to achieve.
------------------------
True, 'we pay our money and take our pick' <G>
------------------------
Post by Darrell Bellerive
Therefore I would believe that a non-resonant doublet connected at the
feed point to a remote balanced-balanced tuner either directly or via
ladder line would have less loss across all 9 bands from 160 to 10
metres than would a coax fed doublet with a choke balun or current
balun.
-----------------------------------
For most installations - ABSOLUTELY - but there may be situations where that
is not practical. For another solution, Cecil Moore (ex W6RCA, now W5DPX)
described a system that switched feedline lengths in 1 ft increments to
achieve a match - a 130 ft. flattop antenna with a 450 ohm feedline variable
from 90 to 121 feet. He dubbed it his 'Mystery Antenna', and it works fine
for 80 through 10. I'm sorry, but I lost his website URL when he changed
callsigns.
-----------------------------------
Post by Darrell Bellerive
Certainly, from a practical standpoint using the KAT2 or KAT100 and a
coax feedline to a choke balun or current balun fed doublet would be
easier to design and construct than coax feedline and control cable to a
remote tuner, however, I can't help but wonder what one looses in
efficiency for the sake of convenience. Does the decrease in loss
justify the complexity of the remote tuner? How much loss are we really
dealing with?
------------------------------
Put the remote tuner at the antenna feedpoint or feed with low-loss parallel
line from the remote tuner to the antenna and the losses will likely be
small. Bottom line - keep the SWR on the coax low and the losses will
likely also be low - high SWR lines need to be open wire or ladderline
balanced lines. Keep in mind that it is not practical to go to extremes -
an SWR of 2:1 on most coax is quite tolerable when considering loss at HF
(VHF and UHF are quite different considerations - the loss becomes greater
as the frequency increases).
---------------------------------
Post by Darrell Bellerive
And finally yes, it is at saturation of a toroidal balun that harmonics
are generated. The source of my understanding about harmonic generation
"More turns means more ampere-turns of magnetic flux in the balun's
core, and high magnetic flux densities can cause the ferrite-core to
saturate. This distorts the RF waveform and creates harmonics. These
harmonics extend well into the UHF TV band."
-------------------------------------
Rich Measures is quite correct, BUT, at 100 watt levels, this is not a
concern with balun cores of any reasonable size. At 1500 watts, much more
care is required in sizing the cores. So the correct answer is 'It all
depends ...'.
------------------------------------
Post by Darrell Bellerive
Darrell VE7CLA K2 #1973
--------------------------------------

Best 73,
Don W3FPR
Mike Harris
2004-03-24 23:55:01 UTC
Permalink
G'day,

| Put the remote tuner at the antenna feedpoint or feed with low-loss
parallel
| line from the remote tuner to the antenna and the losses will likely be
| small. Bottom line - keep the SWR on the coax low and the losses will
| likely also be low - high SWR lines need to be open wire or ladderline
| balanced lines. Keep in mind that it is not practical to go to
extremes -
| an SWR of 2:1 on most coax is quite tolerable when considering loss at
HF
| (VHF and UHF are quite different considerations - the loss becomes
greater
| as the frequency increases).

I'm surprised the SWR police haven't descended upon this. Last time I
suggested that the antenna was the best place to put the tuner it really
wound them up.

Try running the feed impedance numbers of the Cebik 44ft doublet through
something like TLA which is bundled with the ARRL Antenna Book, Smith
Chart or even model it in NEC. You will discover that feeding it direct
with 50 ohm cable gives SWR's ranging from 1.45 up to 93.9 OK select say
150 feet of RG-213 and on those bands, shock horror, anything between
17.6% to 93.4% total line loss. At the rig end SWR's in the range 1.36 up
to 7.66 which are easily matched by the KAT100 but actually the whole
antenna is a dead loss on 5 out of 7 bands if fed with 50ohm co-ax.

So, the above quote is dead on.

Shack end ATU's can give a real false sense of what is happening.

I believe a reasonable rule of thumb is with 50 ohm cable anything outside
100R +/- j100 is potentially bad news.

Regards,

Mike VP8NO
#1400
Darrell Bellerive
2004-03-25 00:45:00 UTC
Permalink
Mike,

I can relate to this! I too have felt the wrath of the SWR police.

There seems to be a lot of confusion about SWR and losses. Maxwell's
book Reflections makes it clear that SWR is not a be all end all
measurement, and that SWR and feedline loss can be an acceptable design
compromise. But as you point out at 93.9:1 SWR the loss over 150 feet of
coax is 93.4%. Hardly acceptable at all to me, but I suppose if someone
had a legal limit power amplifier and wanted QRP ERP levels, it would
work.

I kept worrying that I had missed something new in multiband antenna
design; That someone had found a way to use coax and a balun to make a
feedline that had losses similar to open wire feeder over the entire
MF/HF spectrum regardless of mismatch.

There is also confusion as to the use of open wire feeder between the
antenna and tuner or mounting the tuner at the feedpoint of the antenna.
Some maintain that the feedline will contribute to the diversity of the
mismatch where others content that it is irrelevant. I would expect that
the losses would be lowest by mounting the tuner at the feedpoint, but
the losses in the open wire feeder may be low enough to live with a more
convenient place to mount the tuner. There is a need for more empirical
research.

So all in all I am still a big fan of the remote tuner. The big question
in my mind is whether Elecraft will offer such a product.
Post by Mike Harris
I'm surprised the SWR police haven't descended upon this. Last time I
suggested that the antenna was the best place to put the tuner it really
wound them up.
Try running the feed impedance numbers of the Cebik 44ft doublet through
something like TLA which is bundled with the ARRL Antenna Book, Smith
Chart or even model it in NEC. You will discover that feeding it direct
with 50 ohm cable gives SWR's ranging from 1.45 up to 93.9 OK select say
150 feet of RG-213 and on those bands, shock horror, anything between
17.6% to 93.4% total line loss. At the rig end SWR's in the range 1.36 up
to 7.66 which are easily matched by the KAT100 but actually the whole
antenna is a dead loss on 5 out of 7 bands if fed with 50ohm co-ax.
Stuart Rohre
2004-03-25 19:43:01 UTC
Permalink
Mike,
The point of an all around or compromise, non resonant antenna like the
Cebik 44 foot doublet is NOT to feed it with coax, ever, for multiband use!
Those antennas need parallel line feed, only.

Coax was developed for feeding resonant antennas that operate over a
relatively narrow part of the bands.

Parallel line was found early in radio history to work with low losses on
long or short runs at high SWR. In the earliest days, SWR at the rig was
not a problem. Folks either tuned their feeders or adjusted the coupling of
the rig by variable links, link tuning caps, or later the wide range Pi Net.
Modern solid state rigs leave out the variable, antenna tuning Pi net,
essentially selling transceivers lacking what came standard on rigs of the
50's. That is why a good tuner is essential to today's hamshacks.
73,
Stuart
K5KVH
Darrell Bellerive
2004-03-25 00:18:01 UTC
Permalink
Thanks for the great replies! See below for my comments.
Post by Don Wilhelm" (Don Wilhelm)
One just must 'hit the books' -
I have read ARRL's handbooks and antenna books, Maxwell's Reflections,
and Sevick's Building and Using Baluns and Ununs, as well as Roy
Lewallens' notes. There seems to be a bit of uncertainty with respect to
baluns in multiband antenna systems. One advocates putting the balun
between the transmitter and the tuner, the other states it make no
difference. One states that the balun will transform impedances, another
that impedance transformation is only valid over a small range of
frequencies. It looks like more empirical research is still required.
Post by Don Wilhelm" (Don Wilhelm)
Post by Don Wilhelm" (Don Wilhelm)
Put the remote tuner at the antenna feedpoint or feed with low-loss parallel
line from the remote tuner to the antenna and the losses will likely be
small. Bottom line - keep the SWR on the coax low and the losses will
likely also be low - high SWR lines need to be open wire or ladderline
balanced lines. Keep in mind that it is not practical to go to extremes -
an SWR of 2:1 on most coax is quite tolerable when considering loss at HF
(VHF and UHF are quite different considerations - the loss becomes greater
as the frequency increases).
---------------------------------
Every time I bring up the topic of remote controlled balanced tuners, I
get met with blank stares, or told to "just use a balun". I kept
thinking that I was missing something. Perhaps some new balun design or
particular combination of multiband antenna, and feedline dimensions;
Perhaps that someone had figured out a configuration using a balun and
coax feedline that had losses comparable to open wire feeders.

So all in all, I still believe that a multiband doublet antenna fed by a
tuner either via open wire or ladderline or directly will exhibit lower
losses than coax feed with a balun. While Lewallen's work on the
symmetry of the current balun being the same regardless of which side of
the tuner it is on, there is at least theoretically less loss with it on
the transmitter side. Whether that justifies the added complexity of the
balanced L network is doubtful.

So I am still an advocate of the remote tuner in situations where
routing open wire or ladder line feedlines is not convenient. I would
now however accept an unbalanced L network design followed directly by a
current balun whereas before this discussion I would not have accepted
the balun after the tuner or an unbalanced tuner design.

So Wayne and Eric, back to my original question: Any plans for a remote
controlled antenna tuner?

Darrell VE7CLA K2 #1973
Stuart Rohre
2004-03-25 20:03:01 UTC
Permalink
What is a balun? It is a transmission line and like all transmission lines
it has distributed inductance and capacitance. However, it is so compact,
it emphasizes the inductance and capacitance and like lumped L and C tuned
circuits; then, it must have a finite bandwidth, although as Sevick has
shown they can cover most of the bands readily with high efficiency. Use a
balun, that is fine, but remember there is no free lunch, and it is unlikely
to work 160 to 6m on one balun design.

Hams new to antennas and baluns worry too much about balun loss. Try the
one in your tuner, transmit some typical QSOs, then take the lid off and
feel the balun with RF power removed. Is it hot? Then you have a concern.
Is it cold to room temperature? Then it is doing its job without
complaint.

I am surprised that Lew first found that placing the balun at the input to a
transmatch was preferred over its placement at the output; but later backed
away from that. The reason is that thinking about the impedance
environment, and thus the voltages the balun would experience, obviously in
the input 50 ohm environment, of transceiver to tuner, you have lower
voltages than the variable voltages and impedance extreme excursions at the
output of a transmatch as you go band to band with matching one antenna.
Perhaps, I am missing something else?

In any case, local experiments have shown satisfactory performance, (no
heating) of internal baluns of rugged tuners operated well within ratings.
However, it was shown that an external 4:1 Van Gorden balun tuned up with a
more readily found setting of the tuner for the same band, with same larger
than normal loop antenna. Thus, there are balun differences everyone can
verify. A larger balun than the internal balun may be worthwhile to use
for peace of mind.

In buying used tuners, look inside and look at switch contacts for arcing
signs, and look at the balun for signs of heat. Check that caps plates do
not rub and are equal spaced. (However cap problems are easily fixed).
-Stuart
K5KVH
Stuart Rohre
2004-03-24 23:01:17 UTC
Permalink
Darrell,
When the coax is coiled as an RF choke, it does not have significant losses
as the inductance comes from the SHIELD acting as a coil. The choking
action is all outside the coax shield.

There will be some effect between the turns, of the dielectric outer jacket,
but nothing it can't tolerate.
The added capacitance may make the coax coil mostly effective over a given
set of bands, but you can alter that by varying the number of turns of coax
used.

Do use good quality coax, that will not have the center lead migrate thru
the dielectric by being coiled. Foam coax may suffer that if too tight.
Poly insulation as on old styles of RG 8 and RG 58 is preferred. Check the
diameter suggested for winding a coil of a given coax. IE check the minimum
bend radius. The same problem affects jumpers around rotating masts and
rotors below beams.

Coax is sometimes used to fashion traps for antennas but that is a different
set of loss considerations, where the center conductor and shield perform
both a capacitor and inductor role.
-Stuart
K5KVH
Stuart Rohre
2004-03-24 23:07:00 UTC
Permalink
Darrell,
I missed your main point which is true. Re Read your post, and have to
agree strongly: IN multiband use, the coax run becomes a loss mechanism as
the feedpoint values vary. The choke balun does not lose much, but the
length of coax with its distributed L and C and SWR upon it certainly will.

For multiband doublets, (dipoles) a balanced ladder line feed, or open wire
line, (any parallel line) will have lower losses due to varying SWR over
bands, as it is higher impedance than common coaxes.
This is for the case of long runs of coax vs. parallel lines.

Certainly, parallel line is the way to go for home runs of 100 feet or more,
and even for lesser runs where convenient.
-Stuart
K5KVH
Guy Olinger, K2AV
2004-03-24 02:33:01 UTC
Permalink
There are two issues here. One is using a vertical doublet instead of
horizontal. The other is tuner losses.

A vertical doublet will instantly drop the sum of your far-field power
by one half or 3 db UNLESS you are over saltwater or a copper plated
meadow.

If the radiation is vertically polarized, for all practical purposes
all radiation below the horizon (e.g., has to bounce) is absorbed by
ordinary ground. This is not true for horizontally polarized
radiation.

Salt water at the "bounce point", or sufficiently dense radials/ground
screen at bounce point overcomes the absorption AT THAT SPOT.

If you can support a forty meter 1/2 wave doublet vertically, the top
is at 65-70 feet. If you hang the doublet horizontally at the same
height, the doublet will be an excellent performer, and will not lose
energy "in the bounce".


Considering tuners, the enemy of tuners is circulating current in the
tuner's components, primarily the inductor(s). What is infrequently
expressed, is that from one angle the best tuners for QRP are the 1.5
kW models. As the matching problems become more unreasonable, the
circulating currents in the inductors go up.

Each configuration of tuner has its Achilles' heel, the matching
situation that causes it to be inefficient, that is have strong enough
circulating currents that the inductor (or other conductor) ohmic
losses become significant.

These losses are in db and equally affect QRP signals as QRO. There
are documented instances of small tuners suffering 3 dB internal
losses and more. 3 db lost out of QRP is 2.5 watts, and out of QRO is
750 watts. The first is barely a night light, the second is a heat gun
on high in an enclosed space. Oddly enough, the answer for either can
be a QRO tuner, which makes it at QRO by using MUCH larger conductors,
reducing ohmic losses to a few tenths of a dB.

The effect on far end for losing 3 dB is a lot worse for the QRP
signal which usually has little margin for readability at the far end.
We just don't hear about the 3 dB losses in a QRP tuner because it
doesn't set the tuner on fire at QRP like it would if you were trying
to run 1500 watts through it.

As to avoiding a tuner's Achilles heel, to avoid the circulating
losses, a knowledgeable ham can always design antenna and feedline to
be a good fit with a given tuner. HOWEVER, using a simple doublet and
balanced feed for multiple bands presents a RANGE of situations, at
least one of which will involve high circulating currents on just
about any tuner.

My 1.5 kW ATR-30 will handle it fine because the inductor is a
monster, and it has very low resistance. Does not ever get even barely
warm at 1.5 kW, even in contest operating. Therefore it will be very
efficient for my K2 QRP operation, where last smidgen of a watt
counts.

73, Guy

----- Original Message -----
Post by JAKidz
W4RNL suggests a 44 foot horizontal doublet fed by ladderline is
an optimal doublet length for 10-40m. It's tempting to turn this
doublet
Post by JAKidz
vertical and shorten it with bar hats like the GT-5 if it is
efficient.
Post by JAKidz
But at least one antenna guru (whose call I can't find at the
moment)
Post by JAKidz
has stated repeatedly that W4RNL's doublet design is very
inefficient
Post by JAKidz
because of tuner losses. Who is right? What are the tuner efficiency
tradeoffs of having the structure resonance low, high or
mid-frequency?
Post by JAKidz
73,
John, K7JG
Stuart Rohre
2004-03-25 21:04:03 UTC
Permalink
Guy,
I cannot find your assertion of 3dB loss from a vertical dipole supported in
any of the antenna literature.
(Some dozen books or more) Do you have a reference book?
Thanks,
Stuart
K5KVH
Wayne Burdick
2004-03-25 23:13:16 UTC
Permalink
Folks,

Let's wrap up the recent threads regarding antennas, please. There are probably
better places to discuss these topics at length.

Thanks,
Wayne
N6KR
--
http://www.elecraft.com
Guy Olinger, K2AV
2004-03-26 02:28:00 UTC
Permalink
Run it in any modeling program that has real ground parameters (EZNEC
3 for windows, etc).

In the ARRL Antenna book 18th edition, pp. 3-4 and 3-5, in the text,
also compared very plainly in figure 4. Taking the maximum gain at
7.41 in the pattern in figure 4A, you can see that the gain of the
vertical is about 0 dbi. If the downward radiation was reflected up
into the upper hemisphere, the gain should be AT LEAST 3 dbi.

This is as opposed to a 7 dbi gain over saltwater in figure 4B.

These sort of details are in every antenna book I have.

???

73, Guy.

----- Original Message -----
From: "Stuart Rohre" <***@arlut.utexas.edu>
To: "Guy Olinger, K2AV" <***@bellsouth.net>; "Elecraft Reflector"
<***@mailman.qth.net>
Sent: Thursday, March 25, 2004 3:03 PM
Subject: Re: [Elecraft] OT: Vertical doublets (was: Home made
Sigma-GT5 & KRC2 or SGC?)
Post by Stuart Rohre
Guy,
I cannot find your assertion of 3dB loss from a vertical dipole supported in
any of the antenna literature.
(Some dozen books or more) Do you have a reference book?
Thanks,
Stuart
K5KVH
_______________________________________________
You must be subscribed to post to the list.
http://mailman.qth.net/mailman/listinfo/elecraft
Post by Stuart Rohre
Elecraft Web Page: http://www.elecraft.com
Also see: http://www.elecraft.com/elecraft_list_guidelines.htm
Ron D'Eau Claire
2004-03-24 05:33:01 UTC
Permalink
Not interesting, Don , erroneous!!=20

Thanks... I said it exactly backwards. Yes, higher inductance produces
higher losses.=20

Even MFJ notes that users of its T-match ATU's should always find the
setting with the least inductance that will effect a match.=20

That'll shed some light on your confusion. Thanks for catching the =
error.=20

Ron AC7AC

-----Original Message-----
From: elecraft-***@mailman.qth.net =
[mailto:elecraft-***@mailman.qth.net]
On Behalf Of George, W5YR
Sent: Tuesday, March 23, 2004 4:20 PM
To: Ron D'Eau Claire; ***@mailman.qth.net
Subject: Re: [Elecraft] OT: Vertical doublets (was: Home made Sigma-GT5 =
&
KRC2 or SGC?)


Interesting finding, Ron . . .

Conventional wisdom holds that the loss in a tuner is predominately in =
the
inductor ...
Ron D'Eau Claire
2004-03-24 07:01:01 UTC
Permalink
As you have stated a doublet with open wire feeders can be built to=20
have a finite and manageable impedance range over two or three bands,=20
but getting a manageable impedance range on all 9 bands from 160 to 10 =
metres is almost impossible to achieve.
------------------------
True, 'we pay our money and take our pick' <G>
------------------------

Keep in mind that the impedance extremes are less extreme as the length =
of
the antenna goes up, measured in wavelengths. The impedance extremes are
usually found when the antenna is 1/2 wave or less long. As a wire is =
made
longer, the impedance at the current and voltage loops grows less and =
less
extreme.

The point is that if the system using an ATU to resonate a radiator and
match it to a 50 ohm transmitter output can handle the impedances at the =
low
end of the frequency range, it is likely to do FB on frequencies where =
the
radiator length is > 1/2 wavelength - certainly when it is > than 1
wavelength.

Ron AC7AC
Ron D'Eau Claire
2004-03-25 00:43:00 UTC
Permalink
Mike, VP8NO wrote:=20

I'm surprised the SWR police haven't descended upon this. Last time I
suggested that the antenna was the best place to put the tuner it really
wound them up.

Try running the feed impedance numbers of the Cebik 44ft doublet through
something like TLA which is bundled with the ARRL Antenna Book, Smith
Chart or even model it in NEC. You will discover that feeding it =
direct
with 50 ohm cable gives SWR's ranging from 1.45 up to 93.9 =20

-------------------------

I certainly agree about putting the ATU at the feed point. My preferred
installation is to drop open wire line from the center of a doublet =
straight
down to a balanced ATU near the ground where it can be kept out of the
weather and so the weight of the ATU doesn't have to be supported up =
high.
At the moment, when I drop the open wire straight down from my inverted =
V
doublet it is right at the shack window, so guess where my ATU is =
located? A
remote tuning balanced ATU would be very handy for other situations.=20

As several sharp ops here pointed out when we were discussing open wire
feeders a while back, one of the real advantages of the open wire lines =
in
the range of 450 to 600 ohms is that they show LOWER SWR's in typical
doublet installations. For example, a center fed antenna that is a full
wavelength long might show an impedance of about 2160+j1900 ohms =
resulting
in an SWR of 77:1 when fed with 50 ohm coaxial line. However, the same
antenna with a 450 ohm line would show an SWR of less than 9:1. That's a
huge difference that accounts for much of why open wire line is so =
efficient
with multiband doublets.=20

Indeed, a 66 foot center fed wire 30 feet up will show a maximum SWR on =
450
ohm line of 15:1 on any frequency from 7 to 30 MHz. Over most of that =
range
the SWR is in the range of 5:1 to 8:1.=20

The same antenna with 50 ohm line will show an SWR of 40:1 or worse on =
ALL
frequencies from 7 to 30 MHz except, of course, near 7 and 22 MHz where =
it's
self resonant.=20

Ron AC7AC
Charles Mabbott
2004-03-25 02:07:01 UTC
Permalink
The only thing I can add [if mobile] where the tuner is by the radio and
antenna is on trunk you are tuning a combination of the antenna and coax.
Now I have read the tuner should be [since it is tuning antenna] as close as
possible. However, for the purists I am not sure if the differences are
really that much. It just made sense in my case to put tuner as close to
antenna as possible. It seemed to make the tuner more stable while matching
the antenna during operation.

Chuck

-----Original Message-----
From: elecraft-***@mailman.qth.net [mailto:elecraft-***@mailman.qth.net]
On Behalf Of Darrell Bellerive
Sent: Wednesday, March 24, 2004 6:17 PM
To: Don Wilhelm
Cc: Elecraft Email List
Subject: Re: [Elecraft] OT: Now Balun effectiveness

Thanks for the great replies! See below for my comments.
Post by Don Wilhelm" (Don Wilhelm)
One just must 'hit the books' -
I have read ARRL's handbooks and antenna books, Maxwell's Reflections,
and Sevick's Building and Using Baluns and Ununs, as well as Roy
Lewallens' notes. There seems to be a bit of uncertainty with respect to
baluns in multiband antenna systems. One advocates putting the balun
between the transmitter and the tuner, the other states it make no
difference. One states that the balun will transform impedances, another
that impedance transformation is only valid over a small range of
frequencies. It looks like more empirical research is still required.
Post by Don Wilhelm" (Don Wilhelm)
Post by Don Wilhelm" (Don Wilhelm)
Put the remote tuner at the antenna feedpoint or feed with low-loss
parallel
Post by Don Wilhelm" (Don Wilhelm)
line from the remote tuner to the antenna and the losses will likely be
small. Bottom line - keep the SWR on the coax low and the losses will
likely also be low - high SWR lines need to be open wire or ladderline
balanced lines. Keep in mind that it is not practical to go to extremes -
an SWR of 2:1 on most coax is quite tolerable when considering loss at HF
(VHF and UHF are quite different considerations - the loss becomes greater
as the frequency increases).
---------------------------------
Every time I bring up the topic of remote controlled balanced tuners, I
get met with blank stares, or told to "just use a balun". I kept
thinking that I was missing something. Perhaps some new balun design or
particular combination of multiband antenna, and feedline dimensions;
Perhaps that someone had figured out a configuration using a balun and
coax feedline that had losses comparable to open wire feeders.

So all in all, I still believe that a multiband doublet antenna fed by a
tuner either via open wire or ladderline or directly will exhibit lower
losses than coax feed with a balun. While Lewallen's work on the
symmetry of the current balun being the same regardless of which side of
the tuner it is on, there is at least theoretically less loss with it on
the transmitter side. Whether that justifies the added complexity of the
balanced L network is doubtful.

So I am still an advocate of the remote tuner in situations where
routing open wire or ladder line feedlines is not convenient. I would
now however accept an unbalanced L network design followed directly by a
current balun whereas before this discussion I would not have accepted
the balun after the tuner or an unbalanced tuner design.

So Wayne and Eric, back to my original question: Any plans for a remote
controlled antenna tuner?

Darrell VE7CLA K2 #1973


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Ron D'Eau Claire
2004-03-25 21:55:01 UTC
Permalink
I wasn't aware that there was a "loss", but there is GAIN of a =
horizontal
antenna at a proper height above ground compared to a vertical. That is
caused because the horizontal forms a two-element parasitic array with =
the
earth. The angle of the main lobes from this array vary with the antenna
height.=20

For example, plugging a vertical into EZNEC working against a "typical"
ground will show just about 0 dbi at the peak of the lobes which are at =
26
degrees above the horizon.=20

A horizontal half wave at 1/2 wave above the ground has about 5.4 dbi =
max at
42 degrees above the horizon. To compare apples and apples, the =
horizontal
at the same elevation as the peak of the vertical's lobes - 26 degrees =
-
shows 4.3 dbi or 4.3 db more gain than the vertical at the same angle.=20

The reflection gain is what makes low horizontal antennas such superb
performers for short-haul conditions. As the antenna is brought down to
about 1/4 wave above the earth, the lobe moves straight up and shows =
more
than 6 dbi. Great for NVIS operation.=20

Ron AC7AC


-----Original Message-----
Guy,
I cannot find your assertion of 3dB loss from a vertical dipole =
supported in
any of the antenna literature. (Some dozen books or more) Do you have a
reference book? Thanks, Stuart K5KVH
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