[Elecraft] Remote Controlled Balanced Antenna Tuner

[Jeff Burns]

On my lot the most practical antennas are simple multi-band wire designs.
Unfortunately, there seams to be no way to avoid a lengthy run of coax to
get
into the shack. With the KAT2 I get a good match to the system I have now,
but I
am dissipating a lot of energy in the coax. I also have problems with the
coax
radiating. It seams what I need is a remote tuning unit.

The perfect tuner for my needs would be:
1. Remote mountable.
2. Auto Tuning.
3. Balanced output.

One and Two are available in several commercial units, but a balanced output
is
rare. I recently found this unit
http://www.hamware.de/hardware/tuner402/at402-e.htm it is remote mounted and
has
balanced output, but does not auto tune. Has anyone seen this unit? What do
you
think?

Now if Elecraft had a product that had all three of these characteristics
that
would be nice!

Jeff Burns
AD9T

[k***@ENTERZONE.NET]

Post by Jeff Burns
rare. I recently found this unit
http://www.hamware.de/hardware/tuner402/at402-e.htm it is remote
mounted and has balanced output, but does not auto tune. Has anyone
seen this unit? What do you think?

I believe I would go wth the KW model. That will cover you if you want to
run big power. Otherwise, you have to go out to your antenna and take
this thing out of line, blah blah blah. Other than that, it looks nice!


73 de John - KC4KGU
K2/100 #2490

[Bob Tellefsen]

Jeff
It sounds like you are missing a bet. Using 450 ohm feedline, you would
have less transmission line losses on all bands. Also, you could then use
the K2's ATU right in the shack and avoid the cost of an external ATU.
Here I use two 55 ft dipoles with 450 ohm feeders, and use the K2 ATU to
match on whatever band I want to operate.
73, Bob N6WG

-----Original Message-----
From: elecraft-***@mailman.qth.net
[mailto:elecraft-***@mailman.qth.net]On Behalf Of Jeff Burns
Sent: Thursday, August 08, 2002 3:17 PM
To: elecraft_list
Subject: [Elecraft] Remote Controlled Balanced Antenna Tuner


On my lot the most practical antennas are simple multi-band wire designs.
Unfortunately, there seams to be no way to avoid a lengthy run of coax to
get
into the shack. With the KAT2 I get a good match to the system I have now,
but I
am dissipating a lot of energy in the coax. I also have problems with the
coax
radiating. It seams what I need is a remote tuning unit.

The perfect tuner for my needs would be:
1. Remote mountable.
2. Auto Tuning.
3. Balanced output.

One and Two are available in several commercial units, but a balanced output
is
rare. I recently found this unit
http://www.hamware.de/hardware/tuner402/at402-e.htm it is remote mounted and
has
balanced output, but does not auto tune. Has anyone seen this unit? What do
you
think?

Now if Elecraft had a product that had all three of these characteristics
that
would be nice!

Jeff Burns
AD9T


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[Ron D'Eau Claire]

If you take a look at the schematic you will note that the ATU is a
simple pi-network with a balun at the input.

The fact is, you can use just about ATU in this way by putting a balun
at the input. A solenoid coil of good coax will work nicely. Use solid
dielectric to keep the center conductor from migrating through the foam
and shorting over time. It may be necessary to decouple any other wires
(power, remote control, etc.) for RF using ferrite cores or rods and/or
bypass caps, since the "case" of the ATU may be "hot" with r-f.

The inductances and capacitances in the ATU cancel out the reactance
presented by the radiator, and convert the resulting resistive value to
the 50 ohms your rig wants to see. Unless some of these components have
a great deal of loss, the matching network does NOT need to be
"symmetrical" or "balanced" for a good balanced feed.

I have done this sort of thing with manual ATU's and have been surprised
at how hard it is to produce an unbalanced feed when the feeders present
a low impedance load to the ATU.. I have found that it can make NO
difference in the balance whether I put a balun at the input or forget
about it. Indeed, I can hook an earth ground to the side of the feedline
attached to the ATU case and not see any significant difference in the
current flowing in that side of the balanced feeder. The reason is
obvious if you consider that when the feeder is presenting a very low
impedance load to the r-f most of the r-f will flow in the feeder
instead of any alternative paths. The balance is hardly affected even
when a "ground" wire is attached (so much for the quality of the r-f
ground provided by an 8-foot copper rod in wet soil outside the shack
window).

When you feed higher impedances, connections to the "ground" side of the
ATU can cause an unbalance. These "connections" might be by direct
contact or capacitive. But with the ATU well isolated from ground there
shouldn't be any such effects. That's why it is a good idea to decouple
any power or control lines and the outside of the coax from any stray
r-f with "chokes" to keep the ATU "floating" for r-f.

My experiences are with manual ATU's, as I said. I might question
whether small differences in the r-f potential within an automatic ATU
might have an effect on logic circuits that are not well bypassed or
otherwise well isolated. But I'd expect such problems to turn up with
ANY sort of antenna it might be used with. The ATU designer would be
very naive to assume that the case of the ATU was always held at a good
"r-f ground" in any Ham installation!

Ron AC7AC
K2 # 1289


On my lot the most practical antennas are simple multi-band wire
designs. Unfortunately, there seams to be no way to avoid a lengthy run
of coax to get into the shack. With the KAT2 I get a good match to the
system I have now, but I am dissipating a lot of energy in the coax. I
also have problems with the coax radiating. It seams what I need is a
remote tuning unit.

The perfect tuner for my needs would be:
1. Remote mountable.
2. Auto Tuning.
3. Balanced output.

One and Two are available in several commercial units, but a balanced
output is rare. I recently found this unit
http://www.hamware.de/hardware/tuner402/at402-e.htm it is remote mounted
and has balanced output, but does not auto tune. Has anyone seen this
unit? What do you think? Jeff Burns AD9T

[Robb Romans]

Post by Jeff Burns
On my lot the most practical antennas are simple multi-band wire
designs. Unfortunately, there seams to be no way to avoid a lengthy
run of coax to get
into the shack. With the KAT2 I get a good match to the system I have
now, but I
am dissipating a lot of energy in the coax. I also have problems with
the coax
radiating. It seams what I need is a remote tuning unit.
1. Remote mountable.
2. Auto Tuning.
3. Balanced output.

I have an approx. 80m horizontal loop antenna strung up in the trees=20
around my lot. My solution to the balanced antenna tuner problem is the=20
Icom AH-4 autotuner. It has one high-tension insulator for a "random=20
wire" and an insulated ground wingnut. I simply connect one end of the=20
ladder line to the antenna terminal and the other to the ground=20
terminal. Note that the chassis on this unit is thermoplastic and not=20
grounded, so the tuner "floats". I then run coax from the tuner into=20
the shack. The unit is marketed as weatherproof, but I mounted it under=20
an eave of my house for some weather protection.

It will tune 160-6m at very close to 1:1 all frequencies. No kidding.=20
There is an article on the web on how to use this tuner with other than=20
Icom rigs. See here:
http://www.hamoperator.com/ah-4_universal_interface.htm
http://www.hamoperator.com/ah4/index.html

Here are the negatives:
1. only connected to ONE antenna.
2. limited to 100W
3. $280

=09Hope this helps you,
=09Robb KD5SQF

- --=20
Robb Romans
Linux Commando
http://www.killsoft.com

"If ye love wealth better than liberty,
the tranquility of servitude better
than the animating contest of freedom,
go home from us in peace.
We ask not your counsels or arms.
Crouch down and lick the hands which feed you.
May your chains set lightly upon you,=20
and may posterity forget that ye were our countrymen."

=09=09Samuel Adams
=09=09Addressing the Philadelphia State House
=09=09Thursday August 1st, 1776