[Boatanchors] WTB - Antenna Tuner. . . . .

[The Pollacks]

I defer to Bob's interesting analysis, and it's one that I was unaware of. 

It may be of interest to the original poster if I comment on my personal
experiences of 40+ years of running balanced line with a variety of tuners.

I have used all of the following:  Homebrew link type tuner (butterfly dual
cap), Johnson Matchbox, Murch transmatch with home wound balun, Heath 2040,
various MFJ and TenTec tuners, and probably others.  Using low power (<150W
output), they all performed well with no RF in shack or TVI problems.  I
don't disagree that the MFJ types with baluns have greater loss, but don't
know if they're significant at this power level.  Never experienced SWR
drift, even on AM.

Where I did run into problems with RF in shack is when I acquired a linear,
in this case a 922L.  The RF problems were insurmountable with the tuners I
had, and I eventually replaced the balanced antenna, with its many
advantages, with a G5RV, which works quite well.

I don't know if I would have had more success with high power and a link
type tuner, but my home brew unit, long gone, would not have handled that
much power.  I do have some big caps, so maybe I'll get inspired to build
another one and try it!

Since the poster indicated that cost was a consideration, and power was
moderate, I think one of the coax type tuners would work adequately,
although not ideally, and worth trying considering the power and cost
limitations.

I am always impressed by the knowledge and generosity of those on this list!

Thanks
Ron K2RP

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Rob Atkinson
Sent: Thursday, December 10, 2009 4:27 AM
To: Boat Anchors List
Subject: Re: [Boatanchors] WTB - Antenna Tuner. . . . .

the vast majority of those commercial tuners that claim to handle
balanced line really don't, or rather don't do it properly or very
well.  I have worked hams who have given up on balanced line, or have
all kinds of RF problems only to find they are using some coax tuner
with a balun somewhere between the tuner and the balanced line, either
at the tuner or outside somewhere.

To properly tune balanced line with no issues (common mode, RF in the
shack etc. problems) you must tune the line with a link coupled
balanced tuner that floats the balanced line above ground.  The
Johnson matchboxes do this.  short of homebrewing (which is fine thing
to do) nothing else out there on the market does this.   you can buy a
twin coil balanced tuner from Palstar but it is not link coupled and
will therefore pass common mode RF.  There is information on-line on
how to homebrew a link coupled balanced tuner.   Don't fall into the
trap of trying to get a coax tuner to do everything.  Even if it seem
to work you'll have greater loss in the balun, and at higher power
levels, heating during long transmissions.  This will be noticeable in
vswr changing.

73

Rob
K5UJ
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