Posted by
Jim Brown-10 on
Dec 16, 2011; 7:00pm
URL: http://elecraft.85.s1.nabble.com/Balun-at-input-or-output-of-tuner-tp7087668p7102100.html
On 12/13/2011 12:53 PM, David Herring wrote:
> I'd like to ask a few questions.
David,
I hardly know where to begin in responding to your question. First, if
you want a self-supporting vertical antenna for 30-10M, there are some
really good choices that you can buy, that can be easily installed, that
can be fed with 50 ohm coax, that don't require radials, and that don't
require a balanced tuner. Loss in the feedline should be quite small if
you use RG8 (or even RG8X). Look at the Hy-Gain AV-640, which one of my
friends has used to work a lot of DX and do contesting from a small city
lot. You should use one of my chokes at the feedpoint of this antenna.
See my RFI tutorial, previously referenced.
IMO, balanced tuners and so-called balanced line are highly over-rated
solutions to problems that don't exist, or that could be better solved
with other far simpler and less costly means. IMO, the only GOOD use of
high impedance parallel wire feedlines is for very long runs -- 500 ft
or more. Likewise, I am not a fan of all-band non-resonant dipole
antennas, primarily because it is mechanically difficult choke them at
their feedpoint, which makes them noisy and puts RF on the feedline, but
also because their directional patterns vary widely with frequency.
Since you're trying to make a vertical work on all bands, I'm assuming
that horizontal antennas are not practical for you, hence the
recommendation for the AV-640. I'm not a fan of compact, multi-band
verticals below 40M because their efficiency tends to be poor, but at
30M and above they can work quite well.
As to RF in the shack -- nearly all RF in the shack problems are the
result of Pin One Problems in equipment. See the RFI tutorial for an
explanation and solutions. Also see the pdf on Ham Interfacing for
detailed instructions about bonding all of your gear together with short
lengths of copper wire. This kills hum and buzz, and makes a big dent in
the RFI you're experiencing. In extreme cases you may need to add
chokes to individual cables.
http://audiosystemsgroup.com/publish.htm73, Jim K9YC
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