Alas, the poor G5RV. Now that its been flogged to
death, maybe we need a new target -- say the Windom?
Phil W7OX
On 8/4/16 10:22 PM, Wes Stewart wrote:
The tuner loss also depends on how it is
adjusted. For example the very popular high-pass
Tee with three adjustable elements has an
infinite number of possible combinations that
will effect a match on the same load Z. One of
them is the lowest loss solution, all of the
others aren't.
As I said earlier, in a letter to Dean Straw
dated February 2, 1994 I offered an example
where the SPC tuner, then current in the
handbooks, could be used to match an impedance
of 4.34 +j46 to 50 ohm. (I forget where this
came from but it was a real possibility) I
assumed Qc = 1000 and Ql = 300 (generous). I
used Touchstone to calculate the minimum loss
and maximum loss solutions The best case was 1.6
dB and the worst case was 7.8 dB.
With lower Q components, Qc = 500, Ql =200, the
losses were 2.4 to 9.5 dB!
Wes N7WS
On 8/4/2016 2:00 PM, Alan Bloom wrote:
> It's a pity that too many newcomers, as well
as many oldsters, are
> enamored by this piece of wire.
The G4RV is definitely a compromise antenna.
However its advantage is that is has low-enough
SWR to be easily matched by most tuners on a
number of bands.
> ... the horrific losses that could be
incurred even
> with high quality tuners,
It's true that tuner losses are the
manufacturers' dirty little secret. Loss is
rarely specified, partly because it can be
pretty bad, and partly because it is hard to
measure, but also because it is not constant -
it depends on the particular impedance being
matched.
One exception is the old Drake tuners. Their
Pi-L topology makes the loss almost independent
of the load impedance. If you can get it to
match, you know that almost all the power is
going into the feed line. For example, the
MN-2700 that I designed when I was at Drake was
specified at 0.5 dB maximum insertion loss and
I did a lot of testing and tweaking to achieve
that on all bands.
Alan N1AL
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