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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