Date: Sun, 28 Nov 2010 07:14:02 -0800
From: jimlux <jimlux@earthlink.net>
Subject: Re: [TowerTalk] Tuners
I think that's a general problem in the ham radio equipment world.
There's no "real" objective definition for "handles 1.5kW"... is that
1.5kW into any load? 1.5kW into a matched load? 1.5kW when immersed in
carefully stirred and refrigerated cooling oil?
And that's not even considering the usual implied duty cycle (e.g. 1.5
kW PEP on SSB is somewhat different from a 20 minute bulletin
transmission on RTTY).
## Then we have mosely, with their.. '5kw rated traps'.
Mosely engs tell me that was INPUT power. They also assumed
60% eff...so 3 kw pep out. Wait. it gets better. Eng tells me they also
assumed a 20% duty cycle....so it's really good for .2 x 3kw = 600w CCS.
On CW, they rate em at 2.5 kw. Same deal, but this time it's not only
input power, it's also a 40% duty cycle, so again, 600W average.
I asked Mosely, to cut to the chase, and what's the rating on RTTY.
Their answer was... "600 w... but only where the swr is flat". Good thing
I didn't spend huge $$ on a PRO-96. I would have vaporized it.
In the commercial world, one typically sees ratings with a specified
mismatch (e.g. 2:1 VSWR) and the implication is that this is at any
phase angle.
ARRL has done a bit towards testing under somewhat standardized
conditions, but more from a "what's the loss under some not too
difficult to setup tests" standpoint.
## The arrl used a bank of switched globar [ on inductive] type sp
resistor's to test various loads. I think the worse was a 12.5 ohm resistor
[4:1 swr]. Now they could have also used a 200 ohm resistor, and had the
same 4:1 swr. Now what are the chances of having a 4:1 load that consist
of a 12.5 OHM, PURE RESISTIVE LOAD, and NO reactance....abt zero %.
What they really need to do is put a vac var cap in parallel with the globar,
and simulate some real world conditions, and none of those will consist of
zero reactance loads.
And, various online ham writers have done some analysis (and testing) on
some moderately common scenarios.
There's also an enormous amount of repeating in one form or another
guidance from the books by Terman and LaPorte.
What I'd like to see is some work looking at real components used in
real tuners. Just how much dissipation is there in those ceramic caps
used in the LDG or SGC tuners? Ditto for the inductors.
## coils typ have UN loaded Q's from 100-800. Air variable caps
are way higher than that. Ceramic vac caps are typ 5000.
## Ceramic caps, like HEC brand, all that has ratings vs freq.
## No rocket science here....provided we know exactly what the load
the tuner see's. The peak/average current's + voltages can all be
determined in software.
## 3/8" ribbon coils are the eq of 1/4" tubing. 8 ga wire = .128"
## rauch claims..with any T network tuner, MIN loaded Q occurs when
High C is used [ low L]. On any PI network, it's just the opposite.
Low loaded Q = low C and high L.
## A G5RV that's 102' long originally was a 20m ant, that operates
on it's 3rd harmonic. That's no different than using a 40m dipole
on 15m. How we got from using a G5RV on 20m....to using the same
G5RV on 160-10m is beyond me. The folks with G5RV's and tuners on 80m,
always seem to be way down in sig strength, from folks with full sized 80m
ants.
Jim VE7RF
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