At 09:17 AM 5/17/97 +0000, you wrote:
>Hi Phil,
>
>Warren Bruene gave me that same song and dance years ago, but he
>could never answer a few simple questions. I asked if the Collins
>PA's were tuned with a phase measuring meter installed in line
>between the PA and the exciter and the answer was no.
It sounds like asked and answered to me..he answered "no."
Perhaps he knew your background and didn't want to talk "out of
school" to a competitor. I think Mr. Bruene has more answers than
most of us have questions!
The phase measuring is done with the tuning meter in the amp.
Since the goal was lower distortion, why waste time measuring phase
shift anywhere but the source?
>I asked if the Collins KWM-2 and 30S1-2-3 always had the same phase
>shift in the tank when loaded to full output and the answer was
>"perhaps", if they are tuned exactly correct.
The tuning in the exciter is not critical. The tuning of the PA tank is.
That is why Collins put the tuning meters in the 30 series amps.
The phase shift is correct if the meter reads zero and is properly
calibrated.
>Anyone can test the validity of this claim for themselves by a simple
>analysis. Ask yourself what is the phase shift of the cable on each
>band from 10 meters to 80 meters. Next assume the amplifier input
>is tuned to resonance and calculate the phase shift in the input
>network.
The phase shift in the cable is only part of the total phase shift of
the SYSTEM...PA tank, tuned input, coax, and exciter tank.
>You'll find the phase varies greatly from ten meters to 80 meters,
>rotating through MORE than 180 degrees. With a VF of .6 the line is a
>full wave on ten, 3/4 wl on 15, 1/2 wl on twenty, 1/4 wl on 40, and
>1/2 wl on 80.
Again, this is compensated for by the sum of the parts of the total
SYSTEM.
>The phase shift of the line is 360, 270, 180, 90, and 45 degrees.
>The input circuit is a simple pi with the same Q (and phase shift) on
>10 through 40 meters, and changes to a very low Q L network on 80.
>The low Q L network has less phase shift than the pi.
Apparently you have access to a schematic and parts list. I'll take
your word for "simple pi."
As I stated earlier, this is all a moot issue. The SS exciter
and foam coax made it a dead horse. New distortion measurements
are needed to see what's necessary, if anything.
>
>There is no electrical way possible that phase shift excuse is
>correct. Early on Collins used to tell people thee longer line was
>needed for stability.
There is no aeronautical way possible that a bumble bee can fly.
How can furnishing a 20.5 piece of coax with each radio require an excuse?
Was there an over-stock of RG-8 at Collins, or a conspiracy with Belden?
(I don't recall any other manufacturer of amps giving me any coax of any
length.) I am sure the price of the coax was justified in improvement of
specs.
They might have "told people" but my post was right out of the manuals .
(Collins has a very stiff policy about keeping their engineering
in-house.")
These were the official operating instructions. Anyone can test the
validity of these instructions by measuring the distortion of a Collins
station with different lengths of coax. Trying to "out-engineer" or
re-invent a successful piece of Collins equipment is an exercise in
futility. It may take more time than you might want to spend on it.
(((73)))
Phil, K5PC
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