You and Carl are both correct, Pete. It depends upon what exciter you are
using.
When the 30L1 (and 30S1 for that matter) were driven by the S-Line or the
KWM-2
TUBE type exciters, the 20.5 ft. length of coax played a vital part in the
reduction of over-all system distortion. Here's why:
It was necessary to have an EVEN multiple of 180 degree phase shifts
between the
driver plate and the PA grid. The cable length PLUS the tuned input circuits
together accomplished this. An even multiple of 180 degree phase shifts is
necessary
because modulation components cause a change in the resistive PA cathode
impedance
which is translated to a shift in reactive impedance, at the driver plate,
resulting
in phase modulation of the driver and increases the TOTAL OVER-ALL
distortion of the
SYSTEM. The S-Line cable length was 20.5 feet, and the KWM-2 length was
23.0 feet
for minimum distortion.
Then enter the SS exciter. All bets are now off because of the nature of the
broad-band untuned output of the SS exciter. Only an array of test
equipment will
tell us if any improvements in distortion can be made via the coax length.
I will
take Carl's word for it, that it is now a moot issue, except for our BA
friends
who still use those Collins exciters.
(((73)))
Phil, K5PC
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