What the coax probably does is to supply the input C for to make an L
network in the PA into a PI. The L network leaves more mismatch while
the 29 pf per foot of the coax contributes to the match. Adding 56 pf to
the input connector may make the length of the coax less critical by
completing the PI to have a better match to the coax.
The Collins S-line and KWM2 had a limited loading range that made the
coupling line more critical. However, recent reports from the factory
indicate that the line length is less critical than previously required.
E.g. it has no effect on efficiency, input match, nor PA distortion.
When I worked with the designers of the 30S1, I didn't think to ask what
their reasoning was for the specific line length. The 30S1 does have a
set of tuned inputs.
73, Jerry, K0CQ, Technical Advisor to the CRA
--
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|