[Collins] Re: 30L-1 Tuned Input

[Herzog]

I think the 11 percent reflected power is a minimum because of 
harmonics.  You are right in that you can't tune to "better" as long as it 
is a broadband cathode driven (grounded grid) final.
A test I ran with a 750 watt transmitter, (with it's harmonics filtered to 
over 40 DB down by a double tuned circuit), driving a 10 KW grounded grid 
final with broadband input showed that the harmonics were equally strong in 
either direction, only the fundamental was directional, (about 20 DB)..
    If one thinks about it, the current pulses that  of the tube  must 
include the fundamental and harmonics, and they must go somewhere, and so 
they go backwards and forwards. Most designs ignore this, at peril of 
failures and weird quirks.
Will, K 2 L B.


At 04:25 PM 2/3/03, Dr. Gerald N. Johnson, electrical engineer wrote:
>I'm not saying the cathode choke is necessarily faulty, just that its
>design is imperfect. And that imperfection may be adding to the
>difficulty of match. If the factory accepts 11% reflected power, you may
>never do better over the whole band no matter how much you fiddle. You'd
>be happier with the match if the Bird had 10' of RG-58 between it and
>the 30L1. Not that the match would be better at the input of the
>amplifier, just the Bird (and the driver) would see a better match just
>due to the loss of the coax.
>
>73, Jerry, K0CQ, Technical Advisor to the CRA.
>--
>Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
>Reproduction by permission only.
>Sponsored by the Collins Radio Association
>http://www.collinsra.com