[Amps] RF Choke At Amp Output ??

[Ian White GM3SEK]

Bill, W6WRT wrote:
>ORIGINAL MESSAGE:
>
>On Thu, 20 Aug 2009 01:37:32 +0000, RICHARD SOLOMON <w1ksz at q.com> wrote:
>
>>Several HB Amp circuits I see have an RF Choke across the Output. Other than
>>the obvious (protection against Plate Coupling Cap short), what are the other
>>Pro's and Con's ?
>>
>>I was thinking I should use an Ohmite Z-50 on the output of my 6 Meter Amp.
>>Comments ??
>
>REPLY:
>
>If your antenna is an open circuit for DC as many are, there would be a 
>HV pulse
>applied to the coax through the plate blocking cap. If the DC leakage on your
>coax and antenna is very low, this pulse could take a long time to decay. This
>pulse is equal to your HVDC and might be enough to arc the coax, the antenna
>itself or any switches, etc, in the feedline.
>
>It's been about 50 years since I used a Z-50, but from what I remember 
>it should
>be ok.  :-)

A shorted quarter-wave coaxial stub would make a more robust safety 
'crowbar' than a choke wound with fine wire, and it also attenuates the 
2nd harmonic in the FM band.


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek