[Amps] parasitic LC>load?

[Ian White, G3SEK]

R. Measures wrote:
>> Been thinking.
>>
>> If some of these rigs 'want to' go parasitic, would it be beneficial 
>>to help them via a broadband VHF resonant circuit that is coupled to 
>>the HF RF tank with that VHF LC discharging into a dissipative  side-load?
>>
>According to a friend who used to work for an amplifier manufacturer, 
>their 100kW MF-HF model had a resistance-wire hoop suspended in the 
>output compartment to dampen the compartment's VHF resonance.

It's a standard technique in amplifiers that have very large (like, 
walk-in) output compartments, where the cavity resonance could come down 
to 50-100MHz or even lower. No doubt John Lyles could tell us some 
stories, if he's around.

On the other hand, the cavity resonances in the output compartments of 
amateur-sized amplifiers are typically up in the UHF region, and are 
nothing we'd normally need to worry about.

But what amazes me is the number of amateur amps (both HB and 
commercial) that don't even *have* an RF-tight output compartment! The 
power supply, control wiring, mains wiring and even the RF input circuit 
are all swimming in RF. And then we wonder where instabilities come 
from...


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek