Re: [Amps] parasitic LC>load?

[R.Measures <r@somis.org>]

On Nov 11, 2004, at 11:45 PM, Ian White, G3SEK wrote:

> 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.

Interesting, Ian.  I have seen a number of Ham amplifiers whose output 
compartment is larger than a 2m repeater cavity.
> 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...

But of course, with so many possibilities, how is one to choose which 
is causing the hitch?
> --
> 73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.co.uk/g3sek
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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