[Premium-Rx] Simple clean audio amp

[Brooke Clarke]

Hi Tim:

Some years ago I wanted to monitor the military HF frequencies and had 
the exact problem.  The solution was to build an audio based squelch 
circuit based on a magazine article.  This book sized solid state unit 
was placed between the radio and a speaker.

73,

Brooke Clarke, N6GCE

-- 
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Tim Shoppa wrote:

>Ka9p at aol.com wrote:
>  
>
>>I've finally reached the point of frustration with a couple of radios and 
>>would like to add a simple, clean outboard amp to the back of them, something on 
>>the order of 2-5 watts into 8 ohms, very good THD specs, at 12 vdc.
>>
>>Can anyone suggest any source of reasonably priced built or kit amps fit for 
>>this purpose?
>>    
>>
>
>LM380 and LM384 (Very common NatSemi audio amp IC's for circa 12V power
>supplies) are very commonly used. Official THD specs are not impressive
>but in the real world they do very nicely. They are DIP packages
>(so very easy to homebrew with Radio Shack proto boards)
>and deliver 2.5W/5W nominally (with much better THD if you do not go
>to the limits).
>
>For typical HF comms I'm personally satisfied with sub-percent THD.
>
>Here's a slightly different question:
>
>Say I've got 3 or 4 receivers, each tuned to sideband voice utility
>HF frequencies. I want to be able to monitor these frequencies
>but don't want to listen to the audio unless there's a signal
>present. This implies some kind of squelching ability. Radios are
>not identical but generally have AGC level out or IF out ability
>(actual levels vary from radio to radio.) Is there a "common" solution
>to this problem? I look at say old WJ price lists and see squelch as
>an extra-cost option, but I'm not about to pay those kinds of prices :-).
>
>With some radios I can turn AGC on and turn the RF gain down to the
>point where background static isn't objectionable, and then when a
>signal comes in the AGC takes over. But... AGC on my WJ-8716's doesn't
>work this way! (Is it supposed to? If I turn on AGC I have no manual
>RF gain control, and if I turn on RF gain control I have no AGC. This
>is different than my other receivers.)
>
>Tim.
>
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>
>  
>

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