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Subject: Re: auotmatic gain control circuit
Date: Sat, 11 Jan 2003 04:43:16 -0700
Organization: Posted via Supernews, http://www.supernews.com
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On 11 Jan 2003 00:21:32 -0800, firstname.lastname@example.org
> I am trying to build an automatic gain amplifier for bandwidth of 160
>MHZ with ripple less than 0.1 dB. I tried to use a JFET as a variable
>resistor, but the dynamic range is not large enough (require at least
>10 dB) and I am getting signal distortion.
> Does anyone have experience in building this kind of circuit?
Yes.............But your leaving out alot of the finer details on this
What Op-Amp are you using?(part number) If not, Is this an RF amp?
I'm only assuming this by the bandwidth.
Have you tried using a transistor inline with the drain and the source
in the feedback loop? You may have to tie the base to the collector
and this will control gain much better than just the JFET by itself.
Try a couple bias resistors around the transistor which are variable
untill you find the range you want. Use plently of decoupling
caps(0.1uF) in your design.
For this circuit you may want use the dead bug technique, where
you place an op-amp or an IC upside down on a copper clad board
and make large holes for connections, and use the entire surface of
the copper for ground, then solder in parts directly on the pins of
the IC. What you have is nest of parts floating above the board, but
the results will better than using a bread board or wire wrap.
I don't have all answers for you, I hope this will give some ideas on
improving you amplifier.........O.K
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