[Amps] increasing rf gain in driver stages ?

[Will Matney]

Dan,

Increasing gain can be had by resetting the bias if the transistor can stand the extra current through it. Also, you have to watch and not overload the stage ahead of it. However, you said it did better with about 4X extra drive. You would want to select a transistor that will withstand the amounts of current needed for the gain, and that it's frequency spec will match. Then re-do the bias so you acheive the gain with (or without) a new transistor. I'd check what the transistors specs are that's in there now. You may find it can handle it by doing the math. If it wont, look for one that will. Try looking through the Motorola books, etc. You might even be able to use a NTE, etc., replacement by crossing the original, and finding one similar but a little stronger.

Best,

Will


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On 3/15/06 at 6:59 PM Dan Sawyer wrote:

>All,
>
>I have an older transistor based transceiver. I have separated the 
>circuit and substituted an external signal generator in place of the 
>internal circuit. The circuit drives a mixer, by varying the amplitude 
>the mixer performs better with about a 4x increase in drive.
>
>My question is: what is the best way to increase the output of an 
>amplifier stage?
>
>Is it as simple choosing a transistor with a higher beta?
>
>There are two nearly identical stages. Both are NPN, the collector bias 
>is a resistor - inductor in series and the emitter circuit is a 
>capacitor - resistor in parallel.  Would reducing the resistor values 
>increase gain?
>
>If this question is too general - where is a good source for reading 
>about stage gain variables?
>
>Thanks - Dan
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