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active antenna attenuator, what value of pot to use?

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neazoi

neazoi

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Hello, I have built this antenna preamplifier and it works nice
**broken link removed**

I would like to insert a pot between the antenna and C1 in a voltade divider configuration, to achieve input attenuation when needed. I have tried a 10K pot and it works nice, but is that the right value I should place there?
 
An input potentiometer isn't a good idea. Assuming that the input transistor isn't yet overloaded, you can use a potentiometer in place of R3, connecting C3 to the wiper.
 
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    neazoi

    neazoi

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FvM said:
An input potentiometer isn't a good idea. Assuming that the input transistor isn't yet overloaded, you can use a potentiometer in place of R3, connecting C3 to the wiper.
Click to expand...

Why an input potentiometer is not a good idea? Maybe because of impedance problems?
If going as you desctibe, strong out of band (and adjacent) signals will overload the fet and rise many unwanted signals.

Saying so, I have not noticed any difference in the signal strength with the potentiometer in place (turned to max sensitivity) and when leaving this out
 
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The potentiometer will add noise and possibly load the antenna, depending on it's impedance. To find a better value than the original 10k, the antenna impedance should be known, too.

Because you most likely don't know it, keep the 10k potentiometer or add a local/DX attenuator switch in front of the amplifier.
 

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