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 Post subject: Re: 30 dB Gain Broadband Amp
PostPosted: Jul Sun 07, 2019 3:35 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Somers, CT
The most important considerations are the first stage noise figure and out of band rejection.

I can not imagine any receiver that needs 20 or 30 dB of gain to show improvement. A modest
10 or 12 dB preamp with a very low noise figure is what I would shoot for. A If you want to run the
math, here is a start:

https://en.wikipedia.org/wiki/Noise_figure

Something like this could be easily built dead bug style:

http://www.techlib.com/files/fmpreamp.pdf

A better design would use a GaAs device for lower first stage NF.

http://www.techlib.com/files/fmpreamp.pdf

Pete

Pete

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 Post subject: Re: 30 dB Gain Broadband Amp
PostPosted: Jul Sun 07, 2019 11:24 pm 
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Ummmm, your two pre-amps go to the same page.

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 Post subject: Re: 30 dB Gain Broadband Amp
PostPosted: Jul Mon 08, 2019 12:03 am 
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SUCCESS! For the first time, I'm able to get a signal stronger than the muting limit and that gets the stereo indicator to light up. Plus there's full quieting on stereo.

Those of you were correct when you warned against too much gain. There was noticeable improvement when I simply terminated the amp's output with a 75 ohm resistor. So I read up on attenuators and used a simple resistor network to additionally drop the signal to where it wasn't overloading the tuner input. The third step was to use a short antenna instead of tuned dipole. I expected a broadband amp to benefit from a tuned input, but the one I had been using put out too much signal. The amp works without the dipole as long as the antenna is short enough not to grab too much signal.

As stated before, this amp's output is dependent on current, and yes, I have to keep the voltage below 6V to prevent overloading. I guess I could add another attenuator stage and use higher voltage, but I've pretty much learned what I wanted to. Thanks for all the help!


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