[HomeBrew] Bipolar IF amplifier

[James Kearman]

Loren Moline WA7SKT wrote:

> This amp will be fixed gain after adjusted and wont be AGC'ed. I don't think the IF signals of the receiver are very strong so it will probably not be overloaded.
>   

You need to find out what the signal levels are, first.

> The IF output level at the jack of the IC-R7000 receiver ( 25MHz to 1.999GHZ ) are rather low so need a little boost.
>
> The output to the SoftRock receiver from this amp would need signal levels comparable to what was received by an antenna.

So assume you want to amplify the strongest likely signal to be 50 uV 
across 50 ohms going into the SoftRock. Now you can calculate the 
necessary gain.


> Most signals will be weak from Deep Space probes and VHF and UHF ham radio signals, satellites etc.
>   

So you don't want to be adding anymore noise than possible.

> Im just using a 2N3904 type transistor.

If it's low noise you're after, I can't think of many worse devices to 
use! I would use a low-noise FET. A U309 or U310 is dirt cheap and would 
work much better. A FET stage will be easier to design for high input 
impedance, thus not loading the IF output.

If you looked back through older Handbooks you could probably find a FET 
preamp designed for 15-10 Meters, that probably has about 20-dB gain. 
That's probably in the neighborhood you're looking for, and you could 
work from there.

73,

Jim, KR1S
http://kr1s.kearman.com/