LNA Amplifiers on Video Receivers - Why this result ?

[JetPilot 0]

Hi RC Cam,

I have tried two different types of LNA amplifiers on my 900 MHZ video receivers, both times with very poor results. Both attempts were very good LNA's from reputable companies with very good specs. The latest was this one for 900 MHZ

http://www.minicircuits.com/pdfs/TAMP-960LN+.pdf

My results were more noise in the picture, and slightly less reception of a weak video signal. I am using the standard 900 MHZ video receivers with upgraded saw filters ( no cheap chinese stuff ). Any idea why I would be getting such poor results whenever I put an LNA in the antenna line of my receivers ?

Thanks,

Mike

[Terry 5]

This may not be the case for you but when I used a high gain LNB I found it worked best with a good bit of co-ax between the amp and the receiver. I think the high gain of the amp was swamping the good front end of my receiver.

Have you got an attenuator you can use?

Terry

[JetPilot 0]

I have not tried one, but guess I could build one into the circuit. This is something I may try in the future, so the question of the day is, will amplifying, then attenuating the signal increase prformance ? And how much attenuation should I put in ?

Mike

[Terry 5]

Its hard to say how much is right for your setup, I found 3ft of RG58 did the job great but you will have to experiment.

Amplifying then attenuating is not the point, the point is you effectively get a really good low noise front end. If you have ever done any long range CB or Ham you would find that you hear the weak signal best when you turn down the RF gain so the background noise is just about gone. If you just keep adding gain two things happen, first the signal gets lost as the noise gets louder and secondly you may well push the receiver into overload or at very least force it to work at a higher level than it was designed for and so lose performance.

Terry

Edited January 22, 2012 by Terry