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Measurements >> RF Measurements >> Downconversion Problem
https://designers-guide.org/forum/YaBB.pl?num=1160959572

Message started by uncle_ezra on Oct 15^th, 2006, 5:46pm

Title: Downconversion Problem
Post by uncle_ezra on Oct 15^th, 2006, 5:46pm

Hi,

I am measuring a Zero IF RF receiver. I input -60dBm signal and see the downconverted signal at 5MHz in the output. However, the signal is noisy instead of a single tone when you look at the spectrum analyzer. I have not done any input matching yet just AC coupling the signal. Any idea what is going on? Is the circuit oscillating? Or should I match the input first?

Thanks

Title: Re: Downconversion Problem
Post by ACWWong on Oct 16^th, 2006, 2:38am

uncle_ezra wrote on Oct 15^th, 2006, 5:46pm:

When you say "noisy" on spectrum analyser, do you mean you get discreet side tones on a 5MHz main tone?

If so i guess you are into compression or limiting either intentionally (ie you are looking at a 5MHz square wave) or unintentionally (you are compressing in your chip somewhere, or at the analyser input).

Firstly ensure you are not overloading your SA input.
Then turn your input power down, if the sidetones are a result of compression, you should see them recede quickly as you reduce the input RF. Also ensure you have setup your chip gains correctly.

hope this helps
aw