Mixer LO selection for up conversion

[buyan]

Dear All,

I have a question about the LO frequency selection for a mixer used for up conversion.

I have a IF input signal at f1 and the desired RF output signal is f2. There are two ways to get the RF output. One way is to use LO frequency at fL, f2=(f1+fL). The another way is to use fH, f2=(fH-f1).

Is there any rule-of-thumb to select the LO?
Thanks for your help.

rgds
buyan

 

[echo47]

You want to calculate where all the mixing distortion products wind up. In many cases, up-conversion gives the happier results. Other times down-conversion wins. Sometimes it's a coin-toss. I normally build low-frequency system, but I think the same things happen at RF/MW.

Remember that down-conversion reverses the spectrum.