# subtraction of two frequencys

Discussion in 'Electronic Basics' started by Torbjörn Klemensson, Sep 24, 2003.

1. ### Torbjörn KlemenssonGuest

I have two frequencys f1= 30 MHz, f2=13 MHz that I want to get the
difference of (f=f1-f2). Is there a IC or a simple circuit that can
help me with the operation?

/Torbjorn

2. ### grahamkGuest

For a start have a look at
http://homepage.ntlworld.com/g.knott/elect113.htm

3. ### DboweyGuest

klemensson posted:
You will need, at least, an RF mixer into which you will send the two signals.
When the signals combine (multiply) in the mixer, the output will contain the
sum and difference of the two frequencies as well as other frequencies you may
need to filter. Diodes connected as a balanced mixer works well, but there are
other components that can be used.

You don't say what are the signal sources or what will be the recipient of the
difference signal so not much here can be said about what filtering you may
need. If the output is to a receiver, it might provide all that is needed.

In a google search you should probably look for balanced modulator as well as
balanced mixer. They are essentially the same. You will note that to make an
RF mixer work well, that one frequency (selected as the "carrier" frequency,
should be about ten times higher in level than the "modulating" frequency.

Don

5. ### John FieldsGuest

---
You need a double-balanced mixer and a filter. 30MHz goes in the RF (or
LO) port, 13MHz goes in the LO (or RF) port, and you'll get f1+f2 and
f1-f2 out of the IF port. If you want 17MHz you can get it by putting a
17MHz. bandpass (or lowpass) filter on the IF port which will let the
17MHz through and block the 43MHz.

Check http://www.minicircuits.com/dg03-92.pdf for some likely
candidates.