# mixing frequency of intermediate frequency (IF) and radio frequency (RF)

AM broadcast signal covering 995-1005 kHz radio frequency (RF) range is to be down-converted to an intermediate frequency (IF) range of 395-405 kHz where main amplification takes place in AM receivers. I need to find the mixing frequency.

i solved it this way

IF=Fmixer-RF
fm-1005=405 .     fm=1410
fm-995=405        fm=1400
fm-1005=395 .      fm=1400
fm-995=395 .      fm=1390


so the mixing frequency is 1400. I was just wondering if that the way of how to find the mixing frequency?

• Please explain exactly what you're asking for. You've stated something that sounds like an exam question and your solution, but not what kind of answers you want from us. Jan 17, 2019 at 22:05
• I was just wondering if that the way of how to find the mixing frequency? @KevinReidAG6YO Jan 17, 2019 at 22:30
• Please edit your question to say that, then. It's also good to ask a question that has an answer more complex than "Yes, you got it right." Jan 17, 2019 at 22:32
• did I got it right? i am discussing my idea to solve it @KevinReidAG6YO Jan 17, 2019 at 22:39

This question is solved in the same way as the last question you asked. The formulas are the same:

$$f_s=f_1+f_2 \tag 1$$ $$f_d=f_1-f_2 \tag 2$$

This time, the sum and difference is called IF (intermediate frequency) - a common term in mixer circuits. Then rearrange to find the LO (local oscillator) frequency:

$$LO=| IF-Signal | \tag 3$$ $$LO=IF+Signal \tag 4$$

Start with the low end of both ranges and plug them into the equations. There are two possible answers for the LO frequency.

You can then plug in the upper frequencies of the ranges in the same way to see that it works out to the same LO frequency.

$$LO=| IF-Signal | = | 395 - 995 | = 600 \text{ kHz}$$
$$LO=IF+Signal = 395 + 995 = 1390 \text{ kHz}$$