RF frequency division

Hi,

I'm designing a simple RF transmitter/receiver. I transmit 4 frequencies: 270MHz, 290MHZ, 260MHz ou 380MHz. At the receiver, I need to simply recognize the frequency. I thought I could amplify the signal received to a 5V saturation, and then feed a frequency divider (/24 for example) circuit and sampling the signal at 4MHz with a PIC to recognize the frequency. But my problem is that it seems difficult to easily divide such a high frequency. Would sb have an idea? Know a high spee divider? Or perhaps I could use a frequency to voltage conversion? How can I do that?

Thanks!

I would suggest to try Hittite frequency dividers. I have used one /4 several years ago, and it worked well. "www.hittite.com"

If the receiver is more than a few 10 centimeters apart from the transmitter, your transmitted 4 frequencies won't be the only signal received by it. How do you want to amplify the signal of interest "to saturation" but ignore any other signal that's in the air at the same time?

A RF receiver needs first of all selectivity. it can't be achieved by your intended method. To avoid "re-inventing the square wheel", start to learn about usual RF receiver technics.

As your transmit frequencies are well apart, I would build separate transmitters and receivers for each frequency. At those frequencies you can make simple oscillators with coaxial resonators for a good stability, and use the same resonators in the receiver for selectivity.
Then the detector output from each receiver can be used to trigger a comparator when the signal level exceeds a preset limit. Comparator output can drive a LED indicating the appropriate signal at the given frequency was received.

You should design all transmitters and receivers to transmit over a needed distance with a good (>20 dB) S/N ratio; It also needs designing antennas. If you transmit modulated signals, use a voltage integrator between detector and comparator to reduce modulation effect upon the indicator of signal presence.

Hittite has a 5bits counter that can divide RF freq from 2 to 32.

Would you have some good documentation for oscillator design from coaxial resonators?

I am sorry but I wrote a paper on coaxial-resonator oscillators in ~1970. I used quarter-wave coaxial resonators, shortened ~20% to use a tuning trimmer. The LC circuit made in this way is simply used as an ordinary LC resonator in a transistor oscillator. Not too much design needed, give it a try.
Instead of using then expensive AF139 UHF transistors I found that low-frequency ones also can oscillate up to ~800 MHz used in UHF TV. First I used a 2-3 pF feedback capacitors between emitter and collector, base grounded through a 1 nF capacitor. Later I used a short loop in emitter to get more power and wider tuning bandwidth.
Try to open an old UHF TV tuner, best with a mechanical tuning, to see how to do it well.