Generating a frequncy

Helo all.i need a circuit which can generate a frequency of 27Mhz having a pulse rate of 800 pulses per second."Pulse on duration" should 100 micro seconds.Any one have any idea about the implementation of cicuit?Antena size should be 8cm

Have a 555 circuit generating the modulation waveform and a 27 MHz crystal oscillator enabled by the pulse signal. 8 cm is rather short for 11m wavelength, don't expect large antenna efficiency.

Any schematic?

I think you are confusing this forum with Google.

A modification of FvM's suggestion would be to use two 555 timers, one tuned to 27MHz and the other to 1/800 Hz and then do a logical AND of the two signals. At the beginning and towards the end of the pulse edges, you may get spikes. If that is not acceptable, then you need to do synchronization.

Why didn't I think of that ?
Oh yeah... Because it is not feasible.

Yes. I had forgotten the maximum range was around 5MHz. By bad.

555 datasheet has application circuits and formulas for pulse width and frequency calculation.

As for the 27 MHz generation, I was expecting a frequency stable sine oscillator (e.g. crystal based) because a radio transmitter has legal requirements for frequency stability and low harmonics.

27MHz crystal osc, NE555 or similar to produce the pulses, use the pulses to bias the 27MHz oscillator. That's how almost all ASK transmitters work.

For the antenna - it depends whether any special radiation patterns are needed but the only practical way of squeezing 11m of wavelength into 8cm is to use a tightly coiled helical antenna. Given the small size, it wouldn't be very efficient but it would work.

Brian.