RF Tx and Rx using crystal oscillator

[mr_byte31]

Hi All,

I tried to implement AM or FM circuits using LC oscillator but it seems I fail , Maybe the circuit doesn't oscillate.

I found some circuits that use crystal oscillators. That interest me a lot.
I found they use the crystal oscillator in the Tx circuit only and in the receiver they use LC circuit

I am planning to use single frequency for operation so I don't need to tune the frequency.

this is one kind of the ASK circuits that I found over internet :
broken link removed
anybody have any idea for Rx that use a crystal oscillator ? I dont care if the circuit is AM or FM , the most important thing is to avoid the LC oscillator

 

[jiripolivka]

Using a crystal in TX oscillator is OK, using it in a receiver requires to find a pair of crystals with exact frequencies. Using a RX with a LC oscillator is easy and you can tune it to more TX frequencies.

I think you need to get hands-on experience with oscillators in general, with crystals, too. You must know how to adjust transistor operation point and how to detect oscillation by current rise. In short, you must experiment!
Use an analog mA meter to adjust your oscillators

 

[mr_byte31]

I think if there is a drift in the oscillation frequencies between the Tx and Rx this wont be a big value , maybe few Hertz.

I didn't get what you mean by using mA meter to adjust the oscillator !

 

[jiripolivka]

I think if there is a drift in the oscillation frequencies between the Tx and Rx this wont be a big value , maybe few Hertz.

I didn't get what you mean by using mA meter to adjust the oscillator !

Exactly, your answer confirms that you never designed or made any oscillator. So go ahead and try it!
The mA meter you need to see important changes of collector current. By this change you can see if your oscillator does oscillate or not.
Your oscillator also must start well after switching ON the DC power supply.

 

[vfone]

For the receiver you can use a direct conversion front-end, which could be a simple additive BJT mixer with RF going in the base, oscillator injected in the emitter, and audio output from the collector.
The receiver local oscillator could be identical with the transmitter oscillator, using also a 27MHz crystal. The frequency of the RX oscillator should be slightly off, compared to the TX oscillator (use a trimm capacitor in series with the RX crystal).
The audio output could be amplified using a transistor stage or an OpAmp.