Originally posted by joelacrane
So do i just have to buy 1 dual conversion crystal for my tx, and one single conversion fo my rx?
No.
1) You don't need to and should not change your crystal in your TX.
I'm not an expert here but here is my understanding about the difference between single conversion and dual conversion:
Each component in the circuit (resister, inductor, capacitor, crystal, etc) plays a part in establishing the center frequency of the signal the RX is sensitive to.
In a single conversion RX, a single circuit combination with crystal will react to a certain frequency generated by a TX.
In a dual conversion RX there are basically 2 separate circuit combinations, the crystal reacts to 2 separate frequencies interpreted by the circuits. These two circuits are then compared with each other to arrive at a concensus of the center frequency the RX is sensitive to.
I'm sure my explanation above would not satisfy my electronics instructor but it has been 30 years since I took basic electronics.
In addition to a center frequency the RX must be sensitive to the same type of modulation. There are currently 3 different modulations being used in most RC radios: AM (amplitude modulation -- information is interpreted from the signal by measureing the change in the amplitude of the signal.) FM(frequency modulation -- information is interpreted by minute changes in the frequency of the signal around the center frequency) and PCM(pulse code modulation -- information is interpretted by measuring the width of signal pulses)
Hope this helps with your understanding -- maybe someone more current can provide a better layman's explanation.
In summary, your RX only needs to match you TX by frequency (channel) and modulation. Crystals for RX must be matched to whether they are for single conversion or dual conversion. You must also use a specific manufacturer's crystal. Only use Futaba crystals for Futaba RXs and only use Hitec crystals for Hitec RXs.