WRX,

The long answer:

The 72 MHz signal from our transmitters has to be converted down to a low frequency for the information to be extracted from it. The conversion is done by mixing the 72 MHz signal with another steady signal to generate a lower frequency result. In a single conversion RX the Incoming 72 MHZ signal is mixed with another 72 MHz steady signal to yield the output PPM or PCM information directly.

In dual conversion the signal is first mixed with a steady signal that will result in some intermediate frequency (often 455 kHz) and then this signal is mixed again to yield the actual information.

In general the single conversion RX has fewer parts and can be lighter and use less power. However it can be more prone to interference because the filter has to be fairly broad.

The dual conversion RX wil have a larger parts count but can include a very precise filter for that intermediate frequency so they usually have better range.