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Jun 22, 2003, 03:42 AM
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What type of crystal do you need ?


Since this seems to be a rather frequent question I'll attempt a general answer to it.

First the basics, pardon me if you already know this. In most of our R/C equipment it is a crystal that determines the channel or frequency that the equipment is working on (the exception is equipment with frequency synthesizers like the Hitec Spectra module). With no crystal a transmitter will not transmit at all. With the wrong crystal it will transmit on the wrong frequency. A receiver with no crystal will pick up garbage from the air and with the wrong crystal it will be "listening" to the wrong transmitters. Both the transmitter and receiver must have crystals with exactly the same channel number.

There are 3 main types of R/C crystal. These are Transmitter crystals, Single Conversion receiver crystals and Dual Conversion receiver crystals, commonly called Tx, SC Rx and DC Rx for short.

These are all very different and you must not mix them up. A transmitter crystal will not work in a receiver, a DC Rx crystal will not work in a SC Rx etc.

PCM receivers do not need special crystals. All PCM receivers are either Single Conversion or Dual Conversion and use a standard crystal of the correct type.

The different manufacturers sometimes use different specifications for their crystals so the only safe advice when you are changing a crystal is to use one sold or recommended by the equipment manufacturer. Hitec equipment, Hitec Crystal, JR equipment, JR crystal, Futaba....you get the picture. Some aftermarket manufacturers don't sell their own crystals but say to use a Futaba or other make crystal. Do as you're told .

Note: the crystal you use in a receiver is not affected in any way by the make of transmitter you are going to use it with. If it is a Hitec Rx it uses a Hitec crystal no matter if you're going to use a Futaba/JR/Hitec/Sanwa/Airtronics transmitter with it (or any other I've missed).

You'll probably see people telling you that a Brand X crystal works fine in a Brand Y receiver. They may be right but it's up to you to decide a) how much you trust them and b) if their advice will definitely work for your equipment. Just as one example, I've often seen people making a general statement that one brand of DC Rx crystal will work in a different brand receiver. It may be true in North America on 72MHz where they are (I don't know I've never tried it) but it is completely untrue for the 35MHz European equipment I use (I do know I have tested it). Beware of wide-ranging general advice given by people with only limited knowledge.

I'm going to freeze this note at the top of the Radios forum. If you want to debate any of the advice or it hasn't answered your questions feel free to start a new thread any time.

Steve
Last edited by steve lewin; Jun 26, 2003 at 11:21 AM.
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