sikm8 said:I have a 27mhz 2 channel radio (smartech), can you use 29mhz crystals in it?
nismo if your gunna fork out the money from 27 to 29 u would get FM and stop p faryting around with toy'ey AM
they are all standing there holding their wheels...ahahhhh
</font>Nothing wrong with AM radios, those that say FM is better can't tell the difference between marketing & the truth!</font>
FM has its uses and maybe the signal filtering is a bit better, but in 95% of the cases AM works fine.</font>
AM gear is also cheaper, more robust because its simplerand the xtals are $20/pr instead of $40-50.
What type of crystal do you need ?
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<div>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
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
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.