Daft Question - Crystals

[OrangeSport]

Hi - probably a daft questions, but only just noticed this. Have always just used my crystals by their colours, but have just noticed that the TX & RX usually don't match. For example; T27.195 R26.740, or T26.995 R26.540

Is that usual / right?

Thanks

[knotty]

Just checked mine and they match t27.095-r 27.095 t 27.105-r27.105 etc.Where yours new or did you get them with a car of ebay or something?

[merckx]

do they actually work as sets? because yes, rx and tx should have identical numbers on them.

[HomerJHandley]

they should all match numbers, thats why one colour doenst mess with another.

[igbandy]

I have some that match and some that dont match but work as they should.

The truth of the matter is that the frequencies are different, just that some mfr`s mark the crystals the same to avoid confusion with us end users.

I have several sets of "generic" crystals that I have bought and acquired, these are marked up with different numbers but work together.

Sets sold my Acoms and Futaba for instance, generally have the same number on them.

[OrangeSport]

Yes, they do all work. That's what's odd.

They were bought as sets, a long time ago though. Strange...

[WillyChang]

yes the RX xtal is always 455kHz different from the TX xtal... that's why you shouldn't swap them round;

the TX xtal is the freq it transmits at. If you put the RX xtal in the TX it'll transmit at the different freq.

Frequency is just the carrier, difference in vibrations is how the RX decodes the control signal being transmitted.

When you amass a huge collection of xtals, some of which are outside the usual RC frequencies,

occasionally you discover xtals of 455kHz lower than an existing RX xtal... yep that makes a new pair.

Or you can also specially order single xtals to be cleaved in any custom freq you need.

[OrangeSport]

Thanks - yes, it is 455 between them as you say..

[markbt73]

Are you talking about the number on the little round sticker on the TX and RX themselves, or on the crystals? The crystals have to match, but the stickers on the components themselves is usually the frequency of the crystals that originally came with that radio. if you've changed the crystals, obviously the stickers aren't accurate anymore. I usually peel off the stickers on the TX and RX so I don't get confused as to which frequency I'm actually on.

[OrangeSport]

It's the numbers on the actual crystals - as WillyChang said above, the are 455 apart. All work fine...

[WillyChang]

xtals themselves usually have their actual freq printed on their little metal can

then they get bought & packaged by the radio mfgs who either put a sticker over the can

or a little plastic carrier - marking "TX" & "RX" with same freq for each pair

[Live Steam Mad]

455KHz is the Intermediate Frequency (IF) needed for modulation of the RC signal onto the carrier, read this ;-

http://en.wikipedia.org/wiki/Intermediate_frequency

The use of IF makes it easier for the circuitry used to cope with the decoding process. It does a very similar thing to what an LNB does in Satellite TV i.e. reduces the frequency down to one with which the decoder / receiver circuitry can actually cope with.

At least that's my understanding LOL.

It's perfectly standard for 27MHz AM Digital Proportional (non error protected i.e. 'raw') RC radio systems, most manufacturers use it as far as I remember. At least ACOMS and Futaba do as their TX crystals are interchangeable and their RX X'tals are as well. BUT you cannot swap a TX for an RX X'tal, nor vice versa, as has been aforementioned above.

Cheers,

Alistair G.