Difference between the TX and RX crystals

[sameershah]

Hi,
I have a Futaba 6EXA TX on ch 18. I lost the crystal when I took it out to use the tx with a simulator.
Now I am having trouble geting a TX crystal.
If the size of the crystal is same, then is there a difference between a TX and RX crystals?
The reason I am asking is that, if I find a RX crystal on Ch 18 and is it the same size as tha TX crystal adn single conversion then can I use it with the TX with experiencing deterioration in signal strength?
Any suggestions?
Thanks.
Sameer


Note to all: I am not trying to change the frequency of my TX, only to replace the crystal with the same frequency crystal as teh original one.

[john whitehead]

[QUOTE=sameershah]Hi,
I have a Futaba 6EXA TX on ch 18. I lost the crystal when I took it out to use the tx with a simulator.
Now I am having trouble geting a TX crystal.
If the size of the crystal is same, then is there a difference between a TX and RX crystals?
The reason I am asking is that, if I find a RX crystal on Ch 18 and is it the same size as tha TX crystal adn single conversion then can I use it with the TX with experiencing deterioration in signal strength?
Any suggestions?

*****Yes! :censored: A transmitter crystal will have a totally different frequency to that of a receiver crystal. :mad: Single conversion is usually 455khz difference, dual conversion can be either 10.7mhz or 11.155mhz, these frequencies refer to the RX crystals. So NO..you cannot :eek: fit a receiver crystal into a transmitter, their respective physical size is totally irrelevant.

In UK we are allowed to buy and change crystals in any RC systerm which uses them, however this ruling does not apply in USA and other countries, you will be breaking the law.

[electrotor]

Very often the actual frequency of the crystal is stamped on the metal case - you might find it on the top or side under the channel no. sticky label. As John says Tx and Rx crystals for the same channel do not resonate on the same frequency as each other due to the way the Tx generates the basic RF and the way the Rx converts the RF, be it single or dual conversion. Tx and Rx crystals are matched pairs. Always go by the channel no. Also bear in mind that you should be wary of using crystals from one manufacturer in another manufacturers Tx and RX. Most times they work but not always. Again due to the internal circuitry of the gear.

BTW Hi John. Haven't heard from you for a while. Been in hibernation? :D
Eric

[vintage1]

*****Yes! :censored: A transmitter crystal will have a totally different frequency to that of a receiver crystal. :mad: Single conversion is usually 455khz difference, dual conversion can be either 10.7mhz or 11.155mhz,



No, only 10.7Mhz difference. The 11.155Mhz Xtal is the local oscillator that converts down from 10.7MHz to 455KHz.


these frequencies refer to the RX crystals. So NO..you cannot :eek: fit a receiver crystal into a transmitter, their respective physical size is totally irrelevant.

In UK we are allowed to buy and change crystals in any RC systerm which uses them, however this ruling does not apply in USA and other countries, you will be breaking the law.

They will never know..the practice is to prevent the transmitter going out of spec from either the wrong Xtal type, wrong xtal frequency, or misaligment when tuning up to a new frequency.

You need a new channel whatever TX Xtal..whether you can buy these over the counter in the USA I do not know. It should be marked wit the exact channel FREQUENCY since the transmitter transmits on that frequency.

A receiver crystal, even if of the right frequency (which will be a completely different channel) may well not work or be severely off tune. Even another manufactures TX crystal cannot be guaranteed to work correctly in your transmitter. The circuit is adjusted to a precise crystal cut..and no other will do.

[Pinecone]

But if they do find out, you can be subject to a $10,000 fine. Not worth it.

[A.T.]

Check the stickies on RCGroups Radios:
What type of crystal do you need (http://www.rcgroups.com/forums/showthread.php?t=127560)
Transmitter crystal swapping (USA) (http://www.rcgroups.com/forums/showthread.php?t=94580)

and for an exchange or new crystal in USA, try
Radical Crystal Exchange (http://members.aol.com/davthacker/radicalrcxtalexchange.htm)

Much more information under sub section "Crystals, Oscillators & Piezo " on my web page.

Regards
Alan T.
Alan's Hobby, Model & RC Web Links (http://homepages.ihug.co.nz/~atong)

[Rodney]

Transmitter crystals are rarely if ever the same as the transmitted frequency. Most transmitters use either 3rd or 5th overtone crystals, i.e. the crystal frequency is much lower than the transmitted frequency.

[john whitehead]

But if they do find out, you can be subject to a $10,000 fine. Not worth it.

I totally agree with you Pinecone.

Perhaps it's somewhat wreckless to openly encourage fellow modellers to break local laws and regulations, these are introduced for a purpose and that is to PROTECT other users from the possibility of interference generated by such actions and of those who are clearly inexperienced.

There's also been a request to increase transmitter power to over 5 watts, clearly this is nonsense for general modelling purposes, that assumes this is the purpose of such a long range device. A BFY51 was mentioned and suggested it could run at 5 watts....mmmmmm????? A very good transistor indeed, maybe not good though!

[vintage1]

Transmitter crystals are rarely if ever the same as the transmitted frequency. Most transmitters use either 3rd or 5th overtone crystals, i.e. the crystal frequency is much lower than the transmitted frequency.

yes, but if they are stamped with a frequency it WILL be the correct frequency.

[vintage1]

I totally agree with you Pinecone.

Perhaps it's somewhat wreckless to openly encourage fellow modellers to break local laws and regulations, these are introduced for a purpose and that is to PROTECT other users from the possibility of interference generated by such actions and of those who are clearly inexperienced.

There's also been a request to increase transmitter power to over 5 watts, clearly this is nonsense for general modelling purposes, that assumes this is the purpose of such a long range device. A BFY51 was mentioned and suggested it could run at 5 watts....mmmmmm????? A very good transistor indeed, maybe not good though!

27MHz john. Have you seen what a good CB rig can turn out?

A 5W AM transmitter is nothing on them..

And in the rural Phillipines?

Not under European or US jurisdiction.

And its 'reckless'

not 'wreckless' :D

[john whitehead]

27MHz john. Have you seen what a good CB rig can turn out?

A 5W AM transmitter is nothing on them..

And in the rural Phillipines?

Not under European or US jurisdiction.

And its 'reckless'

not 'wreckless' :D

Goodniss me fansy spelllin a worb rong eh? Eitha way doode iss still "reckless"

[pilotpete2]

Hey Doode,
Nice T' see y' still around :)
Cheers,
Pete

[sameershah]

To some of you who are talking about fines and 'reckles' etc..Please read the note in my first post.
I already said that I am not trying to change the frequency.
Also I asked this question to make sure whether I can use the rx crystal or not.
As most of you have already said that it I should not use rx crystal, I am not going to do that. That's all I was looking for.

[flatfour]

You can get one right here, but it comes as a set with a DC RX crystal

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXH26018&P=7

[Pinecone]

To some of you who are talking about fines and 'reckles' etc..Please read the note in my first post.
I already said that I am not trying to change the frequency.
Also I asked this question to make sure whether I can use the rx crystal or not.
As most of you have already said that it I should not use rx crystal, I am not going to do that. That's all I was looking for.

Relax, sometimes threads take slight jogs in direction.

But for your purpose, you are correct, you cannot use a Rx crystal.

WRT not swapping freqs in US, the other thing to consider is the lawsuit if you happen to injure someone. The plaintant's lawyer will take of the cry of you wantoinly and illegally changing the channel of your radio is flagrent disregard of US laws and regulations. Not a pretty picture.

[Bruce Abbott]

For an R/C transmitter to get FCC approval, its crystal must be permanently fixed in place or inaccessible, to prevent the user from changing it. Therefore your radio is already illegal :(.

It's safe to replace it with another Futaba FM transmitter crystal only. Do not use another brand, do not use a receiver crystal of any type!

Transmitter crystals are rarely if ever the same as the transmitted frequency. Most transmitters use either 3rd or 5th overtone crystals, i.e. the crystal frequency is much lower than the transmitted frequency.FM transmitter crystals are usually on a sub-multiple of the channel frequency (typically 1/4) which is slightly different from the overtone frequency. AM transmitters may use overtone mode. However, the crystal will still be marked with the frequency of transmission.

[Pinecone]

The manufacturer has to glue the crystal in to get Type Acceptance, but it doesn't become illegal is the glue comes off. Only if you swap to a different frequency.

But I agree, ONLY use a Tx crystal from the same manufacturer.