Crystals Set doesn't match?
 

I've searched the archives, but no answer to exactly what I'm asking.

I just bought a simple RC heli. It came with two crystals (of
course), TX and RX. They are, however, not the same *frequencies*;
they are 72.89 M and 72.97 M, or something similar (but they're close
together). TowerHobbies' website also shows some crystal sets with
the TX and RX being different *types* (like 72-7 FM TX and 72-12 FM
RX) for the same set.

But, other crystal sets have TX and RX at the *same* frequency.
How can this be?


Do my crystals count as a matched set? The heli does not work yet, and I wonder if that is why (the range is only 1/2 foot with good batteries; needs frequency tuning?)

I am new to RC, and so I clearly need _big_ help with simple matters:)

RE: Crystals Set doesn't match?
 

a link to the tower page would be helpful...

but the two crystals would have to be for the same frequency for it to work......

unless I am missing something

RE: Crystals Set doesn't match?
 

PJC,
Yep, you are right, the crystals have to match. Since they are on different frequencies the radio will not work. That is why your heli won't work. If this is a new radio then contact whoever you bought it from and let them know that they receiver and transmitter are on different frequencies. Or if you want to correct the situation yourself, then purchase a new receiver crystal and change it out. You have to change the receiver because it's illegal in the US to change the transmitter frequency yourself. If you want to change the frequency on the transmitter it has to be sent in to an authorized repair shop.

Hope this helps

Ken

RE: Crystals Set doesn't match?
 

Even thouhg they are defferent they will be the same channel. the TX is the higher on 72.97 and RX 72.89. This difference was explaned to me 20 years ago but can't remember now, maybe some Ham guy can step in and explane.

Cheers.

RE: Crystals Set doesn't match?
 

If you cannot find any satisfaction with the person that sold it to you. . . [:@]

You can exchange the Xtal here;

Radical RC
7046 Harshmanville Rd.;
Huber Heights
Ohio, USA
45424

These fellows have (had) a Xtal exchange service set up so that people (like you) could correct a frequency problem easily and cheaply. The last time that I used them the fee was $5.00. [X(]

Do a search of the RCU to confirm that they are still working, I believe that they also have a web site (but I can't find it :eek: ).

Good Luck

RE: Crystals Set doesn't match?
 

http://members.aol.com/davthacker/ra...alexchange.htm


the main site is www.radicalrc.com

Never used the eschange, but have bought many things from them and recommend them HIGHLY

RE: Crystals Set doesn't match?
 

All right, thanks for the replies. So, maybe there is a terminology issue here. It seems that some of you are saying that 72.89 and 72.97 are the same _band_, or would RC-ers call it the same _frequency_? (That is, "The 72 MHz crystals").

Or are 72.89 and 72.97 considered different frequencies? They are, then, a matched set?

The Towerhobbies crystal set can be seen here:

http://www2.towerhobbies.com/cgi-bin...I=LXEKZ2**&P=0

I didn't think the -7 or -12 were referring to TX or RX, since many sets have -1, -10, etc. I thought the 72-x were a subdivision of the 72MHz band. Is this not true?

RE: Crystals Set doesn't match?
 

The crystals will be different frequenices due to how radios work. The TX xtal should be on the frequency that you expect (ie 72.35MHz for channel 28). For the RX xtal it will be different to the TX xtal by whatever the IF (intermediate frequency) of the RX is. For a single conversion RX this is 455kHz and for a dual it is 10.7MHz (from memory could be different). Even though the xtals are a pair you need to make sure that you use the correct xtal in the RX or TX.

RE: Crystals Set doesn't match?
 

72.89 is channel 55 and 72.97 is channel 59. This combination will not function together if it is truly what you have. Some of the marking issues you are having at the Futaba website that is causing confusion is the fact that RX and Tx crystals are not interchangeable. Also FM and AM crystals are not interchangeable.

John

RE: Crystals Set doesn't match?
 

Post the model numbers of your Tx and Rx, along with any designations on the crystals you have. Futaba has several different types of receiver and transmitter crystals. It's important to get ones that match your model. Also look at your Tx for a channel number or frequency designation. If the original channel number of the transmitter doesn't match the crystal that's in it you really should send it in to get it tuned to the frequency you plan to use.