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Changing TX crystals...

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Old 02-05-2005, 08:52 AM
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JD380
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Default Changing TX crystals...

I was at the Beginners' forum and someone brought up changing TX crystals, which I thought was not good to do without having it recalibrated. Anyway, some said it was OK as long as it was within a few(?) freq numbers of one another. Others said they would not want to be around anyone that does this. I figure this would be the forum to get some good anwers to this.
Also, someone there mentioned that freq 38 can receive some interferences from outside sources. Is there any truth to this. I have one TX on 38, hence my concern.

For your info: both of my radios are Futabas, Skysport 6s ( older style, ones with the metal handle) one on 38, one on 42.

Thanks for any and all enlightment on these subjects.
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Old 02-05-2005, 09:50 AM
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Default RE: Changing TX crystals...

first of all, changing crystals is illegal and will void pretty much any insurance you have, so if you crash into anything for any reason that could come back to haunt you in the worst way. even if someone shoots you down, you might be liable for damages since a non-modified radio might not have had a problem...

anyway, that out of the way. I personally would change no more then maybe +/- 5 frequencies. yes they are tuned for a particular freq, and the further you go from that the worse things could be.

as far as 38 being prone to interference, that is area specific, so maybe your area does have something putting out noise on that freq. in general there isn't any one freq that is more prone then any other.
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Old 02-05-2005, 10:12 AM
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Default RE: Changing TX crystals...

I understand that changing the TX crystal is a big no-no according to FCC regulations. I then have a question: Why are the TX-RX pairs available from Tower Hobbies (Futaba US) and from many LHS's?

It seems similar to the crazy situation where you can buy an assault rifle, but the magazine has a capacity of only 20 rounds - but you can get the standard 35 round mags from gunshops.

Personally, I send any radio equipment to the service centers if I want a frequency change. It is cheap enough insurance that the equipment will work.

Safety is no accident!
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Old 02-05-2005, 12:48 PM
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Default RE: Changing TX crystals...

These radios are made to be used in many different countrys where the rules are different where these things are made possible so an end user can do the mods where it is legal
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Old 02-05-2005, 03:15 PM
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Default RE: Changing TX crystals...

I had three very knowledgeable R/C Universe guys tell me that as long as it is the same # crystal as was in before it will be fine. I will not mention any names. I also asked a guy on e-bay that sells new equipment, tx's, rx,s and simulators that he flew racing contests and that every body changed crystals like jellybeans, his exact words. He owns a hobby shop and said he flew shoulder to shoulder with guys changing crystals all the time. I would send it in if you are changing to another crystal. As for the Europeans changing crystals all the time, they do not have near the channel conflicts that we have in the US. As far as I know, which is not a whole lot, You may be getting interference on 38 at your field because of something in the area. Try your radia at home and see what happens. Hope this helps. When in doubt, send it to Futaba or Radio South in Florida. Dave....Watch the flak from this one.
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Old 02-06-2005, 11:39 AM
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Default RE: Changing TX crystals...

There is a reason that just replacing the Xtal with one of the same frequency may not work without causing interferance to adjacent channels or those using the spectrum between our channels. Each crystal is simply a piece of ground quartz (other material might be used but I'm not aware of any) which is ground to approximate size. There is a tolerance on how repeatable that grinding can be so then the individual circuit (your transmitter) is then fine tuned by adjusting either/or the inductance or capacitance comprising the tuned circuit to pull that frequency spot on the required value. Each crystal, even if marked with the same frequency, requires slightly different capacitance/inductance to be exactly on frequency. A spectrum analyzer is required to be sure you are not splattering into adjacent band space, that is why, in the USA, you are required to have any crystal change certified by a qualified technician with the proper equipment.
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Old 02-06-2005, 12:33 PM
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Default RE: Changing TX crystals...

So if a customer orders a new radio from Tower and tells them he wants it on channel 54, they actually tune that transmitter on a test bench prior to shipment? Or do they maintain a stock of radios tuned to every channel at the factory?

Seems hard to believe they devote any labor to tunig radios. At about $110 for Tx, Rx, batteries and charger for their basic system, they cannot afford to tune.

Maybe they do a quick go/nogo frequency check?
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Old 02-06-2005, 01:24 PM
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Default RE: Changing TX crystals...

So if a customer orders a new radio from Tower and tells them he wants it on channel 54, they actually tune that transmitter on a test bench prior to shipment? Or do they maintain a stock of radios tuned to every channel at the factory?
they maintain stock of individual freq's. if you notice they are frequently out of certain freq's, while other radios are in stock on that channel.
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Old 02-07-2005, 11:44 AM
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Default RE: Changing TX crystals...

well said rodney........but you are never going to convinve those who keep repeating the mantra "i've done it for years and I havent crashed yet "
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