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01-09-2010, 04:20 PM | #1 |
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I am: Floyd S
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Futaba Crystal Swap
I hope everyone knows the following regarding crystal swaps on Futaba FM TX Radio's. If your using a Futaba Radio without a module in the back you can't change crystals without sending it out for tuning.
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01-09-2010, 04:57 PM | #2 |
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Re: Futaba Crystal Swap
Well technically that is true (its also old news) and i say this at the risk of getting flamed but i have been swapping crystals since day one *o)..
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xv-townboy Last edited by xv-townboy; 01-09-2010 at 04:59 PM. |
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01-09-2010, 06:02 PM | #4 |
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I am: Cedric V.
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Re: Futaba Crystal Swap
In the States it isn't legal, but I'm almost sure that is not so in Canada. However that being said, it isn't a good idea at all to stray too far away from the original frequency to which the transmitter was tuned. The output circuits determine how clean the transmitted signal is and the sidebands will start to exceed the prescribed limits if the carrier is moved too far from that channel to which it was originally tuned and you Tx will be 'narrow-band' no more. It will still seem to work as before but you will have increased the RISK TO OTHERS when they fly on a close-by channel. To use crystals other than say, Futaba in a Futaba Tx is downright irresponsible.
Upon changing the channel, the Service people will look at the Tx output on a device called a 'Spectrum Analyzer' which will clearly display on a clibrated screen, the transmitters output energy and whether the sidebands are within the prescribed limits for acceptable operation. Hence, desirable if you don't move too far from the original spot and more or less essential if you move too far. The service job would probably cost less than replacing a fellow fliers aircraft and keep you popular in your group. |
01-09-2010, 07:44 PM | #5 |
RCC Supreme Contributor
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Re: Futaba Crystal Swap
Thanks Spitball. It may work fine for your Radio but switching crystals can cause interference on neighboring channels because the tuning information is in the Radio not the crystal. Unlike the older Radio's that have the tuning inside the module located at the back. That's why swapping a module is fine.
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01-09-2010, 10:09 PM | #6 |
!!! CONFIRM YOUR ACCOUNT !!!
I am: Cedric V.
Join Date: Oct 2004
Location: St. Marys, Ontario N4X 1C1
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Re: Futaba Crystal Swap
Yup floyd, you got it but most radios do not in fact use a module. It's a good feature and the entire radio frequency system is inside the module. However you can get at the crystal in the module (certainly Futaba modules) and cause the same problems.
The circuits coupling the output transistor in the Tx to the antenna determine the filtering action and reject the sidebands outside the prescribed limits and keep the output clean enough to prevent adjacent channel interference. So called 'narrow band'. FM 'frequency shift' modulation as used in RC results in weird sidebands being generated but they carry the information on the carrier. Shaping them is part of narrow banding! This is effected by the tuning. With that, goodnight! |
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