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Swapping crystals between identical transmitters???

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Swapping crystals between identical transmitters???

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Old 05-19-2003, 05:44 PM
  #1  
SkyDude
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Default Swapping crystals between identical transmitters???

Is this a bad idea? I have two Futaba 4VF radios included with my two Avistar Selects (first one R.I.P). Radios are on FM, dual conversion narrow band. One is on channel 42, the other on 44, FM dual

My flyable Avistar's receiver is on 44. Since the batteries in the 4VF are a pain to change, I was thinking I would just charge both radios, use the first one for several flights, then put the 44 crystal into the 42 radio and use that radio for several more flights. I'd swap battery packs in the plane as well.

Is this going to break a rule and be asking for trouble? Since the batteries are NiCads, I didn't want to try to recharge at the field without cycling them first, and I don't trust the plane batteries for more than 30 minutes or so of heavy flying.

Thanks!
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Old 05-19-2003, 06:18 PM
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mjd3
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Default Swapping crystals between identical transmitters???

You might consider modifying the battery pack instead by cutting the wires and installing a futaba connector. This way you can leave the crystal alone and bring spare batteries to the field.

Added benefit is that this will also allow you to safely cycle the battery with a charger / cycler, which you cant do with Futabas out of the box because they have a protective diode in the circuit. (Don't discharge your battery by leaving the TX on, particularly with the antenna down, you could damage it). The downside is that I think you void your warranty on the radio.

Another solution is to buy another crystal for about $15.

I think either solution is preferable to disturbing the crystal regularly. It might just be a matter of time before it becomes damaged in some way that might cause trouble.

Also, don't get so wrapped up with the TX battery and forget the closely monitor the RX battery. Thats the one that gets most folks in trouble because it is not as easily monitored.
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Old 05-19-2003, 08:45 PM
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Mustang Man-RCU
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Default Swapping crystals between identical transmitters???

I certainly no expert on Tx's but I have been told by those who supposedly know that each Tx has been "tuned" to the frequency that matches the crystal from the factory, whether this is true or not I can't confirm. Michaels solution makes sense to me for the reasons he states.
Steve
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Old 05-19-2003, 11:51 PM
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Stick Jammer
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Default Swapping crystals between identical transmitters???

Right from Tower's website:

*Transmitter Crystals Can Not be changed to another channel except
by a licensed service center. It is against FCC regulations, and
illegal for the user to change a frequency determining component
of a transmitter. If the radio is not retuned, it can be a hazard
spectators, modelers or property, and void AMA insurance coverage
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Old 05-20-2003, 01:24 AM
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DMcQuinn
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Default Swapping crystals between identical transmitters???

And if the transmitter battery is in good shape, you should be able to have a total "on" time of at least 90 minutes. If you have a discharger, test your transmitters after 30 minutes of use. My guess is that you'll still have 2/3 of your capacity left.
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Old 05-20-2003, 01:28 AM
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David Cutler
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Default Swapping crystals between identical transmitters???

You can't swap the crystals in the transmitters legally, but you can buy another crystal for the receiver and swap that. It should have the same effect.

Alternatively buy a field battery charger and top up the battery after a few flights (and the receiver battery at the same time). $50 will buy you an excellent charger that runs of the 12 volt starter battery.

http://www2.towerhobbies.com/cgi-bin...?&I=LE2267&P=1


-David C.
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Old 05-20-2003, 01:36 AM
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Default Swapping crystals between identical transmitters???

All very good info. I think I will ditch this idea. I like the idea of adding a connector for the Tx batteries. I wonder why Futaba chose to make the batteries so difficult to remove.

Maybe so we have to but another radio when the batteries wear out? Who do they think they are, Bill Gates? 8)

Thanks again for the replies.
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Old 05-20-2003, 03:17 AM
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Default Swapping crystals between identical transmitters???

An expanded scale volt meter would be a good investment to keep track of your batteries.

Roy
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Old 05-20-2003, 01:03 PM
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mjd3
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Default Swapping crystals between identical transmitters???

The TX battery is not all that difficult to remove. There is a two pin connector where it attaches to the board, but it does involve removing the TX back cover, so it's inconvienient to do it at the field without another connector in there...
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Old 05-20-2003, 04:28 PM
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Default Swapping crystals between identical transmitters???

I agree with your decision. I have JR and the only thing that I have done is buy an extra receiver crystal so I can swap radios and still fly the same plane. I have an 8103 (Channel 25) and a JR662 (Channel 52). The only thing that I have done is to buy an extra (channel 25) rx crystal so I can fly my trainer on the 8103. I have flown my Avistar trainer on both channels (Channel 52) on without any problems. I have also been told that JR is one radio that you can do this with and others prohibit this. My biggest problem is I am due for a real awakening if I get dyslexic and read 52 as 25 or the opposite.
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Old 05-20-2003, 08:01 PM
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Default Swapping crystals between identical transmitters???

hooked,
I think you've been lucky. Changing crystals between high and low band Rx's isn't a very good idea either.

Skydude,
Why the concern over charging the NiCDs without cycling? NiCDs no longer have that "memory" problem from years ago.

I frequently fly a few flights, leave the plane in the car, and "top off" the packs on another day to fly again. Many of my packs are 4 or more years old, and a cycle or two every once in a while shows them to hold full capacity.
Dennis-
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Old 05-21-2003, 02:11 AM
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Default Swapping crystals between identical transmitters???

DBCherry: Actually, when I considered it I did a lot of checking. LHS, other club members etc. I got a lot of opinions either way, but finally was told that Futaba does, in fact, have a high/low issue. JR on the other hand does not. I have almost 40 flights on my Avistar where I changed from the 52 to 25 and not one single glitch, dead spot, range problem etc. I am not saying that I am an expert, I am far from it. But it seems that I had correct information when I made my decision. I don't mean to be vague, but I honestly just can't remember where I read it or who told me.
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Old 05-24-2003, 02:03 PM
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Mike Buckley
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Default Swapping crystals between identical transmitters???

I'm quite surprised by the information I'm reading. I've got a JR783 and when I first got it it came with channel ?? (I can't remember). I've switched immediately to channel 53 that I had in my old radio. I've been flying for over a year this way and have never had a problem. Yet, if I'm reading the orginal post correctly a transmitter is tuned to a specific channel when you buy it. If that's true why do they sell transmitter cystal at all? Just for replacements?

Mike
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Old 05-24-2003, 04:43 PM
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Default Swapping crystals between identical transmitters???

Mike: Just want to clear something up if there is some confusion. I never changed tx crystal, I only changed the receiver channel. When I got my JR662 it was set at channel 52 and still is. The radio went in the shop under warranty which left me without a tx. I got a great buy on a JR8103 on channel 25. All I did was to take the rx and put a 25 crystal in it. So once I got the 662 back, I have a choice of using the 662 or 8103. It is my understanding that there are legal issues with changing the tx channel.
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