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Transmitter Channels

Old 02-03-2004, 05:52 PM
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BreakNbalsa
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Default Transmitter Channels

You can change the crystal in Futaba receivers to change the channel, Of coarse following the high range low range guidelines, but what about transmitters? I've never done this but often wondered.
Old 02-03-2004, 05:54 PM
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bhole74
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Default RE: Transmitter Channels

Most transmitters can be changed the same way.
Old 02-03-2004, 05:55 PM
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Primodus
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Default RE: Transmitter Channels

I just changed both crystals in my Futaba 6EXA and it works flawlessly. Just follow high/low band rules and it's fine.
Old 02-03-2004, 05:57 PM
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BreakNbalsa
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Default RE: Transmitter Channels

Thanks, I,ve never tried it, but it seems logical. Just thought i'd ask.
Old 02-03-2004, 06:02 PM
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BreakNbalsa
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Default RE: Transmitter Channels

Does anyone know where the high/low band dividing line is. Is it right down the middle at 35.
Old 02-03-2004, 08:07 PM
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greenboot
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Default RE: Transmitter Channels

This thread wouldn't be complete without someone pointing out that changing the transmitter crystal is a violation of FCC rules. Much has been written in these forums about it.

Tom
Old 02-03-2004, 08:10 PM
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Stick Jammer
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Default RE: Transmitter Channels

BreakNbalsa,
Here's a little info for ya. Pay special attention to the last item.

*72MHz- Low band channels 11 to 35; High band channels 36 to 60.
Receiver crystal channels (11-35 or 36-60) Within Each Band
Can Be Changed, and Do Not Require a retuning of the receiver.
*72MHz Frequency Band (low or high) for the receiver Can Not Be
Changed from low to high band, OR from high to low band without
sending it into Futaba Services for retuning.
*50MHz, 72MHz, 27MHz and 75MHz Frequency Bands Can Not under any
circumstances be interchanged with each other. 72/75:receiver Must
be sent in for retuning to the appropriate band. 50/27: can't do.
*50MHz, 27MHz and 75MHz receiver crystals Can be changed anywhere
within the respective bands. There are no high or low bands such
as the 72MHz band has.
*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.
Old 02-03-2004, 10:50 PM
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fritch1969
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Default RE: Transmitter Channels

if crystals are not to be messed with why are they so easy to get to ? hmmmm
Old 02-04-2004, 12:36 PM
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Rodney
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Default RE: Transmitter Channels

What most people do not realize is that a crystal marked at a certain frequency is most probably not exactly on frequency. A crystal is a piece of quartz which is ground until it resonates at close to the desired frequency (each company has a tolerance criteria which is available). After the crystal is mounted (inserted) into a circuit, individual inductances or capacitors are adjusted to pull that crystal into the exact range required. Each individual crystal requires a slightly different inductance or capacitor change to be exactly on frequency. Just changing the crystal may be close enough to work your receiver but it may also be just far enough off frequency to adversely effect other users sandwiched in between our allocated channels or spill over into the next channel. That is why the FCC has the rule that the transmitters must be checked by authorized (trained technicians with adequate test equipment) to guarantee that the unit still functions within the allowed spectrum. So yes, many do change the crystal albeit illegal, but, if found out and you have an accident, neither your insurance company or AMA will help you out financially or otherwise.
Old 02-04-2004, 01:11 PM
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Default RE: Transmitter Channels

Does the same violation apply for synthesized frequencies? I'm assuming not as these frequencies are not developed with crystals, eh?
Old 02-04-2004, 01:54 PM
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Default RE: Transmitter Channels

Synthesized radios are exempt as they use PLL / servo loops to lock the center frequencies.


A single frequency transmitter can be channel-changed by the manufacturer or his agent who is capable of recalibrating the radio and that will satisfy the FCC requirement. The only reason that the FCC cares about this is that there is a slight possibility of center frequency drift upon changing crystals (i.e. meaning you can broadcast over a larger frequency spectrum possibly interfering with other radio signals) With most modern radios this is unlikely, but it still can occur. Center freq drift may also create an opportunity for errors at the receiver, so really - it is in your best interest to have it checked out / recalibrated anyway.

Best is just to use a JR or FUT tx with transmitter modules, while expensive, they are truly interchangeable.

I changed a crystal in a transmitter once. The plane crashed due to radio hits. It might work fine, but is it really worth the risk?
A radio calibration costs about $30 - $50 Money well spent.

DP
Old 02-04-2004, 02:57 PM
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FHHuber
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Default RE: Transmitter Channels

ORIGINAL: fritch1969

if crystals are not to be messed with why are they so easy to get to ? hmmmm
They are easy to get to because... Futaba doesn't want to make one case for the US and another for Europe and another for somewhere else. In Europe the end user can change the crystal legally. They are also in the 35 mhz band and have a bit wider percentage frequency seperation.

****

Technically... its even illegal to replace the original crystal in the TX with one for the SAME frequency here inthe US. (unless you are licenced for it...)
Old 02-04-2004, 11:23 PM
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fritch1969
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Default RE: Transmitter Channels

well I bought a new superstar 40 back in Oct. and the "factory" radio/receiver setup was messed up, I was on channel 46 and another club member was on 57, when he turned his radio on my servo's were dancing. I put in a 52 crystal set from another r/r and it range checked great with no more dancing servo's. Now my question is, should a radio calibration be done by the man. before shipping ?

Why waste $30 -$50
Old 02-05-2004, 12:02 AM
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DBCherry
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Default RE: Transmitter Channels

1) It's illegal to change them. (Which should be enough, except a LOT of people don't think things are illegal unless they get caught.)
2) You could interfere with someone on an adjacent channel. Do you want to be responsible for "shooting down" a club member on 51 or 53? (Not likely, but is it worth it?)
Dennis-
Old 02-05-2004, 10:11 AM
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famousdave
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Default RE: Transmitter Channels

The fact that is illegal does not concern me, I think a lot of laws are stupid anyway and exist just because some people create them to feel important. This law however, does make sense. If not for the reason written, at least as a courtesy to your fellow flyer.

As someone who has designed radio circuitry and understands how this stuff actually works, the crystals CAN and sometimes DO create center frequency drift. On the high end JR and Fut radios, this probably won't ever surface, but on the cheaper analog radios and especially on older radios, this is not only possible, but likely.

The FCC passed this law mainly so that other (non R/C) users in the same band would not be subject to spurious noise from drifting R/C radios. There are very few receiving devices left that share our frequency band, so the fact is, this scenario is unlikely at best, and probably would never happen, so the way the law was written, is useless. It is possible however for the R/C radio to drift creating interference on other's R/C radios, and that is why it makes sense to have the radio calibrated - law or not.

I have seen first hand the effects of radio drift. I would feel like crap if due to my cheapness, I changed crystals and shot down a fellow flyers (or worse, some kid who's scraped together every penny for his first plane).

Personally, I think the FCC is a joke - after all these are the people who are outraged and disgusted at a 1/2 second flash of a woman's body part on TV, but are fine and dandy with showing everyone a slow motion sequence of a guys brains splattered all over a wall by a gunshot. Like they know what is right and wrong! HA


I will however get my radios checked to protect MY investment and that of others.

DP
Old 02-05-2004, 12:54 PM
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TyBryner
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Default RE: Transmitter Channels

ORIGINAL: FHHuber

ORIGINAL: fritch1969

if crystals are not to be messed with why are they so easy to get to ? hmmmm
They are easy to get to because... Futaba doesn't want to make one case for the US and another for Europe and another for somewhere else. In Europe the end user can change the crystal legally. They are also in the 35 mhz band and have a bit wider percentage frequency seperation.

****

Technically... its even illegal to replace the original crystal in the TX with one for the SAME frequency here inthe US. (unless you are licenced for it...)
Could this also be for the hams who (If I understand correctly) are allowed to change their tx crystal?
Old 02-06-2004, 11:47 PM
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fritch1969
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Default RE: Transmitter Channels

I'm done

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