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Old Aug 24, 2005, 12:47 AM
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Indianapolis, IN
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crystal changing ?'s

Okay, I have read the fcc statement about changing crystals and all, and am a bit confused. I see no discrepancies in what band being used except for the 27 mhz band. So does this rule apply to just aircraft bands (49,ham and 72) or for 75 surface frequencies also. I have tried to find the answer to this but no luck. It seems to me that if 75 was restricted also, then an enforcer would just need to show up at any r/c race night at any facility and bust and confiscate everyone's equipment. When I was racing trucks, they required at least two channels for you to enter any race. And I do not remember anyone who used the original channel their radio had came with. If this is the case, I have 4 surface radios that are in violation, as I don't even have the crystals for the channels they came in. And these 4 are used at least once a week, my old magnum am is used daily in my cul-de-sac. I am a newb into air r/c, so never heard of this fcc rule and not sure if it applied to everything but 27 band. I am also confused about which ones are certified to be changed out, is it up to the manufacturer or the certification level to be allowable to change the crystal? I found somewhere on ezone that if the crystal has a small plastic housing around it then it is changeable. both my radios have this, but never read a second opinion on that. I have a futaba skysport 4 out of an avistar .40 trainer that I am using and an old conquest fm 4 channel that I use as a buddy box. the channels are 50 and 58. Last night I was checking some of my electric setups and switched the crystals to check my second plane which is under construction still, and range checked it, just fine. So I am a bit confused on all this, and whether it was just older technology or newer radios that were included. thanks for any help that could be provided and all the help I have already received. this forum is GREAT!!!!
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Old Aug 24, 2005, 10:40 AM
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United States, FL, Jacksonville
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FCC rules apply to transmitters regardless of thier use.

Enforcement is another issue.

Transmitters are whats covered under the rules becasue they are "type accepted" by the FCC.

The newer models that feature the RF Plugin modules, the module contains all the components required to tune the output and maintain type acceptance so you can change the modules legally.
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Last edited by barracudahockey; Aug 24, 2005 at 10:53 AM.
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Old Aug 24, 2005, 10:17 PM
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Indianapolis, IN
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Ok

so, does that mean anyone that changes a crystal in their radio w/o a module is breaking this rule? If so, then why is it advocated and common practice at any car race in the U.S. and never mentioned about the fcc rules? I've been to national races sponsored by ROAR and IFMAR, with no mention of this. I had never heard of this before getting into planes, so is there a reason that plane guys are so knowledgeable about it and not car/surface guys? If this is the case, I suppose I've been breaking the rule since I started in r/c. My first race it was determined that I had a bad rx crystal and the shop didn't have one in my channel so I bought a new channel pair. Been the same with that tx ever since-15 years ago. I'm confused
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Old Aug 24, 2005, 10:51 PM
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The details are printed in the FCC Part 95 rules. Despite the banter about how unreasonable it might be, Tx xtal changes on type accepted R/C transmitters, operating on 72 or 75Mhz, is not permitted.

Yes, a huge number of folks ignore it, including the officials that run R/C car events. It's the same deal with nearly every other law on the books; rules that are not all that convenient to our wishes are often ignored.

There is a never ending dialog about this on every RC web site. Yet, no one has officially taken up the cause to lobby the AMA to force a change in this rule. Frankly, if a majority of the AMA members demanded it, there would no doubt be some attempt to negotiate a FCC rule change. After all, what we have today, in regards to the revised 1991 spectrum, was the result of the work done by the AMA and some key R/C industry players back in the 1980's. They did it once (actually, at least three times), so they could do it again. However, I have to warn you ... be careful of what you wish for.
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Old Aug 25, 2005, 12:31 AM
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so, are ROAR and IFMAR in the wrong, and AMA follows this rule I assume? Kinda new to rc forums, been out for 4 or 5 years and wasn't into internet when I was. Got back in recently and decided to go with planes as well. Like I said, I had never heard of this with just ground freq. So if I showed up at an AMA field, they would want it on the original channel, or do they ignore it pretty much like every other sanctioning body? I know it might depend on which field it was, but looking at overall. Not too concerned really, but I just joined up with my 2 local fields and that's kinda what I was wondering mostly.

Seems like all three could put up a petition or something to fcc, but like Mr.RC said, be careful what you wish for. I realize that if there was enough hype about our freq. and the rules on them, they could just make us go to a more crowded band with less channels, or even worse, take it all away from us. I just thought it kinda weird that big bodies blatantly ignore this rule.

thanks for the quick replies.
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Old Aug 25, 2005, 12:51 AM
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Quote:
So if I showed up at an AMA field, they would want it on the original channel, or do they ignore it pretty much like every other sanctioning body?
It depends on the field and perhaps the pilots that are there when you show up. Some clubs have no issue with xtal swapping (despite the AMA's position on it), others will not tolerate it, even on an informal basis. Ask the club's safety officer first. Above all, respect the club's rules if you wish to remain a member.
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Old Sep 01, 2005, 11:14 PM
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[QUOTE]Got back in recently and decided to go with planes as well. Like I said, I had never heard of this with just ground freq. So if I showed up at an AMA field, they would want it on the original channel, or do they ignore it pretty much like every other sanctioning body? [QUOTE]

If you were to show up at my field I would leave, hopefully before you took to the air. On the ground you can run into the wall or whatever barrier there is .

When you start talking about a plane spinning a prop at 10,000 rpm it is a whole different story. Something goes wrong, radio related and you could be ducking that prop.

Last year one of the Pro fliers was talking to a friend, not paying attention to the flying when a giant scale Pitts took off and after lifting off went out of control. The guy would have lost his leg as well as the other injuries suffered from the carbon fibre prop had it not been for the quick response from people administering first aid. He spent at least 2 weeks in the hospital.
It is not worth the risk to swap AIR crystals without having the TX tuned. If you can go where they do the work ask them to explain what the tech is looking at to make sure the Tx is tuned properly. Swapping crystals DOES NOT put the Freq dead on.

And when you are talking 20 Khz that is the same as tuning your car radio from 99.1 to 99.3. If 99.1 was tuned off to 99.15 it would affect both stations sound quality.(the same as a glitch or loosing control of your plane)

Steve
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Old Sep 02, 2005, 02:21 AM
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Written in jest only !!.

Apparently xtal swapping is only dangerous in the USA, since everywhere else it is allowed.

As stated before, this discussion goes on for ever. Easy fix to this whole "problem" is to buy a radio that has a synth module in it. I did a long time ago.

One facet I always wonder about is "what does the manufactuer do" Does he really tune each and every radio to a specific frequency ?? If so, no wonder they are so slow in production, and how does the manufacturer decide which frequencies to deliver ?? Nuff sed !!!
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Old Sep 02, 2005, 05:00 AM
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The manufacturer either band or half band tunes the TX, theyre not tuned to the specific channel at all... crystal swapping is perfectly legal and extremely common here...
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Old Sep 02, 2005, 06:59 AM
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Perhaps it's time the FCC caught up with the rest of the world which legally crystal changes without a second thought. It's the crystal which defines the fundamental frequency the tx transmits on. No amount of tweaking or tuning the tx will alter that. All that could possibly be acheived would be a slight (if any) peaking of the performance on the frequency already determined by the crystal. The same principle applies to the rx. Crystals are not variable frequency devices, they are very precise single frequency devices - that's what makes them so useful for r/c where you can have a lot of sets working alongside each other. Perhaps no-one has informed the FCC that reeds and super-regen are no longer in use!
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Old Sep 02, 2005, 12:01 PM
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Quote:
Originally Posted by electrotor
Perhaps it's time the FCC caught up with the rest of the world which legally crystal changes without a second thought. It's the crystal which defines the fundamental frequency the tx transmits on. No amount of tweaking or tuning the tx will alter that. All that could possibly be acheived would be a slight (if any) peaking of the performance on the frequency already determined by the crystal. The same principle applies to the rx. Crystals are not variable frequency devices, they are very precise single frequency devices - that's what makes them so useful for r/c where you can have a lot of sets working alongside each other. Perhaps no-one has informed the FCC that reeds and super-regen are no longer in use!
Yes, crystals are very precise frequency determining devices, but it is very easy to "pull" them off frequency. That is exactly what happens in order to generate the PPM (or really, FSK) transmitted signal. And, the transmitter can be tweaked to be right on channel.

Bill
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Old Sep 02, 2005, 12:43 PM
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Slopeking and electrotor what is the channel frequency separation in your homelands. In the USA it is 20Khz eg: Ch 55 is 72.890 and Ch 56 is 72.910 is your channel separation the same?

TIA
Steve
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Old Sep 02, 2005, 12:53 PM
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Quote:
Originally Posted by indoruwet


One facet I always wonder about is "what does the manufactuer do" Does he really tune each and every radio to a specific frequency ?? If so, no wonder they are so slow in production, and how does the manufacturer decide which frequencies to deliver ??
The radio has to be tuned There has to be a crystal in the radio to be tuned Makes no sense to tune the radio with one crystal and put a different one in and be off frequency. Each crystal as well as being a specific frequency affects the capacitance and impedance of the circuit.
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Old Sep 02, 2005, 02:06 PM
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Haralson County GA. USA
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When you swap Transmitter crystals in the US you are not only breaking an FCC Rule but also an AMA Rule. The AMA frequency committee has works long and hard to obtain and keep frequencies for our useage. No other orgainziation which I am aware off puts forth such an effort in time and money.
Perhaps all FCC and AMA Rules on frequency useage should be droped, the FCC could then sell the frequencys to commerical users and we could all go back to U control and Free Flight.
THe use of radio specturm in the US is a previlage not a right.


Charles
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Old Sep 02, 2005, 05:06 PM
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Staffs, UK
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Quote:
Originally Posted by Funfly8
Slopeking and electrotor what is the channel frequency separation in your homelands. In the USA it is 20Khz eg: Ch 55 is 72.890 and Ch 56 is 72.910 is your channel separation the same?
Nope, in the UK on 35MHz separation is only 10KHz. OTOH we have a completely dedicated frequency band. On 72MHz in the US you have commercial users interleaved at 10KHz separation BETWEEN the RC channels.

Things are rarely as simple as you think .

Steve
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