fotta

I understand that the FCC prohibits swapping transmitter crystals in radios that have removeable crystal modules (Futaba 8U, 9C, etc.). Then again, speeding is also illegal...

This is not meant to start a flame war, but just in case, be aware that I am wearing my asbestos underwear and tin-foil hat.

THE question:

Have you ever swapped Tx or Rx crystals and experienced a problem attributed to this? i.e. glitching, interference with nearby bands, decreased range, etc.?

Phil Cole

The FCC prohibits swapping any transmitter crystals, module or not.

If your Toronto is the one in Canada, you need to look at the Canadian regulations, however.

Ed Smith

To answer your question, I do it frequently and have not experienced any problems.

I pylon race. In a race there can be four pilots almost bumping in to each other and dueling with antenna. Interference is not an issue.

Ed S

Ladyflyer

My Feedback: (2)

Laws are for pions. The Elite can do what they want.
My favorite laws ignore are traffic laws. When we drive to Buffalo thru Canadada we always stop at the duty free. We get snockered on CC and charge across the 401 at 110 clicks. Heck we've been doing it for 20 yearch wiff no problem. Musht be OK

mulligan

LOL, LF.

fotta, Ed, if you change your TX transmitter and show up at our field, shoot someone down, or worse yet, cause an accident that jeopardizes our club- well, perhaps some in our club won't be too concerned with that other pesky laws regarding assault and battery.

The above should not to be construed as a threat, but when you ignore laws and put others at risk, be prepared to face the music one day.

- George

fotta

well, hmmmm, the purpose of this thread was to learn if anyone had ever experienced any problems and thus to forestall the possibility (or probability) of anyone getting shot-down.

I am sure that this sort of thing has happened due to use of damaged crystals or transmitters. I want to know if swapping undamaged crystals per se, has ever caused a problem.

promag

I change constantly but only in high channels ( 35 - 50). no problems at all.

Never change between low and high channels

mulligan

If you search RCU, you will find numerous threads on the subject. Experts (LadyFlyer, AM Cross of Futaba, et. al.) have chimed it on the technical pitfalls.

LF's satire above illustrates the point we are trying to make. Just because some have claimed they've had no problems doesn't mean there haven't been or that others haven't had (if you search, you'll find posts by those who have been shot down). Keep in mind that its not the person who changes their TX crystal that typically would have a probelm, but rather an innocent co-flyer- and if someone is shot down, the cause might likely go unknown.

And this isn't even the basis for the FCC rule. As secondary, non-paying users of the frequency band, if we interfere with the primary users (e.g., pager sites), then the hobby as a whole risks being ostersized by the FCC with no where to transmit unless we pay- and you think the hobby is expensive now?

All you need to do to avoid this is have the radio changed/checked out by a licensed radio technician- done. Sheesh, it seems like less trouble to just do it right than to research the potential problems of cutting corners on RCU!

Bottom line, AMA santioned clubs require you to follow AMA rules. AMA requires you to abide by FCC rules. If your club tolerates this, have at it. Ours won't.

- George

Jax RC-RCU

My Feedback: (7)

How would one know that one has changed his crystals, even in Orlando? Unless you broadcast it to everyone around, I dont see how anyone would know. Is there a secret code or frequency thing inside a transmitter or receiver box? Are there marked FCC patrol units prowling around your field with ATF antennas? At our field, everyone gets hit on channel 44, so I switched both crystals with a top of the line set of new crystals on channel 41. No problems experienced with my plane or with other close channels.

Ed Smith

Maybe George should preach to the AMA. I fly at AMA sanctioned contests with AMA approved Contest Directors. I have been asked to change frequency to participate in flyoffs. So have many others.

If, as I have now been informed, this is breaking the law then the AMA should ban the practice.

Beware of LF's satire as she obviously does attack the C.C. If she charges across the 401 she will not end up in Buffalo.


Ed S

mulligan

I don't preach, Ed... but thanks for the barb.

I would bet, though, that THAT CD at THAT contest at THAT field would not find support from the AMA regarding asking people to switch CRYSTALS at the event.
But the AMA is not a law enforcement agency. There would be an issue regarding an insurance claim maybe, if that came to pass. If the FCC discovers that a significant number of people are not following the rules and chooses to revoke their permission for us to use our current free frequencies, then we'll know who first to thank.

And, Don, any kids?? What if I told you that when I was a kid I drove 120 mph while drunk... but I didn't tell anyone, and no one was hurt, and no one caught me?? Does this make it ok?? This is a different order of magnitude issue, but I just don't understand the logic you are presenting. If you want to break the rules, then do it, don't tell anyone, and hope you don't get caught. But don't tell me that it's ok to ignore the rules because you know better by your/others experience.

- George

fotta

George,

Sometimes rules don't make a whole lot of sense in some ways.

i.e.
- Alcohol is legal, marijuana is not, whereas in my experience (I drove a taxi while in University) it is drunks who cause problems rather than people who are stoned and tend to giggle a lot.

- Speeding fines are an excellent source of revenue for governments. Though going 20km over the speed limit on a highway designed for much higher speeds is illegal, is it really dangerous?

I am sure that one could come up with many pieces of legislation of this sort.....

Does this FCC regulation make sense? It seems that the consensus is that changing crystals between widely spaced bands is a problem, but that it is not a problem when doing so between closely spaced bands. Perhaps the legislation addresses this issue and in doing so lumps everything into one broad category.

SwampFlier-RCU

Did I miss something here? Aren't crystals tunned in for a pre-defined band, so if I swap crystals (and have done so) from lets say ch 44 to ch40 how does the transmitter (or the receiver know?)
What I would expect is, for the person who swapped the crystal to display the correct frecuency on the tag and to also pin the correct frecuency on the freceuncy table.
The problem is if a flier swaps crystals and without telling or pinnning the correct channel turns on the tx an shots down another flier or causes an accident

Which brings to mind the Spectra Module on some Hitec Modules. If I understand correctly, you can change frecuency on the radio by using the Spectra module, now there is no crystal swapping involved so no rules are broken but still I managed to change frecuencies....hmmmmm mybe the laws should be checked

Best Regards,
Patrick

Phil Cole

Some technical information.



Crystals are not absolutely accurate frequency references. The actual frequency of the transmitter depends on how accurately the crystal was made, and also on the tolerance of certain component in the transmitter.



In and ideal world, the crystals for each channel would be identical, and the components in the transmitter would be identical as well.



However, they are not. So, when you plug a crystal into a transmitter, it will operate at some frequency which is close to the nominal frequency for the channel. The FCC requires that the transmitter be within 20 ppm (parts per million) of the nominal frequency. At 72 MHz, 20 ppm is 1.4 kHz. This has to be acheived over the full battery voltage and ambient temperature range. Most of the time the transmitter will be within 20 ppm with a randomly chosen crystal, but not always. While it's possible to build transmitters and crystals that meet this specification without adjustment, it requires the use of precision components, and some element of temperature compensation.



While the necessary precision components may not make much difference to the cost of a high-end transmitter, they will affect the margin of a $99 radio noticably.

It's cheaper to pay a factory worker to spend 30 s adjusting each transmitter as it comes off the line than build a bullet-proof design. If the radio were manufactured in the US, the cost trade off would most likely swing the other way.



It is possible for this to be done. Muliplex have apparently been certified with user-changable crystals. To do this, my guess is that they've explained how the tolerances of the compenents in their oscillators stack up, and demonstrated with a sample of production transmitters and crystals that the frequency is always within specification.
If Futabe, JR, etc. chose to , they could go through this process.

The FCC is not concerned about whether we shoot each other down, or that the transmitters bleed over into the next RC channels, or are so far off frequency that the model flies out of range and crashes. They are concerned that the transmitters don't interfere with the license fee paying users of the 72 MHz band who occupy the frequencies between the RC channels. There is only a 10 kHz frequency difference, so with a 10 kHz bandwidth, an RC transmitter does not have to be far off frequency for its sidebands to interfere with the paying users.



Synthesizers use a single crystal oscillator as a frequency reference for all output frequencies. Provided the reference is within 20 ppm, any channel on the output will be withing 20 ppm. The reference will be adjusted to the exact frequency required as part of the manufacturing process.

Ladyflyer

My Feedback: (2)

Sorry ,this law does exist to protect licensed users sharing the band. Like it or not whether or not you think yourself more astute it IS the LAW ! That is the bottom line. Comply or not.
As for CHANGING the law ,you may be right . There has been floated the possibility of POTTING or otherwise making inaccesible the frquency determining components or making ALL complying radios use modules.That should boost the radios price :stupid: Yes the Spectra and other modules HAVE been approved as well as the Multiplex. They were approved because they DEMONSTRATED stability and purity of signal when frequencywas changed.
The others have not demonstrated this ability. IF they had ,it would be allowable.
YES ! YES ! YES ! THERE HAVE BEEN DOCUMENTED PROBLEMS WITH PEOPLE CHANGING THEIR OWN FREQs . It should not be required to cite these cases every time someone wants to exempt themselves from the law.
So if the question is have there been problems ? YES ,some from the human factor and some electrical.
Is it against the law in the US ? YES
Do you want to pick and choose the laws you want to obey? That is a personal choice and has more to do with character.
If you want to change crystals LEGALLY just get a ham license. They are EASY to get NOW !

gubbs3

My Feedback: (1)

I used to race r/c cars where we had up to ten cars on the track at a time. Even more during practice. I had 3 sets of crystals that I used just incase someone was on the same frequency as I was. This was sometimes the only way to get on the track because sometimes 3 other people also were on the same channel. To me, changing channels is a way of life. However, if you were to use the 72 mhz band (air) for cars or the 75 mhz band (surface) for planes, then that is a major problem.

Sport_Pilot

Ed,
It's not against the law, it's BS started by the Futaba people. It may be against their FCC certification but the FCC reg does not address this issue. If it did then Multiplex would not allow changing the crystal of the transmitter either.

thomasb

I suggest that you read the FCC's Part 95 doc. Here is the passage that clearly indicates the intent of the ruling:

§ 95.645 Control accessibility.
(b) An R/C transmitter which incorporates plug-in frequency determining modules which are changed by the user must be certificated with the modules. Each module must contain all of the frequency determining circuitry including the oscillator. Plug-in crystals are not considered modules and must NOT be accessible to the user.


The FCC has questioned the radio makers on the accessibility of the Tx xtals. For sure, their visible location promotes swapping. In a response letter I read from a JR submission, they (JR) claimed that they glued them in place. What baloney, since mine are not glued in.

An article in last year's AMA's monthly magazine also mentioned that xtal changing was illegal and as such was against the AMA rules too. I suggest you write to them to get the bad news first hand.

The way to stay legal is to get a Tx with a plug-in RF module and outfit it with a couple different modules. This is the solution that we have been offered and IS the answer to the problem. The non-module radios are for those that want to stick with one channel. All others are granted this module swapping trick. This may seem like a big expense to some, but it is all we got until someone organizes a serious effort to change the law.

Frankly, given the limited lobbying power of our hobby, and the demand by big industries that need RF space, we are fortunate that we have we we got. The R/C channels are still free to us, but as mentioned before, we are SECONDARY users on a band utilized by money paying licensed operators. So, be careful what you wish for.

I wish to make it clear that I am not the FCC police. If you want to change xtals then that is your business. But be aware that you are in violation of FCC and AMA regulations.

Lastly, this topic has been so overly debated, on so many forums, it would sure be nice if someone created a factual web page on the Xtal changing subject. Otherwise, the xtal related jabs and barbs are sure to start all over again next month.

Sport_Pilot

Thomas,
That paragraph is speaking of transmitters with the very plug in frequency modules you recommend. It says that all components must be inside the module and that the crystal must not be accessible to the user. It does not say that there cannot be a user accessible module on the TRANSMITTER!

The FCC does not intentionally certify equipment which does not comply with its regulations. So why did they certify radios from all manufactures with user accessible crystals? Why does Multiplex claim that the users of their radios swap the crystal without breaking the law?

It may be that the radio manufactures got sued at some time because the radio crystal was swapped by the user and that radio failed causing injury or property damage. But I cannot see anything in that reg that says it's against the law!

thomasb

You are correct. Modules that contain all the frequency determining components, including the oscillator (the XTAL), are just dandy. It specifically says that the xtal is NOT such a module.

Yes, the XTAL on all the popular Tx's is VERY accessible. But it is against the FCC regs for an end-user to change it. Rx xtal swaps are fine. Amateur radio operators (hams) on six meter R/C can swap all they want too. Us USA 72/75Mhz users are in shared RF space so we have the noted restrictions.

I'm not sure where the confusion lies. I did my best. In all due respect, you are incorrect and I am sorry that I was not able to help convince you otherwise.

The Part 95 rules are "the law" and they also mention the federal penality for infractions. On a litigious level, an important issue is what AMA's insurance would honor in a case involving an suspicious RF problem. Contact them for clarification -- perhaps they have changed their position in your favor (doubtful).

You may not like the ruling, but it is there. I will not pass judgement on the act of Tx xtal swapping -- I am only attempting to share the facts.

thomasb

I forgot to add that the xtal is considered an "internal component."

Part 95, § 95.210
(d) You must not make, or have made, any internal modification to a type-accepted transmitter. (See R/C Rule 22.) Any internal modification to a type-accepted transmitter cancels the type-acceptance, and use of such a transmitter voids your authority to operate the station.

Rule 22, Internal modifcations do NOT include:
(2) Changing plug-in modules which were certificated as part of your R/C transmitter.

Hence, FCC type accepted RF modules can be legally swapped. This also includes the use of synthesized modules that can dial the various R/C channels.

Sport_Pilot

Ruling? What ruling? You state I may not like the rilling but you never said a rilling was made. I do not know of any court cases on this at all!

I work with specifications and regs regularly. You cannot take a paragraph talking about a frequency module and apply it to a transmitter without a frequency module. And there are not regulations on changing an external crystal either. If it's legal to change Multiplex's external crystal's then its legal to change the other brands. And I know the FCC doesn't certify radios that do not meet their regs, they may slip up every now and then, but not every non frequency module radio ever made by several manufactures!

thomasb

Multiplex took the time to submit the additional data to obtain this exemption. The other R/C makers have not.

Just contact USA based Hitec, JR, and Futaba. They will confirm that their gear is not type accepted for end user xtal swaps.

BTW, if you are outside the USA then none of this applies to you.

Ladyflyer

My Feedback: (2)

Sport, you are wrong on this one . What Thomas SB is saying is correct. It is obvious you have never held an FCC license or you would not be arguing the point.
No ,the Futaba has NOT been certified for user frquency change.
Multiplex has DEMONSTRATED the suitability of thier equipment,the others have not . It may well be the REASON the others haven't is to generate a bit of work for thier factory service centers. Don't put it past them .
But till they do it IS against the law and it seems odd after about 50 zillion word on the subject ,people will not understand .
IT IS ILLEGAL. There is NO excuse for ignorance,the manufacturer,the AMA, and the FCC have spelled it out in plain English.
There are those who twist anything written to suit what they want it to mean. A sign that says SPEED LIMIT 35 AHEAD to those peoples twisting would mean if you have three people in the car(or whatever with HEADS) it is OK to go 105MPH. Three heads x 35 mph = 105 MPH.
Until the JUDGE sets them straight

In the mean time the logic of those folks is best ignored !!

Crash_N_Burn

Folks, please correct me if I am wrong....

Crystal (frequency) changing by an unlicensed end-user on Hitech, JR and Futaba radios operating on 72/75MHz is a violation of FCC rules.

They must be changed and verified by a holder of an FCC 1st. Class Radiotelephone License.

Crystal changing on any 50 or 53MHz radios/receivers can be done by a licensed radio amateur (technician or higher).

This is what I believe...is it correct?