chall

I've always heard that you shouldn't try and change the Transmitter frequency crystal due to FCC rules, and on my older radios the crystal has always been hidden behind a cover you'd have to pry off.

But the newer radios I've bought (72 MHz and 27 MHz) both have the crystal right up front and easily accessible. Have the rules changed on this? Plus I read on an RC sailboat forum a recommendation that you "always carry of pocket-full of crystals so you can change frequencies if you need to"!!!

HUH? This isn't what I've been taught. But then why ARE the crystals right up front on my 27 MHz ParkZone transmitter and my Airtonics VG6000?

guver

My Feedback: (325)

I am under the impression that is ok to change tx on 27 mhz but not 75. what about 72? I dontknow.

RX I think is ok to change on both.. I am taliking about being lawful.

JohnW

My Feedback: (6)

This has been beat to death... As per FCC Rule 95.222, you may NOT make any internal modifications to your RC transmitter. This means no crystal changes as this is considered an internal modification to the electrical working of the TX. The only way you can change the TX freq is by modules, or you may send the TX to a authorized service center for the XTAL change as per 95.222. This applies to the 27MHz, 72MHz and 75MHz bands as per Rule 95.207. I believe the 50MHz (HAM) band is the only band which is exempt.

The XTAL is easily accessible such that the radio maker can easily insert XTALs at the factory on otherwise completed units. The easy access was not inteneded for the end user. The FCC will often allow this easy access becuase they don't wish to become a burden, or unnecessiarly restrict time to market on new devices.

Whoever posted the pocket full of xtals on the sailboat forum is giving bad advice. If you want to change TX freqs, get a TX that accepts modules. If you want full flexibility, get a synth module.

Unlike TX Xtal changes, RX Xtal changes are OK.

TLH101

My Feedback: (90)

Here we go again.

guver

My Feedback: (325)

Thanks for clearing it up for us.

chall

The 27 Mhz theory sounds the most plausible. Those crystals are clearly labelled, and that would explain the sailors. I think a lot of sailors use 27 Mhz because their radio needs are so modest compared to aircraft. (They think 2 channels is a lot.)

If I can find a definitive answer to this from an authoritative source I will come back and post it here.

Thanks for the input so far.

smokingcrater

see JohnW's post... That applies to all RC use, not including the ham bands on 50 AND 53 mhz... (53 is still legal, just not recommended for use)

chall

I have also found some of the regulations quoted on a Futaba FAQ:

http://www.futabarc.com/faq/service-faq.html#q2

They quote yet another section of the FCC regulations than any of those mentioned by JohnW.

All of which begs the question, why does my Futaba radio have the crystal on the front, as easily removable or changeable as any switch. I can imagine it's due to the radios being sold overseas, where it is legal for the end-user to change transmitter crystals.

At any rate, thanks for all the specifics. While I knew it was historically not permitted to change crystals here in the US, I thought perhaps the rules had recently changed.

s3nfo

My Feedback: (14)

Because your Futaba radio is not built for the US market, it's a worldwide radio, and FCC regulations don't apply in Japan, China, Australia, France..............

Jim Schwagle

My Feedback: (1)

27Mhz transmitters used for RC are not Type-Accepted. The rule forbidding internal modifications refers specifically to Type-Accepted transmitters. See 95.209.

chall

I hope Jim's right, otherwise the Amateur Model Yacht Assoc. members are in trouble. Check out this:

http://www.amya.org/frequencycontrol.html

I can't tell if they're joking or not, as it is written in a somewhat tongue-in-cheek style. But this is the kind of thing THEY'RE saying:

"Swapping crystals is no problem because most every newer radio has the readily accessible crystal socket on the outside of both the transmitter and the receiver."

As an airplane guy, you can imagine my horror at reading this!

chall

I found the text of 95.209:

http://www.nsea.com/PART95/95.209.txt

Fascinating!

Jim Schwagle

My Feedback: (1)

The whole shebang can be found here...

http://www.fcc.gov/Bureaus/Engineeri...98/47cfr95.pdf

PS... The frequencies mentioned in the AMYA article are 75MHz, therefore type accepted transmitters.

smokingcrater

I stand corrected! make sure you have that latest version of the part 95, there are lots of older ones floating out on the internet that do NOT have the '98 additions to 95.209

JohnW

My Feedback: (6)

I may be incorrect on the 27MHz band. The rule that says no modifications (95.222) doesn't clearly state that non certified TX's are exempt, but they may be, which would allow a TX change on 27MHz. I'd ask my FCC sources (parents) to get a "real" answer on how that rule in interpeted, but they live(ed) in Kenner, LA and had to run to higer ground in Baton Rouge. I cannot get ahold of them at this time.

chall

By all means let us know what your sources say. And let them know we're all thinking of them and their neighbors during the current crisis. Memories of Fran are still fresh here in Raleigh.

Jim Schwagle

My Feedback: (1)

This particular topic has been discussed to death and I'll bow out after this, it's too tiring. It seems to me, reading FCC regs that different parts are somewhat contradictory, not surprising coming from a government bureaucracy, in fact, it's in their favor. I don't think anyone would be surprised to find that the FCC would interpret the rules any way they wished to their convenience, should a lawsuit, etc. come up. My own take on it is that I won't do it (crystal swap) because I don't need to, synthesized modules make that unnecessary. People are going to do what they want regardless of rules, perceived rules, perceived lack of rules or any discussion here. This is one way for lawyers to get rich, interpreting language.

swede-RCU

How does the Hitec Spectrum and the Polk Tracker II and III fit in to all this frq/crystal swapping?

S

chall

From my reading of the FCC stuff they're OK. There seem to be exceptions for "plug-in modules". However, I have my own misgivings about radios like the Hitec. If you switch the module to the wrong frequency by accident, you'll be in a fix. I think the Polk is smart enough to sense another radio already using the frequency and refuse to let you on.

JettPilot

My Feedback: (6)

You are OK to swap transmitter crystals. The only thing the FCC says is that it must not cause the radio to operate on an unathorized frequency..... Do a range check, if the range check is good, you are on frequency. If you are far enough off frequency to be a problem, then your range check will be horrible or not even work at all.

Bax

My Feedback: (11)

This is being hacked over in another thread. The consensus of the R/C equipment manufacturers, the Academy of Model Aeronautics, and the FCC advisors is that it's not permissible for an individual to change the channel of their transmitter by swapping out the crystal unless they can assure that the transmitter conforms to the technical requirements as stated in its FCC Type Acceptance. If you are qualified to do so, and have the proper equipment, then you can perform the needed service upon your transmitter to change its frequency.

An individual can change the channel of their transmitter if they have to change a plug-in module that contains all of the transmitter's frequency-determining circuitry. The modules would be certified. This applies to both fixed-frequency and synthesized transmitter modules. If the transmitter has controls on it that allow you to change its channel, that's legal, too, because the transmitter would have been certified with those controls.

Crystals alone are not considered "frequency modules" by FCC definition, and changing a crystal is considered a modification of the transmitter from the state in which it was sold.

Rodney

Jettpilot is totally wrong on saying crystal changing is legal. Perhaps if he would spend a few weeks studying RF and crystals, he would see the error of his ways. Crystals are not, repeat NOT, identical even when set up to be the same frequency. They are ground quartz and all will have slightly differend parasitic properties of capacitance, inductance and impedance due to the gtrinding and mounting variations as well as to cut. Are they X cut, Y cut or ???. When you change one, the sidebands, spurious sidebands etc. all change and, in some cases will fall well outside the design parameters of a type accepted circuit. Since, in the USA, there are others users of the frequency spectrum we occupy, such spurious signals could (not likely but possible) cause those users to have problems, perhaps even life threatening problems. Such advice worries me as, after many years of work in the electronic and test labs, I can see how this could be a big problem which, if practiced often enough, could cause all of us to have serious limitations put on our use of the spectrum.

smokingcrater

That has to be the most ignorant thing I've heard all day, and I've heard alot today! yes, PART of your transmission is on frequency, but how wide are your sidebands, how much spurious garbage are you sending out on someone elses frequency? without test equipment you have no way of verifying it, and a range test doesn't count as test equipment...

jettpilot, have you called the fcc yet and asked them, instead of bringing this up in every thread you can? it only takes a minute and then hopefully this will be put to rest.

BillS

Don’t throw stones. I have never changed a TX crystal. The issue may be similar to driving 60 in a 55 MPH zone.

Right or wrong 4 or 5 people at every flight field I know sometimes change the TX crystal. The people who change crystals don’t broadcast or talk about it. Likely the electronics are so much better today that the rules (whatever they are) have become obsolete. There have never been any identified ill affects from the crystal changes.

The real issue it that there is no easy method to verify a change or to simply test to see if a transmitter is OK. Range testing is a very rough and non-conclusive test. My experience indicates JR equipment will range test five times further away than Futaba.

Rather than hashing an old non resolvable to death it would be better to apply effort towards methods of verifying safe transmitter output. Some people are going to change crystals regardless of what is said here.

Bill

Rodney

Bills, yes and some people are going to murder, speed, steal etc. That doesn't make it acceptable.