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Ever had a problem when swapping crystals?

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Old 06-20-2002, 01:03 AM
  #26  
thomasb
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Default Ever had a problem when swapping crystals?

Crystal (frequency) changing by an unlicensed end-user on Hitech, JR and Futaba radios operating on 72/75MHz is a violation of FCC rules.
That is the basis of this endless discussion. USA only.

They must be changed and verified by a holder of an FCC 1st. Class Radiotelephone License.
I am not sure if this is necessarily true. The "factory" and service center technicians that install the xtals probably do not personally hold such a ticket. But they are acting under the approval of their employer's established radio business and use the procedures blessed by their firm. This does not necessarily mean that every R/C Tx is verified for spurious emissions (they are not) -- it only means that there is a procedure that is followed.

Crystal changing on any 50 or 53MHz radios/receivers can be done by a licensed radio amateur (technician or higher).
As long as they follow the part 97 restrictions, 6-meter ham R/C'ers (technician class & higher) are allowed to perform the necessary maintenance (including changing xtals).
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Old 06-20-2002, 01:21 AM
  #27  
Crash_N_Burn
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Default Ever had a problem when swapping crystals?

Thanks, Thomas!

I know in the television, 2-way and FM radio business there is usually only one 1st class license holder, he signs the log for 2nd class, third class or unlicensed workers (never admitted!), but he is responsible.

I'll bet it is just like you said, the house has the license.

I guess their main goal (the techs) is to set the transmitter on frequency. A spectrum analyzer would show any spurs, but I'll bet they don't see many of them in a licensed, commercially manufactured radio.

Thanks, again for verifying that for me.
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Old 06-20-2002, 01:44 AM
  #28  
Glen Merritt
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Default Ever had a problem when swapping crystals?

You folks are killing me. I try not to jump in too often on this stuff but here goes...

It's not the FCC "law" (which is real BTW and yes Americans really did walk on the Moon, it was not a Hollywood sound stage or a stunt perpetrated by Futaba), but the laws of physics that are at issue here.

So let me take you to School.....

First of all,
All transmitters, from all manufacturers are tuned to the crystal that is in it. Not to the "channel" but to the unique, one of a kind, crystal that is in it! PLL or Synthesized Tx's and reportedly one or two Multiplex products are the exception here.

Changing the crystal in your transmitter will de-tune your transmitter from the optimum signal. Period. There should be no argument. Physics.

Fact: Futaba, Hitec, JR and Airtronics all recommend on their web sites and in all their radio manuals that users should not change transmitter crystals.

Fact: Flying a plane with a de-tuned transmitter is not smart.

So why would you do it? Just to see if you can "get away with it" or are you too cheap to have your radio tuned?

Sure it appears to work the first 10 times you go to the field and fly....and I bet your fellow club member won't even know that your de-tuned radio transmitter shot down his $2000 scale P-51. Just his bad luck to be on an adjacent frequency. Can't beat the laws of physics.

For those who wish so hard to believe in conspiracy theories, trust me, crystals are a huge pain in the a@@ for radio companies, we hate them. Do the math,

6 channels of 27MHz,
Tx and Rx equal 12 crystals

30 channels of 75MHz,
Tx AM equals 30 crystals
Tx FM equals 30 crystals
Rx AM single conversion equals 30 crystals
Rx FM single conversion equals 30 crystals
Rx RM dual conversion equals 30 crystals

50 channels of 72MHz
Tx AM equals 50 crystals
Tx FM equals 50 crystals
Rx AM single conversion equals 50 crystals
Rx FM single conversion equals 50 crystals
Rx AM/FM dual conversion equals 50 crystals

412 part numbers just for crystals. Nightmare time.

Now are ya ready for the reality check?

At Hitec alone we have about 4 different 27MHz systems, 22 different 75MHz system configurations and 35 different 72MHz system configurations.

Do the math, that’s why it’s often difficult to get “your” specific channel on a new radio system or to get a specific crystal from a dealer. No manufacturer, no hobby distributor and no hobby dealer can afford to stock 1/1000 of the possible combinations of system configurations that can be offered. We are limited by manufacturing ability, warehouse space and component availability.

For all the above reasons, radio manufactures hate crystals. Physics once again raises its beautifully manicured un-yielding head.

So forget the whole FCC issue and any paper law that may be “in the books” just be a good citizen and don’t break the laws of physics or you, or worse, some unwitting modeler will pay for your indiscretion.

Just to clear up a couple of things, the car guys on 27 and 75MHz do change their channels all the time. It’s just not that big a deal if their radios are de-tuned a bit, rarely will an out-of-control 1/10th scale R/C car kill someone.

Another issue is “why do Futaba, JR and Airtronics sell 72MHz Tx crystals” if it’s not safe (or legal) for the user to change them? Go figure.

Ciao,

Glen Merritt
35 year modeler
Advertising and Marketing Director for Hitec USA
Currently a Board Director of RCHTA
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Old 06-20-2002, 02:13 AM
  #29  
thomasb
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Default Ever had a problem when swapping crystals?

I try not to jump in too often on this stuff but here goes...
I tried to stay out too, but like a moth to a flame...

For those who wish so hard to believe in conspiracy theories, trust me, crystals are a huge pain...
But I am nearly positive that the spurious gunman was a third overtone crystal hiding on a grassy knoll.

So forget the whole FCC issue and any paper law that may be “in the books” just be a good citizen and don’t break the laws of physics or you, or worse, some unwitting modeler will pay for your indiscretion.
I think that nearly every angle has been discussed here. Something tells me that the advice offered here will not sink in with everyone. This topic will be back again and the same dialog will once again consume forum bandwidth. Till then, I am off to work on my model.
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Old 06-20-2002, 02:19 AM
  #30  
Crash_N_Burn
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Default Ever had a problem when swapping crystals?

Thanks, Glen for setting us straight on this.

I always thought that most current transmitters were manufactured as broadband devices. i.e., changing a crystal (to effectively change the channel, or frequency) imparted a minor degradation in power output (without tuning). The 72MHz ban is split, I believe, into two broadband segments.

A power degradation from 750mW to 500mW would be minor, and unnoticeable, to most fliers.

Unless I misread your post, the power output vs. the on-frequency condition are two different criteria. The FCC doesn't care about a reduced power output from a crystal change, only an off-frequency condition.

The chance R/C modelers are taking by changing their own crystals is an off-frequency condition. Reduced power output would only harm the owner/flier, and no others.

Do you agree?
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Old 06-20-2002, 03:48 AM
  #31  
ftomteen4cat
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Default Ever had a problem when swapping crystals?

I've always held the belief that it's easier to make rules than it is to educate the masses.

Case in point - I frequented a factory in a company I worked at where it was mandatory to wear static-dissipative smocks. Since we weren't handling boards during this visit, we didn't have smocks on. We were promptly chewed out by a line manager because static electricity was going to jump off our bodies and fly eight feet into the assembly line and arc the panels going through the line into pure carbon.. We thought about explaining triboelectric effect for a moment, but no. It's easier to just make a rule.

If you make it okay for everyone to change their own crystals, some bozo is going to screw up his radio and kill someone when he loses control - nevermind that not everyone has a spectrum analyzer and counter in their garage. Once he does this he'll expect the AMA to dutifully pay his claim or litigate them to death. It's illegal. Problem solved.
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Old 06-20-2002, 07:04 PM
  #32  
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Default Ever had a problem when swapping crystals?

Exactly ! Even the case at our field where a crystal swapper "Ive been doin it fer YEARS!" misread the partially obliterated 48 as 43 and proceeded to endanger everyone at the field while he crashed the plane of the poor guy on 48 legally ! Not to mention the kid he narrowly missed now has no interest at all in coming back out to see dad fly !
He almost got away with it too . Of course he tried but others at the field knew his track record and we were not surprised to see him putting his plane away and try to make a break for it . A quick check of his TX was all it took . We did warn the members of his new flying club of his habits .

The human element is a BIG part of the equation and some of the comments right here reinforce the reasoning behind the law !
Some people think it is a matter of the center of the carrier being on freq and that is not even 1 % of the issue. If they don't understand that what they need to know is beyond the scope of this forum .
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Old 06-20-2002, 07:08 PM
  #33  
Glen Merritt
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Default Ever had a problem when swapping crystals?

Dave, the issue is a de-tuned Tx will be "off frequency" and there lies the obvious danger. Swapping X-tals will not effect the power output.
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Old 06-20-2002, 07:47 PM
  #34  
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Default Ever had a problem when swapping crystals?

As I understand it the fear is that you might have a bad crystal. The transmitters we use have the same basic design as those overseas where it is most definitely legal to swap the crystal, and some of these country's are also using narrow band. The only difference is the modifications to shift the frequency and bandwidth. Our club has a frequency monitor, while not as accurate as a spectrum analyzer it does give a graphic display of the entire transmitted frequency, strength, and bandwidth. Swapping a crystal will often cause the signal to widen, or strengthen, too my knowledge we have never found swapping crystals to be off frequency. And they are well below the minimum limit on adjacent channels and yes a legal transmitter will interfere with an adjacent channel a few dB at close range. When comparing to other radios on the same channel they also have slightly different characteristics on other channels, including those with Spectra modules. I attribute most of the slight differences to atmospherics.

I had my radio re-tuned and frequency swapped by Radio South I chatted with the technician, he admitted that he rarely has to re-tune radios after a crystal swap unless it was out of tune before swapping the crystal. And when it is out of tune it is usually fixed by replacing the crystal. Maybe the problem is bad crystals? He does not make any changes to the radio if it is in spec, even if it is slightly different.

I thought that the regs on repair was relaxed a bit a few years ago. I think now the 1st class lic is required only for avionics and high powered commercial stuff, the rest only need certification from manufactures. Tried to find this on the FCC web site but it is slow today.

Not sure I understand what happened LF, but I don't see what misreading the channel label has to do with changing crystals. That could happen with the original crystal, especially if someone bought a used radio, or someone pulls out an old not often used transmitter.
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Old 01-06-2004, 09:55 PM
  #35  
jcosta
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Default RE: Ever had a problem when swapping crystals?

Fact: my brand new Hitec Laser 4 35MHz has compartments for storing crystals

Fact: In Europe it is perfectly legal to swap Tx crystals

Fact: any LHS in Eurpe selling Hitec products will sell both Rx and Tx crystals

Is Hitec in this forum telling me they are trying to sell me a product that will affect my Tx?

Why do people claim that swapping crystals will make the TX work incorrectly?

Is it a 72MHz specific problem, or is it just excess bureaucracy in the States?

My instruction manual states that, in the USA, the crystal must be changed by Hitec,

I'd really like an answer from Hitec... With technical reasons on why I shouldn't swap crystals in my TX.
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Old 01-07-2004, 06:45 PM
  #36  
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Default RE: Ever had a problem when swapping crystals?

Oh Geez ,the euro thingy AGAIN . YOU CAN CHANGE THE FREQUENCY IF THE LAWS <REGULATIONS AND OR STANDARDS IN YOUR COUNTRY ALLOW IT. Most frequency regulating /administrating authorities could care less it you break your toy airplane PERIOD. The !QUOT!danger!QUOT! in some areas ,and YES a demonstrated DANGER ,YES YES there HAVE been !QUOT!incidents!QUOT! is to SHARED frequencies in locales where the separation is 10 KHZ. We have had clowns stick receiver crystals in their transmitters ,CB crystals and scanner crystals. The result is a signal radiated far from the intended channel.
What Spurtpilot and others tries so hard not to understand is that a mis marked crystal would be caught upon installation when the RESPONSIBLE tech check the output frequency. A MISREAD crystal by some greasy fingered 55 year old who left his glasses at home and is now sharing channel 58 with someone else ....he READ 53 ! THAT is why the AMA is concerned with the practice.

Bottom line HITECH only owes you a good product and a warranty ,they deliver that part . No one !QUOT!owes!QUOT! an explanation.
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Old 01-07-2004, 09:21 PM
  #37  
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Default RE: Ever had a problem when swapping crystals?

So I guess there is no problem if I missread the numbers on a Spectrum module? Isn't that as easily missread?
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Old 01-08-2004, 06:55 AM
  #38  
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Default RE: Ever had a problem when swapping crystals?

There you go again "guessing"

Yes there is a problem ,you may have shot someone down .Like I said (A FEW TIMES) before . THE FCC DOESN"T REALLY CARE IF YOU SHOOT A TOY PLANE DOWN . But , the SPECTRUM module CANNOT transmit on the SHARED frequencies and cause INTERFERENCE with LICENSED industrial users . The mismarked crystal is only ONE actual cause of interference that a tech would have avoided ,try not to make your entire case on that one point. It waas only mentioned as ONE actual case.
The system is meant to eliminate as much harmful interference as is practical . If the system weren't working as it is we wouldn't be flying on these frequencies

Quote:
"What Spurtpilot and others tries so hard not to understand is that a mis marked crystal would be caught upon installation when the RESPONSIBLE tech checks the output frequency."

Of course the markings on the spectrum module are much better than the printed tape on some crystals. And you are still trying .
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Old 01-08-2004, 11:17 AM
  #39  
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Default RE: Ever had a problem when swapping crystals?

why are there companys that have exchange crystals for sale if it is unlawful.no penalty for doing this? I know nothing about the inside of a radio i send them in every couple of years to have them tuned.
lonnie
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Old 01-08-2004, 03:32 PM
  #40  
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Default RE: Ever had a problem when swapping crystals?

. May be because there are no laws regarding trading ,buying or selling . One does not disallow tne other .You may go down to the amateur radio supply store and buy any transceiver, transmitter or amplifier on the shelf. My husband bought a 20 Kilowatt AM broadcast transmitter . That does not mean you are allowed to transmit with any of it .

Used crystals have their own risks too.
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Old 01-08-2004, 10:06 PM
  #41  
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Default RE: Ever had a problem when swapping crystals?

ORIGINAL: crownvic
why are there companys that have exchange crystals for sale if it is unlawful.no penalty for doing this? I know nothing about the inside of a radio i send them in every couple of years to have them tuned.
Good for you lonnie. Now if we could just get the rest to do the same.

It is Illegal to SWAP crystals. It is LEGAL to sell them. Just like it is leagal to buy an sell radar detectors, but it is illegal to use them in many states and provinces.

By the way, the Canadian laws ALSO prohibit crystal swapping. This issue crops up every winter (when pilots arent flying). Last year I did the research into the Canadian laws to confirm we prohibit crystal swapping too.

Inquiries about the RSS-210 Standard may be directed to Industry Canada's local office or to:
Manager
Radio Equipment Standards
Industry Canada
300 Slater Street
Ottawa, Canada
K1A 0C8
Tel: (613) 990-4699 / fax: (613) 990-3961
E-mail: res.nmr@ic.gc.ca
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Old 01-08-2004, 10:26 PM
  #42  
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Default RE: Ever had a problem when swapping crystals?

I think the intent of the statement about not changing freq is to prevent one from modifications that would cause a TX to operate outside the assigned band we have been assigned. I think we are hard pressed to to read into this a violation for someone which stays within the band.

The problem they(FCC) are trying to address is those that modify Transmitters to broadcast outside our assigned range.

It is not allowed to modify a HF (HAM) Transmitter to broadcast outside of the Bands that are licensed to the operator -- (the most common case is Ham bands - which are blocked from transmitting on many frequencies) - the same intent is meant for our RC Transmitters.
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Old 01-08-2004, 11:21 PM
  #43  
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Default RE: Ever had a problem when swapping crystals?

I'm sorry coveredup,But I have to dissagree! I'm quite certain that the FCC's "intent" is to prevent the innocent RCer (who knows far to little about electronics and radio theory to understand WHY it would cause a problem) from changing the crystal in his transmitter.
The frequency mudule in an RC transmitter(be it "plug-in" or affixed) contains far more than just the crystal,output transistor and antenna connection.They ALL have at least 2 pairs of a capacitor and inductor combination.The purpose of these is to "TUNE" the output of the transmitter.By adjusting the inductor in each pair,they are "TUNED" to permit ONE frequency to pass through AND to "Supress" all others. The "Narrow Band" requirement states that the signal level Must be down 55 db at 20khz from the center frequency.The "Tuning" circuits in the rf module are what "supress" the off frequency components by the required 55db.
When Anyone takes a transmitter which has been tuned to transmit on one frequency(channel),and replaces the crystal with a crystal of a different frequency, the tuning circuits will supress the signal at the new crystal's frequency(unless they are ReTuned for the new frequency).In addition,the tuning circuits will NOT supress the frequency they were originaly tuned for.If your transmitter was originaly on channel 32,and you replaced it's crystal with a channel 31 or 33 crystal(do you remember reading "a few channels won't make any difference"?),the signal at channel 32(the frequency the circuits are tuned for/ 20khz off frequency)will NOT be 55db down.And the signal at the new channel Will Not be up to full output strength.
"If you change the crystal in an RC transmitter,and you don't have the transmitter "ReTuned"
You Will NOT get full full operating range from the system!You WILL transmit unacceptable signal levels at the "Original" frequency(read that," INTERFERANCE")!AND You wil be violating the FCC regulations allowing you to use your RC radio (read that,"Breaking the LAW"?"Voiding you authority to operate the equipment")!"
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Old 01-09-2004, 12:20 AM
  #44  
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Default RE: Ever had a problem when swapping crystals?

if I understand all of this it sounds like its ok to change the crystal in the RX but not in the TX is this about right?
lonnie
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Old 01-09-2004, 01:01 PM
  #45  
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Default RE: Ever had a problem when swapping crystals?

. Yes ,Crownvic that is exactly correct. And it IS legal to open up Ham gear to transmit outside the Ham bands. It is NOT legal to transmit there however. It is legal to buy old police and military radios that transmit outside the ham bands ,but od=f course don't use them outside the ham bands.
. The main reasons for licensing hams are 1 ,to assure they are aware of basic radio technical aspects. 2 To assure they are aware of regulations regarding their operation . Once a person is tested and swears they have read the rules and regulations they can no longer claim ignorance as a defense. I like the license thing and it would go a long ways to eliminating some of the misconceptions we have in this hobby . Some people may not like that attitude .
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Old 01-09-2004, 03:02 PM
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Default RE: Ever had a problem when swapping crystals?

So, there are additional restrictions on the RC frequencies(operators)?

We can not physically modify our TX even though they are still operating on the same legal frequencies(band)?
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Old 01-09-2004, 05:19 PM
  #47  
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Default RE: Ever had a problem when swapping crystals?

Yes , you MAY modify your transmitter outside the RF stage . A little loophole . You can change pots ,batteries switches etc legally . The RF section including the antenna are technically off limits.
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Old 01-09-2004, 06:13 PM
  #48  
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Default RE: Ever had a problem when swapping crystals?

Yes, let's do the Math!

OK we'll only count unique TX's. I've added the totals to the numbers you posted earlier. So according to your statements hitec manufactures approximately 2434 unique transmitter models for the US alone. Sorry, but I have a hard time believing that.

AFAIK, hitec radios are neither designed nor manufactured here in the US. So how do you, as an advertising and marketing director in the US, really know that there is someone hand-tuning each TX to it's specific xtal somewhere on an assembly line in Asia? Have you been there and seen the operations in the factories? If the TX's come out of the factory within specs, would you know or even care how they did it? Just because they are within specs doesn't mean they are all specifically tuned to a certain Xtal.

I'm sorry, but by posting your numbers, you've only further cast doubt that TX's are really tuned to a specific Xtal. Manufacturing 2434 unique TX's would be way too cumbersome when you could get by with 61.

Everyone asks why the manufacturers continue to make the xtals user accessible. It's not for our sake but for theirs. They can make up a bunch of units all tuned to 72MHz, and when there is demad for channel 42 TX's, they pop in the corresponding xtal, box it up and ship it out.

I've said it before, and I'll say it again, manufacturers don't tune to a specific channel or xtal, but to a band (ie. 72, 75, 27) and they do it within specs.

Nathan


ORIGINAL: Glen Merritt
For those who wish so hard to believe in conspiracy theories, trust me, crystals are a huge pain in the a@@ for radio companies, we hate them. Do the math,

6 channels of 27MHz,
Tx and Rx equal 12 crystals

6 X 4 = 24 unique TX's here

30 channels of 75MHz,

30 channels X 22 models = 660

50 channels of 72MHz

50 channels x 35 models = 1750

Nightmare time.

Now are ya ready for the reality check?

At Hitec alone we have about 4 different 27MHz systems, 22 different 75MHz system configurations and 35 different 72MHz system configurations.
Glen Merritt
35 year modeler
Advertising and Marketing Director for Hitec USA
Currently a Board Director of RCHTA
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Old 01-10-2004, 02:56 AM
  #49  
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Default RE: Ever had a problem when swapping crystals?

OK!! You people have FINALLY convinced me that the Politicians in office aren't all idiots!
They CAN'T be! All the idiots are flying R/C planes,and using this forum!!!

"Beware!! If anyone else shows up while You are flying your model,You'de better just pack up and go hide.He's almost Surely swapped his crystal,and the world is not safe."
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Old 01-10-2004, 09:30 AM
  #50  
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Default RE: Ever had a problem when swapping crystals?

What a lot of the xrystal swappers fail to realize is that, while their equipment works to their satisfaction when they swap crystal, other users sandwiched in between our channnels may be adversly effected because of the now out of spec spectrum they are transmitting; such things as cranes, heavy equipment, cell phones etc. Please guys, obey the law and save our free use of the spectrum.
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