Changing Crystal On TX
 

Tell me is it safe to change crystals on transmitters. Like go from one channel to another.

Thanks,

Mike

RE: Changing Crystal On TX
 

Depends upon your definition of "safe"
1. RC system in use?
2. Regulations and penalties pertaining to the country in which the system is being used?
Subject is well covered in sticky FAQ - Transmitter crystal swapping (USA)
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links

RE: Changing Crystal On TX
 

Its illegal and unsafe.

RE: Changing Crystal On TX
 

It is illegal in the USA but not in some countries, check your local laws. It can be unsafe in any area as different brands of transmitters may require different types of crystal even when the frequency is the same due to type of oscillator design. Does it require Xcut or Ycut crystals, does it use 3rd or 5th overtones etc. Also, since crystal are usually a piece of quartz ground to specific mechanical size, there will always be slight variations between similarly marked crystal requiring that the crystal be pulled (adjust the LC circuitry of the oscillator) to bring it right on frequency.

RE: Changing Crystal On TX
 

He's from Illinois, that makes it illegal. Case closed. IF he has a MODULE based system it is legal and safe for him to swap complete modules.

Whenever changing a RX crystal (legal in all cases) best to use a crystal from the original manufacturer.

RE: Changing Crystal On TX
 

Unless he has a Multiplex crystal based radio, since those are certified and legal (in the US too . . ) for end-user crystal changes. It all depends on how the Mfg. got the radio certified . . .

All the rest, by todays technology, should be totally safe to swap, but that doesn't get past the burocratic B/S prohibiting changes in the US. The same basic modules are magically safe and legal to change in other countries . . . The power levels in R/C are so low, that the current brand of modules are broad-band enough that I doubt that even the factory tunes them when they load a crystal - they most likely just peak 'em up in the center of the band.

- Tim

RE: Changing Crystal On TX
 

Works fine changing the crystal. Know a guy that's been doing it for years. Not a hint of a problem. Don't worry about it.:D

RE: Changing Crystal On TX
 

Unfortunately MrBigg won't be paying the 10 grand per occurance fine so 20 or 30 bucks to do it right is cheap.

RE: Changing Crystal On TX
 

So who's checking? I'm sure the feds will drop their search for Usama bin-Laden and go after the guys changing crystals.[>:]

RE: Changing Crystal On TX
 

Why would I be paying the fine? I didn't say that I do it. You just assumed it. From what I've witnessed, there is no problems at all swapping crystals and I encourge everyone to try it and see for your self. Do it at home away from the field. Do some range tests. Use a gasser with a magneto ignition. Then check your frequencies with one of those frequency checkers. You'll see that the crystal you swapped out is not jumping in between channels like some people might have you believe.:D

RE: Changing Crystal On TX
 

WOW, guess I'm really behind the times. I wasn't even aware the FCC had gotten involved in the search for Bin Laden........

RE: Changing Crystal On TX
 

I've tested out changing a transmitter crystal and it worked fine as long as your original crystal is the same band as the new crystal. I believe low band is like ch 1-30 and high band is 30-50. I certainly don't condone it, but it works.

I would also like to add that I swapped crystals for a total of like 10 minutes just to test it, out of curiousity.:D I'm personally just going to move to spread spektrum and be done with it.

RE: Changing Crystal On TX
 

The problem arise from those companies that PAY to use the channels in between the channels assigned to modellers. If they start getting interference from you and your transmitter, you can guarantee that they will complain to the FCC. As they are paying customers, don't you think somebody would start looking at the cause ??

Remember that they are only 10KHz away from you, if your original crystal is off frequency (as they can be quite easily), the deviation adjustments will bring it back on frequency. You then change the crystal for one that happens to be spot on freq, no unless the deviation is readjusted, those initial offset adjustments (for the old crystal) can easily cause you to be off frequency and splattering into adjacent channels.

RE: Changing Crystal On TX
 

The irresponsible attitudes displayed by some people just amazes me. There are several reasons to NOT do this, fine or no fine.

First, we SHARE the 72 mhz band with other users. If your transmitter bleeds over onto a shared frequency, there's a risk of interfering with them. A field frequency checker WILL NOT CATCH THIS. If we routinely start causing such interference, at some point, the FCC WILL do something about it. And when they have to choose between irresponsible people playing with toys who can't follow the rules, and business users, guess who will lose.

Second, interference is not the only problem. This winter I sent a second hand transmitter to Radio South that I picked up from someone else. The original owner had changed the crystal to a different frequency. I got a phone call from them explaining that due to the crystal swap the power output was only 50%. Tuning brought it back up to 100%. I don't know about you, but I sure as hell don't want to be flying my planes with my radio at 50% power output.

Given these things, it's hard to understand why anyone would be irresponsible enough to advocate changing crystals without sending the transmitter in to be checked and tuned.

RE: Changing Crystal On TX
 

It bothers me to see so many people not complying with the law and in some case advocating the noncompliance. In most cases, I think it is just ignorance on their part in not understanding the consequences. They figure just because they get by with it, it is okay to cause others problems or, in some cases, large monetary losses. I guess this is the same mentality that causes them to drive drunk or speeds on crowded highways. It is to bad they can not take the time to educate themselves on the consequences.

RE: Changing Crystal On TX
 

What Chuck and Rodney said are exactly the point I was making.

RE: Changing Crystal On TX
 

Who has the channels in between our channels?

RE: Changing Crystal On TX
 

72 - 73 MHz
# Private land mobile fixed operation [90.257(a)]
# Special Industrial, Manufacturers, Forest Prducts, Railroad and Fire Radio Services, mobile operation, 1 watt max. [90.257(b)]
# Public land mobile control and repeater stations [22.591]
# Radio control: model aircraft [95.207(a)(2)]
# Aviation Services - Operational Fixed Stations [87.449]
# Auditory assistance devices, 80 millivolts meter max. [15.237]

RE: Changing Crystal On TX
 

Are you one of those that has to see who you are harming to make you a believer?

Rafael

RE: Changing Crystal On TX
 

How am I harming others?

RE: Changing Crystal On TX
 

That's all nice and all, but who's in between "our" individual channel numbers? I'm not trying to be smart here, I just don't understand what your trying to say here. Say someone has a radio that was factory shipped with channel 30. Then they swap crystals to channel 31. They get NO bleed over to 30 or 32. How are they going to "bleed" over to a frequency that is further away?

RE: Changing Crystal On TX
 

Changing crystals, which you haven't said you either do or don't do, is harming others. Suggesting that it's ok merely because you tried it and found that your radio still works ok potentially puts others in a position to cause harm. Either you're trolling to see how long you can keep this discussion going, or you're having trouble grasping the basic concept that we should not be changing Tx crystals on our own, and we shouldn't advocate others doing it. Whichever it is, it's probably gone on long enough.

RE: Changing Crystal On TX
 

Why on earth does it matter WHO is between our channels? What matters is that SOMONE is there and WE are obligated to not interfere with them.
In your example above, you cited a change from channel 30 to channel 31 and then talked of bleeding over to a frequency that's farther away? Perhaps this is the source of the misunderstanding. Channels 30-32 are on 72.390, 72.410, and 72.430 respectively. Since the FCC may allocate the space between these frequencies, it's possible that someone else is using 72.400 and 72.420. If the transmitter is not exactly on 72.410 when the crystal is swapped to channel 31, there's an exposure to be interfering with the user on 72.400 or 72.420. This would be a bad thing.

If the radio isn't tuned properly, it could bleed to a number of different frequencies besides these. But again, why does it matter WHERE they are going to bleed? The FCC regs require that WE send our transmitters to a qualified person for crystal changes. They will ensure that the transmitter doesn't bleed ANYWHERE, thereby ensuring that EVERYONE is safe.

RE: Changing Crystal On TX
 

Wow, you amaze me. You're calling me a troll because I'm asking questions? Thanks alot. Go look at some of my other posts and you'll see that I don't come here to cause trouble and I resent the fact that you are saying that is why I'm here.
What I want to know is whether or not there is a legit reason not to change crystals or has a ban been put in place by the government because they know a few "idiots" will have forgotten that they changed frequencies and will bring potential harm to themselves or others. That's all I want to know.

RE: Changing Crystal On TX
 

I don't think the FCC cares a whit about what you do to yourself. What they care about is interference with someone who has paid them for the use of a frequency.