zep77

Tried to get a better TX and wanted to use my old FUTABA 6A and switch the crystal in the crap Dynam NEKO 4 that came with the HAWK SKY. Both are 72 MHZ so I thought I could take the crystal out of the Dynam and put it in the Futaba and it would work, WRONG. Why would it not work ? Dynam crystal is 72.790 going into the Futaba which was 72.810. I left the 72.790crystal in the receiver thinking it would work. know there are about 15 years or so apart in age. What has changed in crystals ? Thanks.

BarracudaHockey

My Feedback: (11)

You learned the hardway that crystals are manufacturer specific for the most part.

Also, changing transmitter crystals is illegal.

zep77

Did not know that it was illegal. I have been out of the hobby for over ten to fifteenyears now. I use to change crystals all the time if a radio malfucntioned or traded. I will have to look into that one. Thanks !

zep77

"If your transmitter uses a plug-in module then you can purchase additional modules on different frequencies and legally swap modules in the transmitter. " This is what I found. So you can switch on the same unit just not between units?

BarracudaHockey

My Feedback: (11)

A module isn't the crystal, its the entire RF module like plugs into the back for the radio that includes the tuned assembly including the crystal.

Its illegal unless your trained to properly tune the radio to change frequency determining components such as the crystal.

mrlogdog

My Feedback: (61)

I find it utterly ridiculous that it's "illegal" to swap crystals. It works fine if you don't jump too many channels. Curious what law makes this illegal? Just go fly.

BarracudaHockey

My Feedback: (11)

The FCC makes it illegal, please don't give illegal and potentially dangerous advice.
Thanks

mrlogdog

My Feedback: (61)

two key parts here, potentially and Fcc (federal) The ama and fcc have been working for years to screw the little guy out of the simple joy of flying model planes. I suppose it's illegal to fly AM radio's too. switch your crystals, do a range check and go fly. Next it will be required to fly nothing but 2.4.

BarracudaHockey

My Feedback: (11)

I'm not sure what you're talking about.

The AMA had been after the FCC for years and worked to get the 50 channels we have in the 72mhz band. Part of the agreement to get those channels was sharing the band with other users that operate between our channels.

Go and swap transmitter crystals, without the equipment or knowlege to verify that a transmitter is within output specs, and create interference with other users, paying users of that space, and find out what kind of power the feds have.

Flying in the country with nobody else around? Probably no issue other than reduced range. Try it and cause an accident, and an investigation determines that you acted illegally, and you'll probably be on your own.

I'm not really trying to change your mind, just hoping that others don't think you're offering good advice.

Red Baron Gary

My Feedback: (59)

It is not illegal to swap receiver crystals. It IS illegal to swap TX crystal UNLESS you have the transmitter checked by a FCC licensed technician to make sure that your radio is on the frequency you have changed to.

As most of us do not have the test equipment to do this checking, most of us either buy a new receiver or just leave well enough alone.

My .02,

Gary

Rodney

BarracudaHockey has given you some good advice above. While you may have things working when you swap transmitter crystals, you may also be generating lots of sidebands that will interfere with other users, that is the reason for the law. As to crystals, they are not a simple item. They can have an X cut, Y cut or a variations as well as quite a variation in capacitance. Now they can be used in different types of oscillators as well and each circuit is set up to work within a definite set of parameters so, when you swap crystals you may also be detuning the circuit which can create spurious side bands.

Red Baron Gary

My Feedback: (59)

If you *really* want to swap tx crystals. contact either International Crystal in Oklahoma City, OK or Sentry Crystal in Chicashaw, OK.

Tell them the radio you have and the frequency you want to be on and the can probably make a crystal for you.

Minding however, the fee for this will more than likely be in the $15.00-$20.00 range.

As a ham radio op, both of the above have made custom crystals to suit my needs over the years.

Gary

Bill G

Someone can correct me if wrong, but I had heard that crystal transmitters are also tuned (such as with adjustable pots) for optimization with a specific frequency crystal. My understanding was that if you swapped a crystal with one from more than 1 channel in number from the original crystal, the tuning issues would become significant. The crystal type can also be different, as someone stated before, such as the Hitec Feather and Futaba micro 72MHz receivers using a different crystal type from GWS/Berg.

Red Baron Gary

My Feedback: (59)

Th-re are many types of crystals,referred to as "cuts" that determine the frequency of the actual crystal itself in relationship to the frequency the user wishes to be on.

The object of the pot or trimmer it is called is to allows for small adjustments to the circuit the crystal is in to allow either the transmitter (or the receiver if that is the case) to be precisely tuned.

Hope the above is helpful,

Gary