spirit pilot

I recently read a thread on this forum that brought up a question?

What I had been planning on doing was to purchase a few crystals of differing frequencies so that if I got to the field and someone was on the same frequency installed in my system, I could change crystalls to an open frequency and be ready to fly. The thread I was reading questioned the legallity of this.

What is the situation?

Thanks
Rich

Rodney

In the USA, it is illegal to change the transmitter frequency by just changing the crystal unless you have it done by a service center that has the proper equipment to check for spurious frequency splatter. There are some transmitters designed to use replaceable and/or adjustable frequency modules which is legal. You can legaly change the receiver crystals however as any malfunction in them will not effect other users of the bandwidth (there are a number of users of the bandwidth sandwiched between the frequencies used in RC in the USA).

JohnW

My Feedback: (6)

In the states, it is against FCC regs, i.e., illegal, to change the operating frequency of a TX if it has been certified/tuned for a single frequency. In practice, what this means is if your radio uses a removable crystal, you cannot legally swap crystals without retuning the radio. If your radio uses a transmitter module, you can change the modules as the module is a self contained transmitter that is pretuned for the module's listed frequency.

You can however legally change the RX frequency by swapping crystals. The logic behind the diff between TX and RX is that a RX just receives while the TX transmits. If the TX isn't tuned properly for the crystal installed, it may transmit on undesired frequencies. Since a RX doesn't transmit any significant RF, it can't interfere with other frequencies if it is mistuned.

The FCC reg is in place for a good reason. While more than likely you can change crystals illegally without any significant problems, and many do this, you could potentially cause interference to other modelers and/or other commercial radios. Locally at my club, I have experienced several fellow pilots that use TX's that are seriously mistuned. They still work for thier plane, but they cause problems for other pilots. I don't know if these issues were due to a crystal swap or just a radio that needs service. But reguardless, as a fellow modeler, I ask that you don't field crystal swap your TX. If you want to change the freq of your TX, send it to the factory so it can be retuned. If you desire the ability to easily change your operating frequency, get a TX that uses legally swappable modules or a synth module.

Thanks.

Shane B

My Feedback: (3)

On the futaba 9c radios cant you change the transmiter module out with no problems,,

JohnW

My Feedback: (6)

Warbird, I mentioned this above, but you may have missed it. You can swap self contained transmitter modules, but you can't swap the just a crystal. This means that yes, on the 9CAP, 9ZAP and other radios that use TX modules you can change freq to your hearts desire legally.

spirit pilot

So much for that idea.

Thanks for the input and explanations guys!
Rich