BR289

My Feedback: (106)

Greetings,
I work at my local hobby shop part time. Its one of the bigger ones on the East Coast, and we get alot of Airplane guys from all around.
I frequently get asked ( also being an instructor at our local field ) why it is that you can buy transmitter crystals, but you are not supposed to change them?
I tell them it is against FCC regulations ( I personally dont know why myself ), and that the radio needs to be "tuned" to that frequency. Some are smart and cant understand why you can put a 26 crystal in a receiver that was on 22, but you cant do it to the transmitter, and if you did, why would the transmitter need to be retuned?
I really dont like to make up stuff to tell them, so any explanation would be a great help!
Thanks,
Blair

blikseme300

My Feedback: (118)

Technically, it is a good idea to check that the transmitter is producing the correct signal after a xtal change. Usually no tuning is needed. A good spectrum analyzer check will tell you this. Sometimes though, it needs to be tuned. Even though a range check might appear to be fine, the adjacent channels could be interfered on. I, personally, would be extremely p1$$3d off if someone shot me down because of a cheap approach to the hobby/sport/obsession.

Secondly, as a wise man once said, "the law is an ass."

Safe flying!

Bax

My Feedback: (11)

The FCC regulation is in place because the transmitter emits radio signals. Changing a crystal will change the channel, but also allow other emissions to be emitted. Tuning reduces those emissions to the proper levels specified in the FCC regulations. The unwanted emissions can affect the non-RC users on the channels immediately adjacent to the RC channels.

A receiver does not emit anything of consequence, so changing its channel may only affect its reception range (if you're changing over a large range).

The FCC isn't really worried if you crash your model, they want to make sure that transmitters will not interfere with other transmitters in different radio services.

BR289

My Feedback: (106)

Thanks for the great reply.....Thats just what I wanted to know!
Blair

Gravityisnotmyfriend

My Feedback: (2)

I understand the transmitter crystals can't be changed outside of a shop, but BR289 poses a good question, why are they for sale? Also, why are they so easily accessible on the transmitter? Also, I have a transmitter that has a place labeled "xtal storage" inside the battery compartment. I guess it could be for reciever crystals... I also suppose that transmitter crystals could be easily accessible to buy and replace if one goes bad, but if my transmitter stopped transmitting, I would take it to a shop anyway. I wouldn't replace the crystal myself and risk a plane. I guess the bottom line of my question is: Why isn't the transmitter crystal safely hidden inside the transmitter? If it takes a shop to replace it, I assume that they have to open the case to retune it anyway.

Bax

My Feedback: (11)

Crystal sets are sold because there ARE people qualified to tune transmitters.

Crystal-swapping of transmitter crystals is allowed in countries outside of North America, and Futaba makes their equipment for a world-wide market. The crystal covers on North American transmtters are glued down, which conforms to the FCC's regulations that the crystal is not accessible to the user.

Gravityisnotmyfriend

My Feedback: (2)

I thought about the world market after I posted that question. I suppose the "Federal" in FCC means it only applies to the US.

Bax

My Feedback: (11)

The FCC, Federal Communications Commission, is the regulatory agency for radio frequency telecommunications in the U.S. Other countries have different names for their regulartory agencies and, of course, different laws.