Transmitter reciever comaptibility

[Andrewg]

I am interested in anyones thoughts re the compatibility of the Hitec 3d transmitter with other brand recievers - particularly JR and Jeti.

[Steve Vasdekis]

I talked to someone over at Hitec and they said the 3D will work with all brands of recievers. Now with the old style Airtronics you will have to swap the positive and negative wires around. I didn't ask about Jeti because i didn't know they made recievers.

[AndyKunz]

The Jeti will be a standard European receiver - only North America has the problem with positive/negative shift equipment.

It will work.

Andy

[Andrewg]

Andy

could you give me an outline of the +ve/-ve shift thing and other issues

I knew we used different frequencies for rc but didnt realise there were other issues as well

[AndyKunz]

This is an FM-only issue. AM radios operate on a different principle and are all compatible.

Our FM radios nominally transmit on 75.xxx MHz in a 20 kHz channel (over here anyway). What that means is that the radio outputs a signal 75.xxx-5kHz at some times, and 75.xxx+5kHz at others. What determines when the + or - happens is whether the radio is sending "idle" or "active" information.

For Futaba and Hitec radios, they normally transmit ("idle") on the + side of the channel. When it is sending a chunk of data, it goes to the - side. That is a negative shift.

A positive shift radio is normally sending on the - side of the channel. WHen data goes out, it changes to the + side.

The receiver doesn't know which side of the channel the radio is actually transmitting on. It has a very accurate crystal which gets it to the center frequency, and the detector circuitry adjusts it to match exactly to the loudest nearby transmitter. (Hopefully yours). As the transmitter shifts from one frequency to the other, the receiver tries to track it. The electronics in the receiver are set up to catch either a low-to-high (positive shift) or high-to-low (negative shift) frequency change to clock data out to the servos.

The receivers can only detect a change (what we call an "edge"), not an absolute (FM vs. AM). This is more reliable, because it means that it must actually see the frequency change. In AM, it only has to see the carrier frequency present.

The major manufacturers are Futaba (80% of North American market), Hitec, JR, Airtronics, Sanwa, and Multiplex.

Be sure you either have a smart transmitter like the Hitec radios which can do either, or stick with compatible equipment.

Andy

[Andrewg]

Andy

thanks for that it was very informative.

Well I have the right transmitter!