If you are using two computer radios cabled together for a buddy box setup, it may or may not be necessary to program both. How two radios are buddy boxed together and how they function seems to vary significantly depending upon the models of specific equipment used and from manufacturer to manufacturer.

There are no absolutes, your best bet will be to sit down with the two radios you intend to use and see for yourself exactly how they behave.

I have a Futaba 7C 72Mhz transmitter and a Futaba 4YF buddy box setup with square-to-square trainer chord. The 7C takes care of any mixing or programming needs when in trainer mode, the 4YF buddy box only provides basic stick input. The buddy box needs to be unpowered and in the "off" position when pairing it with the 7C 72Mhz transmitter.

I also have two Airtronics RDS8000 radios with an Airtronics 477100 trainer chord. With this setup, the two transmitters can be set up with different control throw rates and trimmed independently. The advantage to this setup is that the instructor's radio can have more "throw" or control authority to aid in quicker recovery while the student radio can be set up with more gentle control settings to prevent oversteering the plane. In this setup, the student radio must also be powered off to work as a buddy box.

JR and Spektrum equipment often requires both radios or boxes to be powered up and in the "on" position. Some radios, like the Spektrum DX6i, won't work if you try to buddy box them with a standard trainer box or sport radio; instead they require a second computerized transmitter that must be programmed identically to the first to work as a trainer box.

Hitec radios come with trainer ports that look like older Futaba trainer ports, but Hitec uses a special "one way" trainer chord. Mixing Futaba and Hitec radios for buddy box setups is possible, but I honestly don't know what the purpose of Hitec's one-way trainer chord is nor do I know the problems with mixing Futaba and Hitec equipment incorrectly.

The new 2.4Ghz radio systems don't always behave like their 72Mhz counterparts did. New 2.4Ghz radios like the Airtronics SD-10G or the Hitec Aurora 9 don't operate using the same kinds of trainer chords like previous models did. I've also been told that the 2.4Ghz version of the Futaba 7C requires a computer radio to buddy box with and that it won't work with my Futaba 4YF trainer box the same way the 72Mhz version of the 7C does. I also don't know if this is true.

Anybody who tells you that buddy boxing two radios is easy probably hasn't had to work with much of the new radio equipment that's out there. It's all very tricky and requires specific testing to figure out exactly how it all works.

Good luck, and let us all know what you learn!