[chirp_users] GMRS Channel Locking

[Jim Unroe]

Hi Chris,

On Mon, Feb 21, 2022 at 6:08 PM Chris Romp <chrisromp+chirp at gmail.com> wrote:
>
> Hello,
>
> I have a question about how CHIRP handles GMRS radios, e.g. BTech GMRS V1 and Retevis RB26. I've noticed that CHIRP enforces that GMRS channels follow the FRS channel number and frequency pairings, e.g. Channel 1 is 462.5625, Channel 18 is 462.625, etc.  I've been trying to find in the FCC regs if this mapping is a requirement of GMRS operation. The only place I've found the channels spelled out is on 47 CFR Part 95B §95.563 "FRS Channels" (link), but GMRS seems only to specify the frequencies and bandwidth which may be used via Part 95E §95.1763 "GMRS Channels" (link).  It's entirely possible that I've missed the clause requiring this mapping, and I am not a lawyer, so apologies if I've overlooked it.
>
> When I am programming a GMRS radio, I don't always want what my family refers to as our "channel 1" to be 462.5625.  Likewise I may want to set up different repeaters that may use the same frequencies, but different tones (especially on radios where I cannot edit the tone from the radio itself)  I am able to program the RB26 to accept an alternate GMRS-legal frequency with a little trickery, so there does not seem to be a firmware restriction enforcing this and it hasn't bricked my radio (yet).
>
> Would it be possible for CHIRP to accept GMRS-legal frequencies in any channel slot, and not require the FRS channel-frequency mapping?
>
> Thank you,
> Chris Romp

The BTECH GMRS-V1 channel assignments are in firmware. Even if CHIRP
would let you put in different frequencies, it wouldn't make any
difference. Channel 1 will always be 465.5625 MHz.

The Retevis models are programmed to match how the OEM software
behaves. Some of the newer Retevis models let you program the GMRS
frequencies in the radio however you please.

Jim KC9HI