MARS/CAP Mods

Radio modification information for MARS and CAP operations

What Are MARS/CAP Mods?

MARS = Military Auxiliary Radio System
CAP = Civil Air Patrol

Both organizations operate on frequencies just outside the regular amateur bands (VHF and UHF). A “MARS/CAP mod” is a hardware or software change that expands a radio’s transmit range so it can legally operate on those assigned government/emergency frequencies when you are a properly licensed and affiliated member.

U.S. amateur band limits:
2 m: 144–148 MHz | 70 cm: 420–450 MHz

Not all radios can be modified – some are locked by firmware or hardware design.

Why Would I Need This Modification?

Interoperability during emergencies.

Example from real life:

Joint exercise with county Fire/EMS, CERT, and ARES
Used authorized itinerant frequencies to coordinate search teams and officials
A real medical emergency occurred; the Fire Battalion Chief was in a dead zone on county radios
With a MARS/CAP-modified radio, I could hear him and relay critical traffic to medics

Without the mod, that relay would have been impossible.

Legality & Responsible Use

I am not a lawyer – this is not legal advice.

New hams almost never need this modification.
It becomes relevant only if you formally join an EMCOMM, AUXCOMM, MARS, or CAP unit that requires out-of-band transmit capability under their official authorization.
Your local EMCOMM/AUXCOMM leadership is the best source of guidance.
Using a MARS/CAP mod to transmit on GMRS, FRS, MURS, or other services you’re not licensed for is not legal and not a valid reason to perform the mod.