Band Conditions

12 November 2018

Clipping the Diode

Two official .gov/.mil organizations hams get involved with are Civil Air Patrol (CAP) and Military Affiliate Radio Service (MARS). Historically, MARS and CAP were allocated frequencies just past the edges of the ham bands, such as 142-144 and 148-150 MHz. Hams in MARS and CAP would use their existing radio equipment on their organizations' frequencies. Typically, there was a jumper or diode on the radio's circuit board that would open up the TX frequency coverage and enable operation outside the ham bands. While CAP has adopted technical standards that preclude the use of most ham equipment for their comms, MARS still allows the use of ham gear. Most radios are still being made with a jumper or diode that will enable transmitting out of the ham bands when clipped. We call this the "MARS/CAP" or "freeband" mod. Most radio places will give a ham the mod info, or perform the mod for a small fee, if they present a MARS or CAP radio license. This would give an HF rig TX coverage from 1.8-30 MHz., and a dual band HT 136-174 and around 400-470 MHz. Some of the Chinese HTs come already opened up, which is what got that Baofeng in hot water with the FCC.

In the early 1990s it was considered a title of passage among radio hackers to "clip the diode" on their recently purchased HT. Many non-hams found themselves bootlegging on 151.625 MHz. and other low-power/itinerant frequencies where there were thousands of licensed users and no one paying much attention. This was before the creation of Part 95 services like FRS and MURS. CB skip shooters would buy a used Kenwood or Yaesu HF rig, clip the diode if not already done, and run 100 watts on 11 Meters and the 27.415-28 MHz range which is still a free for all today.

In regard to modified gear, the following provisions of Part 97 are of interest:


§97.403 Safety of life and protection of property.
No provision of these rules prevents the use by an amateur station of any means of radiocommunication at its disposal to provide essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available.

§97.405 Station in distress.
(a) No provision of these rules prevents the use by an amateur station in distress of any means at its disposal to attract attention, make known its condition and location, and obtain assistance.
(b) No provision of these rules prevents the use by a station, in the exceptional circumstances described in paragraph (a) of this section, of any means of radiocommunications at its disposal to assist a station in distress.
It is legal for an amateur radio operator to have a ham transceiver that will operate outside the ham bands, and in certain emergencies, it is legal to transmit out of band. Your typical HF-UHF amateur radio station, with the appropriate diodes/jumpers in the radios clipped or otherwise reconfigured, should be able to interoperate on CB, MURS, FRS, GMRS, and conventional analog LMR systems.

While this is legal under §97.403 and §97.405, in reality YMMV and keying up on the local PDs' repeater (assuming they still have an analog conventional system up and running) may result in you getting a rash of s**t if their idea of what constitutes an "emergency" is different than yours. I wouldn't expect the FCC to go to bat for you if that happens. Put aside a couple thousand bucks in case you need to lawyer up.

Realistically, you can expect most 2m radios to stay in original spec from around 140 to 160 MHz., and 70cm radios from ~400 to 470 MHz. Past that you can expect progressively worse transmit power output and receive sensitivity the further you get away from the ham bands. TANSTAAFL. Furthermore, running them regularly on Part 95 or 90 allocations is a regulatory no-no as they aren't "certified" for those services. Again, this is what got that Baofeng in hot water. Yes, I know everyone does it, and for the most part the FCC doesn't pay attention until they get a few complaints.

For what it's worth, my opinion is that if you want to run on Part 95 bands, you should run Part 95 gear as it is generally simpler to operate than Part 90 gear. I've met many a no-code, single test session Extra who despite being able to memorize all three test pools was still unable to program and effectively operate his Baofeng HT. I expect his clueless Aunt Matilda would be even less successful if handed one, and that's not taking into account what might happen if the wrong button was pressed. The simple CBs and FRS handhelds I pass out to non-techies have a minimum number of controls to get confused on, and are simple enough for everyone to operate.

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