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Mike,

Excellent question, and sorry for the long answer.? The question applies to everyone with their own low-power hotspot (typically 10 milliwatts)? or even higher-power hotspot or full duplex homebrew repeater.? It also applies to whatever mode, whether DStar, DMR, Fusion, P-25, etc.

What people forget is that even low power transmissions can interfere with others.? A common problem is when a hotspot is put on the same frequency reserved for earth-moon-earth QSOs.? Those folks are dealing with really weak signals coming back from the moon, and even a low power errant signal can destroy their day.? Ditto frequencies reserved for satellites, whether stationary or low earth orbit.?

One answer is to refer to published band plans that apply to our area.? Most digital voice radios work on 2 meters and/or 70 cm.? For people in the SF East Bay, NARCC (Northern Amateur Relay Council of California) is the primary frequency coordination organization.? Their website at has a link to their band plans and currently-coordinated repeaters.?

While I am not an expert on what NARCC would recommend for hotspots, it is obvious we want to stay away from frequencies set aside for Weak Signal and Satellite.? We also want to avoid any frequencies already coordinated for repeaters within RF distance of our area.? Their website has a link to coordinated repeaters in the area.?

Note:? We have an unusual situation in this area.? NARCC has not been coordinating digital mode repeaters, including the W6CX DStar repeater, so unlike some regions, they have not been able to re-farm their spectrum to put narrow-band repeaters like digital mode repeaters into lower-bandwith segments.? (DStar repeaters have a theoretical bandwidth of 6.25 kHZ, though some use up to 10 KHz.? DMR repeaters require at least 12.5 KHz but may take a bit more, perhaps 15 KHz.? In any case, digital repeaters do use less bandwidth than NARCC sets aside - 25 or 20 KHz-? for the repeaters they coordinate.)

Since FCC Part 97 does not disallow having more than one frequency coordination organization in a given geographical area, there is in fact another organization that has taken over coordinating digital mode repeaters in NorCal? – NCDCC Northern California Digital Coordination Council – They are carefully coordinating digital voice repeaters (DStar, DMR, etc.) and keeping NARCC informed about their coordinated frequency pairs.? People out of this area might think this is a bizarre solution, but it has been working for nearly 10 years.? In fact, the list of repeaters on the NARCC site (for example, for 2 meters) shows the NCDCC-coordinated digital repeaters but lists them as not coordinated. (They ARE coordinated, but by another entirely legal coordination organization.)? But you will find the W6CX DStar repeater there, which makes it easy for people to stay away from all the repeaters in the area.

Back to your question – stay away from allocated band segments like those for weak signal and satellite and stay away from repeater frequencies.? You are probably ok using a frequency in the Digital segment, as long as listening reveals that is not already being used in your area.?

? Jim – K6JM