One of the fastest growing modes in Amateur radio is DMR or Digital Mobile Radio. One of the groups that’s been at the heart of this growth is NorCal-DMR.
DMR was introduced to the amateur ranks in 2009 and one of the first DMR repeaters in California was installed on Mt. Diablo in 2010. This repeater, K6MDD, became the first of what is now NorCal-DMR’s 40+ repeater network.
With the assistance of some professional software, NorCal DMR boasts that more than 90% of Californians can now hit a DMR repeater from their home.
DMR is an open digital standard and today has many manufacturers building radios repeaters and other equipment. Motorola, who first championed the technology, builds most DMR repeaters in the amateur ranks. Our own W6CX multi-mode repeater is DMR capable.
DMR is built on TDMA technologies. The benefit of TDMA is that one repeater using just one frequency can support two simultaneous and separate transmissions. In other words, it’s like having two repeaters on one box with just one pair of frequencies. Further, the technology is built to operate in narrow band. With these technologies there’s hope that the Amateur community can implement more infrastructure in what little spectrum is currently allocated to our wonderful hobby.
For many years DMR has been plagued by high costs. Not so much in terms of repeaters but for the radios themselves. Up until about two years ago a user might expect to pay around $750 for a handheld. This changed in November 2013 when Connect Systems Inc., based in Agoura Hills, California introduced a sub $200 DMR radio. Since then, several other companies have introduced radios for as little $150.
Great coverage combined with less expensive radios is driving DMR’s massive growth, but NorCal-DMR points to another, unlikely, factor for growth in our neck of the woods. They credit Pave Paws for helping them to grow.
Pave Paws is a U.S. military radar system with an installation at Beale Air Force Base, about 50 miles north of Sacramento. It uses the UHF frequency band which hams share with them. As a result, MDARC and other Bay Area groups have been required to severely reduce the power of our UHF repeater. Therefore, Pave Paws has nearly shut down the UHF bands in Northern California.
But another capability of DMR is its roaming ability. Just as you would switch from tower to tower on your cell phone when driving, DMR radios have that capability as well. A user can pick a talk group (a channel within the repeater), turn on roaming and the radio searches for the repeater with the strongest signal. It automatically adjusts to the new repeater without operator intervention. The switch happens instantly never interrupting a transmission…In fact you may never know which repeater you’re using without looking at the radio’s screen.
What roaming has enabled NorCal-DMR to do is put up many very low level repeaters that don’t interfere with the Air Force’s radar system. Each repeater has very limited coverage but together, and with the use of roaming, the system is vast. Pave Paws has made many UHF frequency pairs available and rather than lose them NorCal-DMR has put them back to good use in the amateur ranks.
There’s much more to this technology, and our friends at NorCal-DMR have put up a website to help us all learn as much as we’d like. That site can be found at https://norcal-dmr.org/.
Content provided by Curt Kundred, W6FQ. 05/23/2015.
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