This thread is an offshoot of "The HT Thread" and the "Source for Marine VHF Radio reviews?".   I had mentioned that I was getting a portable DMR repeater and there was some interest about it.

I wrote up some information over in this blog post,
http://competition-dynamics.com/blog/cd-upgrades-field-communications-for-2016/
but I'll repost a bunch of it here and expand a little bit.

I am head of an organization that runs big field-style shooting matches.  The smallest parcel of land we use is 1000 acres; the largest we've used was approx 230 square miles; and right now we're using about 40 square miles for our 2016 adventure race.  These are typically out in the middle of nowhere with no cell coverage (unless you happen to be on top of the mountain).  This presents a logistical challenge for match operations. Staff need to be able to communicate, and in some cases, competitors need to communicate with staff as well.

We had evolved from using bubble pack radios, to VHF, to VHF with a mountaintop human relay.

I was originally looking for a VHF repeater solution and found Tactical Repeater http://www.tacticalrepeater.com/.  This is a side business for Kent, whose main job is owning and running a very large (I believe the dominant) linked commercial DMR system in CO, WY, and NE.  Kent oriented me to DMR for maximum coverage and flexibility.  I bought two of the Connect Systems DMR radios (under $200 each) and tested them out for a couple months.  They basically blew away analog VHF/UHF for everything we were trying to do.

In testing UHF DMR in simplex mode, I found on typical terrain or on road convoys, the DMR radios gave us approx 2-3x the distance and had many fewer coverage holes in a given set of terrain.  Another anecdote, from the basement of my house in Fort Collins, I can hit the Boulder area DMR-MARC repeater, using a HT, in DMR mode.  This is pretty amazing considering the distance and stuff in the way.  On analog UHF, I am lucky to hit the local Fort Collins (Horsetooth) repeater from the exact same position.

Only problem, the DMR repeaters Kent deals with are fixed position enterprise-level units, and the "manpack" repeaters he builds are typically built around ultra low power VHF/UHF.  So I did a bunch of research online and found the Hytera RD965 repeater.  It's small, a little larger than an old Hayes Courier HST modem.  The downside compared to the other manpack repeaters was going to be its power requirements.  I said that I didn't mind if we needed to have more batteries or solar panels, so we just went ahead with the project.

The idea is that we ID the best mountain-top position for the repeater to give maximal coverage of the event area, drive/hike it up there, and then leave it there for about to two weeks, until we're done with the site.  The repeater is to run autonomously during that time.

Anyway, this is what he came up with:

The RD965


Packaged into a Pelican 1500


The Pelican case is fully sealed and operates closed, out in the elements.  It contains the repeater, 40 Ah of reserve battery power, a charge controller, and a custom-tuned very clean duplexer.  When closed, the only controls/ports the box has are: (1) the on/off switch, (2) the RF connector for the antenna, and (3) an optional DC power plug.  With a 60 Watt milspec solar panel plugged into the DC power port, the repeater will continue operations indefinitely.



The DC power port can also use an external battery bank or wall power supply.

It packs up quite small.  The repeater case is about 42 lbs (batteries) and then there's the bulk of the antenna tripod stand and antenna.  Technically this is man packable, but it can be strapped to the back of an ATV and taken anywhere with ease.





With DMR, you get two timeslots, near infinite talk groups, unique caller/radio ID's, encryption, and an effective SnR advantage over analog.  What's not to love..

I am running this on FCC-licensed commercial UHF frequencies.  With a change in the duplexer, there's no reason it couldn't be operated as an amateur repeater.

Now radios-- There are few choices for inexpensive but decent DMR radios, where "inexpensive" means under about $250 per radio.  These CS710's came in about $180 per each.  The cost constraint comes in due to the number of radios we need.  Connect Systems, especially Jerry and Chris, have been good to work with.  The downside of the CS radios is that the programming/firmware is not very mature.  Everything mostly works, but there are surprises here and there, which will be fixed in future firmware releases (hopefully soon).  But I can buy 4 or 5 CS radios for each 1 /\/\ I could afford, let alone the hassle for software and programming support from /\/\.

While we have a commercial FCC license to operate this system, I am also a HAM (Extra).    A buddy (also a HAM) familiarized ourselves with DMR technology and capabilities by making contacts over the local DMR network and DMR-MARC.  That was helpful.

There you go-- a tactical DMR repeater.

Additional info

The solar panel is a P3-60W from P3 Solar.  http://p3solar.com/portfolio/p3-60w-portable-solar-charger-2/

Tech info on the Hytera RD965 repeater itself.  http://www.hytera-mobilfunk.com/dmr/radios/repeater-tier-ii/repeater-details/details/rd965/
http://www.hytera-mobilfunk.com/uploads/tx_wwdownloads/90RD965_Fly_eng_v05_web.pdf

Power on the repeater is configurable up to 10 W, however you will program it to match the limits imposed by your license and/or frequency classification.

The repeater itself is about $2500.  The packaging, duplexer, charge controller, batteries, misc connectors, etc, and antenna and tripod added about a grand to that.    The solar panel was about a grand too.  There were cheaper solar options but this one is ruggedized. We can't really afford to have comms go down during an event, so the bigger hammer was applied.      We also went very conservative in our battery life calculations and solar panel requirements.

One of the downsides of the DMR repeater was the cost compared to a tactical/manpack analog UHF repeater.

Another cool thing about DMR is that you can link them together using directional wifi networks and create a mesh that covers a much larger area than any one repeater could.  Typically commercial or amateur DMR networks use the internet (or a private internet) as the backhaul for a wide area radio network.

The repeater can operate in simultaneous dual analog/digital mode, however we have that disabled right now.

I don't have the calculations handy at the moment but for the most conservative I believe we ran a 30% duty cycle (wildly overestimated) and the solar and batteries were rated to keep it up indefinitely

Not using Hytera HT's (and I am aware of some of the additional features if we were to).  We are using only Connect Systems CS710's right now.  The primary consideration on the HT's was per-unit price due to how many we needed.  The batteries are SLA 20 Ah per each.  I don't know the exact model.

Another application for this thing is to throw it in the back seat of a vehicle, plug into its PLO-259 connector (or use a mag mount on the roof) -- voila, mobile repeater.

Well, that's HAM for ya right there.

A lot of the problems with HAM radio is that it's amateur.  Once you get it set up, you can't actually do anything useful with it* -- in the majority of cases anyway.    Now that I have a couple buddies with Tech licenses we can use the repeaters along the front range on car trips, but that's about it.  I've used my HAM license more testing out viability of different systems and capabilities of radios (all in amateur compliance) that I would later go on to use for something "real", which in most cases, is expressly forbidden by amateur rules.   Not saying it should necessarily be any different, but there you go....

To the little I've been exposed to them, commercial DMR as implemented by Motorola and Hytera has features set up for industrial use (as one would expect).   Seamless roaming, capacity rollver, etc, all work (or can work).  For their intended use models, it's damn good.   The end user has a simple interface that "just works" over an entire coverage area, and he doesn't have to worry about TS's, TG's, which repeater, etc.

IMO, for HAM use, here are the downsides:

1. Technically is it more complex than getting on an analog repeater

2. Programming the radios is fairly complex (must get radio ID right, TG's right, TS's right, color right, RX groups right, scan groups right, TX group right, etc, etc).  Code plugs are not compatible across radios and the ability to export into a neutral format is limited.

3. In my experience at least, the radios and programming software are set up for industrial use, not typical HAM use.    For HAM use, you want sort-of a library of repeaters (freq, color), and then a list of what TG's are associated with what TS on which repeater, and then the orthogonal ability to select a repeater AND THEN scroll through what TG/TS's are available on that repeater.   Another usage model is to set a TG and then be able to scroll through all the repeaters in a region that are associated with that TG on a given repeater/TS.   (The latter is somewhat possible to do given programming-- for example, I have a zone for each of RMHAM NCO, DEN, SCO, and Wide.)

4. Proper roaming is either impossible or virtually impossible

5. There is apparently a lot of strife about actually USING the linked/routed TG's on DMR MARC, e.g. North America.    The constant complaint (at least on the email list) is about the cost of keying up 52342292 repeaters but you listen to the TG and it's idle 99% of the time.  So what gives, you have a great system that nobody ever uses.  Nice.

6. The internetworking standard depends on Motorola repeaters and apparently some non open source software, or something.   There's no technical reason this couldn't be run on a RasPi and a series of low-powered VM's out in the cloud on open source software.

7. The cheap (under $300 say) radios have limited features and/or limited implementations of standard DMR features.  The nice Motorola radios cost in the range of a nice mobile HF radio (cost comparable to a FT 857D), and they are extremely unfriendly to non corporate users for things like software access terms, license keys, etc.


Anyway, just some thoughts on it.  

I'll report back here once we've deployed the portable DMR repeater in the field the first time and have some results.

Here was the first deployment.  Left it in place for a week during a match.  Worked great.