Acquired a pair in 2007 when I worked in the LMR business to play with. A rather horribly edited (in my opinion) review showed up in the December, 2007 issue of PopComm which one can download via
https://drive.google.com/open?id=1sgdOBpzTawvCoo1JaRfHvPw3qfcbaQJw. The original, more gonzo, version of the article can be found at
https://ticom.livejournal.com/104713.html.
They were awesome jobsite radios, especially when dealing with large office buildings and urban locales where the VHF/UHF LMR spectrum is crowded. Talk-range was about two miles in typical urban/suburban conditions. a friend and I tested them in midtown Manhattan and managed to talk as far up as the 50th floor in the Empire State Building (from street level) before losing comms. Conversely, hiking around the [url]old SAC bunker at The Notch[/url] we only managed about a quarter-mile.
A few years back when I was living in DN53, Brent N7HYF had some DTR-650s and paired them with some small (5-6 el) 33cm band beams he pulled off an old SCADA system, You can actually get 20-30 miles with these things if you use enough antenna and don't have any obstructions in the way. Much like the early HSMM experiments with 802.11 stuff, he published the channel and talkgroup ID (42672346 or HAMRADIO) on the WYAME FB page to make it all legal.
There are 5 or 6 default "public channels" available on the DTR radios, and most users just use these defaults. The DTRs had a channel scan function which you can use one to monitor them. If you're in any decent-sized city you'll probably hear some building maintenance and construction communications.
There's a few interesting things about these radios. The operate in a kind-of synchronous manner, so a receiving unit has to hear you first before you can transmit. Otherwise you get the Motorola "bonk" sound. The DTR-650s have a supervisory mode enabled that allows one to either remotely key-up or deactivate other radios on the net. This is either useful, entertaining, or annoying depending on the circumstances involved.
After doing the gonzo and PopComm articles in 2007, published some updated research in 2009 as part of the "Prometheus" book (
http://files.diydharma.org/other/Musings_Of_A_Man_In_Black-Prometheus.pdf). This got picked up around 2013 by a bunch of prepper/militia types, including "DanMorgan76" (
https://danmorgan76.wordpress.com/2013/09/21/intersquad-tactical-radios/ and
https://danmorgan76.wordpress.com/2013/11/05/the-motorola-dtr/). That scene comes and goes depending on whether or not the current POTUS has a "D" or "R" after his name, and since it's now the former the more political prepper/militia types are going to start becoming more active and posting up stuff.
Motorola still offers the DTR series:
https://www.motorolasolutions.com/en_us/products/two-way-radios/commercial-business-two-way-radio-systems/on-site-business-radios/dtr-series.htmlThe DTR audio is unencrypted VSLEP, and one can definitely discern a pattern to the FHSS sequence if they look at it on a spectrum analyzer and don't have any other nearby 33cm FHSS signals to add confusion. So while, yes a police scanner won't hear it, I suspect that a monitoring hobbyist of advanced skill level could do it if they were so inclined, especially considering the bandwidth capabilities of more recent SDR models.
_________________
-Tom, W1WSO -- Plymouth, CT
http://tf.sdf.org/monitor/
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