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Radio Oddities

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Motorola DTR review - Gonzo style [Sep. 1st, 2007|09:34 pm]
Radio Oddities


[Current Location |Shadow Gallery]
[mood |accomplished]

The first warning I heard was Rambo asking Jimmy Dean "Want me to play
'Bubba Shot the Jukebox'?" Looking like a more worn version of Willie
Nelson, Rambo is a feral, slightly unhinged Army veteran of both
Vietnam and Desert Storm. He's really useful at getting broken
equipment working again in the field, and when you need a bodyguard
when visiting such entertaining locales as Hartford and Bridgeport. At
any other time he's best kept out of sight of the customers. He was in
a foul mood today as he was getting sued by the families of a group of
Norwalk youths who thought he was a homeless person when they tried to
assault him. The police dropped the charges as it was five against one
and self-defense, even if three of them are still in a coma. He was
just finishing up his lunch with a copy of Edward Abbey's The Monkey
Wrench Gang, and listening to The Doors on his Ipod at a volume that
would bring Jim Morrison back from the dead. Having been exposed to
too many loud noises while serving his country, Rambo needs to crank
his Ipod's volume up full bore despite having the earbuds jammed so
far into his auditory canal that Jacques Cousteau couldn't find them.
Jimmy, not being the brightest of bulbs, made the mistake of telling
Rambo "Yea, that's a good song." That's when I dived over the
workbench, as Rambo was in the process of pulling his .45 out from his
toolbox in an attempt to silence Jimmy's annoying noise source. Afraid
that the round would overpenetrate the boombox and fly off to hit some
innocent person or piece of test equipment, I knock Rambo off his
chair, and wrestle the .45 out of his hands while he's cursing at me
in Vietnamese.

It started out innocently enough and with the best of intentions (much
like a Warren Zevon song). How was I know what started as a simple
exercise in boredom-induced technological funkenspiel would introduce
me to the next quantum leap in portable personal communications
systems. That's one of the more interesting things about this hobby. I
was at the shop and had just been asked to stop harassing my co-worker
Jimmy Dean. Jimmy likes both types of music, and therefore keeps his
radio tuned to the local FM station that plays his particular genre of
acoustical entertainment. Sometimes he likes to play his music at
excessively high volume, and his co-workers are forced to defend
themselves. In this instance, the implement of defensive destruction
was an Ipod playing Cruxshadows and E Nomine hooked up to a service
monitor. After several loud inquiries of "What the heck is that?!",
the boss comes in and asks me to play nice. I actually was playing
nice, as I made sure all the songs from The Mentors were not on my
defensive playlist.

So I soon found myself on this slow day surfing Motorola's product
website when I came across *them*. I'm always keeping an eye out for
neat exotic communications equipment at hamfests, and when I saw the
Motorola DTR portables I thought to myself "I have to check these
things out!". The DTR series are one watt license-free handhelds
operating on the 902-928 MHz band along with other Part 15 and ISM
devices. Unlike other license-free radio services such as FRS,
MURS,and CB that operate on a single analog FM or AM frequency per
channel, the DTR series use digital frequency hopping spread spectrum
modulation (FHSS). This means they are less susceptible to
interference, can't be received by police scanners, and have a longer
communications range than analog single-frequency radios running a
watt. Motorola in fact claimed a two-mile range with these units. FRS
radio manufacturers claim a 2 mile range with their little half-watt
460 MHz handhelds, and anyone who has played with them knows that at
best you get a half-mile to mile tops under most circumstances. How
well would the DTR handhelds operate under a variety of circumstances?
I would soon find out. After a few inquiries and a trip into the back
storeroom, I soon found myself in possession of a pair of Motorola
DTR650s. Jimmy went back to playing both of his favorite types of
music. As I walk out into the shop floor, I hear someone with a Texas
accent sing about the differences between divorces and horses, Jim
Morrison telling everyone "This is the end. My only friend, the end."
and Rambo asking Jimmy "Want me to play 'Bubba Shot the Jukebox'?"

Frequency hopping spread spectrum is nothing new. The military has
been using it for years with their SINCGARS (Single Channel Ground/Air
Radio System) radios. Instead of staying on one frequency when
transmitting, the radio "hops" through a number of different
frequencies in a pseudo-random sequence. This reduces the
vulnerability of the communications to interference and interception.
Frequency hopping is also used on the ISM bands such as 902-928 MHz
for telemetry and control aka "SCADA" (Supervisory Control and Data
Acquisition) systems. Many cordless phones operating in the 902-928
and 2.4 Ghz. bands also use FHSS. In the latter two instances it is
used for spectrum efficiency as well as interference reduction. You
may also find certain cutting-edge amateur radio operators
experimenting with spread spectrum communications on UHF and microwave
ham bands, and the ubiquitous 2.4 Ghz. Wifi systems use spread
spectrum as well. While spread spectrum communications are commonplace
in industrial, government, military, and wireless networking
applications, until the release of the DTR series radios there simply
was not a unit that offered spread-spectrum voice communications in an
inexpensive license-free package.

These radios are comparatively priced with less expensive portable
radios and give a significant measure of privacy over handhelds
operating on a "dot" frequency. If you were putting together a new
portable radio system from scratch, it would be worth your while to
invest in DTR radios. From a management standpoint these radios have
some neat features not found in similarly priced conventional
portables that will enhance your communications system. These features
will be addressed later in this article. These radios are license-free
and truly plug and play. Their operation is uncomplicated. Scanning
receivers cannot monitor them, and it is extremely unlikely that will
change anytime soon. The DTR is an FRS radio on steroids, and just
like FRS, MURS and CB does not require an FCC license. Until now there
was really no way to inexpensively experiment with spread spectrum
voice communications. A pair of DTR410s cost less than a digital
trunk-tracking scanner.

Motorola makes three models of DTR radios for the US market. The basic
entry-level Model is the DTR410. This features six "public
talkgroups". For the purposes of keying-up and talking consider them
the same as a channel on an FRS or CB radio. The other two are the
DTR550 and DTR650. The DTR550 and DTR650 can operate in a private
"unit-to-unit" mode, and the DTR650 can act as a supervisor radio
enabling the user to do remote monitoring and disabling of other DTR
units. Other than these firmware differences, they are all the same 1
watt 900 MHz FHSS radio.

The first thing I absolutely had to do with these things is try a
scanner on them. Ok, I used more than a scanner. To be more specific I
used a Signal Stalker scanner, frequency counter, spectrum analyzer
and old Optoelectronics R-10 Interceptor on them. I started with the
Signal Stalker. This little $100 scannist's friend has since its
appearance on the scene totally changed the way hobbyists look for
frequencies. I turned it on, made sure the 800/900 MHz band was
selected, and keyed up the DTR. Nothing. Nada. Zip. I then did a more
traditional frequency search of 902-928 MHz I found a donut shop's
drive-through, a couple baby monitors and some ham radio operators on
a local 927 MHz repeater. No test transmission from the DTR though.
Neat! Next in line was the Optoelectronics R-10 Interceptor. Finally I
head something. Yes, this deceptively capable piece of intercept gear
masquerading as an innocent piece of test equipment heard something!
What did it hear? A popping "digital" sound that sounded nothing at
all like audio. Not only is the DTR a frequency hopper, it also uses
digital audio! After that test the frequency counter and spectrum
analyzer results were anticlimactic. They confirmed what I already
knew about the units. The frequency counter attempted to lock on the
signal, but didn't have a quick enough gate time and just gave
readings around 900 MHz The spectrum analyzer gave me a nice view of a
FHSS signal.

One aspect of operation I noticed about the units was that they needed
a fellow unit on the same "channel" in order to key up. Otherwise they
give an error message when you attempt to key up. This is a neat
feature as if the radio keys up you can generally be assured that at
least one person you are talking to is within range. It also allows
you to do solo communications range tests if you're lacking a fellow
hobbyist to play with you. In this case, I had help from a number of
friends with these units. First among them was Hank Frost. Hank is a
fellow veteran with a similar interest in electronic communications
who is my usual co-conspirator in playing with things technological.
Hank is much like a technological spider sitting in a big electronic
web (that is if you can imagine the spider looking like an Alaskan
Brown Bear). Hank has the disturbingly cool ability of taking common
consumer electronics equipment and modifying them into interesting
pieces of what refers to as "test gear". It makes me wonder what he
actually did in the Army, but when I ask him he just shrugs and says
"Oh, this and that." After running the gauntlet of electronic security
that separates his residence from the rest of the world, I present a
DTR unit for his examination. He breaks out this piece of equipment
that looked like it was put together from spare parts found in a TV
shop. I ask him what it was and he replies "It was originally a
satellite receiver." Further questions as to the "test equipment's"
origin only elicit that it was originally from "a dude in Green Bay."
After checking out the DTR for a few minutes, he hands it back to me
and says "Nice for something off-the-shelf". I ask him if he wants to
help evaluate it, and he replies "New Hampshire sounds good about
now." The next Saturday, we're in a two-vehicle convoy heading up
Interstate 91 on our way to Keene and parts beyond. This is a
well-known route to us, being the way to get to the famous and
now-defunct Hosstraders Hamfest that was held in Hopkinton, NH.
Talking car to car, we were able to achieve about a two mile range
between radios, thus living up to Motorola's claims about range.
Bouncing around the towns of Southern New Hampshire, the units
consistently gave us a range of about a mile to a mile and a half.
Hiking in the region's mountainous terrain, that range went down to
about a half to three-quarters of a mile.

After playing with them a while up North, I gave The Lone Gunmen a
call. The Lone Gunmen are a group of three friends and fellow
electronics hobbyists who share my interest in exotic communications
equipment. We decide on the most RF-intense, interference-plagued,
radio-unfriendly proving ground that's equidistant between the two of
us: New York City. If they can perform there, they'll perform
anywhere. With Frank Sinatra crooning in the Ipod I hop a train south
and meet them at Grand Central Terminal. Soon were walking down Park
Avenue looking for a suitable place to do a distance test. Motorola
claimed an in-building range of 25 stories, and we wanted to see how
they actually stacked up. There are few if any tall buildings in
Manhattan you can just walk into and start ascending in order to do a
radio test. We notice the tallest thing on the New York skyline, and
figure "Why not?" I would have loved to take one of these up to the
observation deck and attempted a 33cm band DX record, but the line to
the observation deck was oppressively long and we were carrying way
too much interesting shit on our persons to deal with a security
checkpoint. We walk into the "office" entrance and look around.
Despite being one of New York's premier tourist attractions, the
Empire State Building has a more mundane function of being home to
thousands of law offices, accounting firms, and other businesses.
Byers asks me for one of the radios and goes in. A few minutes later
he keys up from the 25th floor with perfect audio quality. Then he
keys up from the 30th floor with perfect audio quality. After the 51st
floor the audio was getting "digitized" and unreadable. Impressed by
the performance so far, we went on to have some fun. By this time it
was getting close to 5 O'Clock, and it was first Friday.

For those of you who are unaware, a very well-known and infamous
hacker magazine has held get-togethers on the first Friday of the
month in New York City since 1987. The location is Citicorp Center on
Lexington Ave. At this get together you get computer hobbyists of all
stripes, including a contingent of radio ninja wannabes with dual-band
ham handie-talkies that like to screw with the security guards. The
last time The Lone Gunmen and I were there, we sported VHF Saber
handhelds and ran DES-XL on 151.88 Mhz. The wannabe radio ninjas
thought we were Feds as their Optoelectronics frequency counters could
lock onto our signals, but all they heard was the open-squelch noise
of an encrypted signal. We figured that tonight would be no different,
and we were correct. We walked in with these radios on our hips, and
the intrepid group of hamsters in training reach for their Signal
Stalker police scanners. Their smug looks changed to that of utter
confusion when they discovered that this time they couldn't lock on
our signal. Langly yells at them "Try a spectrum analyzer!", to which
they reply "What's that?" Soon the word spread around the meeting that
"The Feds are back!" Our mission of inducing paranoia completed, we
proceed to sit down at a chair and loudly talk about our other
favorite subjects: firearms and alcohol. And they all moved away from
our table.

Why would you be interested in a proprietary frequency-hopping radio
when there are other license-free radios available that cost less?
From a hobbyist standpoint, these radios offer a very inexpensive
means to play with practical spread-spectrum communications. Since
these radios are still relatively new, experimenters have yet to work
with them. Much like hobbyists have done with WiFi and other
electronics gear, I expect to see a whole host of "mods" to become
available for these excellent little radios. From the point of a group
of individuals looking to implement a small portable radio system, the
cost of these radios is the same as any medium-grade business band
radio, but with the superlative quality that Motorola products are
known for. Their use of FHSS provides a high-level of privacy than a
handheld operating on a "dot" frequency, and the added features of the
higher-end units offer better functionality for a small business. In a
similar vein, the higher privacy level would be valuable for such
users as CERT, search and rescue, and disaster response teams for
relatively private communications when mobile phone service is
unavailable for whatever reason. A few years ago, communications at
this level would have been out of reach of most individuals and small
businesses. The Motorola DTR series represents the next step on
communications, and are a good value for a small group wanting some
extra privacy and management ability for their communications or a
hobbyist wishing to experiment with the new generation of wireless
communications. If you fall into this category, the DTR series radios
are highly recommended.

While scanner hobbyists may as expected decry the advent of such
technology as the end of their voyeuristic hobby, the advantages of
such technology as represented by the DTR series of radios outweigh
such fatalistic rants. The communications hobby is a beautifully
diverse pastime represented by intelligent and forward thinking
individuals. Such individuals will see the DTR series of radios as
having the potential to add new excitement to their hobby, and embrace
it with open arms much the same way 802.11 wireless networking was
embraced. Individuals and groups with a need for inexpensive private
communications will likewise see the DTR radios as a useful tool for
whatever their mission happens to be. As crowding becomes more of an
issue on the RF bands, I expect to see more equipment utilizing spread
spectrum communications. So no matter where you might be in the wide
world of radio, I would recommend you take a look at these radios.
They are the future.

From: fall_of_sophia
2007-09-02 12:58 pm (UTC)
what a review! thanks for this.
(Reply) (Thread)
[User Picture]From: ticom
2007-09-02 09:00 pm (UTC)
You're welcome!
(Reply) (Parent) (Thread)