[Scan-DC] Analog/Digital (cellphones/radios)

[Charley Armstrong]

Please don't take this as an attack/flame:

In the Loudon report, there were 2 major issues with the radios.
Unintelligibility and system busies.  Unintelligibility was caused by water
in the speaker-microphones, wearing breathing apparatus, and shouting.
Fireground comms are notoriously garbled - not a new problem, and something
that is unfairly attributed to digital radios.  System busies are caused by
too many people trying to transmit at the same time, again not a new
problem, but one with a new manifestation.  On top of this, there can be
multiple radios assigned to each unit - the more people to talk on top of
each other.  Analog radios are just as unreadable when too many people key
up/ step on each other.  

Theoretically, digital radio is more efficient and causes less interference,
which allows more reuse of frequency pairs.  The relatively long range VHF
signal had to be powerful enough to blanket the county. This is why you were
able to hear MC fire on Skyline Drive.  But it meant that it had the
potential to interfere with other jurisdictions, causing the frequency pairs
to be more geographically dispersed, which is less efficient.  In fact, MC
had run out of usable VHF pairs because of potential interference.  It had
to move to shorter range 800UHF band to expand.  And now 800UHF pairs are
scarce, which is why PS is moving south to 700UHF. 

The Public Safety golden standard is 95% coverage OUTDOORS.  I can't speak
for current coverage in MC, but back in the day when I ran calls in MC, it
was not uncommon for our 154VHF portable to be out of range, or otherwise
fail to hit a tower, particularly when indoors or in the "country." If it
happened indoors, we just used the landline.  Outdoors, we used the mobile
in the unit instead.  I'd gamble that coverage in MC is better now than
then.  The use of VRS (vehicular repeaters) is common practice in
jurisdictions with 800UHF TRS's.  It actually makes a great deal of sense -
it is a functional equivalent to a tower site.  Why build 10 more towers
which will marginally improve coverage, when you can bring a repeater to
exactly where it is needed?

FWIW, when I step into an elevator, my cellphone quits working, except in
buildings with indoor cellular repeaters.  Maybe MC needs to get with
building owners to install PS repeaters in their buildings - it's happening
in NYC.

And for practical reasons, MC fire doesn't need to be heard on Skyline Drive
- but it would be nice :)

CA
Annapolis


  

-----Original Message-----
From: scan-dc-bounces at mailman.qth.net
[mailto:scan-dc-bounces at mailman.qth.net] On Behalf Of David Lloyd
Sent: Monday, February 25, 2008 10:45 PM
To: Scan-DC at mailman.qth.net
Subject: [Scan-DC] Analog/Digital (cellphones/radios)

The recent discussion on analog/digital communications really has me
thinking.   Why DIGITAL?  Maybe I'm naive, but I REALLY haven't ever been
impressed with digital.  I bought a Uniden 396T scanner a year ago - I still
don't know how it works.. and I'm a nerd!! The only benefit I see with
digital is that you can do more with less.

The reason why I bring this up is that I spent an afternoon reading the
Loudoun County firefighter Line of Duty Death report and was I was really
disturbed with all the squawks and beeps and unintelligible audio on the
radio.  In my years in the fire department, I experienced the switch between
analog radios that worked great (okay, decent - there were still coverage
problems), to digital that worked terribly for the aforementioned reasons.
(Everytime I got on an elevator I got "BEEEEEEEEEP" no signal!)   I guess
this why more towers are necessary (ie: DC) and why MoCo is now using
repeaters on vehicles.   It's been a few years since I have been in the
service--I'm wondering if that changed anything.

Just for grins, I took my radio to Skyline Drive two years ago.  The
Montgomery County digital signal - D E A D.    The 154 UHF was perfect.

Sorry if this seems more like a rant than a question, I guess it's just my
fustration with the whole Public Safety initiative in the Washington area to
"improve things".. but it's certainly making things more difficult for all
parties invovled.  Just my observations,  being old-fashioned and hating
the digital transmissions.. what next? Computer voice dispatching?


David





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