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

Tue Feb 26 20:13:38 EST 2008

Believe me, I hear you...

CA
Annapolis

-----Original Message-----
From: Ed Tobias [mailto:edtobias at comcast.net] 
Sent: Tuesday, February 26, 2008 8:01 PM
To: Charley Armstrong; 'David Lloyd'; Scan-DC at mailman.qth.net
Subject: Re: [Scan-DC] Analog/Digital (cellphones/radios)

All good points, Charlie.

As we all know, going from a VHF analog system to a trunked system (only 
possible with digital) MCFRS went from, basically, 3 channels to more than 
40, most of which are repeated.  It also gave the department the ability to 
use the same radios, and radio system, to communicate with any of the other 
fire/rescue systems in the metro DC area, something we all know is extremely

important.  The FMs can also come up on police talk groups.

I'm told that the 800mHz radios are supposed to be better at penetrating 
buildings than are VHF radios, but I have no specific evidence to show that 
they are.  Overall, however,  I think you hear much more consistent and 
reliable communications with ECC than you heard in the VHF days.

Ed
Derwood, MD

----- Original Message ----- 
From: "Charley Armstrong" <armstrong.c at verizon.net>
To: "'David Lloyd'" <lloydde at comcast.net>; <Scan-DC at mailman.qth.net>
Sent: Tuesday, February 26, 2008 12:46 AM
Subject: RE: [Scan-DC] Analog/Digital (cellphones/radios)

> 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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