http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201-8.pdf - page 182 of 294 - on May 19, 2001 a MAYDAY was missed and the new digital portables were taken out of service
IIRC it was determined that when multiple P25 transmissions occured at the same time, that the P25 portables would mute completely (since the Bit Error Rate was too high) - reportedly this has been "fixed" via software change(s)
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From the fireradio@yahoogroup March 21, 2001
I have been on both sides of the street as a Law Enforcement Officer and as a
Reporter for a Daily Newspaper in NYC.
Yea it's hype on the media end. If you have ever been to a working fire in NYC
and listen to fireground coms you will hear Uniforms talking over each other
often. Members often are within shouting distances at fire scenes and often can
read the lips of the other FF while communicating on the radio. The audio delay
must drive them crazy. Many FF have been "On Da Job" for many years and find it
hard to adapt to change. I remember when they installed MDT's in the trucks
.......Talk about confusion ............It took about six months to get the
units to use them! It's just going to take a while for members to adapt.
When you hear 3, 2, and the Rescue going in.............. you know it's going to
be a job you don't need to worry about your radio working.
I know the FCC is promoting Spectrum Efficiency however there needs to be some
exceptions .............this maybe one of them.
>
> >Two weeks ago I predicted issues would occur with the new XTS-3500R radios.
>
> That's a shame! I bought a several of these radios for Emergency Management
> and they work very well in our application. We use three modes: analog FM
> (98% of the time), unencrypted digital P25 (FDMA with IMBE vocoding)
> (0.25%), encrypted digital P25 (DES-OFB with a key variable loaded in each
> radio) (1.75%). In encrypted P25, there is no similar degradation as DES/
> DES-XL has had. Our experience on VHF has been that digital is usable with
> a clear signal (no noise) to about the 12 dB SINAD point (maybe a little
> lower). The audio quality is about the same as Nextel direct connect. Not
> quite FM sounding, but not horrible, either (a left handed compliment?).
>
> I just saw the leader for Channel 4 (WNBC-TV) news via satellite. They
> showed the portables. I hope the media does not blow this out of proportion
> with hyperbole.
>
> >NYFD firefighters are a customed to their VHF convential radios. It's
> >going to take training for the Uniforms to get acustomed to the new units.
>
> Like everything, it's a learning curve. In digital, they are different
> animals. They can be programmed to work in analog, but there would still be
> a slight delay (not as long as the delay in digital). It's the audio
> processing.
>
> >
> >
> > Thanks for the comments.
>
> We all learn when we share. I'm glad I had something non-stupid to say :o)
>
> > I think the delay problem will cause Havoc with Fire
> > Fighters operating on the FG. Many will think their radios
> > are not working
> > properly.
>
> And, that's the point. *Think* is a powerful word if your whole career has
> been based on using the radio in a certain way. The radio is working, but
> there are several things that are no longer what they're familiar with. The
> inability to do man-down search because of the echo instead of the feedback
> is one - the inability to gauge how far away you are in the building from
> another firefighter solely based on the white noise in the background is
> another. Those FDNY guys get 100% of the utility value out of everything
> they carry. Now that there is echo, that function needs to be worked
> around. Likewise for the white noise (there is none in digital - you go far
> enough and it sounds like broken words until you fall off the face of the
> earth).
>
> Digital audio is kinda funky sounding and lacks the dynamic range of FM. It
> almost sounds synthetic. Background noise is reduced because of the DSP
> (vocoding) and much of the time, it sounds like there is a noise gate on
> the audio. That's another learning issue. While we get the words through,
> many of the elements of unspoken communications are lost.
>
> >Has the simplex radio ranged been decreased?
>
> They are using 6.25 kHz channel spacing, so the transmissions are
> definitely narrowband. That, and UHF characteristically has less range than
> VHF - except that in a highrise environment, it may scatter better,
> penetrate through narrower apertures and yield a more usable signal. There
> is a tradeoff. If they lost any range by narrowbanding, the digital should
> make up for that. There is also less co-channel interference. Hoboken, Fort
> Lee, Hackensack and just about everyone else on the other side of the river
> used to share 153.830 (out here in the Midwest, *every* local department
> also uses 153.830 as its first choice for fireground). The 483 channel is
> exclusive to NYC - and out there, that's an absolute plus. Another thing is
> that in many of the facilities they are using the equipment in, there are
> engineered solutions, such as distributed antennas/ Radiax with repeaters
> and bi-directional amplifiers. That should offset any coverage problems.
> IMO, though, I think it's not a coverage thing, but a matter of learning
> something new. The usual stuff follow - none of us likes change much and we
> usually resist it when it happens.
>
> >Fire commissioner Thomas Von Essen says that he intends to fix the problem
> >and try to get the radios back in use because they are, he says, the
> >latest technology.
>
> Commissioner 'Put-a-baseball-bat-into-the-EMS-Bus-windshield?' There's a
> problem in and of itself. (Folks, please excuse my off topic comment, but
> after what this man did to FDNY EMT Denise Chapman -
> http://members.aol.com/webmedic4u/Denise.html - and other EMS personnel, he
> doesn't deserve to be in the same species as the rest of us. I'm biased.
> I'm sorry - I won't go there again.)