Virginia FD Report: Digital Radios Extremely Vulnerable

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Also explain what benefit the end user (which by the way is the whole point for user A to be able to talk to user B) gains by being digital. The end user could care less about system capacity, talk group capacity, ID capacity etc. Capacities issues should be addressed correctly when the systems built or upgraded, not an end user problem. System coverage, another issue not related to the end user. There are no advantages that I know of with a digital system that cant be overcome in analog, ie feedback. But vice versa the ambient noise issue cant be over come with training, it can be lessened but not overcome. So if you have two systems one with a problem you cant over come and one with, what do you do? Remember our number one goal is being able to communicate an intelligible message from our calmest time to our worst time and analog at this stage in technology is the only choice. Another point to consider here is that alot of the people working on this have been on very well designed digital systems are now transitioning back due to experience .

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[Raccon]

Another point to consider here is that alot of the people working on this have been on very well designed digital systems are now transitioning back due to experience .

Why are they transitioning back, when the system is designed so well? Obviously there must be some advantage the analog system offers over digital, but what exactly is it?

 

[jim202]

To put it bluntly, the Motorola radios in the digital mode, use a vocoder that doesn't
know what to do with a high background noise. In the analog mode, these radios don't
use the vocoder. What the vocoder does is translates the sound from the analog mic
input and converts it into a digital stream. (simple terms of an explanation).

Problem is that this vocoder has a major problem when you add a high background
noise to the voice. It doesn't know what to do with this steady high level of audio
and the conversion turns into just unintelligible noisy trash. The receiving end
just hears noise and little or no voice.

There have been a number of papers published on this subject. One of the more
out spoken people is chief Charles Werner from the Charlottesville, VA fire Dept.
His radio system is a Motorola trunking system. If you do some searches, you
will find a number of articles on this subject from a number of the trade magazines.

Jim

Why are they transitioning back, when the system is designed so well? Obviously there must be some advantage the analog system offers over digital, but what exactly is it?

 

[ads47]

Jim you are exactly right. Its not a Motorola issue though, its industry wide. Any radio capable of P25 uses the DVSI VOCODER. The engineers also say its not a DVSI problem either, that a VOCODER in theory will never be able to work well with low SNR levels. Chief Werner chairs the DPWG committee that spawned Testing Committee that put together the NIST test I spoke of.

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[Raccon]

Thanks for the explanation.

 

[hoser147]

The area Im in has a contract to switch over to the digital MARCs system, the Fire chiefs in my county have opted out of the switch over, they have gotten a base and couple portables on the system for interops, but have decided to stick with realigning the analog channels and to continue using those for day to day ops. and with other counties going to the digital it has opened up other channels for the department to all go to their own freqs, and leave the paging for the county on the same channel it has been on for years. Law enforcement is going to go with the MARCs system however. For right now there are just to many problems with going to digital and they decided to go this route and see what the future brings............Hoser

 

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Hoser there has been several guys from your area participate in the research and meetings. They all seem to be up to speed. Glad to hear they are making an informed decision.


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[PHOENIX_SCANNER]

Phoenix Fire Digital still not ready for prime time

It has been several years since our PD switched over to our huge and expensive digital system, with a half dozen simulcast towers and a huge investment.

One out of ten transmissions includes "can you repeat that, you went digital". The cops I have talked to, who can remember the vhf high system, miss it. The ratio of complete, intelligable transmissions was higher. The system was far cheaper, and there was better range with just two transmit sites.

And what of the fire department? They have at this point not been willing to implement the system, because they do not feel it works well enough. Testing continues. I hear within a few years, it will be forced upon them, like it or not. After all, we spent a fortune on this new system. But the old timers don't want it, and don't trust it.

Yeah, I know people are creatures of habit, and are scared of new things, and all of that. I am sure people complained swithing from low band to high band and uhf systems years ago too, and they worked fine. I know many of the challenges will be worked out with time, and that some of this is engineering error.

The bottom line here though, is that the new trunked p25 system is still not trusted for use by our fire department.

Millions of dollars later.

Looking back, I can see why the change had to happen for PD. Two chase channels just doesn't cut it for a 3.5 million person city. I can remember four hot calls at once being worked on one frequency, what a mess! Now there are so many talk groups its nuts!

But I really wonder if the huge investment of moving our fire department to this system was necessary, or just a way for certain people to make money. The 15 or so frequencies they have seem to work just fine to this day.

But the new mega-buck system will become a self-fulfilling profecy. With all the money spent, they feel obligated to make use of it now.

 

[ads47]

PFD has some of the most thorough documentation out there on the downfalls of TRS and Digital systems. I seriously doubt they will be forced on, unless the city wants to assume a huge liability. There current way of running Firegrounds with respect to communications should be the model for the US. It is very thorough safe, and operator friendly. Some of there command and communications vehicles makes the NSA stuff look like a can and string.


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[wlmr]

PFD has some of the most thorough documentation out there on the downfalls of TRS and Digital systems. I seriously doubt they will be forced on, unless the city wants to assume a huge liability. There current way of running Firegrounds with respect to communications should be the model for the US. It is very thorough safe, and operator friendly. Some of there command and communications vehicles makes the NSA stuff look like a can and string.


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If you go back and re-read the very first post in this thread, you will see a reference to PFD testing a DVRS (Digital Vehicular Repeater System). That testing continues today and depending on what area they are testing in can be heard repeated on various sites in the PRWN system. Someone in the Arizona forum area may be able to fill in the blanks on what talkgroup(s), what site(s) etc.

 

[ads47]

If you go back and re-read the very first post in this thread, you will see a reference to PFD testing a DVRS (Digital Vehicular Repeater System). That testing continues today and depending on what area they are testing in can be heard repeated on various sites in the PRWN system. Someone in the Arizona forum area may be able to fill in the blanks on what talkgroup(s), what site(s) etc.

Yes I am aware of that, I will be meeting with some of those guys next week and am sure that will occupy some discussions. DVRS is one of the very viable alternatives to keep firegrounds analog and conventional while still being able to record it and broadcast it out.

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[richardc63]

Richard, your saying I am wrong then leaving the topic again. My post were about Analog vs Digital in reference to ambient background noise. The evidence is out there and very well documented and tested both subjectively and objectively by both practitioners and engineers who are experts in the field. The foundation of my statements are based in fact. After May 23rd I will be more than happy to share the documentation with you. Feedback is not a problem in our view as it is an easily correctable situation and completely avoidable with a very little bit of training. Believe me there is a ton of very sound technical based research that was done in the last 18months that proves this. So where is your documentation and proof of your theories that Digital P25 compatible radios perform well in loud environments. Just a note the NIST test involved over 54,000 combinations of radios and noise, listened to by over 30 sworn practitioners in environments that both the radio manufacturers and firefighters believed would be accurate and fair to the day to day firegrounds and worse case scenarios.

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I just wanted to follow this one up as in the past few weeks we've been working with Moto testing a new version of bone conduction BA microphone for use by our fire service. We have just completed training our "test" stations and have found them to work quite well on certain types of BA masks (some brands of mask didn't work well). I will eat some "crow" regarding the accoustic feedback as the use of bone conduction removes any risk of feedback on analogue simplex. It now will come down to the success of the 6 week trial as to whether we go ahead with these- and if we do then they will most likely become part of the Moto product range.

Cheers,


Richard

 

[ads47]

Richard we have tested them extensively. There are many places that those type of devices work very well. The major problem is in structural firefighting. If its an in ear device what do you when it becomes dislodged inside the structure. You cant replace it, and you also cant use your radio then because its expecting audio from the BCM. If its helmet based, or resides on the skull, nomex, longer hair, etc drastically effect performance. Some of the BCM ear units are still very effected by masked based vibrating low air alarms since they actually vibrate the facial structure.


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[richardc63]

Richard we have tested them extensively. There are many places that those type of devices work very well. The major problem is in structural firefighting. If its an in ear device what do you when it becomes dislodged inside the structure. You cant replace it, and you also cant use your radio then because its expecting audio from the BCM. If its helmet based, or resides on the skull, nomex, longer hair, etc drastically effect performance. Some of the BCM ear units are still very effected by masked based vibrating low air alarms since they actually vibrate the facial structure.


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Ads,

This is a new design- we've trialed numerous different types over the years without success but this one looks to be the closest to being a winner. Our primary need for this is in structural firefighting so the next 6 weeks will prove interesting as a number of the guinea pigs attend alot of structure fires.

Our firefighters rejected any in the ear option- this version uses the bone in front of the ear.

Cheers,

Richard

 

[ads47]

I would be interested in hearing how they work out. One of the reasons we didnt like the temporal transducers was they seemed to heat sink worse than any others because of there larger mass.

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[ads47]

As promised here is the link to the Digital Issue report. The page explains its one of several parts to the report this is just the scientific study.

http://www.its.bldrdoc.gov/pub/ntia-rpt/08-453/


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