Virginia FD Report: Digital Radios Extremely Vulnerable

[DaveNF2G]

The conventional frequencies are not actually part of the trunked system. They are loaded into memories in the mobile and portable radios. They might be identified as if they were talkgroups, but that is done in order to simplify operations for the end users and does not really mean that they are actual talkgroups.

 

[N4DES]

The trick with trunking is not to break your fleet down into ridiculously small talkgroups. I would question why any site with 5 channels would ever have 250 talkgroups affiliated to it. If I was the system manager I would be taking a look at the traffic stats to see whether some of these were warranted. We are a very very large organisation covering a very large area on a trunk system of 100+ sites and we have about 80 tgs of which about 4-5 are used daily and the rest used for special ops. Our smallest regular talkgroup would have 40-50 radios on it and we have stuff all contention between radios needing to transmit simultaneously.

Cheers,
Richard

Your very close in your thinking Richard, I have 2 municipalities that are on the SmartZone system that I manage. Both have the same identical number of talk-groups but one is a 5 channel and the other is a 7 channel system. The 5 channel system always busy's out during peak times while the 7 channel rarely if ever gets a busy and their traffic stat's are almost the same # of PTT's daily.

We used the criteria that APCO set many years ago of no more than 20 active users for a public safety talk-group and 30 for general govt. and since then I have steered toward the high side by only turning on another requested TG for 30 PS users and 40 local govt. I think they did this more for dispatcher loading (human overload) but it's a good starting point for system loading numbers.

 

[kyparamedic]

Clyde,

I think I understand what you are saying but I'm not sure how it works in practice (in a multsite trunking system). Are you saying that the conventional frequency used is one of the voice channels (base tx) on the trunking base? I can "get" that but in a multisite trunking system different frequency pairs are used at different sites (for obvious reasons) so how do you choose the conventional freq to match?

Cheers,


Richard

I think he's describing some sort of patch, from a conventional channel to a trunking talkgroup. This is what it sounds like to me anyway. Just having a radio transmit on the same frequencies the TRS uses won't work as it's not going through the TRS and it will just consider it interference and not assign that frequency. Plus, talkgroups hop frequencies all the time, especially on an EDACS system. Correct me if I'm wrong about any of this.

 

[richardc63]

The conventional frequencies are not actually part of the trunked system. They are loaded into memories in the mobile and portable radios. They might be identified as if they were talkgroups, but that is done in order to simplify operations for the end users and does not really mean that they are actual talkgroups.

Hi Dave,

OK, now I understand! This is no different to the way we operate. They respond to the call centre via the trunking system and when they arrive at the incident they have a pool of simplex channels to use for local comms. There is a "default" simplex channel they use as a matter of routine and when an incident grows they split up using the other simplex channels within each team. In a situation like this they would often move the comms to the call centre to a special operations talkgroup to keep the routine tg free.

Is this how you operate?

Cheers,


Richard

 

[zerg901]

KYparamedic and Richard - you both seem to understand what I am saying about switching from trunked to conventional.

Please consider this question. When you are on a trunked system, and you get into a hole - what frequency can you switch to so that the other folks on the trunked system will hear you (without also requiring them to switch channels)? Since trunked radios are always hopping from freq to freq - this is a tricky situation.

I suppose that every portable radio could have a Channel 1 as the emergency simplex / conventional channel. And you could put a receiver on every fire truck, ambulance, and police car to monitor this Channel 1. Then all of these receivers could be fed back to the dispatcher (infrastructure) somehow - and any emergency message from 'Channel 1' could be rebroadcast via all talkgroups. But this is the 'long way around' in comparison to just going 'direct' on the output of a conventional repeater channel.

I have been kicking these types of questions around for many years. Someone from Sweden named Hubie ((IIRC) used to chat with me about this stuff. I suppose there is no harm in batting this idea around the Internet a few more times. Maybe it will stir up a few more creative thoughts on the subject.

Peter Sz

 

[richardc63]

KYparamedic and Richard - you both seem to understand what I am saying about switching from trunked to conventional.

Please consider this question. When you are on a trunked system, and you get into a hole - what frequency can you switch to so that the other folks on the trunked system will hear you (without also requiring them to switch channels)? Since trunked radios are always hopping from freq to freq - this is a tricky situation.

I suppose that every portable radio could have a Channel 1 as the emergency simplex / conventional channel. And you could put a receiver on every fire truck, ambulance, and police car to monitor this Channel 1. Then all of these receivers could be fed back to the dispatcher (infrastructure) somehow - and any emergency message from 'Channel 1' could be rebroadcast via all talkgroups. But this is the 'long way around' in comparison to just going 'direct' on the output of a conventional repeater channel.

I have been kicking these types of questions around for many years. Someone from Sweden named Hubie ((IIRC) used to chat with me about this stuff. I suppose there is no harm in batting this idea around the Internet a few more times. Maybe it will stir up a few more creative thoughts on the subject.

Peter Sz

Peter,

Now that is easy... in Australia we have a company by the name of Omnitronics that produce very good quality "bridging" units. You have a number of different manufacturers in the US that have much the same- basically all you need is a radio in the appliance switched to the simplex channel... this is bridged to a radio operating on a talkgroup. When the appliance radio receives the call it is automatically rebroadcast to comms.

While I understand that some see that as one way to record the simplex traffic (another is to use recording equipment on the appliance) but I would caution anyone from unnecessarily loading down the trunking system with incident ground traffic. Anyone who has listened to firefighters on simplex knows they chatter far more- we all do under stress. I wouldn't want this kind of traffic on a shared network that I'm on... no way.

Cheers,


Richard

 

[rescue161]

When you are on a trunked system, and you get into a hole - what frequency can you switch to so that the other folks on the trunked system will hear you (without also requiring them to switch channels)? Since trunked radios are always hopping from freq to freq - this is a tricky situation.

It really wouldn't do much good for every mobile unit to monitor it since the distance that radios can transmit in simplex is very short, especially at 800 MHz. The dispatch console should be set up to monitor all simplex (radio to radio - "direct") channels via voting receivers set up all over the county/city/etc. Dispatch would be able to hear any traffic out in the field using this method no matter if they went through the repeaters on the TRS or not. Other users would not be able to hear them, but chances are, other users would be too far away for simplex ops anyway. If two users were close enough to communicate, but too far away from the TRS to use it, then they could switch to one of the simplex channels and talk.

 

[Raccon]

I was wondering about this. So it's possible to switch to a simplex mode on a trunked radio and talk to someone who's operating on a trunked channel? How does this work? We have a walkie-talkie mode on our trunked radios that is just a conventional, simplex set of channels but we cannot hear anyone operating on a trunked channel nor can they hear us, so it's rarely used.

I understand 'direct' as communication between two radios, which I believe is the same what you call walkie-talkie mode.
zerg901 said that you can't do this in a trunked system, but as I said it's a matter of the radio, not the system - there isn't much stopping a trunked radio from having a direct / walkie-talkie mode.

BTW: TETRA (which is a trunked network) supports a feature called dual-watch that allows radios to scan trunked and direct mode frequencies, making it even more convenient.

 

[zerg901]

Sure - a trunked radio can operate either trunked or direct. But if you are going to switch from trunked to simplex at a firescene, you have to make sure that someone else is listening to the direct freq.

Do you see how this is different from switching to direct on a conventional repeater output? (Everyone is already listening to the 'direct' freq in this situation - the 'direct' freq is the same as the repeater output freq).

Its not an insurmountable problem, but it has to be addressed beforehand. Bottom line - the IC will always need to be listening to 2 radios if a combination of trunked and simplex is used at a scene (unless we get fancy and set up the relay system mentioned earlier that would bring the direct comms over onto the trunked system).

Unless I am totally wrong

Peter Sz

 

[wlmr]

(unless we get fancy and set up the relay system mentioned earlier that would bring the direct comms over onto the trunked system).

Peter Sz

One example of a vehicle relay system I found. (Google is my friend!)

http://www.futurecom.com/mbx_nf.htm

I expect there's more, I stopped after I found one.

 

[gcr33]

I love it the union says it's no good and the cool aid drinkers say they agree.
How about the agencies that use digital day in and day out?

Stop towing the Union line and start thinking for yourselves.

 

[Raccon]

Sure - a trunked radio can operate either trunked or direct. But if you are going to switch from trunked to simplex at a firescene, you have to make sure that someone else is listening to the direct freq.

Do you see how this is different from switching to direct on a conventional repeater output? (Everyone is already listening to the 'direct' freq in this situation - the 'direct' freq is the same as the repeater output freq).

Its not an insurmountable problem, but it has to be addressed beforehand. Bottom line - the IC will always need to be listening to 2 radios if a combination of trunked and simplex is used at a scene (unless we get fancy and set up the relay system mentioned earlier that would bring the direct comms over onto the trunked system).

Unless I am totally wrong

Peter Sz

Sounds about right though you need nothing fancy, not for TETRA at least where you can so-called DMO gateways, which are radios that work as the relay. They are available as portable and mobile (same size as the non-gateway models), so they can either be placed anywhere at the scene or are already installed in the vehicle(s). It takes virtually no effort to set it up - just switch the gateway function on and throw the radio somewhere (in case of the portable). Thereby every radio, regardless if it's in trunked or direct mode, will hear you; and the dispatcher, too, if he is part of the trunked group.

 

[suttles1972]

Sure - a trunked radio can operate either trunked or direct. But if you are going to switch from trunked to simplex at a firescene, you have to make sure that someone else is listening to the direct freq.

Do you see how this is different from switching to direct on a conventional repeater output? (Everyone is already listening to the 'direct' freq in this situation - the 'direct' freq is the same as the repeater output freq).

Its not an insurmountable problem, but it has to be addressed beforehand. Bottom line - the IC will always need to be listening to 2 radios if a combination of trunked and simplex is used at a scene (unless we get fancy and set up the relay system mentioned earlier that would bring the direct comms over onto the trunked system).

Unless I am totally wrong

Peter Sz

I couldn't agree more. The incident commander should monitor 2 radios. In most cases, a scribe is selected to assist in monitoring both radio groups, while incident command adhere to operations and its request. As a firefighter myself, I understand how complacency becomes commonplace on the fireground, where we rely solely on a trunking system that isn't 100%. But after experiencing some close calls, it is being address that the "direct" frequency be used during condition where the radio system becomes 70% inoperable.

 

[richardc63]

I couldn't agree more. The incident commander should monitor 2 radios. In most cases, a scribe is selected to assist in monitoring both radio groups, while incident command adhere to operations and its request. As a firefighter myself, I understand how complacency becomes commonplace on the fireground, where we rely solely on a trunking system that isn't 100%. But after experiencing some close calls, it is being address that the "direct" frequency be used during condition where the radio system becomes 70% inoperable.

Hi,

Thanks for that info- it lines up with what we are doing here in Australia. Just a quick question- under your ICS when the f/f's report in does anyone record the radio ID on the ICS whiteboard? Just curious- I'm being asked to extend the emergency call to simplex fireground channels (technically very easy) but how do they know who the radio user is if ICS doesn't "track" the radio user?

Cheers,

Richard

 

[kenisned]

Hi,

Thanks for that info- it lines up with what we are doing here in Australia. Just a quick question- under your ICS when the f/f's report in does anyone record the radio ID on the ICS whiteboard? Just curious- I'm being asked to extend the emergency call to simplex fireground channels (technically very easy) but how do they know who the radio user is if ICS doesn't "track" the radio user?

Cheers,

Richard

Our radio ID's correspond to the seated position on the apparatus. We keep the radios on the apparatus and not assigned to an individual person.

So, using the MDC1200 format:

Engine 56 mobile is 5600
Eng 56 Driver portable is 5601
Eng 56 Officer portable is 5602
Eng 56 FF portables are 5603 and up

Each radio is professionally engraved on the case with the ID

 

[ads47]

I love it the union says it's no good and the cool aid drinkers say they agree.
How about the agencies that use digital day in and day out?

Stop towing the Union line and start thinking for yourselves.

This thread has gotten way off topic, back to the topic, Analog VS Digital. Do your research on Unions they were formed to protect the safety of workers. The Analog/Digital Issue is a safety issue.

The agencies that use it day in and day out agree, and those that don't once shown with there own radios how poorly they will perform in a loud environment compared to the same radio running analog quickly change there mind.

I doubted this was a problem at all until I did some basic real world testing and some research and now understand it. Too often people are saying... like you.... our digital is great.. when you upgraded from an older system with poorer coverage, or technology. We are comparing the same radios operated at the same place in two modes, one digital, one analog. Not a new shiny apple compared to an old rotten orange.


Given two identical systems or situations analog radios outperform digital radios when it comes to voice intelligibility every time. Running digital in a simplex mode makes no since at all since there is no advantage. In TRS, there are advantages for the stake holder, ie more capacity in TG's and ID's, but at a cost of audio quality in moderate to loud noise environments. Some one mentioned it was better due to the "error correction" done on the digital side. Wrong your forgetting one very important part. The audio is already processed at that point. If the audio was processed with noise and it sent junk it..... you will get junk out not matter how much error correction is done. Also remember the whole theory of digital sounds better farther? There are no subjective test done that back this up. Real world practice also doesn't support it. If the audio sounded bad in a poorly covered analog area, it will sound worse in digital. Also remember when the analog sounds bad there is still voice being transmitted and the human ear is excellent at deciphering voice out of junk. In digital, the ear doesn't have a clue because of the digital junk that comes back out. The reports that are talked about will be published next month and were agreed upon by both the practitioners and manufactures. The bottom line is that no VOCODER on the market can handle random loud ambient noises and the engineers say its not possible to make one that will at the db levels experienced in day to day emergency services. Yes there are gadgets and gizmos that you can put in your helmet, wrap around your neck, etc that help (or band-aid) the problem but what are you going to do when they fail and your inside, you cant fix it then, and theres only one on the market that can be disabled while suited up and still allow full radio functionality. Not to mention anything in your ear or around your neck that has mass will heat sink like no bodies business.


ads

 

[richardc63]

This thread has gotten way off topic, back to the topic, Analog VS Digital. Do your research on Unions they were formed to protect the safety of workers. The Analog/Digital Issue is a safety issue.

I doubted this was a problem at all until I did some basic real world testing and some research and now understand it. Too often people are saying... like you.... our digital is great.. when you upgraded from an older system with poorer coverage, or technology. We are comparing the same radios operated at the same place in two modes, one digital, one analog. Not a new shiny apple compared to an old rotten orange.


Running digital in a simplex mode makes no since at all since there is no advantage.


ads

Ads,

Sorry but you are wrong, wrong, wrong! I wish that the "anti-digital" camp would actually produce some evidence rather than making sweeping statements without any foundation.

Analogue simplex suffers from acoustic feedback when radios are in close proximity to each other (such as in a fire situation). Digital simplex does not. You can wind up the volume on your handheld and not cop feedback while at the same time analogue radio users have to turn their volume down as background noise rises to avoid feedback from being generated. There is your advantage- and our guys back me up totally!

I respect your right to an opinion, but in this case the anti-digital camp are showing more prejudice than any sound technical basis for their arguments.

Cheers,


Richard

 

[DaveNF2G]

Analogue simplex suffers from acoustic feedback when radios are in close proximity to each other (such as in a fire situation). Digital simplex does not. You can wind up the volume on your handheld and not cop feedback while at the same time analogue radio users have to turn their volume down as background noise rises to avoid feedback from being generated. There is your advantage- and our guys back me up totally!

That is not a technical issue. It is an operational one. When several people are in close enough proximity to see each other, only one of them should have a radio turned up (or on) to deal with the outside world.

The fire service in particular has devolved into a radio mess. Every single person on the fireground does not need a radio turned up full blast.

The background noise issue, however, is a technical one. Power tool and other sounds in the background cannot always be avoided. Analog radios have no problem, combined with the good old human ear and brain, sorting out important voice data from extraneous noise. Anyone who has operated a digital cellphone or any other kind or grade of digital radio knows from experience that background noise at the source screws up just about any digital signal.

 

[ads47]

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.

ads

Ads,

Sorry but you are wrong, wrong, wrong! I wish that the "anti-digital" camp would actually produce some evidence rather than making sweeping statements without any foundation.

Analogue simplex suffers from acoustic feedback when radios are in close proximity to each other (such as in a fire situation). Digital simplex does not. You can wind up the volume on your handheld and not cop feedback while at the same time analogue radio users have to turn their volume down as background noise rises to avoid feedback from being generated. There is your advantage- and our guys back me up totally!

I respect your right to an opinion, but in this case the anti-digital camp are showing more prejudice than any sound technical basis for their arguments.

Cheers,


Richard

 

[JoeyC]

I find it equally difficult to listen to a weak analog signal while in a noisy environment as l do listening to a noisy digital signal in a quiet environment.