Digital Vs Analog

[Anesti 329]

I always wondered why do departments go digital, and what the advantages and dis advantages of digital over analog.

[PEMO3 523]

Can not be followed by conventional scanner buffs.

[bronxfireradio 45]

One disadvantage of digital is if your signal to noise ratio drops below a certain point, the receiving station gets nothing. Not like analog where you could be heard weakly with a little static. With digital, it's either receive or not. Called digital cliff drop - if you get too close to the edge, you fall off....

[SteveOFD 176]

In my opinion the main reason an agency goes digital is because a radio sales rep sold them on the idea that they need to go digital to meet an FCC deadline for this or that regulation. Currently the main FCC deadline for Part 90 (Land Mobile Radio) radios is that these radios meet narrowband requriements by January 1, 2013. Most radios manufactured after the mid 1990's can meet this requirement by programming. Narrowbanding just means theat the radio will transmit in a narrower portion of spectrum thatn wideband.

A more in depth explanation can be read at Daryl Jones' Weblog. A portion of this article follows:

Industry-standard codecs (or vocoder software) that convert spoken voice to digital data can not adequately distinguish between voice and background noise. For example, a firefighter using a digital portable radio while standing next to a fire engine that is pumping water will probably not be understandable over the radio because the codec cannot isolate the voice from the pump noise. Another example is a police officer who is trying to announce his or her location during a pursuit. The officer’s digitized voice may be unintelligible because of the siren. A canine officer with a dog that is barking loudly may not be heard because of the competing noise from the dog. In all of these examples, it is likely that analog modulation would provide reliable communication.

Digital radios can be more efficient in utilizing limited radio spectrum by utilizing error correction technology. Encryption is another feature that is available with digital radios. Some agencies have been sold digital radios with the assumption that they could not be heard by scanners. This is not true, APCO P25 digital, which is the digital format the Federal Government has accepted as its digital radio standard, can be scanned with a digital scanner. Digital scanners are considerably more expensive than conventional (analog only) scanners.

[ny10570 745]

What about radio id capabilities for accountability? Is that available with analog systems?

[antiquefirelt 994]

What about radio id capabilities for accountability? Is that available with analog systems?

My understanding is that radio ID's are possible with analog systems that use a very specific set-up. Our county just upgraded to all digital capable equipment on the dispatch side (though staying analog for now). In this project they planned on requiring all radios to send an identifier, but found that due to the various manufacturers and the age of the equipment in the field, only a small percentage could utilize the system decode required for the ID's. Now, most of those whose radios who send the ID, have that digital "chirp" upon keying up each transmission. If I recall, this audible chirp is a feature option, so not all radios need to be set up to send the ID with an audible (it's annoying!)

As was noted, most of the work out county did was to fix some coverage gaps and strengthen the system by adding a voting repaeter network. A large factor was moving everyone to narrowband and then being ready for the digital requirements coming up. So far, my FD specifically has seen no upside and had a temporary downside of losing some coverage, that was corrected with proper antennas and alignment. One thing that lingers is that the use of narrow band and some features that "clean-up the signal" reduces the audio of most radios/paging devices. It appears we may have lost 25-50% of the volume of most receiving units.

Edited October 25, 2011 by antiquefirelt

[Guest alsfirefighter]

As with anything both have advantages and disadvantages. I can tell you the recommendation for fireground communications is analog and line of sight meaning no repeater. Less technology and systems to cause problems.

[antiquefirelt 994]

As with anything both have advantages and disadvantages. I can tell you the recommendation for fireground communications is analog and line of sight meaning no repeater. Less technology and systems to cause problems.

During our recent upgrade it was and remains a constant battle to convince some chief's that fireground traffic should be on a simplex (direct radio to radio contact) frequency. It's dangerous to need to hit a transmitter 10 miles away when you're calling command just 40 feet away on the front lawn. Opponents of this state it is dispatches responsibility to listen for MAYDAY's, of which we tell them, no it's the IC's responsibility to ensure a safety officer or someone is doing that on site. I think older fire chiefs are using the Hackensack Ford fire to further this rather than see that as a "lucky" break, or a break down of the fireground communications system. Edited October 25, 2011 by antiquefirelt

[ny10570 745]

During our recent upgrade it was and remains a constant battle to convince some chief's that fireground traffic should be on a simplex (direct radio to radio contact) frequency. It's dangerous to need to hit a transmitter 10 miles away when you're calling command just 40 feet away on the front lawn. Opponents of this state it is dispatches responsibility to listen for MAYDAY's, of which we tell them, no it's the IC's responsibility to ensure a safety officer or someone is doing that on site. I think older fire chiefs are using the Hackensack Ford fire to further this rather than see that as a "lucky" break, or a break down of the fireground communications system.

Aren't there vehicle based systems that can rebroadcast the simplex transmissions to the repeaters so that they can be monitored and recorded by your dispatchers?

[antiquefirelt 994]

Aren't there vehicle based systems that can rebroadcast the simplex transmissions to the repeaters so that they can be monitored and recorded by your dispatchers?

There are, but as our radio engineer explained, with a voting repeater system, which we have, adding repeaters that change location and therefore cannot be aligned perfectly, can interfere with the systems ability to work properly. The voting repeater system hears every transmission, and determines which site is getting it strongest, and that site is voted to rebroadcast the transmission to the receiver via the RX freq.

They may be able to do this on the simplex fireground channels all FD's are supposed to have in our area, but the cost would have to be borne by the local FD's not he county communications budget. The second issue for us would be the lack of enough comm center staff to monitor the 18 fireground freqs, main fire/EMS dispatch for 22 agencies and 4 PD's. They're already over taxed and short personnel, so adding to their burden without more staff is not an option.

[SteveOFD 176]

My understanding is that radio ID's are possible with analog systems that use a very specific set-up. Our county just upgraded to all digital capable equipment on the dispatch side (though staying analog for now). In this project they planned on requiring all radios to send an identifier, but found that due to the various manufacturers and the age of the equipment in the field, only a small percentage could utilize the system decode required for the ID's. Now, most of those whose radios who send the ID, have that digital "chirp" upon keying up each transmission. If I recall, this audible chirp is a feature option, so not all radios need to be set up to send the ID with an audible (it's annoying!)

As was noted, most of the work out county did was to fix some coverage gaps and strengthen the system by adding a voting repaeter network. A large factor was moving everyone to narrowband and then being ready for the digital requirements coming up. So far, my FD specifically has seen no upside and had a temporary downside of losing some coverage, that was corrected with proper antennas and alignment. One thing that lingers is that the use of narrow band and some features that "clean-up the signal" reduces the audio of most radios/paging devices. It appears we may have lost 25-50% of the volume of most receiving units.

Chief,

Just to clarify some points in your post, true in analog mode there are several different radio ID formats (typically proprietary to each manufacturer). So yes you would have an issue with ID decode with mixed brands. The ID "chirp" can usually be programmed to transmit at either the beginning (when radio is keyed up) or end of the transmission (upon release of PTT). All of my Departments' radios are programmed for end of transmission, this way the FF does not need to remember to wait a 1/2 second before starting to talk, otherwise the first part of the transmission may be cut off with the chirp at the beginning.

Lastly, and this is probably being perpetrated by sales reps, there is no FCC requirement to go to digital either now or in the future. As I stated above narrowbanding is mandated by 1/1/13. This means that agencies must use (and update their FCC licenses) to transmit on 12.5kHz channels (narrowband) as opposed to the previous 25kHz channels (wideband). There had been a proposal to mandate further narrowing of the channels to 6.25kHz (ultra narrowband), but there is no date set for this at this time. From what I understand this would be difficult to achieve in analog mode.

For more information and confirmation that digital is not required see this FCC.gov webpage. Scroll down to the eighth question regarding is digital required.

[antiquefirelt 994]

Chief,

Just to clarify some points in your post, true in analog mode there are several different radio ID formats (typically proprietary to each manufacturer). So yes you would have an issue with ID decode with mixed brands. The ID "chirp" can usually be programmed to transmit at either the beginning (when radio is keyed up) or end of the transmission (upon release of PTT). All of my Departments' radios are programmed for end of transmission, this way the FF does not need to remember to wait a 1/2 second before starting to talk, otherwise the first part of the transmission may be cut off with the chirp at the beginning.

Lastly, and this is probably being perpetrated by sales reps, there is no FCC requirement to go to digital either now or in the future. As I stated above narrowbanding is mandated by 1/1/13. This means that agencies must use (and update their FCC licenses) to transmit on 12.5kHz channels (narrowband) as opposed to the previous 25kHz channels (wideband). There had been a proposal to mandate further narrowing of the channels to 6.25kHz (ultra narrowband), but there is no date set for this at this time. From what I understand this would be difficult to achieve in analog mode.

For more information and confirmation that digital is not required see this FCC.gov webpage. Scroll down to the eighth question regarding is digital required.

Thanks Steve, I think I was aware that it wasn't a requirement to go digital by 2013, but has been "sold" as an upcoming mandate at some point. The dates and advice vs mandates has been blurred by the sales people to push us toward a more expensive system, though the real cost of maintenance for analog vs. digital was one of the selling points toward our becoming truly digital ready. I must say I have no specific knowledge of the radio business, just a seat on a board that always seems to be presented with just a little less information than required. Thankfully we may have turned the corner on misinformation and relying on the word of a single vendor who stands to gain through our decisions based on their advice.

[16fire5 693]

Digital Trunked systems are pushed very heavily by vendors. They are extremely expensive but can work well if properly set up. They also promote interoperabily since everyone is sharing the channels for talk groups. These trunked systems are nothing new but a big problem today is there are not enough available frequencies. Trunked systems make efficient use of the frequencies. Lets face it many departments have more frequencies than they need and in many places don't use common channel line ups or fireground frequencies.

All that being said simplex analog communications are still best for the fireground in my opinion. Simplex analog UHF radios are relativly inexpensive enough to allow departments to equip each riding position with one. They have the PTT ID's and emergency buttons too. Another good reason to put the PTT squak on the end of the transmission is it is an audible reminder that the person has finished their message (No need to say K). Background noise and SCBA make fireground communications very difficult but IMHO analog digital is still our best bet for now.

Manufactures are aware of our issues and are working on digital equipment to make it work for us.

[tbendick 27]

No I repeat No fireground communications should be on a repeater or trunked system. It should be simplex and analog.. end of story..

Can you use repeaters and other things to enhance communications sure.

As far as departments who want a dispatcher to listen, Simple solution is a vehicle repeaters.

Look up Phoenix fire's reports on the issue.

http://phoenix.gov/FIRE/radioreport.pdf

At last check they use VHF simplex radios linked to the trunked system using vehicle repeaters/

One of the units tested http://www.futurecom.com/uploaded/tiny_mce/File/8Q100X07-Rev-1-DVR-Fire.pdf

[Guest alsfirefighter]

During our recent upgrade it was and remains a constant battle to convince some chief's that fireground traffic should be on a simplex (direct radio to radio contact) frequency. It's dangerous to need to hit a transmitter 10 miles away when you're calling command just 40 feet away on the front lawn. Opponents of this state it is dispatches responsibility to listen for MAYDAY's, of which we tell them, no it's the IC's responsibility to ensure a safety officer or someone is doing that on site. I think older fire chiefs are using the Hackensack Ford fire to further this rather than see that as a "lucky" break, or a break down of the fireground communications system.

Sad part is they don't have the slightest clue then as to why the Hackensack incident went down the way it did. Whoever has the mindset that is dispatches responsibility to monitor for MAYDAY's I'm sorry to say is partially right...as its EVERYONE'S responsibility to listen for the phrase...however if they are that worried about it...then write a policy that if you declare one and its not heard...switch to your primary channel and call it again. What is also lost is that if you on your main channel...and this happened to me once when working...if you are using it for operations..you can drown out another dispatch. And dispatch will leave the volume up to normal level for them for only so long before they get tired of having to monitor every ounce of chatter they don't need to hear for the 1 call to them. This is especially tough on dispatching centers like 60 control that have multiple frequencies to pay attention to.

Speaking of radios...how many of you actually look at your portables and how the channels are programmed? Do they make sense or is it just a list that was put together? I lobbied hard and it took some time to break through to make both the first and last position on the dial our main frequency....that way if you were in trouble and not getting an answers or had another emergency, no matter which way you twisted the channel selector you got back to our main dispatch repeated frequency.

[antiquefirelt 994]

Speaking of radios...how many of you actually look at your portables and how the channels are programmed? Do they make sense or is it just a list that was put together? I lobbied hard and it took some time to break through to make both the first and last position on the dial our main frequency....that way if you were in trouble and not getting an answers or had another emergency, no matter which way you twisted the channel selector you got back to our main dispatch repeated frequency.

Another great point, very few FD"s pay enough attention to how their portable operate and fail to see some safety issues. Our county comms director wanted to mandate the freq. lineup in every radio for the first 5-8 channels citing "interoperability". This would have put the primary dispatch channel in the #1 slot and everyone's fireground in the #2. We refused, saying we will always have our fireground in #1 and in 95% of the cases in the last slot as well.

Unlike yours, we wanted our failsafe to be on a simplex analog frequency. We have some near deadspots on the repeated dispatch freq and in most of the box stores and large concrete buildings, the portables can't hit the closest repeater tower (we do not have in vehicle repeaters). Having the fireground or your "failsafe freq" in in the first and last, as ALS noted, ensures that on any radio that has a selector "stop" you can spin it either way until it's stops and know you're on the right freq. Many of the newer radios do not have these "stops" and now we've started de-programming the knobs which get turned too easily and use a front button for channel selection. Some firefighters noted the radio "beeps" when you select the primary/channel 1 freq, so you know when you're there, but we felt that that wasn't reliable enough in a MAYDAY when PASS devices may be sounding and who know's what other noise might not allow it to e heard. The front keys allow channel selection than key lock up requiring at least two keys be "bumped" to knock the portable off the selected channel.

All our officers carry two radios, one is on the fireground and one is on the repeated dispatch freq at all times. All firefighters radios are left on "fireground" and if they don't have a radio with selector "stops", they must use the "no knob" function and front keypad to change freqs.

Edited October 27, 2011 by antiquefirelt

[tbendick 27]

Another nice feature is channel announcement. Works very well

[wraftery 1,275]

My understanding of trunked systems, be they digital OR analog, is thst they operate on a system similar to your cell phone. It is shared use of a system.

It is like eight people living in a house with five beds. The system works as long as no more than five people want to sleep at the same time. Otherwise it fails.

Did your cell phone work on 9/11/01? No! Why? All 9 people wanted to use the beds. OK, it was a major event, andd a surprise so EVERYBODY wanted to check on loved ones, so cell lockout was expected.

How about that teeny-weenie earthquake we had on the East Coast a month ago? You guessed it...all nine people wanted to use the beds, so your cell phone got locked out.

I am not a communications expert, but I do know a little about Baseball. Three strikes and you are out. I am afraid, my brothers, that we will go down swinging.

[Guest alsfirefighter]

My understanding of trunked systems, be they digital OR analog, is thst they operate on a system similar to your cell phone. It is shared use of a system.

It is like eight people living in a house with five beds. The system works as long as no more than five people want to sleep at the same time. Otherwise it fails.

Did your cell phone work on 9/11/01? No! Why? All 9 people wanted to use the beds. OK, it was a major event, andd a surprise so EVERYBODY wanted to check on loved ones, so cell lockout was expected.

How about that teeny-weenie earthquake we had on the East Coast a month ago? You guessed it...all nine people wanted to use the beds, so your cell phone got locked out.

I am not a communications expert, but I do know a little about Baseball. Three strikes and you are out. I am afraid, my brothers, that we will go down swinging.

Excellent post and far too true. I've operated on trunking systems elsewhere where to simply put it...you got a busy signal when you attempted to talk due to radio traffic volume during a few major events we had where I was at..at the time. Not a good feeling when you have critical info to get to dispatch or trying to up your response resources when your running a single engine to a call because you're all that was closest at the time.

[stvrap79 8]

Speaking of radios...how many of you actually look at your portables and how the channels are programmed? Do they make sense or is it just a list that was put together? I lobbied hard and it took some time to break through to make both the first and last position on the dial our main frequency....that way if you were in trouble and not getting an answers or had another emergency, no matter which way you twisted the channel selector you got back to our main dispatch repeated frequency.

Great poInt!! I can't even explain how frustrating it can be to be on an ops channel and have to switch through god knows how many frequencies to get on 46.26. Does anybody know if it's possible to assign individual frequencies to the numeric keypad on an HYT portable?? I am guessing it's a feature that can only be used/unlocked by hooking it up to the computer software.