emergency Services bands in use

[woodruff13]

I work in the wired world, but want to learn about mobile sources in common use.

Is it safe to say public safety has gone 100% to 700MHz and 800MHz bands?

How common is VHF in use by public safety / security / EMS?

I'm testing the hypothesis that VHF is not longer in wide use, that any responder will use the 700MHz+ bands. VHF has become primarily the domain of the Ham.

Who primarily uses VHF these days?

Thanks for any comments.

Bill

 

[selgaran]

I work in the wired world, but want to learn about mobile sources in common use.

Is it safe to say public safety has gone 100% to 700MHz and 800MHz bands?

Absolutely not.

How common is VHF in use by public safety / security / EMS?

Extremely common. VHF is the statewide standard for fire mutual aid, for example.

I'm testing the hypothesis that VHF is not longer in wide use, that any responder will use the 700MHz+ bands. VHF has become primarily the domain of the Ham.

Absolutely and utterly wrong.

Who primarily uses VHF these days?

Every type of service who has ever used it in the past. Go to the database and pick a county at random, you'll be hard pressed to find anywhere that doesn't have heavy VHF use even with the growing number of large UHF and 800 MHz trunked radio systems.

 

[SCPD]

VHF is the most common band in rural areas. It works better in the mountains than any other band, and I mean western mountains, not eastern mountains. Many federal agencies use VHF, especially natural resource agencies, and those are the agencies that handle large wildland fires. So Selgran's observation that VHF is the band for fire mutual aid is correct.

Take a look at the Los Angeles County Fire Department. They use UHF for dispatch, response, and command. They also carry VHF handhelds that contain most of their fireground frequencies. Since they also have a heavy wildland fire workload these radios work well for them when a large wildland fire occurs in the county as many agencies responding to their request for mutual aid will be coming with VHF equipment. When L.A. Co Fire responds mutual aid for a wildland fire out of county it is likely that VHF will be used.

The National Interagency Fire Center's (NIFC) wildland fire cache radios are VHF. The frequencies used for command, tactical, and some air to air functions are on VHF. Many years ago (doesn't seem that long to me!) when radios had limited channel capacity (1-5 channels and used crystals) units responding to fires had to be issued NIFC radios for tactical and command. Now every wildland fire unit has a radio with hundreds of channels and include the NIFC frequencies so they don't have to bother with reprogramming or being issued radios. It is often very critical that responding fire suppression resources have the capability to communicate on common channels without any delay. The only exception is the use of UHF for logistics and camp purposes because it is fairly easy to move a NIFC cache system into camp along with the responding incident management team. Delays are not as critical for these functions.

 

[SCPD]

I should also mention that the fire service in many areas of the country are finding that use of digital trunked systems for fireground communications to be both difficult and dangerous. When other firefighter tools such as gasoline powered saws, alarms on air bottles, and PASS ("Personal Alert Safety System") motion alarms are used digital transmissions become garbled. I know of at least one death where the unintelligible transmission of a trapped firefighter, caused by interference from his PASS, resulted in a fatality. Many departments and now some larger fire associations are questioning the conversion of VHF/UHF radio systems to digital trunked. The consensus seems to be, "we have radios that work and have worked for decades and now you want to take those away from us. Why?" I first heard about this issue when the Phoenix Fire Department raised it relative to the implementation of the regional digital trunked system in the Phoenix metro area.

The use of 800 MHz in and around high rises in metro areas is causing fireground communications problems, especially when digital is used. Some discussion of requiring these types of buildings to be equipped with a building repeater, similar to the requirement of having a stand pipe system, has taken place in many metro areas.

For dispatch and command purposes, where frequency availability is an issue, VHF can be trunked. Conversion to 800 MHz trunked systems, especially those using digital, does not always work. Radio manufacturing marketing is creating an image that it is a "wave of the future" and VHF is somehow old fashioned with limited utility. This ignores plain physics. Some wavelengths work better in certain situations and locations than other wavelengths and that is not going to change. VHF is not always the answer but neither is the use of 800 MHz for everything.

I have a background in wildland fire management for a federal natural resource agency and am experienced in the use of VHF for incident and daily communications in western U.S. topography. I'm also a licensed ham. Hams get to have fun seeing how HF works best for some situations; and how 54 MHz (the 6 meter band), 144-148 MHz (2 meter band), 222-225 (1.25 meter band) 420-450 MHz (70 cm band) and frequencies as high 900 and 1240+, work in comparison. Double band and even quad band radios enable us to work several bands quite easily and see how each works in the same location. I find the propagation of the 1.25 meter band to be particularly interesting. It has some of the characteristics of 2 meters and the 70 cm bands, those being the ability to bend with terrain and reflect in metro environments as well, to be quite interesting. In some locations I'm unable to get through on 2 meters or 70 cm, but easily get through on 1.25 meter repeaters.

800 MHz digital trunked systems require an enormous number of repeater sites as compared with lower frequency bands. It is very hardware intensive. Sometimes bending with the topography is needed and sometimes reflectivity is needed. Radio does not lend itself to a "one size fits all" approach.

 

[inigo88]

When other firefighter tools such as gasoline powered saws, alarms on air bottles, and PASS ("Personal Alert Safety System") motion alarms are used digital transmissions become garbled. I know of at least one death where the unintelligible transmission of a trapped firefighter, caused by interference from his PASS, resulted in a fatality.

Can you cite this source Fred? My local fire department which I was formerly involved with as an explorer is a member of a 100% IMBE digital UHF T-Band Motorola Type II Smartzone trunking system. Even the fireground tactical talkgroups are digital. I can absolutely verify that in the fireground environment, background noise from chainsaws and PASS even a fair distance away can make voice audio unintelligible, and people are constantly having to repeat themselves. This is a totally unsafe situation because if someone is trapped and can only make one radio call for help, it might not go through. It's absolutely horrifying to hear that scenario may have finally come true.

One thing that you haven't mentioned that I've heard countless times are the range issues. It's not that IMBE digital won't travel as far (in fact I've heard unofficial first hand accounts that it can propagate further in some cases although I find that counter intuitive), but vocoder has limited error correction. If someone is stuck in an area of bad coverage and calls for help on an analog system, it's at least possible that their voice can be picked out of the static by the human ear. Since the vocoder is software driven (literally converting voice into binary computer code and back again), and our ear cannot understand raw IMBE data, the software simply cannot convert the digital data back into voice past a certain percentage of lost data. On digital scanners like my PRO-96 this sounds like beeps and bloops akin to R2D2 from Star Wars as the audio is being put back together erroneously, but on the Motorola XTL and XTS radios it is simply muted entirely! This has been discussed on this forum in the past better than I'm describing it now, but in a staticy analog radio call where we may be able to pick out half of each word and figure out what was said - the same call in the same conditions on a digital radio would yield complete silence. (I've also heard some Motorola radios have an audible no signal alarm evidenced by dispatchers saying "You bonked out" or "All I heard was the bonk," but I don't have enough experience with the radios to comment on this personally.)

Either way, it is extremely unsafe for fireground conditions where a life or death call on the radio may only be able to be made once!

Bravo for bringing up this topic and I apologize for "thread-hijacking," but if there is actual legitimate evidence of loss of life as a result of the digital vocoder I would like to pass the story on to my friends, who use it as their life-or-death lifeline every day.

Thank you,

Inigo

 

[mancow]

Click on the database link at the top of the page. It will answer all of your questions.

I work in the wired world, but want to learn about mobile sources in common use.

Is it safe to say public safety has gone 100% to 700MHz and 800MHz bands?

How common is VHF in use by public safety / security / EMS?

I'm testing the hypothesis that VHF is not longer in wide use, that any responder will use the 700MHz+ bands. VHF has become primarily the domain of the Ham.

Who primarily uses VHF these days?

Thanks for any comments.

Bill

 

[SCPD]

Can you cite this source Fred? Thank you,

Inigo

It was a news item on the home page of this site, within the last month or less. The news item linked to a magazine or newspaper article. I believe that someone who posted a comment provided a link to additional information.

I will try to find the item, but it may be a day or two.

 

[SCPD]

Found it sooner than I thought I would. I could not find the story on RR, but found it using an Internet search. The link is:

Uneasy Silence: Researchers Study Digital Radio Problems on Fireground | FIRE CHIEF | Jun 2008

To the best of my memory this is the same article that was the subject of a news forum thread on RR. I wish I could find that thread.

You were correct regarding the vocoder. The above article cites the vocoder as the problem.

 

[inigo88]

Thanks a lot.

Inigo