[Repeater-Builder] P25 (mis)Information?
Not wanting to start a flame war, but since I know there are some P25 gurus on here, I am posting this email exchange between an EDACS user and their local representative. Its rather self explanatory, I am looking for comments on the response; specifically, don't P25 radios have an analog mode? All (constructive) comments welcome. From: MA/COM REP To: EDACS USER Hi, Thank you for the article and the opportunity to clarify a couple of points. The system mentioned in the article is a Motorola system. This is just another great benefit of EDACS technology...It is able to provide both digital AND analog features. For Fire, we plan on programming all of their radios with an analog on-scene talk-around group in addition to all the other talkgroups as an added feature in the event it is preferred in those particularly noisy environments. There have been some cases reported like the one in Orlando with P25 systems, since the systems only offer digital technology and does not have the capability of using analog. All P25 vendors including M/A-COM and Motorola are aware of the issue and are looking for ways to improve the technology. Without getting into all of the technical reasons, a lot of it has to do with vocoders. P25 technology in general uses less vocoders and therefore can sometimes leave out some of the audio. EDACS technology has not had a significant number of complaints from Fire Departments as the technology uses more vocoders. I am trying to find a technical explanation to send to you as well. But in the meantime, MA/COM shouldn't pose the same problem. Please call me if you have any other questions. Sincerely, - Original Message - From: EDACS USER To: MA/COM REP Subject: FW: Orlando FD Radio Article I sure hope MA/COM is working on this issue. _ From: Concerned Citizen To: EDACS USER Subject: Orlando FD Radio Article Digital Radio Switch Upsets Firefighters POSTED: 8:12 am EDT May 21, 2008 UPDATED: 8:49 am EDT May 21, 2008 ORLANDO, Fla. -- The city of Orlando replaced its police and fire radios, but firefighters said the new multimillion-dollar system sometimes goes silent. During a recent supermarket fire, firefighters were forced to use their old radios to communicate because the new system was distorted. Noise was the problem. Warning bells on firefighters' air packs cause microphone distortion on digital signals much more than with analog channels. We keep on the analog tracks so that we have the clarity that we need. So, like I said, get the bugs worked out in the digital system, said Fire District Chief Keith Maddox. The digital radio channels are also hard to hear when the firefighters are working next to trucks because the engines have to be revved to pump water. Fire departments nationwide have known about digital signal problems for over a year, but Orlando's fire department thought that the bugs had been worked out. With this one, we didn't know the problem was there until recently for us, said Fire Chief Jim Reynolds. So they conducted a test that proved the new channels were too hard to hear. The big question is, why switch the channels now when the federal government does not require it for four years? Steve Clelland of the firefighters' union said he believes the Orlando Fire Department should have waited until the bugs got worked out before switching channels. It is serving us no purpose sitting there and us not being able to use it, said Clelland. For now, firefighters will stick with the old radio channels when fighting in noisy conditions until radio makers can create a fix. The city spent $6.8 million to convert to the new radio system. City officials said the money would have been spent regardless of the current radio signal problem. They added that buying sooner rather than later saved taxpayers money. The national study results on the digital radio problem for firefighters is due out next month. **Get trade secrets for amazing burgers. Watch Cooking with Tyler Florence on AOL Food. (http://food.aol.com/tyler-florence?video=4?NCID=aolfod000302)
Re: [Repeater-Builder] P25 (mis)Information?
Most if not all P25 radios (both portable and mobile) have the ability to do analog and digital communications from the same radio. While most can receive both analog and digital communications on the same channel if set up for mixed mode use, I am unaware of any that can transmit on both analog and digital on the same channel. All radios only have one vocoder, for P25 that is the DVSI IMBE vocoder. It is the same vocoder used by all the manufacturers and DVSI is the only producer/supplier of the vocoder. Thus any manufacturers radio set for P25 should work on any other manufacturers system since P25 is a standard. I know from personal experience that Thales/RACAL, motorola and EF Johnson radios all talk to each other when in P25 as I have several of each and enjoy playing with them. (now if I could just get this VHF Quantro up and working) So I would guess that the gentleman from M/A-COM was from marketing and not a technical person and just spewing marketing crap (no offense to those that use M/A-COM) and i would ask to talk to a technical person for any article. It has been recommended by many organizations, including APCO, that when on fire ground (scene), any department that has a digital system should revert back to an analog system for firefighter safety. It still boggles my mind why some department don't follow this recommendation to this day. (yea, I know, it's a recommendation not a regulation) Dan KA8YPY On May 29, 2008, at 9:48 AM, [EMAIL PROTECTED] wrote: Not wanting to start a flame war, but since I know there are some P25 gurus on here, I am posting this email exchange between an EDACS user and their local representative. Its rather self explanatory, I am looking for comments on the response; specifically, don't P25 radios have an analog mode? All (constructive) comments welcome. From: MA/COM REP To: EDACS USER Hi, Thank you for the article and the opportunity to clarify a couple of points. The system mentioned in the article is a Motorola system. This is just another great benefit of EDACS technology...It is able to provide both digital AND analog features. For Fire, we plan on programming all of their radios with an analog on-scene talk-around group in addition to all the other talkgroups as an added feature in the event it is preferred in those particularly noisy environments. There have been some cases reported like the one in Orlando with P25 systems, since the systems only offer digital technology and does not have the capability of using analog. All P25 vendors including M/A-COM and Motorola are aware of the issue and are looking for ways to improve the technology. Without getting into all of the technical reasons, a lot of it has to do with vocoders. P25 technology in general uses less vocoders and therefore can sometimes leave out some of the audio. EDACS technology has not had a significant number of complaints from Fire Departments as the technology uses more vocoders. I am trying to find a technical explanation to send to you as well. But in the meantime, MA/COM shouldn't pose the same problem. Please call me if you have any other questions. Sincerely, - Original Message - From: EDACS USER To: MA/COM REP Subject: FW: Orlando FD Radio Article I sure hope MA/COM is working on this issue. _ From: Concerned Citizen To: EDACS USER Subject: Orlando FD Radio Article Digital Radio Switch Upsets Firefighters POSTED: 8:12 am EDT May 21, 2008 UPDATED: 8:49 am EDT May 21, 2008 ORLANDO, Fla. -- The city of Orlando replaced its police and fire radios, but firefighters said the new multimillion-dollar system sometimes goes silent. During a recent supermarket fire, firefighters were forced to use their old radios to communicate because the new system was distorted. Noise was the problem. Warning bells on firefighters' air packs cause microphone distortion on digital signals much more than with analog channels. We keep on the analog tracks so that we have the clarity that we need. So, like I said, get the bugs worked out in the digital system, said Fire District Chief Keith Maddox. The digital radio channels are also hard to hear when the firefighters are working next to trucks because the engines have to be revved to pump water. Fire departments nationwide have known about digital signal problems for over a year, but Orlando's fire department thought that the bugs had been worked out. With this one, we didn't know the problem was there until recently for us, said Fire Chief Jim Reynolds. So they conducted a test that proved the new channels were too hard to hear. The big question is, why switch the channels now when the federal government does not require it for four years? Steve Clelland of the firefighters' union said he
Re: [Repeater-Builder] P25 (mis)Information?
On re-re-reading the post, I suspect the MA/COM salesman proposes just adding an analog trunked group to the system and calling that group talk-around. Just another group in the trunked system. Any group can be either Provoice (EDACS only) or P25 digital or Analog FM. To many folks in the land mobile business talk-around refers to simplex operation on the output frequency of a repeater station and operation independent of the repeater station. (hence my earlier post about collisions with trunked and simplex operations). From what I understand the problem with high noise environments and intelligibility is due to the characteristics of the DVSI IMBE vocoder and how this noise is treated in quantizing. Another talk group will not help in building coverage issues because the trunked system treats all groups alike unless a group by attributes is steered to one particular site in a multisite system. I am most familiar with simulcast. I believe the problems with P25 digital are exactly that and have nothing to do with brand or manufacturer. 73, Steve NU5D [EMAIL PROTECTED] wrote: Not wanting to start a flame war, but since I know there are some P25 gurus on here, I am posting this email exchange between an EDACS user and their local representative. Its rather self explanatory, I am looking for comments on the response; specifically, don't P25 radios have an analog mode? All (constructive) comments welcome.
Re: [Repeater-Builder] P25 (mis)Information?
On May 29, 2008, at 8:11 AM, Dan Blasberg wrote: It has been recommended by many organizations, including APCO, that when on fire ground (scene), any department that has a digital system should revert back to an analog system for firefighter safety. It still boggles my mind why some department don't follow this recommendation to this day. (yea, I know, it's a recommendation not a regulation) Probably they have never heard what a transmission from a firefighter in full respiratory gear (face shield/oxygen mask) sounds like when stuffed through the IMBE vocoder... give 'em a demo sometime. A styrofoam cup, and your voice, and give 'em a call on their own radio system... should be a close-enough approximation. If they can't copy you, they'll get your point. Make sure you're saying something like, I am making this test transmission that sounds like a firefighter in full headgear. Then when they say, What? two or three times, pull the cup away and say it again. Basic communications theory... if you take an analog signal and filter it (mask) you lose intelligibility, then you stuff it through another filter (vocoder) and what comes out the other side is crap. I love digital tech and am playing with both D-STAR and P25 in Amateur use... and I'm also admittedly NOT a Public Safety or other professional RF person... But even I can see the limitations of a lossy CODEC! (Plus I've heard the above on the air in real life... and the resulting Say again? three times from the Battalion Chief. Made me cringe. If they were calling for help, that would have been a lot of time lost to get their message through.) -- Nate Duehr [EMAIL PROTECTED]
Re: [Repeater-Builder] P25 (mis)Information?
On May 29, 2008, at 7:48 AM, [EMAIL PROTECTED] wrote: P25 technology in general uses less vocoders and therefore can sometimes leave out some of the audio. Wow that's so amazingly... wrong... Less vocoders... sigh. Time to send MA/Com's sales guy back to class. Start with Nyquist's theorem, and don't let him out of the room until he can understand the concepts of sampling and digital audio compression. -- Nate Duehr, WY0X [EMAIL PROTECTED]
Re: [Repeater-Builder] P25 (mis)Information?
Midland P25 radios and repeaters do analog and digital both. - Original Message - From: [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Thursday, May 29, 2008 8:48 AM Subject: [Repeater-Builder] P25 (mis)Information?
Re: [Repeater-Builder] P25 (mis)Information?
Nate, Nice way to demo the concept without actually putting anyone at risk. I will have to remember that when our P25 Phase 2 system goes active in 2010, yep, P25 TDMA. Dan KA8YPY On May 29, 2008, at 3:51 PM, Nate Duehr wrote: On May 29, 2008, at 8:11 AM, Dan Blasberg wrote: It has been recommended by many organizations, including APCO, that when on fire ground (scene), any department that has a digital system should revert back to an analog system for firefighter safety. It still boggles my mind why some department don't follow this recommendation to this day. (yea, I know, it's a recommendation not a regulation) Probably they have never heard what a transmission from a firefighter in full respiratory gear (face shield/oxygen mask) sounds like when stuffed through the IMBE vocoder... give 'em a demo sometime. A styrofoam cup, and your voice, and give 'em a call on their own radio system... should be a close-enough approximation. If they can't copy you, they'll get your point. Make sure you're saying something like, I am making this test transmission that sounds like a firefighter in full headgear. Then when they say, What? two or three times, pull the cup away and say it again. Basic communications theory... if you take an analog signal and filter it (mask) you lose intelligibility, then you stuff it through another filter (vocoder) and what comes out the other side is crap. I love digital tech and am playing with both D-STAR and P25 in Amateur use... and I'm also admittedly NOT a Public Safety or other professional RF person... But even I can see the limitations of a lossy CODEC! (Plus I've heard the above on the air in real life... and the resulting Say again? three times from the Battalion Chief. Made me cringe. If they were calling for help, that would have been a lot of time lost to get their message through.) -- Nate Duehr [EMAIL PROTECTED] Yahoo! Groups Links
Re: [Repeater-Builder] P25 (mis)Information?
Steve S. Bosshard (NU5D) wrote: At a quick glance I see a problem using TA in a trunked radio system because unless the RF channel is removed from the trunked system and subscriber radios set up for conventional TA on that frequency, other traffic on the trunked system will collide with users on the (was trunked - now being used for TA) TA channel. I doubt it would be legal to use interoperability channels for fireground simplex, and I doubt a busy system would want to remove a channel from their trunked system for simplex operation. Another difficulty would be listening to communications on the trunked system, and listening to simplex communications on a conventional channel. No, using one of the channels in the trunked system in a talk-around mode won't work. You'll be competing with the trunk transmitter on that channel anytime it came up. Legal or not, it's a bad idea. One would license a separate frequency specifically for the purpose of using as a fireground. To open another can of worms, would a single channel autonomous trunked repeater channel deployed in a incident commander's vehicle be a viable option ? The users would continue to operate trunked and have any benefits that a repeater may offer, and depending on the complexity of the portable repeater, be able to cross connect to the primary trunked system. 73, Steve NU5D SCAT-yes, that would work well, especially if you program the radios so that it's another site in a multi-site system. If you use ProSound (it has a different name now...drat...), the radio can automagically go to the SCAT. Unfortunately, I think SCAT is only available in EDACS and MPT1327. I don't think there is any provisions for that type of operation in P25 or any Motorola format.
