P25 in the Amateur Community

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by N4NJJ, Nov 10, 2015.

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  1. N4NJJ

    N4NJJ Ham Member QRZ Page

    P25 is growing here in Las Vegas. With the flood of inexpensive equipment coming onto the market since government agencies are making the switch to Phase II. I am really impressed with DMR and P25. Check-out this video from our net last night.

     
  2. WA9WVX

    WA9WVX Ham Member QRZ Page

    P25 Type I is very popular around the United States as the manufacture couldn't get the FDMA signal to work at 6.25 KHz (Narrow Band) so that's why P25 Type II came into existence for the Public Safety and the Federal Government Agencies as they're using a TDMA format. I would have to say that the P25 Type I Repeaters are all Motorola Quantars most likely set up as Mixed Modes being FDMA & the older Analog thus being backwards compatible.

    The RF range for P25 FDMA is 98% of the 50% RF range of the older Analog signal. You would need to speak with the technical hams that maintain the repeater to understand the RF foot print coverage area but I can say it's amazing the way it's able to detect the Digital signaling even in areas that you couldn't access the older Analog system signals. BTW, the Analog system coverage was based on 90%, 70% & 50% coverage and with the newer software packages for system coverage, this alone would provide a better understanding of the Las Vegas Repeater System. I like the older ASTRO Sabers but when you've got the larger battery attached to the transceiver, it can almost be used a weapon to protect yourself.:eek:

    I've heard that the Motorola DMR MotoTrbos are very good too, they use TDMA Digital Signaling and were designed for the Commercial Land Mobile Two-Way Business Band Radio Market although the hams working on those units immediately found the advantage for Amateur Radio. I've been waiting for some company to manufacture a Multi-Digital Mobile & Handheld that does DMR, P25, Fusion, D-Star and any other Digital Voice Format. About the only thing holding anyone back are the Patent Rights which equals Dollars $$$$$.:rolleyes:
     
    K9OS and KB0MNM like this.
  3. N4NJJ

    N4NJJ Ham Member QRZ Page

    We have set our repeaters up here to NOT operate in mixed mode. A few of the owners have grown tired of the Baofeng crowd on their machines. These 100w Quantars on mountain tops do quite well. The one on top of Potosi has tri-state coverage at 90% reliability, which is really amazing.

    Out here in Vegas we have both TRBO and P25. Both modes are popular. The club that sponsored Dstar machines in town seems to be taking them down in lieu of DMR. We're really lucky that we have machines on both the MARC network and Hytera network.

    You're right about having an "all in one." Jerry at CSI has promised it, but it looks like CSI is starting to drop their product offering and just acting as a dealer for the affordable (are arguably better performing TYT MD-380). The big draw back is the licensing for the vocoders. I think they only ones who would make an "all in one" would be the Chinese since their respect of intellectual property isn't the best.
     
    VE3TLT likes this.
  4. WA9WVX

    WA9WVX Ham Member QRZ Page

    I don't think the Chinese even understand "intellectual property!" Well I can understand how some Digital Repeater Owners would be frustrated with Baofeng crowd and setting the units up as Digital mode only. There are some drawbacks to using Digital, one is multipath Digital signals by bouncing off of water towers, buildings and even mountains therefore the receiver will not pass any audible signals through the repeater and/or the handhelds. Another problem is when a mobile or handheld is below high tension lines, the Digital receiver doesn't have the ability to determine whether the signal is Digital or just noise so no receive audio is heard.

    Two mobiles are communicating on the repeater and either mobile's Digital signaling is being transmitted, the Digital begins to garble because the ones and zeroes start flipping even with Forward Correcting Bits and eventually the entire transmitted signal is Garbled and unable to recover to a normal signal. I've discovered that high gain mobile and Base Station Repeater antennas without the proper down tilt can and do cause coverage problems ... basically the umbrella effect is the problem.

    Otherwise Digital systems have many pluses compared to the older Analog Repeaters. Well Good Luck on getting more hams to switch to these two different Digital Repeaters as I believe this is the future of Amateur Radio.

    Dan
    WA9WVX
     
  5. K8JD

    K8JD Ham Member QRZ Page

    I have heard the distinctive noise of Mototrbo on a few 440 repeater channels, but not the hiss of P25 so far (in my FM scanners) in the Detroit Metro area. .
     
  6. W6KCS

    W6KCS Ham Member QRZ Page

    FWIW

    We set up a P-25 Phase 1 800 trunking system along side an analog system at a large prison. We tried to make the systems as identical as possible by making sure the TX powers were the same, and both systems were combined into the same TX antenna. The receivers were multicoupled from the same receive antenna.

    We walked just about the entire prison doing voice tests in both directions using two portables, a Motorola MTS-2000 and a P-25 Motorola, I think it was an XTS-9000, maybe?

    The thing that I remember the most was that the analog system had a few dead spots in stairwells and other rooms deep within the prison, but the P-25 system seemed to cover them better. There wasn't a huge difference between the two, but the P-25 system always seemed to have the edge in those areas and I don't think the P-25 actually had any real dead spots. I also noticed that areas that had multipath on the 800 radio with resulting bad audio didn't seem to have a problem with P-25.

    One weird thing was when one of us transmitted while standing next to a loud ventilation blower. You could hear it on the 800, it was almost as loud as the voice, but you couldn't hear it on the P-25 transmision. It was as if the radio didn't know how to reproduce the sound, so it didn't bother.

    The two things we didn't like about the P-25 were the sound of the audio, which I don't care for and most of agreed was harder to understand, and the delay in the audio heard on portables nearby. It's distracting when you're trying to talk and your voice is coming back at you, delayed. But we didn't see any areas with loss of coverage, if anything we gained coverage in some spots.
     
  7. WA9WVX

    WA9WVX Ham Member QRZ Page

    I remember a P-25 system that was sold out east to an open pit mine that used huge dump trucks and the dispatcher could only hear the sound of those trucks when a driver applied the PTT. Those units included Shure Noise Cancelling Microphones but those Microphones didn't remove the low frequency noise. It came down to the design of the Transmitted Audio Circuit on the Digital units.

    In the prior Analog Circuitry, the design was to cut off the low frequencies and generally either PL / DPL or a Digital Word was used in that frequency range and standardly set for +/- 750 Hz of Deviation. Not so on the Digital transmitter, the frequency goes from Zero to 3 KHz Audio Response and instead of PL / DPL, there are Digital Codes used in place so they're embedded into software bits. The only solution after spending weeks out at the customer's site was to modify the Noise Cancelling Microphones by installing a Styrofoam baffle with a Pin hole in the middle, then the Digital system worked A-OK. Unfortunately the customer wasn't impressed with the fix and had all of the Astro mobiles ripped out of the trucks and returned to Motorola.

    Motorola then supplied an Analog system to the customer and he was happy. How would anyone ever think that the latest and greatest product would end up having such a problem without testing the mobiles or handhelds in that situation. As good as Astro was or is in my opinion, you'll always find someone or something wrong with the product. I have to wonder if you and your people dislike the P-25 Type I Audio, then if you had a chance to use P25 Type II Audio as the RF Channel is 6.25 KHz wide unless that's what you're using on 800 MHz.

    Dan
    WA9WVX
     
  8. W6KCS

    W6KCS Ham Member QRZ Page

    Dan, that's an interesting story about the engine noise I thought noise cancelling mics would have helped more with the low frequency noise, but I don't know much about them (other than the ones in my avatar :)). The system we tested at the prison was Phase 1, and it's all I really have experience using. We just finished spec-compliance tests on a Phase 2 GTR-8000 trunking system, and it did fine, but I didn't get a chance to fool with it much so I wasn't able to listen to the audio much or compare it with Phase 1.
     
  9. WA9WVX

    WA9WVX Ham Member QRZ Page

    Steve,

    Remember that the older Analog Audio Response Curves rolled off the low frequencies and there were Sub-Audible Tones (Signaling) that was used so using a Noise Canceling Mic would normally attenuate any exterior Noise being generated. On the Digital Audio Circuitry, the Audio Response goes from Zero up to 3 KHz before any thing get attenuated and in that 3 KHz, the software was written to use the entire Audio Bandwidth with embedded signaling. With everything you'll always find trade-offs.

    I always thought the Astro P25 Type I using a 12.5 KHz RF Channel had good audio probably not as good as Analog but darn close. Motorola engineering did a study between Astro P25 Type I FDMA and iDEN / Nextel TDMA on Two-Way Dispatch transmissions and the Astro P25 Type I won out for Audio Response, this test was done in 1997 while I was employed in the iDEN Group. I transferred back to the Infrastructure's SP Bid & Quote Engineering Group in 1999 and carried an Astro System Saber with P25 Type I. That unit was unbelievable the way it operated on the 450 Business Band Repeater. They calculated the RF range of the repeater to be 20 air miles. I stood out on my deck with the house blocking the RF 4 W signal 25 air miles away and I got into the repeater just like I was standing on the Motorola campus in Schaumburg.

    I even used the handheld down in a river valley in town about 300 feet below grade so the hill was creating path losses but you would have never known it as I was solid into the repeater back in Schaumburg. It became like a game where we tried to have the least amount of signal and still pass audio traffic through the repeater. We even had accessories that allowed passing JPG photographs to another engineer ... slick. What ever was thought up, the group of engineers would try out in the field. It kept us out of trouble in our spare time.:D

    Dan
    WA9WVX
     
  10. KV6O

    KV6O Ham Member QRZ Page

    I would be nice to see some VHF P25 here in Colorado, I think the one machine there used to be in Denver is now gone.

    Very little Phase II here, we have a pretty big state system with lots of Phase I subscribers. Heck, we still have lots of XTS3000's in service!

    I do have a collection of 800Mhz Quantars that's growing as we upgrade to GTR8000's... wish I could put them to good ham use!

    Steve
    KV6O
     

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