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Lscott

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Posts posted by Lscott

  1. Well then it wasn't DMR after all.

    The FCC database shows Delta Com is licensed for 462.53125, which is a standard frequency. The location shown is in Southfield, another is in Novi. NX48 is the very narrow mode of NXDN. This was the result of doing a search on digitalfrequencysearch.com under NXDN. Then looked up the license on the FCC's ULS license database.

    https://wireless2.fcc.gov/UlsApp/UlsSearch/licenseLocDetail.jsp?licKey=1925372&keyLoc=15068559

    The building in Southfield I think is the huge gold coated glass building near Evergreen and 10 Mile in Southfield. Right across the expressway from Lawrence Technological University, LTU, and down the street from Channel 7 TV.

    The signal might be a strong reflection off the water tower by the AAM plant in Royal Oak.

    I can't monitor an NXDN trunked system using my Kenwood NXDN radios. The firmware will refuse to open the audio on the radio. It detects the packets are coming from a trunked system and as a security measure won't produce audio unless the radio is registered on the system. Entering the frequencies as simplex won't work either. I've been told that Icom NXDN radios would likely work, they don't have that quirk builtin to their firmware, however I can't confirm that.

    NXDN Standards.zip

  2. I’ve attached one of the DMR standards documents I have on file. Starting in section 10 the RF specifications start. That covers permissible frequency errors, slot timing etc. 

    Elsewhere the various types and headers are covered. The are about 7 documents for the base DMR protocol. 
     

    When reading the document “BS” is read as Base Station and “MS” as Mobile Station.

    ETSI TS 102 361-1 V2.5.1.pdf

  3. This looks like it’s going off the rails. 
     

    I would quit looking at what’s coming out of the packet decoders until with 100 percent certainly the mode is positively identified. For the various modes the RF has some very characteristic features. For example DMR, P25 Phase-2 and Tetra are all TDMA based with particular bandwidths of the signal and slot timing. P25 Phase-1 is like NXDN, both are ONLY FDMA based. But, NXDN has two bandwidths, narrow and very narrow that are used.

    Once there is zero doubt about the mode then worry what’s coming out of the decoders. For now it looks like garbage mostly. Even if the voice payload is encrypted the headers are not. It’s has to be this way for the state machine in the radio’s firmware to figure out what type of packet it is and what to do with it. If you’re getting good decodes then at least the packet type should be identifiable even if the payload is encrypted.

    Assuming it’s a Motorola system then the encryption is likely one of several types, basic - enhanced - AES/DES. 
     

    The basic mode used on Motorola radios is a low bit count scrambler type proprietary to Motorola. It’s available on many of their digital radios.

    The enhanced encryption is usually RC4, a 40 bit stream encryption, available on many radios besides Motorola. I have it on several of my Kenwood NX-1300DUK5’s.

    https://forums.mygmrs.com/gallery/image/290-nx-1300duk5/?context=new

    The AES/DES encryption is available on the higher end Motorola radios only, I believe, and on other manufacturers as well. It’s also on my Anytone D878 and D578 too at no extra cost. 

    Currently you’re not likely to find much in the way of decryption software since the FCC rules now make it clear it’s against the law to decode encrypted transmissions you’re not authorized to receive. The guys doing the SDR software have said they won’t touch it for that reason. 

  4. 3 hours ago, SignallyCurious2 said:

    The frequency I’m measuring is the transmitter as I have confirmed multiple times through this process by adjusting the PPM of the oscillator via software used against stable, confirmed signals in the same band. The SDR is not part of the equation as I’ve done multiple controlled tests to rule it out.
     

    Not to mention it’s a RSP1A, not some cheapo China boy. 

    What we are left with is a transmitter that is inbetween those channels. That’s what I’m here to figure out. 
     

     

    Microprocessor crystals are not that accurate compared to communication grade TCXO’s.

  5. 1 hour ago, SignallyCurious2 said:

    I have a HT but again, the freq they’re on isn’t centered so using anything it will sort of pick it up but it’s just interference between multiple channels unless you can tune inbetween channels. 

    If it’s really a transmitter you can only program in fixed step sizes unless it has a “true” VFO. The common usual step sizes I’m aware of by are 2.5, 3.125, 6.25, 12.5, 20 and 25 KHz. The frequency you’re measuring is likely a combination of the frequency error of both the SDR dongle and the transmitter’s reference oscillator.

  6. 1 hour ago, SignallyCurious2 said:

    It’s is a moto trbo NXDN trunking system operating in dual capacity direct mode, and contrary to what I thought, there is activity today. 

    NXDN is FDMA only. There is no TDMA mode, so it can’t be DCDM. The later is for DMR only. Motorola doesn’t sell any NXDN equipment I’m aware of.
     

    Now if it’s really TDMA it could be a P25 Phase 2 trunking system. So far TDMA mode is only used with P25 on trunking systems, not used for simplex as far as I know.

  7. 3 minutes ago, markskjerve said:

    If I had to guess they are running MotoTrbo GPS tracking on the radios. The GPS system can be programmed to poll the radios every 10 minutes or every 1 kilometer of movement. They are short bursts, around 600ms to 1 second. If a car is moving it sends a lot more traffic than if it doesn't. 

    Now that would start to make a lot more sense.

  8. 10 minutes ago, SignallyCurious2 said:

    SOCWA with the water tower called back, it is not them but they’re also interested and going to help out. 
     

    That’s how the transmissions are for me too, most of them data, very very few actual calls more than 1.2 sec. Latest call so far was 4:45pm.

    They have no idea whose antennas are on THEIR tower!

    The repeater is likely in the small block house at ground level. Maybe if you could gain access to the inside you might find some contact info on the equipment. That would save you a lot of research.

  9. 1 hour ago, WRYZ926 said:

    @Lscott That's good information for those considering the BTech amp. 20 or 30 watts is still better than 5 watts when using a decent base or mobile antenna.

    Yup, just don't expect to get the full boogie out of it. 

  10. For the moment I have my cheap tri-band radio tuned for 462.5325MHz before screwing around with my DMR radio. I am getting sporadic bursts, mostly noise. The building I'm in has metal mesh in the concrete walls so its a bit of a Faraday cage. However every-once in a while I can make out the TDMA pulsing.

    Water Tower In Question - 2852 Samoset Rd - Google Maps.pdf

    This is the water tower right behind the AAM plant.

  11. 36 minutes ago, SignallyCurious2 said:

     

    I’ve been doing the SDR stuff since 2015, and im using a RSP1A, and have also confirmed through various other signals, I am calibrated correctly and am using hands down the most robust SDR decoding software freely available SDRTrunk v6.1
     

    the facts of the matter are: 

    its not delta com

    its not on center with any frequency it should be

    its an encrypted DMR trunked repeater 

    its causing interference with GMRS

    Its causing interference with delta com licensed frequencies for their own subscribers in the area

    It’s more than likely originating from the water tower south of American axle at 14 mile and Coolidge

    It’s either intermod or not licensed transmitter

     

    I would trust Delta Com if they say it's not them.

    So Delta Com is saying they are experiencing interference too? A complaint to the FCC from them may trigger some response since they are a business paying for the spectrum they use.

    I would like to know what the water tower people have to say about it, if that's the antenna and source.

    Maybe it a rouge Chinese Repeater. 🤫 Keep us updated. It might end up like a knit sweater. You find the end of the thread and start yanking on it. Soon the whole thing starts to unravel.

  12. 1 hour ago, WRYZ926 said:

    You would be better off getting the BTech AMP-U25 amplifier from Amazon. Easier to return if it doesn't work and it will have better customer service through BTech. And it will keep you at the legal 50 watt limit for GMRS.

    BTech AMP-U25

    I have one. Bottom right corner of photo.

    https://forums.mygmrs.com/gallery/image/415-amplifiersjpeg/?context=new

    The power output falls off outside of the Ham band. For example the DC current input at 13.8VDC with 4 watts of RF input was about 5 amps. At the GMRS frequencies it dropped to around 3 amps. I need to put it on my Bird watt meter and get a power measurement now that I got some higher power UHF slugs for it. I'm guessing I'm only getting MAYBE 20 to 30 watts at most out of it on GMRS frequencies.

    https://forums.mygmrs.com/gallery/image/321-bird-43-wattmeter/

     

  13. 12 minutes ago, markskjerve said:

    I'd vote the oscillator is a bit off.

    The oscillator in the repeater also could be off frequency a bit too. I have heard of some repeaters where they use an OCXO, Oven Controlled Crystal Oscillator, for very high frequency accuracy.

    I think the cheap SDR dongles use a simple TCXO, Temperature Compensated Crystal Oscillator, module. The usual specifications for those are +/- 0.5 PPM, Parts Per Million, frequency accuracy more or less.

    Usually portable or battery operated equipment use the TCXO module since the power requirements are way to much due to the electrically heated oven on an OCXO module.

    Understanding Ovenized Oscillators.pdf

  14. 3 minutes ago, markskjerve said:

    The closest is actually 462.53125, same company (Deltacom) and licensed for trunk service. It's only .13 KHz down. Also 462.5325 isn't standard spacing, FCC only shows 2 experimental licenses in the the entire country and 100's licensed for 462.5312 I'd vote the oscillator is a bit off. With a SDR dongle using SDRSharp and Simple DMR decoder, I can decode DMR +/- 1KHz easy.

    Good point. I think once the correct frequency is nailed down looking it up in the FCC's database would yield results.

  15. 22 minutes ago, SignallyCurious2 said:

    I’ve been working with the gentleman at delta com on this, he is also actively working to identify the signals, his transmitters are 25w and the nearest is in Southfield. 
     

    ill look some more, still waiting to hear back from the general manager of the water tower who is responsible for its operations. The only licenses I found were for ATT on that water tower. 

    This is turning out to be a bit of a real mystery. I wondering now if the owner even licensed the frequency, and not just stuck up their repeater and said screw the FCC. I'm getting the feeling there is a lot of crap out there on the air that isn't properly licensed and the FCC just ignores it until somebody complains. That's not how it's supposed to work.

  16. A good resource to track down digital licenses in the FCC's database is here:

    https://digitalfrequencysearch.com/index.php

    If it's a trunking system on a water tower I'm going to guess it's owned and operated by a company that rents out capacity on their system to various users who don't want to put up their own repeater and or don't have the expertise to do so. A small company, with a single location, with their own repeater would typically be located on site if they have one. 

    Given the frequencies and location I''m certain it had to go through an FCC frequency coordinator and should be in their database. They would need to make sure the antenna height, power level and antenna gain won't interfere with other users in the coverage area. And in this case it seems like that area is going to be rather large too.

    One company would be Deltacom.

    https://wireless2.fcc.gov/UlsApp/UlsSearch/licenseFreqSum.jsp?licKey=1925372&pageNumToReturn=2

    https://wireless2.fcc.gov/UlsApp/UlsSearch/licenseLocSum.jsp?licKey=1925372

    The closest to your frequency of 462.5325 is 462.5375. Given the tolerance of the oscillator in the SDR dongle this could be it. It's off by only 5.0KHz.

    https://wireless2.fcc.gov/UlsApp/UlsSearch/licenseFreqSum.jsp?licKey=2926515&pageNumToReturn=2

    https://wireless2.fcc.gov/UlsApp/UlsSearch/licenseLocSum.jsp?licKey=2926515

    Here's another company.

    This one is sort of odd. They are licensed state wide with a frequency range. No channel frequencies listed.

    https://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=3770395

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