Lscott

Any updates on the mystery signal?

I've seen this all before years ago on various CB Internet news groups. Same sort of logic. Always ends up in the same place.

What would happen if.... This is starting to sound more like what turned CB 11M in to a garbage heap. I guess with the increasing popularity of GMRS it was bound to happen to this service sooner or later.

FCC database shows them licensed for VHF only and using DMR. https://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=1210947 https://wireless2.fcc.gov/UlsApp/UlsSearch/licenseFreqSum.jsp;JSESSIONID_ULSSEARCH=3P97hIOEmzSE_jvaTR3pepbHCYvM_n-Mf1fkabwZDAB8YVFyLPLy!-1848806523!-1099177123?licKey=1210947

Some basic info to get you started. https://www.brara.org/documents/presentations/The DMR Basics _ No Frills.pdf https://w1yca.org/tech/tips/dmrGuide.pdf

You have a good start to your collection.

Drooling.

OK, you asked. https://forums.mygmrs.com/gallery/image/249-934916052_radiocollectionjpg/?context=new https://forums.mygmrs.com/gallery/image/259-ca-2x4mb-jeepjpg/?context=new

Also NOT certified for GMRS. For new users to GMRS the recommendation is to get a radio with Part 95A, under old rules, or Part 95E under the new rules certification. Some of the older commercial radios are certified under Part 95A and perfectly legal to use on GMRS. Plus, with some effort, they can be used outside of their official band split to allow operation into the upper half of the Ham 70cm band where the repeaters are typically located. Not all commercial radios allow this. This is just one such example: https://forums.mygmrs.com/gallery/image/263-tk-3170jpg/?context=new The difference between a 4 watt verses a 5 watt radio isn't very significant. Some may recommend a higher power handheld radio. What you'll get is a much shorter battery life and a great hand warmer, burner, if the radios is used at high power for more than very brief transmissions. I've read where some people have destroyed their radio from heat, even at the 4 to 5 watt level, when used at high duty cycles.

I've been monitoring 462.5325MHz here at the office. I'm only a few miles directly due east of that water tower. I am getting something on the CCR triband radio I use as a scanner. It's not real strong and just short transmissions, about a second or two at a time.

My biggest problem with DMR is the ever changing repeater settings. Identifying new talkgroups, deleting old talkgroups, changes in which network the repeater belongs to etc. I think I have a radio setup then a few weeks/months later it's all in the crapper and I have to update the zone for that repeater. PIA. DMR is nice, but the frequent changes aren't, and trying to find the current info is a crap-shoot. This repeater example is one of the more messy and busy systems I've seen. N8NOE.pdf

That's really poor coverage for a repeater system if it dies there.

Stranger things have happened. Had a thought. If it's a trunking system then there is an input and output frequency. You should see at least two pips on the spectrum display during each transmission. The lower power signal is likely the input. That one might be easier to zero in on since the area will be smaller and help localize the source.

I looked up the address. Surprise, It's not where I thought it was. The address listed in the FCC's database shows its across the street from the golf course on Evergreen. It's looks like it's almost across the street from the Southfield City offices, library, court house and jail on the east side. They just recently built a couple of round-abouts there I believe.

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

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

Apparently there are some of the VHF NOAA transmitters connected to the studio/control site through a UHF link. See attached file. So far I haven’t had any luck with the UHF link frequencies but others might. NOAA UHF Weather Link Frequencies.pdf

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.

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

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.

That’s the very narrow mode of NXDN. The bandwidth is only 6.25KHz.

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.

That’s a Doppler direction finding setup. You see about the same thing on cop cars, Lojack system I believe it’s called.