Two Talk Groups at the same time, possible?

[iMONITOR]

Using my SDS200 I've been Searching Talk Groups that are not programmed. I'm only monitoring MPSCS P25 Phase 1 / Macomb County, Michigan. I've been logging a huge list, many of which are not in Macomb County. Even Detroit, Wayne County, Oakland County, are collecting on the hit list. Apparently a lot of them are affiliated with the Macomb County simulcast system which surprises me. But what's really weird is that I'm getting double-hit, two Talk Groups at a time! I've never seen this before and didn't even know if it's possible. They show on the display screen of the SDS200 scanner, as well in the ProScan log, so I know it's not ProScan that is doing this.

Anyone ever see something like this?

 

[dave3825]

I believe that's a patch.

https://www.cisa.gov/sites/default/files/2023-02/22_0228_fpic_p25_issi-cssi-features-functions_patching-dynamic-regrouping_508C.pdf

 

[iMONITOR]

I believe that's a patch.

https://www.cisa.gov/sites/default/files/2023-02/22_0228_fpic_p25_issi-cssi-features-functions_patching-dynamic-regrouping_508C.pdf

Thank you! Very informative.

 

[iMONITOR]

I'm actually seeing a few groups of 3 at one time now.

 

[west-pac]

If you're catching TGs that are way outside of your area, or where the TG and RID don't mesh, you might be receiving skip. Other sites and systems may use the same freqs that you are monitor for your local site.

If you catch a distant TG, look at the sites in the area of the TG and you'll likely find a common freq that you have locally.

 

[iMONITOR]

If you're catching TGs that are way outside of your area, or where the TG and RID don't mesh, you might be receiving skip. Other sites and systems may use the same freqs that you are monitor for your local site.

If you catch a distant TG, look at the sites in the area of the TG and you'll likely find a common freq that you have locally.

That wouldn't be happening in this case. For this particular scanner I'm monitoring only one P25 digital trunked system, basically one frequency but a ton of Talk Groups.

 

[GTR8000]

"Skip" affects lower frequencies, i.e. low band and the like. Ducting or tropo enhancement affects the upper bands like UHF, 700, 800. So no, it's not "skip" for a 700/800 MHz trunked system.

It's also highly unlikely that this is co-channel frequency usage, as the scanner does not scan individual frequencies, but rather decodes talkgroup grants that are broadcast over the control channel. It would be quite the coincidence to have numerous instances where a grant on a local site happens to use the same exact frequency as a distant site during relatively brief periods of enhanced propagation. Oh yeah, and the OP already mentioned seeing multiple talkgroups active at the same time, which is....wait for it...

Patching/console multi-select as @dave3825 already pointed out.

 

[west-pac]

"Skip" affects lower frequencies, i.e. low band and the like. Ducting or tropo enhancement affects the upper bands like UHF, 700, 800. So no, it's not "skip" for a 700/800 MHz trunked system.

It's also highly unlikely that this is co-channel frequency usage, as the scanner does not scan individual frequencies, but rather decodes talkgroup grants that are broadcast over the control channel. It would be quite the coincidence to have numerous instances where a grant on a local site happens to use the same exact frequency as a distant site during relatively brief periods of enhanced propagation. Oh yeah, and the OP already mentioned seeing multiple talkgroups active at the same time, which is....wait for it...

Patching/console multi-select as @dave3825 already pointed out.

Skip, ducting, tropospheric ducting.... different words, same effect = receiving distant signals that you can't normally receive.

Also, there are 11 others sites, on MPSCS alone, that use the same controls as Macomb county. I didn't look at MARCs or SAFE-T to see how many more sites share those control channels. So, it is very possible to receive another site on the same control channel as the intended site. I do it all the time. Every week I have hits for DX TGs that didn't come from a local site.

 

[GTR8000]

Okay.

 

[wa8pyr]

So, it is very possible to receive another site on the same control channel as the intended site. I do it all the time. Every week I have hits for DX TGs that didn't come from a local site.

Yes, it is certainly possible.... but not at the same time. The control channel is a continuous signal, and as we learned in Radio 101, a strong local signal (like a control channel) is going to drown out the distant control channel. These systems simply wouldn't work if that weren't the case.

What the OP is seeing is a patch or multi-select. As for the distant talkgroups, with Macomb County/Wayne County/Oakland County being part of the the largest metro area in that state up north, it's entirely possible that they're legitimately affiliating to the site.