167.2125 WNC

[AlphaFive]

This morning in Western North Carolina, I am using my Pro 197. At 167.2125, FM band, I am picking up a DPL of 167. Now according to the latest database, across the country there are several FBI facilities using 167.2125. Though only four are listed as being digital, P 25, MI, NV, TX, AZ. There is one trunked system in Washington State.
On my Pro 197, if I am stationary on 167.2125, entered as a conventional frequency in tune search, I am receiving a constant strength signal, as if a control channel is active, then every five or ten minutes the squelch will break and the 167 DPL (P 25) will show. No modulation.
Does anyone have information on a current digital use of 167.2125 in a surrounding state to WNC? As I am writing this I am doing a "wildcard" search with 167.2125 entered as a P 25 trunked system, nothing yet. Thank you for your time.

 

[riveter]

Pretty much any 167.x frequency with a 167.9 PL or 167 NAC is FBI.

However, 167 is not a valid DPL code.


Rereading your post, do you mean 167 NAC? If it's coming up without any audible mod, your scanner is probably set to mute encrypted P25 voice.

I got confused because you said FM and DPL - just to clear up terms a bit, P25 uses one of four digital waveforms:
- C4FM (conventional, trunked, non-simulcast mostly)
- C4FM-WIDE (old ASTRO SmartZone trunked systems)
- CQPSK (wide-area simulcast conventional and trunked systems)
- DQPSK (trunked Phase II TDMA systems)
While all of those technically modulate the frequency to pass data, they either use frequency shift keying or phase shift keying, which is a different means than the plain frequency modulation (FM) waveform. When you add in something about DPL, it sounds a lot like you're talking about plain FM modulated by DPL. Best to be specific, because getting confused between FM and C4FM/CQPSK and DPL/NAC is a grievous problem when trying to identify a signal.

The Sig ID Wiki is nice for some stuff like that, but doesn't help much with this - however, W2SJW has some recordings that show the audible difference between C4FM and DQPSK (CQPSK is similar) if you're interested in identifying between the two... just an extra tidbit.

Also, I have not yet heard it over the air, but some source or other indicates that freq+NAC may be part of the FBI DC wide area system, channel "DC Metro 1" - not sure if that net might be in operation as far south as you, but it might. Hope that helps.

 

[AlphaFive]

167.2125

Yes, you are correct in what you said. I wish I had the ability on the Pro 197 to set the mode NFM. Unfortunately I have to use what is available on the tune search which is only auto or FM. On that setting it indicates, ' DG 167.2125 P 25 167 ' . I will put it on the BCD 536 and see what occurs. Thank you very much, and I get what you were saying..

 

[SCPD]

NFM

Yes, you are correct in what you said. I wish I had the ability on the Pro 197 to set the mode NFM. Unfortunately I have to use what is available on the tune search which is only auto or FM. On that setting it indicates, ' DG 167.2125 P 25 167 ' . I will put it on the BCD 536 and see what occurs. Thank you very much, and I get what you were saying..

You can set the mode to NFM take it off auto. (AM>NFM>FM)

 

[AlphaFive]

167.2125

Yes, don't understand why I'm only given the choice on the mode setting for AM FM Auto I in tune search, I do believe I used to have the setting available on tune search, I will enter it as a simple conventional search, the setting will work there..., I put the frequency on the BCD 536, it is just too weak for me hear. Using the ARC 536 software, the signal strength 'Signal/ RSSI' is coming in around 172, which is very weak. It will not register an NAC. Normally an average transmission will hit up in the high 300's.. I'm just not close enough, but this signal is still broadcasting around 3:30 EST...
Since 2:21 I have had four hits on the frequency.. sorry, I'm too far out. Thank you though for your help. 3:21 not 2:21.

 

[AlphaFive]

167.2125 transmission WNC

Today I did some very basic follow up on 167.2125.
I am using a Pro 197, in NFM mode. I am in central Western North Carolina. The antenna is a basic Tram discone, attic mounted.
On the Pro 197,, 167.2125 when parked as a stationary conventional frequency, either in Tune Seacrh mode, or as a conventional channel, receives a constant strength signal at either 3 or 4. ( I realize the bars have little relation to true signal strength)...every two minutes on the dot, the frequency generates enough strength to show a received signal on the Pro 197. The display reads ' DG P 25 167. This registers for approximately 1/2 of a second and is gone, returning the screen back to simply showing a constant signal strength.
This action repeats exactly every two minutes. For example, EST. 1:07, 1:09, 1:11, 1:13, 1:15, 1:17, 1:19, and 1:21 PM......
I have no technical knowledge regarding the function of transmitters, or why the function as they do. I do understand that it is likely an impossibility that I am receiving a terrestrial FM signal directly from the D.C. area. So that tells me that somewhere within range of my Tram discone, a transmitter is generating an FM signal for my radio to receive, whether that be a repeater or a separate system. I do hope someone will read this who is closer to the transmitter, and spend a few minutes tinkering with this signal. Thank you for your help.

 

[riveter]

If it's showing a NAC, it's not FM, it's P25.

The wide area system is for the DC office of the FBI, but it being a wide area system, may have transmitters much further afield - Baltimore's WAS has transmitters as far as Ocean City MD. Even if not part of the DC WAS, that transmitter is almost certainly FBI, especially given the 167 NAC.

The transmission you're hearing is likely an idle data burst from the transmitter. It's sort of like a control channel clump for wide area multicast systems - lets subscribers on the system know that there's a repeater out there on that particular channel available for use.

 

[AlphaFive]

167.2125

One of the transmitters you are speaking of certainly sounds like a good suspect. Being the obsessive compulsive that I am, finding that transmitter is an "itch on my brain I cannot scratch", haaaaa. Thanks again, take care.

 

[ecps92]

P25 is FM :roll:

The Burst being heard is likely from someone turning on a Radio to a channel that is part of a "VS" Vote Scan network

If it's showing a NAC, it's not FM, it's P25.

The wide area system is for the DC office of the FBI, but it being a wide area system, may have transmitters much further afield - Baltimore's WAS has transmitters as far as Ocean City MD. Even if not part of the DC WAS, that transmitter is almost certainly FBI, especially given the 167 NAC.

The transmission you're hearing is likely an idle data burst from the transmitter. It's sort of like a control channel clump for wide area multicast systems - lets subscribers on the system know that there's a repeater out there on that particular channel available for use.

 

[riveter]

Bill not really. As I said, it technically modulates frequency to pass data, but it's not 'FM'. 'FM' doesn't use frequency or phase shift keying - it's just straight modulation of a carrier. Of course, here I go dragging the thread off topic, but I wouldn't confuse C4FM or CQPSK with standard FM (though C4FM isn' far off), to the same degree that I would avoid associating any of the above with AM. All are significantly different means of passing data, and as soon as you start using FSK or especially PSK, it's no longer directly-translated FM. That's just my two cents though.

 

[ecps92]

Your Quote confirms FM, Thanks
Make it simple for the basic users. Yes, P25 is FM :roll:

Bill not really. As I said, it technically modulates frequency to pass data, but it's not 'FM'. 'FM' doesn't use frequency or phase shift keying - it's just straight modulation of a carrier. Of course, here I go dragging the thread off topic, but I wouldn't confuse C4FM or CQPSK with standard FM (though C4FM isn' far off), to the same degree that I would avoid associating any of the above with AM. All are significantly different means of passing data, and as soon as you start using FSK or especially PSK, it's no longer directly-translated FM. That's just my two cents though.

 

[AlphaFive]

167.2125

Thank you for the information regarding vote scan. I am going to spend some time learning about this. I just began scanning posts about the subject, I have already seen information that says it is common for mountain top facilities. I am in a valley, less than a mile from one ridge on the east, and several miles from the west ridges. And.. obviously every transmitter in the area that can fit up there is tucked in. Thanks for your help on this, and a lot of other questions before this one.

 

[ecps92]

Not sure where someone is saying Mtn Top facilities, but it is Common for Repeaters.

Depending on the Topography, Repeaters are generally located on a rather HIGH spots.

Those can be Large Bldgs, Radio Towers and of course Mountain/Hill Tops

Thank you for the information regarding vote scan. I am going to spend some time learning about this. I just began scanning posts about the subject, I have already seen information that says it is common for mountain top facilities. I am in a valley, less than a mile from one ridge on the east, and several miles from the west ridges. And.. obviously every transmitter in the area that can fit up there is tucked in. Thanks for your help on this, and a lot of other questions before this one.

 

[AlphaFive]

167.2125

Sounds good, I'm looking forward to reading up on the subject. I've certainly seen it mentioned by technical experts on assorted forums, but never knew exactly what they were referring to. Take care way up there in the northland.

Oh, also, whatever post I had happened to hit on in the wiki search, has mentioned that one reason for the vote scan on mountain top facilities was due to a lack of space when setting up any kind of system, apparently it saves space.... but me attempting to pass this on is like Lancelot Link in my picture trying to explain the propulsion system on one of the space shuttles, just barely worth the effort to read it, haa

 

[ecps92]

Basic/Simple explaination: (there is likely more, but for the scanner user this is the best)

User turns on his/her Radio (Portable, Mobile or Base)
The Radio sends out a short burst saying Hi
The Repeater then send back a Welcome message
The Radio then takes those signals by Strength and then changes the user to that Repeater/site

This explains why users tend to hear the NAC bursts, but no Audio traffic

Saves the user from having to know where each repeater is, and where they are in the radio. Sadly, it's more dumbing down of the end user. No wonder DHS users can't find the Interop Zone

Sounds good, I'm looking forward to reading up on the subject. I've certainly seen it mentioned by technical experts on assorted forums, but never knew exactly what they were referring to. Take care way up there in the northland.

Oh, also, whatever post I had happened to hit on in the wiki search, has mentioned that one reason for the vote scan on mountain top facilities was due to a lack of space when setting up any kind of system, apparently it saves space.... but me attempting to pass this on is like Lancelot Link in my picture trying to explain the propulsion system on one of the space shuttles, just barely worth the effort to read it, haa