• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:
    https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html

HP1 Acitvity Log: Help understanding

Status
Not open for further replies.

Jay911

Member
Joined
Feb 15, 2002
Messages
9,131
Location
Bragg Creek, Alberta
Hi folks -

I am analyzing a system which I know has a base of 150.8 MHz and step of 5kHz. This is what Unitrunker shows and it is confirmed by the fact that LCN 1004, reported in the HP1 Activity Log as the control channel, is indeed the frequency 155.82 I was monitoring when running the activity log.

So when I get this line in the activity log (and others with similar info), how do I translate it? No mathematics I have tried make this work.

Code:
09/15/2011 05:31:12    "34,B4000502002801CC3480445A"    Identifier Update for VHF/UHF Bands    Iden:0    Bw:5    Tofs:128    Csp:40    Bfrq:30160000
I have the PDF explaining the activity log and I know that Bw stands for bandwidth, Tofs is Transmit Offset, Csp is Channel Spacing, and Bfrq is Base Frequency. They're all listed as being in "decimal".

Bandwidth - 5 kHz?
Transmit offset - 128.. channels? kHz? The LcnT shown by the activity log is not 128 channels either up or down from the LcnR. In fact, it's not consistently a set "distance" from the other, and may sometimes be higher than the CC LCN, sometimes lower.
Channel spacing: 40 kHz presumably? Can I use this to help figure out LCNs?
Base frequency: 30.16 MHz? Is that what the above shows? I don't understand how that frequency corresponds to the 150.8 freq I know is the actual base.

I have a couple of reasons for asking. One is because while most sites I am analyzing have only the above one line, "Iden: 0", there are one or two with multiple "Iden"s, i.e. "Iden: 1", "Iden: 2", etc. I presume that refers to different band plans.

The other reason is one site is reporting an LcnT of 4872, consistently. This puts the LcnT in the 175 MHz range, well outside proper values in this part of the world. Other sites report a valid LcnT and I am able to confirm they're in use. I am used to LCNs being from 0 to 4096 within a band plan "block" (I presume "Iden: x" is the equivalent of a block).

Any help will be greatly appreciated!
 

Jay911

Member
Joined
Feb 15, 2002
Messages
9,131
Location
Bragg Creek, Alberta
Looking at my data again in Sentinel, the site that reports LCN 4872 is the one that has multiple "Iden" lines. Iden 1 is identical to Iden 0 (150.8 base, 5 kHz step). On a hunch, I subtracted 4096 from 4872, and got 776 - which is a valid LCN elsewhere in this system. Also, LCN 776 is used as the "input" companion to LCN 1034 on other sites, and LCN 1034 is the one that reported as the pair to "input" 4872 on this site.

Does this mean that LCN, say, 15396 would actually be iden 3, LCN 3108?
 

Jay911

Member
Joined
Feb 15, 2002
Messages
9,131
Location
Bragg Creek, Alberta
I've done some more figuring out...

Identifier Update for VHF/UHF Bands Iden:0 Bw:5 Tofs:128 Csp:40 Bfrq:30160000

The base frequency, as confirmed with other software and as received by the HP1 in its "normal" operation, is 150.8 for the VHF P25 system generating the above. 150.8 is 5 times the above "Bfrq" value.

One site in that system has a unique secondary "Iden":

Identifier Update for VHF/UHF Bands Iden:3 Bw:5 Tofs:128 Csp:40 Bfrq:30032000

30.032 * 5 = 150.16.

Transmit offset of 128 is in channels. 128 * 0.005 = 0.64 MHz. This corresponds with known information about this system.

Another VHF system:

Identifier Update for VHF/UHF Bands Iden:2 Bw:5 Tofs:9788 Csp:20 Bfrq:27600000
Identifier Update for VHF/UHF Bands Iden:1 Bw:5 Tofs:9188 Csp:20 Bfrq:27600000
Identifier Update for VHF/UHF Bands Iden:0 Bw:5 Tofs:9182 Csp:20 Bfrq:27600000

27.6 * 5 = 138.0, confirmed by other software and scanners as the correct base frequency for this system.

Now, the three transmit offset values: Again they are channels, but the actual transmit offset is the remainder of the above channels divided by 4096 (the number of channels in a P25 band plan - at least, for all systems I've seen so far). Remainder of 9188 / 4096 = 996; 996 * 0.0025 (correct step size for this system) is 2.49 MHz. Similarly, "Tofs:9788" = 3.99 MHz; "Tofs:9182" = 2.475. These transmit offsets are confirmed by government licenses for the frequencies as well as other programs and scanners.

The system with these three band plans (and the "27.6" Bfrq) sports an LCN of "4534" for one particular site. This is actually band plan 1 (second plan), channel 438 - frequency is 139.095 (confirmed with what I was monitoring at the time). For what it's worth, that makes it easier to differentiate between sites considering CC freqs are re-used throughout the system. The site with an LCN of "4534" showing in the HP1 logs is going to be the one shown in the government licenses with a transmit frequency 2.49 MHz up from the receive freq. Any other sites using that same frequency would either show an LCN of 438 (band plan 0) or 8630 (band plan 2) depending on their transmit offset.

Now, on to a UHF system...

Identifier Update for VHF/UHF Bands Iden:0 Bw:5 Tofs:8592 Csp:100 Bfrq:80600000
Identifier Update for VHF/UHF Bands Iden:1 Bw:5 Tofs:880 Csp:100 Bfrq:84000000
Identifier Update for VHF/UHF Bands Iden:2 Bw:5 Tofs:8592 Csp:100 Bfrq:90802500

This is a known system in Ontario, Canada, in the 400 MHz range.

For, again, inexplicable (to me) reasons, the Bfrq is either a multiple or fraction of the actual base frequency in use. It would appear that for this UHF system, the Bfrq value is double the actual frequency. Iden 0 is 403.0, Iden 1 is 420.0, and Iden 2 is 454.0125 (even though all freqs yet discovered in this system lie between 421 and 424 MHz).

Transmit offsets for idens 0 and 2 are 5 MHz, which makes sense as that is the "standard" offset in 400 UHF in Canada. Iden 1's offset is 11 MHz. I believe that is an "alternate" offset permissible in that band (or may be specific to that portion of the band).

I thought I had some P25 activity logs in the 800 MHz band, but I don't appear to any more. I'd be interested in knowing if the "Bfrq" for them is on-target or a multiple/fraction again.

Needless to say, I'd also be interested in knowing why it comes up that way in the logs. It's not exactly user-friendly when one is trying to figure out the system. Also of note: Step size is apparently the "Csp:" value (channel spacing), with a value of "100" equaling 12.5 kHz. (100 is the value listed above for the Ontario UHF system, and "40" is listed for the first system - confirmed as using 5 kHz steps - and "20" listed for the second, which uses 2.5 kHz steps.)

All in all, the activity log is great, but it leaves the data a lot more "raw" than I'd expected it would. For yet another example, the adjacent sites broadcasts on a P25 system (the second one shown above):

11/05/2011 11:09:31 "3C,BC00003E94014B203060C709" Adjacent Status Broadcast
11/05/2011 11:09:31 "3C,BC00003E94014511B66026F8" Adjacent Status Broadcast
11/05/2011 11:09:31 "3C,BC00003E94014A20FC60E284" Adjacent Status Broadcast

The sites are not mentioned in the logs or on the screen when the Activity Log is actually running. I'm sure they're in that string there (I presume the "01XX" right after the SID "E94"), but I don't know why Uniden didn't bother decoding and presenting them.
 
Status
Not open for further replies.
Top