Need help preparing for Webster Field, MD – JNCR system with DSD+FL

[wx2watch]

During last year’s safari, I brought along my PC laptop with a copy of DSD+FL (currently using 2.395) and a single dongle (RTL-SDR ver 3). Next week I’ll be located approximately 10 miles SSW of Webster Outlying Field/ St. Inigoes, MD.

I was limited to monitoring one channel (388.1125 MHz) OR, at least I think I could only monitor one channel since I only had one dongle – maybe a false assumption…

Last year I used the following two BAT files:

1R.bat: dsdplus -i2001 -f1 -T -E -Pwav >>April2022.log

FMP24-CC.bat: FMP24 -o2001 -f388.1125 -g20 -b12.5


Several questions for one dongle setup for the JNCR P25 system:

1. Can I monitor all 5 frequencies by using the “FMP24.scanlist” file ?

(Hit “S” while focused on FMP24 window – “Esc” to cancel)

; any entries after <EOF> line are not scanned

386.2750 P25 BW=12.5 DELAY=1 webster01
386.7125 P25 webster02
388.1125 P25 webster03
388.6500 P25 webster04
389.4375 P25 webster05
<EOF>

2. OR should I manually populate the ”DSDplus.frequencies“ file and expect the program to utilize that file? ( OR will the program auto-populate the file?)

P25,1,1,1,386.7125,386.7125,1
P25,1,1,2,388.1125,388.1125,2
P25,1,1,3,388.6500,388.6500,3
P25,1,1,4,389.4375,389.4375,4
P25,1,1,4,386.2750,386.2750,5

Helpful critiques would definitely be appreciated!!

(This year I will have two dongles, BUT, I think those questions can wait until I work out the flaws in my single dongle setup/logic )

 

[maus92]

I am not a DSD+FL expert; I just hack around with it from time to time. I started a single dongle session this morning on the JNCR US Naval Academy site this morning with the following commands:

1R.bat
FMP24-CC.bat

The contents of the 1R batch file are: DSDPlus -r1 -T -E -Pwav -i20001 >>1R-log.txt
The contents of the FMP24-CC batch file are: FMP24 -rc -o20001 -P0.0 -g33.8 -f386.5875

No other entries were used. The system was using 385.3125 this morning as the control channel, so I clicked on it using the FMP24 spectrum display window, which tunes the SDR to that channel. I am making a few edits to the .groups file, and I will adjust the FMP24-CC ppm parameter to match the SDR device. The gain parameter is accurate for my location.

 

[maus92]

Searching the forum, it seems that P25 trunked radio systems do not require entries in the .frequencies file. I'm also not sure of the utility of a scanlist file. Once you tune the active control channel, all the traffic channels are automatically discovered and tuned when they are carrying voice traffic. I think scanlist files are used for conventional scanning of discrete frequencies thus have no utility when monitoring trunked radio systems like JNCR.

 

[wx2watch]

Searching the forum, it seems that P25 trunked radio systems do not require entries in the .frequencies file. I'm also not sure of the utility of a scanlist file. Once you tune the active control channel, all the traffic channels are automatically discovered and tuned when they are carrying voice traffic. I think scanlist files are used for conventional scanning of discrete frequencies thus have no utility when monitoring trunked radio systems like JNCR.

maus92, Thanks for responding.

I felt like I couldn’t absorb any more info on my own after several days of searching/re-searching. My only P25 system that I can monitor locally (up here in MA) is a single channel National Park Service system on 166.875MHz. I see (after looking at your batch files) that I left out some not so subtle commands (-r1 & -rc) in the two batch files for trunking systems application. DOH!!

I have NOT applied an off-set for the dongle as everything here sorta seems to work. (Maybe I could use a NWS weather channel via SDR# to obtain a reference to get an exact ppm off-set so I can enter it into FMP24??)

Was thinking my concept of “auto-populate” for the “dsdplus.frequencies” file applied to different modulation schemes (i.e. something other than P25) Guess I’ll find out when I arrive on-scene in Virginia.

Again, many thanks for taking the time to help me out!

 

[dave3825]

1. Can I monitor all 5 frequencies by using the “FMP24.scanlist” file ?

Yes and no. Scanlist is for conventional freqs. You want to listen to a trunked system. You can add 4 freqs as one will be a control channel. The other 4 would let you hear voice but will not follow any tg;s and would be impossible to follow any kind of conversation unless there was only 1 person talking to another.

OR should I manually populate the ”DSDplus.frequencies“ file and expect the program to utilize that file?

Searching the forum, it seems that P25 trunked radio systems do not require entries in the .frequencies file.

As @maus92 stated, in the newer versions of fastlane, P25 freqs are automatically written and managed in DSDPlus.P25data file.

Start the way @maus92 posted. Then just manually tune to each freq until you land on the control channel.

1R.bat
FMP24-CC.bat

If you look up the system, in its downloads will be dsdplus groups and sites files available for download formatted for dsdplus. They look something like this,

 

[wx2watch]

Yes and no. Scanlist is for conventional freqs. You want to listen to a trunked system. You can add 4 freqs as one will be a control channel. The other 4 would let you hear voice but will not follow any tg;s and would be impossible to follow any kind of conversation unless there was only 1 person talking to another.



As @maus92 stated, in the newer versions of fastlane, P25 freqs are automatically written and managed in DSDPlus.P25data file.

Start the way @maus92 posted. Then just manually tune to each freq until you land on the control channel.




If you look up the system, in its downloads will be dsdplus groups and sites files available for download formatted for dsdplus. They look something like this,

View attachment 140112

Dave3825,

Thanks for the step by step instructions - greatly appreciated!! I'm currently on scene (about 8 or ten miles away from Webster) with a direct line of sight overlooking the Potomac River. My system is working well although the audio is very "muddy." (This seems to be a DSD+ short coming, as with my limited experience with P25 systems, I always have this problem - not encryption but just hard to understand voices - most of the time.)
I think I have reasonable signal strength with a good noise floor - see screen capture. Whoops having trouble converting screen capture to a graphics file - stand by....

Thanks again to you and maus92 for taking the time to assist,
John

 

[maus92]

The signal looks good. Decoded P25 audio can be muddy, and DSD voice decoding is not always the best - but Webster is a multicast site so not as technically challenging as simulcast. One thing to consider are if the field units ( the uplink side) are operating in a good coverage area.

 

[BM82557]

I think that +1148 is high and that can mess up decoding, what's the PPM set at?

 

[maus92]

View attachment 140162


I think that +1148 is high and that can mess up decoding, what's the PPM set at?

Agreed. Although signal strength is good, the tuner is off-frequency. PPM needs adjusting.

 

[wx2watch]

I have not set PPM correction because I wasn't sure about a good method of determining the needed offset... HOWEVER, what I am currently going to try is to tune to a NOAA wx channel with SDR# and look at the graphic display to see if that will give me a clue.

Hmmm, looks like I need a 48 PPM correction. Just a SWAG but I'll give it a try later today.

Thanks to all for the mentoring of my setup - greatly appreciated!!

 

[maus92]

48 ppm is a HUGE amount. Should be somewhere around +/- 1.0 or less for an RTL-SDR v3 as it is TCXO. 48 MHz works out to be roughly .0185 MHz, which is large enough to be another channel altogether.

 

[wx2watch]

48 ppm is a HUGE amount. Should be somewhere around +/- 1.0 or less for an RTL-SDR v3 as it is TCXO. 48 MHz works out to be roughly .0185 MHz, which is large enough to be another channel altogether.

YES, I just found out that my SWAG of 48 was outrageous. Just figured out to look at the FMP24 header bar. By trial and error I have a correction factor of -2.8. Deviation is now +/- 15. The audio is MUCH BETTER - should I try for a smaller deviation swing? (i.e. Is it possible to adjust to the point where there is Zero deviation?)

 

[maus92]

IDK about the deviation, but it looks like you are only off by 1Hz, which is excellent!

 

[wx2watch]

IDK about the deviation, but it looks like you are only off by 1Hz, which is excellent!

Perhaps I misspoke regarding "deviation." What I meant was finding a PPM correction that doesn't fluctuate from zero. Is it worth the time to experiment with a correction factor of, oh say 4 decimal places such as 2.8563, or whatever?

 

[maus92]

Nope, not worth the trouble. The tuned frequency will wander ever so slightly with temperature and other factors. As I said, 1 Hz is excellent.

 

[wx2watch]

Nope, not worth the trouble. The tuned frequency will wander ever so slightly with temperature and other factors. As I said, 1 Hz is excellent.

Just a quick note to thank everyone for their help. I returned from Virginia yesterday and had a successful/interesting monitoring session while down there. 1st day there was some chitchat about a plane coming in that had a faulty #2 engine. Apparently it landed safely...

Also was pleased to discover that Dahlgren signal strength was OK at my location with the RTL-DSR rabbit ears antenna even though I was 31 miles away. (Only 11 miles to Webster field)

Thanks again!