{"id":165,"date":"2017-06-10T15:01:52","date_gmt":"2017-06-10T15:01:52","guid":{"rendered":"https:\/\/geekblog.febo.com\/wp\/?p=165"},"modified":"2017-06-15T16:29:40","modified_gmt":"2017-06-15T16:29:40","slug":"20-p25-trunking-scanner-part-4","status":"publish","type":"post","link":"https:\/\/blog.febo.com\/?p=165","title":{"rendered":"$20 P25 Trunking Scanner (Part 4)"},"content":{"rendered":"

With op25 successfully decoding the control channel, now you just need to set up the trunking configuration. To do this, you’ll probably need to set up three files:<\/p>\n

1. trunk.tsv<\/code> defines the sites to be monitored.<\/p>\n

2. site_name.tsv<\/code> provides a table of talkgroup numbers and names for that site.<\/p>\n

3. Because you probably only want to listen to a subset of the talkgroups, you can optionally create a file called site_name_wl.tsv<\/code> with a list, one talkgroup per line, of the talkgroups you want to hear.<\/p>\n

Here’s what my trunk.csv<\/code> file looks like for the Montgomery County, Ohio MARCS-IP system:<\/p>\n


\n\"Sysname\"\t\"Control Channel List\"\t\"Offset\"\t\"NAC\"\t\"Modulation\"\t\"TGID Tags File\"\t\"Whitelist\"\t\"Blacklist\"\t\"Center Frequency\"
\n\"Montgomery\"\t\"853.600\"\t\"0\"\t\"0x343\"\t\"CQPSK\"\t\"montgomery.tsv\"\t\"montgomery_wl.txt\"\t\"\"
\n<\/code><\/p>\n

Note: (a) the first line needs to be included, and (b) each value is surrounded by quotes and separated by a tab character — NOT SPACES.<\/p>\n

The Sysname<\/code> value is an arbitrary one that you assign. The Control Channel List<\/code> needs to include at least the primary controller (note no need for “e6” here) and can also include alternate control channels. Offset<\/code> is the same value you would enter with the command line -q<\/code> parameter.<\/p>\n

Now, the NAC<\/code> field really threw me. When I went to the Radio Reference Montgomery County Site Information<\/A> page, it listed a System ID<\/code> of 348, and a Site NAC<\/code> value of 25A. Neither of those are correct for this field. I can’t find a web reference that ties 0x343<\/code> to the Montgomery county system. I got this number from my initial monitoring of the control channel before adding the trunking configuration. I strongly advise you to do the same, as this is what kept me from decoding until the light finally dawned.<\/p>\n

The next field is Modulation<\/code>. There are two choices: C4FM, widely used by non-Motorola systems, and CQPSK, which is derived from a Motorola standard called “LSM” — Linear Simulcast Modulation. This was another thing that threw me; the Radio Reference page indicated that the Montgomery County site uses C4FM. I only got things to work using CQPSK, though.<\/p>\n

Next is the TGID Tags<\/code> field. This optionally specifies a field that has human-friendly names to decode the talkgroup numbers. Here are a few lines of my tag file, which I call montgomery.tsv<\/code>:<\/p>\n


\n58232 Kettering Fire Dispatch
\n58238 Kettering Police Dispatch
\n58239 Kettering Police Ch B
\n58240 Kettering Police
\n<\/code><\/p>\n

Note again that the separator between talkgroup number and name must be a space.<\/p>\n

Next are two optional fields, where talkgroups may be whitelisted or blacklisted. It only makes sense to use one of these two. I created a whitelist file called montgomery_wl.tsv<\/code> that limits the talkgroups to a few I’m really interested in:<\/p>\n


\n58014
\n58023
\n58024
\n58293
\n58294
\n58333
\n53334
\n<\/code><\/p>\n

I haven’t tested yet whether the whitelist file can include tab-separated talkgroup descriptions as well, or has to be just a list of numeric entries.<\/p>\n

Now, use the same scope.py command line as before, but add “-T trunk.tsv” at the end. You should now be scanning and will hear audio traffic from the monitored talkgroups.<\/p>\n

One final thing — the display in my recorded demo at Youtube<\/A> looks slightly different as I changed the placement of the system, talkgroup, and frequency information on the display.<\/p>\n","protected":false},"excerpt":{"rendered":"

With op25 successfully decoding the control channel, now you just need to set up the trunking configuration. To do this, you’ll probably need to set up three files: 1. trunk.tsv…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","ngg_post_thumbnail":0,"footnotes":""},"categories":[9],"tags":[13,15,14,12],"class_list":["post-165","post","type-post","status-publish","format-standard","hentry","category-sdr","tag-gnuradio","tag-p25","tag-scanning","tag-sdr"],"_links":{"self":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/165","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=165"}],"version-history":[{"count":6,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/165\/revisions"}],"predecessor-version":[{"id":179,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/165\/revisions\/179"}],"wp:attachment":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=165"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=165"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=165"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}