Rapid AO monitoring of FRS/GMRS HT’s

Rapid AO Monitoring of FRS/GMRS HT’s

By 33G20 

Recently I attended a three-day class entitled “Ground Intelligence Collection” facilitated by NC Scout and the field portion was outdoors. Do I have to add that the weather just had to join the conspiracy against us and add some realism – snow. There are a couple of ways to deal with this type of issue – speed and/or shelter. I am going to address the speed aspect in this short article.

The purpose of the exercise was to discover what frequencies the OPFOR were using and then quickly transition into the next phase – passive monitoring, recording or disruption. Since FRS is divided into twenty-two channels and covers 5.1625MHz of bandwidth and GMRS is across 32 different frequencies covering 5.1750MHz of bandwidth a couple of tools come to mind.

The device needs to be portable to be used in the field so this rules out industrial spectrum analyzers. One solution is the “Close-Call” feature found on many scanners coupled with a suitable antenna. To optimize this configuration a field transportable yagi antenna can add sensitivity to the direction being scanned and also help block strong near-field sign sources.

Another approach – and preferred by the author – is the use of an SDR radio with a laptop. Using this approach it adds full spectrum coverage and visual indication in the event that the target jumps channels to avoid being heard. With the GNU public general license available SDR+ software and any of several SDR devices you are good to go!

Looking to have a system that fits into a backpack or gym bag I chose a couple of portable antennas – the Diamond D220R discone rated 100-1600MHz and a log periodic Kent Electronics 400-1000MHz.

Mounting the Kent log periodic antenna was done via a camouflage, water-repellent cover my industrious wife designed and sewed together. It allows the antenna to be mounted vertically with it’s sleeve to a 15mm carbon fiber or wood dowel. Additionally, the tripod is configured with a “SmallRig” cheese plate with dual 15mm rod clamps that the antenna can be mounted to horizontally.

The Diamond D220R is mounted on a standard, one inch PVC tube base connected together to be broken down into four pieces. The only modifications were the addition of end caps to keep water out, and small cut to allow the antenna lead wire with SMA connector to come out the side.

The Diamond D220R on PVC travel base painted olive drab.

Tripod with SmallRig cheese plate and 15mm x 8-inch rod with antenna cable from CD International Technology, Inc. 

Here is the complete rig with antenna mounted:

For the SDR receiver I was an early adopter of the AirSpy products. The AirSpyR2 is my “go to” choice for its wide-bandwidth and spectrum coverage. Connected via its included USB cable and attached to either of these small and covert antennas you can monitor the radio spectrum from 24-1,700MHz.

Here is a spectrum display example:

The red line is the tuned mid-frequency of the FRS band. The high-end of the frequency band is clearly
in sight as well – all 462MHz channels are in one display.

The units SDR+ software runs on Windows Vista, 7, 8, 8.1 (it’s time to upgrade!) and 10, OSX, BSD and
Linux. What is not to like?

33G20 started his career as a SP5 in the Army Security Agency in the 1970’s. Trained as a 33G20 electronic Warfare/Direction Finding Systems repairman he graduated from AIT after 14 months from Fort Devens, Mass. After working on AN/FLR-9, TRD-15 Autotune and CEFIRM Leader systems he has enjoyed a career as a system engineer till this day. Today his interested are in OSINT, SDR and being prepared. 

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About the Author: johnyMac

8 Comments

  1. Capt. D February 20, 2020 at 08:50

    Thank you JohnnyMac, this is 100% G O O D N E S S! I too am an alumnus of NCScout’s SigInt course, and have been perfecting my SDR quick-mapping capabilities. It looks like you had your system ready for the course. I only got mine up and running after returning to my AO with new skills and knowledge from the course. The discone antenna as a receiver is a great idea. All readers need to know the SigInt course is one of the best investments you will ever make. To all Mutual Assistance Groups out there pony up and send one person from your group to this course. Better yet, take RTO Basic, RTO Advanced, AND SigInt. Time is running out to be equipped.

    • johnyMac February 20, 2020 at 19:16

      Capt. D thank you as always for your comments.

      I just want to point out that although I was at NC Scout’s class titled Ground Intelligence Collection, I did not write this great piece – 33G20 did. When I edited his article before it posted, I changed his handle for PERSEC.

      Now with this written, I tried the software and equipment that 33G20 brought and it worked great. Even between driving periods of snow during the field exercises.

      Just a quick commercial here…NC Scout’s Ground Intelligence Collection class was WAY more than I thought it would be. Over three days we got so much more than HUMINT & SIGINT – There was a lot more. Scout tends to under promise in his class descriptions and always over delivers. A plus is – He is willing to travel. This class was held in NJ for all God for-sake’n places.

      33G20 brought his software and hardware to the class which he described in this article. It was a plus for sure.

      73 & God Bless Brother.

  2. Charlie Prime February 20, 2020 at 10:18

    It amazes me that most Preppers will spend vast sums on the latest gun gimmick, but won’t spend $25 for an RTL-SDR so they can listen to their area.

    https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/

  3. doug1943 February 20, 2020 at 10:43

    Whoa…. a question that I’ll bet others have: suppose you’re a reasonably intelligent, but non-electronics-skilled person. However, you’re willing to put in some hours, days, weeks, getting enough training to use this combo, and also to be reasonably proficcient in all the associated comms tasks that might arise in an emergency situation. What training would such a person need to go through, and how long would it take?

    I’m NOT talking about becoming qualified, say, for a ham radio license. I’m just talking about being a competent user of the gear. The analogy would be someone who can use a tablet well, but has no idea about programming, mark-up languages, internet layer protocols, etc.

    Put it another way: suppose a group of a couple of dozen ordinary Americans wanted to have basic comms capacity, but had no one in their group who had this knowledge. If they chose some one among them to acquire it, how much would it cost and how long would it take? Remember, I’m just talking about basic users’ knowledge, no more technical knowledge than necessary to be a basic user.

    Thanks in advance for all responses.

    • NC Scout February 20, 2020 at 12:02

      I teach a class for that.

  4. WhiteNoise February 20, 2020 at 13:08

    I understand the concept of the discone set up and the SDR receiver, but the programming of it all is way beyond my grasp.
    I read (or tried to read) the link noted above by C Prime about setting it up,
    Trouble is, for this non-computer geek, it seemed like half of it was written in Russian, and the rest in ancient Greek.
    It’s no wonder that many of us would rather “waste time” with a new gun or such, than get involved in this needed skill..

    All that is needed (and probably wanted in many cases) is the step-by-step instructions IN PLAIN NON-GEEK ENGLISH on how to hook up a SDR to a tablet computer (laptops are too big for the field)– to have something compact and useful in the field. (the wiring the antenna to the SDR is simple)

    Until this new technology is presented in some simple “Dick and Jane” format/understanding, it’s basically a waste of electrons or printers ink to many of us.

    ?????????

  5. Capt. D February 20, 2020 at 17:36

    This is a response to WhiteNoise. I am not all that good at computers either, but I went to the website of my SDR dongle and printed out a hard-copy of the instructions. I then slowly went through them and it worked. It took me maybe an hour or so. I did use a laptop because it was all I could get and I wanted to at least map my AO from my home. Now, contrast that with setting up FLdigi which looks way more complicated (but something we should do). I still haven’t done that. Take heart, though, you can do SDR setup!

  6. Joe Fahy May 21, 2020 at 17:40

    How, where, did you mount the log periodic pcb antenna to the 15mm uprights? A pic of the fasteners and where on the pcb they pass through would be fantastic.

    Thanks,
    Joe

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