Antenna Polarization and COMSEC

So you’re out there on a patrol, the commo window is open and you need to make a Cyril Report back to your TOC. Your RTO sets up the yagi getting ready to make contact, checking and rechecking the azimuth. He glosses back over the transmit and receive frequencies to make sure everything is set, double checking the report to make sure nothing was missed, and getting the approval from you, the Team Leader. You notice one small thing- the Yagi is horizontal, not vertical, and a slow grin grows on your face.

You’ve got a good man on the Team who paid attention.

There’s one element to small unit communications that usually gets zero attention- antenna polarization. Let’s take a look at our most common denominator at the basic level- the Baofeng UV-5R. Its a VHF and UHF FM two-way radio. FM nearly always uses vertical polarization, meaning in simple terms, the antenna is straight up and down.

In a conventional environment we do this for two reasons. First, pretty much everyone else is vertically polarized when communicating via FM, and second, there’s 9db of loss between a vertical polarization and horizontal polarization. Wait, what?

Like how we measure light in Lumens, signal strength radiating from an antenna is measured in decibels (db) of gain or loss. With each 3db of gain, we double our effective radiated power (ERP) in terms of signal strength. With each 3db of loss, we cut our strength in half. This is measured in orders of magnitude, meaning that with each 3db, the strength doubles on itself (4w x 2= 8w x 2= 16w, etc). Taking that into account, the difference in strength between horizontal and vertical polarization is 9db- quite a difference. If someone is using a vertically polarized antenna to attempt to intercept my transmission, they’d likely be using vertical polarization. After all, why wouldn’t you? Nearly all FM transmissions are vertically polarized, its common practice. But if I change my operating practice to account for this, now they’re going to have a harder time both intercepting and getting a bearing on me.

Not impossible, mind you. But much harder. And that’s on top of my other operating practices, such as transmitting on one frequency and receiving on another, keeping my transmissions as short as possible, and making sure I’m always using directional antennas. It goes without saying that your intended receiving station should be matched in polarization. Its a basic practice that, when coupled with my other techniques, turns inexpensive equipment into much more formidable gear for clandestine or unconventional forces operating in the field.

 

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By Published On: October 5, 2020Categories: Comms, NC Scout12 Comments on Antenna Polarization and COMSEC

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About the Author: NC Scout

NC Scout is the nom de guerre of a former Infantry Scout and Sergeant in one of the Army’s best Reconnaissance Units. He has combat tours in both Iraq and Afghanistan. He teaches a series of courses focusing on small unit skills rarely if ever taught anywhere else in the prepping and survival field, including his RTO Course which focuses on small unit communications. In his free time he is an avid hunter, bushcrafter, writer, long range shooter, prepper, amateur radio operator and Libertarian activist. He can be contacted at [email protected] or via his blog at brushbeater.wordpress.com .

12 Comments

  1. Jose October 5, 2020 at 09:38

    Great little nugget of knowledge!

  2. Ralph k October 5, 2020 at 10:47

    Nice article. Getting to it is a PIA, especially my biggest pet peeve, “Are you human” gatekeeper. To paraphrase my ongoing experience with this particular system, it sucks, Period. I know you are having DDos attacks and heard you are migrating to another host platform, when you accomplish this task, please utilize some other system other than the dreaded ‘are you human’. It is much too capricious and the images provided contain extremely small portion of the ‘wheres Waldo’ image, it is unhelpful at all. Pure unadulterated garbage, IMHO. I wind up having to go through 3 or more iterations to get the ‘correct answer’.

    That aside, good luck with your battle against the dark forces, and keep that knowledge flowing. Thanks.
    ps please include your IP address so we can have that in case we can’t connect by the lead in, named host address of your site.

    • NC Scout October 5, 2020 at 11:30

      I’m sorry it inconveniences you. You should be the guy trying to write and edit while battling it.

    • Johnny Paratrooper October 5, 2020 at 11:58

      We are in a war. Life is gonna get much, much harder. So hard and miserable you won’t believe it.
      Try going to a modern college and learning that the last 4 years of your life has been wasted because you have been labeled a bad comrade by the media, music industry, movie industry, politicians, academics, and many of your peers.
      I am victimized by NONSTOP propaganda that makes twitter look inviting and welcoming.
      And once you activate your GI bill you are stuck. Plus, there is nowhere to escape to because every single college is the exact same. Meaning that the 20-30 year olds in Baltimore have the same opinions as Wyoming or Colorado 20-30 year olds. There is literally no escaping this nightmare.

      Imagine knowing a train wreck is coming and you cannot stop it and no-one cares or bothers to listen?
      I wrote a college paper last fall EXACTLY predicting what happened this summer.
      I should get a freaking medal and an intelligence officer job offer for that paper. But that isn’t gonna happen; ‘Cause Commies.

      And because all the professors are commies, I will never have the grades to study abroad, or get a grant to do something fun and interesting. I used to get straight A’s and B’s before Trump ran for office. Now I can barely pass my classes. And if Trump wins, You can be PROMISED they are gonna fail as many of the white male veterans as they can get away with and make us pay for our failed semester.

      I wish I could do captcha puzzles all day. That would be the easiest, least stressful part of my day.

  3. pjc October 5, 2020 at 11:54

    One of the best explanations of DB gain/loss I’ve read.

    Also, the lumens point led me to think that a flashlight is a good analogy for a directional antenna. A flashlight in a darken hallway, pointed vertically, will still splash some light down the length of the hall (not very far) but primarily (wastefully) direct the light onto the ceiling. However, it stands to reason that the effective range of the flashlight will be much better when pointed horizontally down the length of the hall sending the full force of the beam the direction desired. (and almost none to the rear…) Further, most flashing lights have adjustable beam width allowing the beam to be reduced in diameter, with further distance gain at the penalty of requiring better “aim’. On the other hand, within a room the flashlight reflector can be taken all the way off (at least for old incandescent lights) for omni-directional illumination that doesn’t go very far at all, but is useful for such things are reading, eating or working on something on a table. The output power of the bulb never changes, but how it radiates and therefore how it can be used effectively does.

    I’m sure I’m not he first one who’s ever thought of this but thankful this article led me to consider the topic.

    • NC Scout October 5, 2020 at 12:05

      That’s the exact analogy I use in class. You’re in good company. :)

      • Johnny Paratrooper October 5, 2020 at 12:24

        Physics; It’s what’s for breakfast at AP.
        Figure it out; Or you are gonna be somebody’s lunch.

  4. Johnny Paratrooper October 5, 2020 at 12:20

    So you use physics and applied sciences to hide in plain sight?
    That’s pretty badass. I wish I choose radio engineer as my major.

    https://www.americanpartisan.org/2020/04/three-simple-home-brew-2-meter-antennas/

    Making these ASAP. These distances noted are freaking incredible. I’m literally shocked.

    Would you consider investing in the Signal stick? or any of the stubby antenna for internal community defense use?

    If so, which brand do you like?

    • NC Scout October 5, 2020 at 12:38

      For sure. Any of them are fine, but the Smiley Antennas are the best on the market.

      Keep in mind the SMA on most handhelds (including the Baofeng) are pretty fragile, so snagging up some SMA-BNC connectors is a good idea.

      • Badger October 5, 2020 at 22:00

        “snagging up some SMA-BNC connectors is a good idea”

        Amen. Everything SMA (Wouxun stuff) gets a BNC adapter in my house. As you say, that tiny form factor connection has a penalty I’m not willing to pay. Besides, BNC is a metric ****-ton faster for setup/breakdown and more tolerant of sudden stupid moves (and I’ve done my share of those too).

        Good stuff.
        .

  5. oldgreyguy October 6, 2020 at 22:10

    In practice, cross polarization is probably between 15 and 40 dB, depending on the antennas and the environment.
    https://ham.stackexchange.com/questions/12918/what-is-the-theoretical-and-actual-cross-polarization-attenuation-from-horizontal

  6. Matt October 11, 2020 at 09:18

    This got me thinking about some of the radio problems we had in the field, poor reception even at relatively short ranges. The radios, being in a person’s web gear, has the antenna roughly oriented in the same direction as the body.

    With one guy being prone and the other guy standing or squatting it sounds like a perfect example of this. Could that be responsible for the lousy comms? Any better antenna mounting solution?

    Thanks for the article.

    Matt

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