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Thread: Yagi Antenna

  1. #1
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    Default Yagi Antenna

    I have a pretty sweet set up for my HF radio. I have an Older ICOM - 7100 base station with a Yaesu FT-450 I won in a drawing at Sea-Pac a few years ago. I use the yeasu as a back-up and sometimes as a mobile in my hunting rig. I run this into an inverted V wire antenna and once I have pulled a station out of the mud, I use a couple Mosely 5 element yagi antennas which all sit on top of a telescoping tower. I hate climbing towers, and I am not getting any younger, so the telescoping aspect is wonderful, especially when I let out the pins and set the whole thing on the ground stand.

    On my rounds, I noticed that the wind had knocked out one of the elements on my yagi, so I started to size up the project and do some repairs. Fortunately, it was only one of the parasitic elements that got broken, so it is just a matter of putting up another piece of aluminum tubing. On an HF yagi, that piece of tubing can be quite large.

    This got me to thinking.

    There is nothing magical about a Yagi antenna. They work on a couple principals of physics, which involve induced current and the ability of radio waves to interact with capacative and inductive surfaces. The principals are highly technical, but basically simple to understand and using these, you can make a 2m or 75cm band yagi that has astonishing gain.

    A yagi antenna has one driven element and two or more parasitic elements that are reflectors (those element(s) behind the driven element) and the directors(those element(s) in front of the driven element). Ideally the driven element is a multiple or harmonic length of the frequency band you wish to transmit. Most are 1/4 or 1/2 wave length. with 2m, a full wave antenna is only 6 feet in width, so it is very possible to create a full wave yagi, that is almost portable.

    Placement of the antenna elements is along a center pole, horizontal, and perpendicular to the antenna mast. I make mine out of PVC if I am putting together a 2m antenna. The reflector is made inductive, and the induced currents are out of phase with the driven element which reflects the power away from the parasitic element back at the driven element. This causes the RF antenna to radiate more power in the opposite direction to this form of parasitic element. Adding capacitive elements, tightens the beam and increases gain.

    An element can be made inductive by tuning it below resonance. This can be done by physically adding some inductance in the form of a coil (expensive and a real pain), or more commonly by making it longer than the resonant length. Generally it is made about 5% longer than the driven element as this saves cost and keeps the element mechanically as one piece which makes it cheaper and stronger. I have experimented with multiple reflectors and it increases the gain, but not so much so that it makes it worth it. One of the interesting things it does, is lower the take-off angle of the signal. This comes in handy when making a DX call.

    But Crazy Uncle, what about the directors? You remember we made the reflector 5% longer to reflect the wave? Well, directors are shrunk by 5% in relation to the driven element to make it capacitive. That way the induced currents are in phase and get directed away from the driven element and the antenna. That's why they call it a director. Doing this several times with smaller and smaller directors increases the gain of the antenna and tightens the beam of the RF signal.

    Yagi.jpg

    I have found that spacing out the elements no further than a 1/4 wave is optimal. Connect your driven element, which is electrically isolated to your radio via co-ax.


    Have fun and let me know if this helps. I am going to try to draw a diagram and copy it into this write-up.
    Last edited by Crazy Uncle; 11-06-2020 at 01:59 PM.
    July 4, 1776 - November 4, 2020
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  2. #2
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    Particularly with U/VHF, a yagi with horizontal polarization also offers 9dB isolation from Vertical polarization, which is how most people use them... So, it's harder for someone vertically polarized - not secure, but lower probability of intercept... And as you say, a U/VHF yagi is not terribly large.


    The same applies to an HF yagi but they get pretty big - especially on 40m and lower.
    Good medicine in bad places

  3. #3
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    Yep. At 7Mhz, the driver on my antenna is 48 feet long! A real monster. I roll down the mast, when it looks like the wind is going to blow hard. The manufacturer of the mast and the antenna both assure me that these guys can stand in a 70mph wind. I don't want to ever test that.
    July 4, 1776 - November 4, 2020
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  4. #4
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    Baofeng question. Which one to buy for use as local and HAM/shortwave receiver and transmit during crisis' and emergencies??

    Baofeng official site has about 100 different models to choose from $25.00-$1,000.00

    Mobile unit as I travel the lower 48 for work.

    Not asking for a friend.
    Approach with a calm resolve, attack with reckless indifference. Gladius Republicae!
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  5. #5
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    Working on my general ticket here, after about 3 years of frustration. Waiting on a class that never happened so three of us are just prepping for the exam together. This thus far is superior to the 8 hour slam to pass the test, we are taking a section od ARRL book weekly and really learning it, not just learning to pass a test.

    I found a dozen of the Baofeng UV-5R 5 watt units, and six of the Baofeng UV-82c 8 watt HT's . With upgrades like better antenna, I got foldable tactical, and extended battery, they are a pretty good unit.
    Once on safari in deepest darkest Afganistan we ran out of Gin, and were compelled to survive on food and water for several days.


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  6. #6
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    Good OP Crazy. Build your own antennas aren't hard and fine tuning one you do yourself is rewarding. I built a VHF and a UHF Yagi years ago out of some scrap copper I had aquired. It worked well, but using solid copper for the elements was was too heavy for portable use. Design would be easy to do with much lighter materials.
    Greater love hath no man than this, That a man lay down his life for a friend.
    John 15:13

  7. #7
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    Bacpacker,
    Try going to the good will. Find yourself a few fishing rods. String 14 or 16 gauge copper wire in the center of the rods. Cut to length and attach to PVC pipe. For that matter, you can make the yagi out of PVC with wire inside of it. It can be taken down and transported anywhere.

    Kingchip,
    Take online practice exams. They will tell you what areas you need to study and give you practical experience dealing with the way they word questions. I took my extra class in 1971. Be thankful you don't have to pass the Morse Code exam at 20 wpm. It was brutal. Here are a couple links. I hope they help you. I included a code trainer, in case you have a desire to do Morse Code. Feel free to ask me anything. I have been a radio geek since I was 6.

    https://www.qrz.com/hamtest/

    https://hamexam.org/


    Morse Code is a great communication tool, when there is massive background noise. I have made contact with someone in East Africa using a 10 watt transmitter. Here is a link to some training software and trainers. If you do decide to learn code, learn the symbols at 20 - 22 wpm and space it out to 5wpm to start. That way your ear becomes accustomed to the cadence of the faster code, while your brain learns what the sounds are. It's called the "Farnsworth" method.

    https://www.dxzone.com/catalog/Softw...Code_Training/


    Hope this helps.
    Last edited by Crazy Uncle; 11-07-2020 at 01:00 AM.
    July 4, 1776 - November 4, 2020
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  8. #8
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    I like a yagi antenna for two meters and particularly 2 meter SSB.

    Have a 13 element yagi in my garage where I took it down,,,,and put up in stead a home made J pole antenna dual band for 2 meters and 70 CM which suits most of my needs.

    One day I might put it back up again. I always wanted to have two of them and cross them up on one boom and have both vertical and horizontal...polarity in my transmissions.

    Have also built myself a vertical and Horizontal Four element Quad antenna for 2 meters...and have used it but never put it up high in the air. I still have it on a 10 foot pole out back and had my Baofeng 8 watt walkie talkie hooked up to it with an Antenna adapter..

    Use the Baofeng walkie talkies in my car as well and hooked up to a dual band magnetic base antenna via an antenna adapter....works fine for me.

    For the monies I like the Baofeng Walkie talkies .....both the 5 watt as well as the 8 watt models. Have switched out most of my batteries on them for the large 3800 mille amp batteries...the oversized batteries.

    My HF antenna is a 500 foot roll of 12 gauge black insulated wire from Lowes....threaded up in the tops of my trees via a fishing pole....to form a wire loop antenna. Works fine for me....and like many here have worked long distances with little power....but have power if I need it. For the most part I get ahold of my friend out in Tennessee on 75 meters with about 20 watts. My antenna is fed by what is called Ladder line..

    I use a Xiegu G 90 H F radio at 20 watts...but occasionally switch out to a ICOM 706 MK II rig...or an olde Yaesu FT 890....but mostly use the Xiegu radio.


    It is a good feeling to know you can make/manufacture your own antennas and get them to work for you....

    I also try to keep my morse code skills up ...by copying morse on my HF rigs or even sometimes listening and copying on my portable short wave set...

    A Very 73 to the members here..


    Orangetom
    Not an Ishmaelite.

  9. #9
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    73 guys
    Greater love hath no man than this, That a man lay down his life for a friend.
    John 15:13

  10. #10
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    Saw one today while out checking on a job... That thing was massive!
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