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Homebrew 2 Meter Antenna

Discussion in 'General Technical Questions and Answers' started by KI4BOO, Aug 4, 2003.

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  1. KI4BOO

    KI4BOO Ham Member QRZ Page

    Hey everyone. I am a new ham, and this is my first post on the boards here.

    For the last 2 weeks, Ive been transmitting on a 2 Meter mag mount ontop of a coffee can in my radio room. It works for talking on the local repeater, but I can't hit the city repeater without going on Full power, which I prefer not to do.

    Ive got a 12 Element 2 meter beam, but I dont have my other tower ready, or a rotor to turn it with.

    For the time being, I want to put up some kind of a Home made 2 Meter antenna on my tower I have up for my CB antenna. Perhaps a mast off the side of the tower with the second antenna on it will be sufficient? It's just something cheap that will last until I can afford to fix my other tower and buy a rotor. (Im only 17 and Money is tight.)

    I have the ARRL Antenna Book, and I followed the instructions on making a 2 Meter Ground Plane using a PU-259 connector. I did it, but my SWR meter is telling me 6 SWRs. Certainly not acceptable!

    Anybody have any suggestions for making a homemade antenna for 2 Meters? Im always willing to experiment.

  2. N0PU

    N0PU Ham Member QRZ Page

    OK, lets take one step at a time...

    1. What kind of SWR meter are you using?
    If it's one of those rat-shack specials then the reading is probably not accurate. Those are for HF up to 30 Mhz only... they rarely work above that...

    2. What dimensions did you use for the ground plane?
    3. Did you put the radials at a 45 degree angle down?

    Next: terminology... I'm not pickin' here just explaining...

    1. A PL-259 is the male connector used on the end of coax of approximately RG-8 proportions. A UG-175 is an adapter you use to reduce the entry hole on the back of a PL-259 so you can use RG-58 cable.
    2. The connector you use for the Ground Plane antenna is an SO-239... it is the female chassis mount variety...
    3. It isn't SWRs ... There is only one ratio [standing wave ratio] per measurement. and there isn't any sense in talking about more than one SWR... it would be [pick a number] swr measurments.
    4. The reading you get is a ratio and therefore requires a reference. I think you meant 6:1 as in "six to one"
    OK, next topic.... the coffee can...
    That is not a large enough surface area to do you a lot of good... minimum would be a large pizza pan... I have one sitting on a pair of file cabinets that does ok...even from the basement... but then I'm in an urban area with a lot of repeaters...

    ok, answer the questions and we'll go on to the next part of the problem...

    BTW: I have built a LOT of those ground planes and they are an excellent little antenna.
  3. KC0KVU

    KC0KVU Ham Member QRZ Page

    What were the dimensions for that ground plane, they should be ~19" for the driven element and ~21" for the radials at a 45deg angle?!  Shouldn't be 6:1 swr though.

    However, there's no good reason not to use that large 2M on your CB tower and point it towards the city repeater.  If the local repeater is in that general direction then there's an added bonus.  Light duty rotors are fairly cheap on ebay if you wanted to go that route as well.  Otherwise just use the ground plane for the local until you can get your other tower fixed.

    Other options include a vertical dipole, putting the magmount on the tower or even building a second beam and putting both up on a mast!  If you want, I have plans for building a 5ele 2M modified from a 6ele Radioshack FM antenna.  The antenna retails for $20 and the rest of the little odds and ends for modification, along with a connector would make the total cost around $30 depending on what hardware store you go to.  Email me,, if you want the plans on pdf.  I've pimped this antenna a lot, but only cause its low cost and works like a dream!

    Hope this helps
  4. W7EET

    W7EET Ham Member QRZ Page

    I would look around for a 20" square piece of sheet metal then place the mag mount in the center of the sheet metal. A coffee can is not enough reflective ground plane.
    kg7wd [​IMG]
  5. Guest

    Guest Guest

    And look up J-pole on google. You'll find a lot of cheap and easy ideas.
  6. KI4BOO

    KI4BOO Ham Member QRZ Page

    OK Guys, some progress.

    The SWRs were 6:1. The way I was testing it was to attach the antenna to the SWR meter (144/440MHz Micronta), a really small "in-line" type with a jumper that was about 5 feet long. The radials werent put onto the coupler (SO-239) yet. I held it out away from my body and as far over my head as I could.

    I tried this today. I punched a hole in the bottom of a coffee can and screwed the coupler to it. I checked the SWR again, and this time it was around 4:1.

    I discussed this with a local guy named Len (KC4GOA), and he suggested I ground the coffee can to my grounding rod, and put it outside my house about 5 or 6 feet in the air. Im going to give that a try tomorrow and see if the SWR drops any more.

    The antenna is made from a brass rod, and is a little over 19 inches long. The solder connection between the rod and the coupler is good. Ive been trimming the antenna slightly and rechecking the SWR, and Im getting close to exactly 19" so I stopped trimming. The antenna book calls for 19 and 5/16 inches for 146MHz.
  7. N0PU

    N0PU Ham Member QRZ Page

    you didn't build the WHOLE ground plane...

    The radials are what MAKE the ground plane work...
    Put the radials on the SO-239 and you'll be fine...
    be SURE to bend them down at 45 degrees... that will set the impedance correctly... at straight out the impedance will be about 35 ohms... straight down will be about 75 ohms... 45 degrees gives you the 50 ohms you are looking for...

    The coffee can is still too small...
    unless you got that bad boy to grow to pizza pan size...
    you HAVE to have enough surface area to accomodate about a 1/4 wavelength...

    An SWR of 6:1 sounds reasonable without the radials... I'm surprized it isn't higher...

    Now, as any good elmer will do, I'll scowl at ya, and tell ya ta go back and follow ALL the flippin' instructions... not just the ones ya like... hehehehe... good luck...
  8. K9STH

    K9STH Ham Member Staff Member QRZ Page

    Make sure that the radials are about 20.5 inches long (5 percent longer than the driven element). Then, like everyone has been saying, bend them down about 45 degrees. With a driven element length of about 19.5 inches this should give an SWR of below 1.5:1 at 146 MHz.

    Actually, it is better to build the antenna on a small "L" shaped bracket. If you use a UHF SO-239 connector, the bracket should be about 2 inches wide with the connector mounted in the center. Then, use 4 radials attached to the bracket and measure the 20.5 inches from the edge of the bracket. This will mean that you will start with radials about 22.5 inches long if you run each one along the edge of the bracket before bending them down.

    You can make a clamp out of another piece of metal about the same size as the horizontal portion of the bracket (about 2 inches square, actually a little larger) with a hole for the SO-239 in it as well. Form this piece over the wires and put a small screw or bolt next to each place that has been formed over the radials. Insert the screws, then insert the wires and tighten the screws. In fact, if you mount the SO-239 at a 45 degree angle to the edge, you can probably just use the four screws that hold the connector in place to clamp down the radials.

    On the other side of the "L" (which normally should go down in direction) you can attach a "U" bolt to make mounting of the antenna on a mast easy.

    Glen, K9STH
  9. KI4BOO

    KI4BOO Ham Member QRZ Page

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (N0PU @ Aug. 04 2003,18:41)</td></tr><tr><td id="QUOTE">Now, as any good elmer will do, I'll scowl at ya, and tell ya ta go back and follow ALL the flippin' instructions... not just the ones ya like... hehehehe... good luck...[/QUOTE]<span id='postcolor'>
    Now is the time when I duck and run. [​IMG]

    I guess sometimes in life you just have to go by the book.

    I made radials out of coat hangars and attached them to the connector.

    The SWR is now 1.7:1. Not quite low enough for my liking, but far better than the 7:1 it was before. I think I can get it functional with a little bit of fine tuning and a pair of wire cutters.

    The book said to use 18 and 11/16th inch radials, so thats what I did. I'll give the longer radials a try tomorrow morning and see how they do. My new roll of coax comes tomorrow, and if I can get the antenna working good, It will be on my tower shortly after.

    The last question I have is about painting the radials. They are made from steel, and will rust pretty quick. If I paint them, will it mess up the way the antenna works?

  10. N0PU

    N0PU Ham Member QRZ Page

    You're on your way...
    you have the right idea now...

    Throw some krylon or something on them if ya want...just make sure it is non-conductive in case ya over-spray near the SO-239... ya don't need a metalic 'path' of paint from the radiator to the radials!

    Me? I always find that no matter what I use, I end up taking the antenna down for changin' somethin' long before corrosion sets in... assuming of course that you soldered the radials...
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