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A Cheap and Easy Ground Plane

Discussion in 'CB Antennas' started by RickC., Aug 19, 2009.

  1. RickC.

    RickC. Hopeless antenna junkie

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    There must be as many ways to build a ¼ wave ground plane as there are people who use them, but this one was cooked up over the weekend. The thread here about Stardusters got me to thinking about my neighbors who had them back in the mid-70s, and I had been asked by a couple in a local AM CB group about them, as well as using dipoles for local communications. Since I already had a dipole up cut for 27 MHz and had not had a ground plane for CB in decades, I decided to build one and play with it for a couple of weeks before all this good stuff has to come down for a new roof.

    Those who have built antennas may want to skip this whole thing, but I get PM questions about things like this so maybe this will be helpful to someone who wants to build something but is afraid it either won’t be any good because it doesn’t have some brand name on it, or else they’ll “blow their radio up” with a homebrew antenna.

    This is nothing fancy, doesn’t require any special materials or fancy matching networks. All the radiating parts are just 14 gauge insulated wire- if you know the innards of an Antron 99 are 16 guage wire then you know this isn’t so far fetched.

    [​IMG]

    The radiator element and the three radials are all cut to 103 inches. That was arrived at by using 234/f and cutting it just a bit short to allow for the small difference the insulation of the wire would make. I figured it wasn’t critical, and it’s not.

    Basically, the radiator element is taped to a fiberglass fishing pole, the pole being fastened to a piece of 3/8” exterior plywood with ½” EMT conduit brackets. I used the pole only because I had one lying around from an earlier project, but if I were buying the materials new I’d just buy a piece of ½” conduit, it’s cheaper. The plywood piece is clamped to the metal mast with two regular 1 ½” muffler clamps from the auto parts store. Those things do rust pretty badly so if you intend for the antenna to stay put long term, some stainless clamps from DX Engineering or the like might be worth while- but cheap was the operative word here.

    The three radials are the same wire, with round terminals crimped and soldered to one end of each wire and the three of them connected to one #8 x 1 ¼” screw with flat and lock washers that goes through the plywood. The vertical radiator element goes to its own screw which is about 1 ½” from the radials’ screw. It may be better to have them separated a bit more, but that’s where I put mine. The coax is of course stripped for a couple of inches with the center conductor being connected via a round terminal to the radiator, and the braid joining the three radials with it’s terminal. You can just solder all that together, but you’ll find that even short pieces of wire make excellent heat sinks, and it’s a whole lot easier to crimp and solder a lug to one piece of wire at a time and then connect them together with terminals and screws than try to get a good solder joint with all of them together. I just used plain hardware store zinc plated screws and washers, but stainless would be a good idea if you were going to leave this up for a long time.

    [​IMG]


    The radials were then taped to the mast just below the bracket for strain relief, and then tie-wrapped to the guy ropes, using tie wraps every 18” or so:

    [​IMG]


    You may have seen and read that ground planes should have 4 radials, all spaced evenly around the 360 degrees and all coming off at about a 45 degree angle. Well yeah, they should, but I just happened to have three ropes for guys (you can’t get away with this if you use guy wires) and the angles are what they are to accommodate various shrubs and things in the yard. But the whole thing is insulated from the metal mast. If the weather gets bad I unplug everything anyway, so grounding at the antenna is not an issue.

    So how does it work?

    Pretty well. First of all, the VSWR is below 2:1 from 25.050 to 29.100 MHz. I didn’t expect that. I don’t have an analyzer handy and my trusty old Palomar noise bridge has given up the ghost so I can’t quote R,X, phase, etc. But it is very broadbanded. If I wanted to play with it some more, I might be able to cover the 12 meter ham band and still get the lower part of 10 meters with it, but that wasn’t my aim here. Maybe someone can take this and run with it and try that, and maybe using the EMT instead of wire would make enough difference.

    The bottom of the plywood mounting plate is exactly 28.5 feet from the ground, and my dipole for 27 MHz is about 40 feet away at an average height of 30 feet, so it’s a pretty good case for comparison. The dipole is part of a fan dipole fed with 80’ of RG-8X and a balun, this ground plane is direct fed with 50’ of old RG-8 and 20 feet of RG-8X.

    The only CB I own is a late 70s Sears 40 CH AM/SSB radio, and it just so happens the first contact on the ground plane was on 38 LSB with no amplifier to a station in Michigan. After that I spent a lot of time talking to the local group that night and switching between the two, as well as switching while listening to passing truckers and another local group some 25 miles away.



    This is getting long so I’ll save the vertical vs. horizontal issue for another time. Suffice to say this ground plane holds its own with the locals- the closest of which is 7 miles from me. I’ve also used it on 10 meters with 100W SSB and have had no TVI/cable/PC interference problems. No choke needed.

    So if you’ve been thinking about building an antenna, just do it. You don’t have to copy what I’ve done here, but this will work, and it costs next to nothing. There have been some other ground planes posted here lately, have a look at those and figure out what you want to do.

    73,

    Rick
     
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    Last edited: Aug 19, 2009
  2. looks good rick . i made a homebrew 1/4wgp also .
    http://www.worldwidedx.com/station-mobile-pics/35421-pics-my-homebrew-1-4wgp.html
    the hardest part was working up the confidence that (exactly as you say) i wouldnt blow up my radio . it does local pretty good and from central va ive talked skip to canada , west indies and texas . ive herd a few folks on the west coast but havnt made the trip back .

    my 4 ground radials (12 gauge stranded speaker wire) are 108 inches and the verticle (also 12 gauge stranded speaker wire) started at about 9 ft 3-4 inches but i tuned down to 1.2 or less across the cb 40 . my back and knee were really thumping so i decided that close enough . i could have gotten a lil lower , but neither my equipment or signal would have ever known the difference . i wish i could figgure out a way to put a 22 1/2 foot verticle on it to make it a 5/8 , but to find materials i feel would hold up gets the material cost close to a maco 5/8 .

    there is a bit of pride in getting flowers on my TX and then telling folks im on a home made ground plane made with speaker wire . they are usually suprised . LOL

    thanks for sharing your homebrew antenna .
     
    #2
  3. RickC.

    RickC. Hopeless antenna junkie

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    Hey Booty,

    Thanks for adding your link-- yours was what I was thinking of, but I had to jump on a call just as I was finished writing that and didn't take the time to go look for it. I'm glad yours is working well.

    I did make a 5/8 wave with a 20' fishing pole once-- I mounted the pole to a piece of 2x2 pine and used a standoff insulator to end the wire element a few feet below the pole. With a wire loop for matching and 1/4 wave radials it worked very well. I had it at roof level and intended to leave it up a month or so- I had it there nearly two years.

    Thanks again,

    Rick
     
    #3
  4. W5LZ

    W5LZ Crotchety Old Bastard

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    I think you both have found out a few facts that seem contradictory to 'common thinking'. First, dang near anything will work as an antenna as long as it will conduct electricity and generally 'fit's some particular 'style' of antenna sort of 'close', sort of. There's nothing really 'mysterious'/'magic' about antennas, only their advertising. Want a particular 'name' on your antenna? Great, write it one there!

    How many radials does a groundplane antenna have to have? Depends on where the dang thing is mounted. If this groundplane is mounted above ground/dirt, then it needs to have at least one radial. If it's ground mounted, it needs quite a few radials. Those radials act differently between 'in' dirt and 'above' dirt. Has to do with the conductivity of the 'dirt', and the amount of 'resistance' that contributes to the radials. If that sounds a bit odd, it is. That's because you are not talking about DC resistance, but AC resistance, 'radiation resistance', or impedance.
    Size/length of radials. Needs to be at least a 1/4w length, or, about the same length as the vertical radiator in the case of shorter than 1/4w length antennas. The length of the vertical part of the antenna or a 1/4w, whichever is longer, sort of.
    Will having just one or two radials affect the groundplane's radiation pattern? Yes, very slightly. If you can even tell there's any directivity with that sort of 'very slightly' you have a much more sensitive radio than I've ever seen! Not something I've ever had the requirement of worrying about, ain't no 'thang'.

    This is personal opinion.
    If you are going to play/mess with antennas the first thing you should invest in is an antenna analyzer. They can tell you loads of things other meters can't, and still be almost affordable. They can simplify things by telling you particular aspects of what's going on. They also complicate things because you have to know what those 'thingys' it tells you do, and why. There are some 'lumps' in that gravey!
    - 'Doc


    (Then again, I like 'gravey', goes good with everything except lime jello.)
     
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  5. RickC.

    RickC. Hopeless antenna junkie

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    Agreed Doc, but I was really attached to that old Palomar, and a noise bridge is a good instrument if you know how to use it. I didn't figure anyone who would be building a first CB antenna would have anything other than an SWR meter (if that), and wouldn't have mentioned an analyzer anyway, but you are right. I think I'll have to wait for Santa Claus for my 259...

    And yeah, I have used all kinds of stuff for antennas over the last 35 years. Some have been surprising successes, most did about what I figured, and some showed me the limits of my genius were a lot narrower than I'd thought!


    Rick
     
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  6. Beetle

    Beetle Well-Known Member

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    From an old National Lampoon high school cafeteria menu:

    Lime or fish Jello.
     
    #6
  7. RickC.

    RickC. Hopeless antenna junkie

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    Deputy Dan has no friends.
     
    #7
  8. Moleculo

    Moleculo Administrator Staff Member

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    Nice work, and really nice pictures. One thing that I hope this thread & Booty's helps people understand is that there it really is easy and can be pretty cheap to get yourself on the air, and your antenna will work just as well as an awful lot of commercial ones that cost a whole lot more.
     
    #8
  9. HiDef

    HiDef Active Member

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    Thanks for the nice writeup. Simple and made from stuff anyone can get.
     
    #9
  10. N5IT

    N5IT W9WDX Amateur Radio Club Member

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    As a result of the slower velocity of the electromagnetic wavefront through and along the surface of the insulated wire as opposed to that of bare copper. (velocity factor)


    73, Dave
     
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    Last edited: Sep 5, 2009
  11. RickC.

    RickC. Hopeless antenna junkie

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    Right.
     
    #11
  12. AudioShockwav

    AudioShockwav Extraterrestrial Admin Staff Member

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    The Crust of the Biscuit.

    Bump.

    73
    Jeff
     
    #12
  13. HomerBB

    HomerBB Well-Known Member

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    Ok. I had to do one. I had a inverted V dipole up so thought I'd just add another at 90* to that one and connect all four wires together to the shield of the coax for the radials. i had a hollow fishing pole so I shoved a slightly longer than necessary piece of 3/16" thick vinyl coated steel cable into it and shoved it into the end of the fiberglass tube I had been running the dipole on. The tube is a handle from a long ago broken post hole digger. The center of coax connected to that cable. I tuned the thing down to 1.2:1 SWR before I had to go into work.
    I did put a cox choke at the connection point of the antenna.

    I had never done one of them so thought I'd try it. Quick and easy.

    [​IMG]
     
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  14. looks cool homer . ricks fishing rod for the verticle verticle and my X for a groundplane .
    we'll send you the bills for copyright infringement shortly ;)

    hehehehe . yours looks a lot cleaner than mine though , good job sir :)
     
    #14
  15. mackmobile43

    mackmobile43 Jock Supporter

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    A regular MacGyver you are.
     
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