Free ground-plane 11m antenna, can I use it?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N4EW, Nov 20, 2009.

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  1. N4EW

    N4EW Ham Member QRZ Page

    Cheers guys,
    My neighbor offered me an old 11m verticle from his roof. It has ground planes, and it looks in serviceable condition. It is an attractive offer because it's free and right now my antenna is our house's rain gutter. I have a Yaseu FT 707 (old HF rig, circa 1980) with an outboard tuner. Think I can get some use out of the freebie CB antenna? I like 40m and 20m mainly, but I guess this antenna may only tune on 10m or higher.
    Thanks in advance for advice.
     
  2. N3XP

    N3XP Ham Member QRZ Page

    Who makes the antenna? It could be tune-able for 10, 12, 15 and maybe 20.
     
  3. AD5ND

    AD5ND Ham Member QRZ Page

    A free 11 meter ground plane, a tapped coil, a couple of capasitors, two wafer switchs, a stepper motor and a power supply to drive it. :rolleyes:
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If it's a "regular" CB ground plane (1/4-wavelength radiator and radials, all about 9' long) it will work fine on 10m, and with a tuner you can make it work on 12m.

    It won't work on 20 or 40m worth a darn, coax losses will be astronomical.
     
  5. K9ZMD

    K9ZMD Premium Subscriber QRZ Page

    Free is Great!

    I've had a lot of fun with the free 11 meter ground plane antenna I got over 25 years ago.

    If the vertical element on yours is about 9' or so, then you have a 1/4 wave radiating element. That is usable on 10 meters (either as is, or shorten it to resonance). It can also be adjusted to 12 meters by making it slightly longer (easy enough if there's excess overlap in the "telescoping"). Don't rely on just formula calculations for lengths; instead, check it with an antenna analyzer or SWR meter). You might also have to adjust radial lengths a bit.

    If the vertical element is actually 16' or so, then it was designed to be a vertical half-wave on 11 meters. It will have some sort of matching at the bottom, in that case. That is probably still OK as 10 meter vertical half wave with only a slight length adjustment. However, that extra tubing length also gives you the option of modifying it for use on either 12, 15, 17, or 20 meters. You would have to adjust the length to 1/4 wave on the desired band, and bypass the matching device. You would be shortening it for 12, 15, or 17 meters. On 20 meters, your original length would only need slight adjustment. All adjustments should be done by changing the tubing overlap (never cut if you can avoid it). I would use wire radials tuned for the desired frequency, too. Actually, I'd make them double as guy wires.

    I've used my old antenna on 10, 12, 15, 17, and 20 meters (only one band at a time, of course). You might have some success using yours on adjacent bands (as in 10/12, 12/15, 15/17 etc) with a 1/4 wave radiator set to one band or the other, and a tuner in the shack to match the impedance to your transmitter. I've never done that , though, due to expected loss in the coax with higher SWR on one band or the other.

    If I'd wanted to use mine as a multi-band antenna, I would have paralleled the aluminum tubing with wire elements cut to 1/4 wave for the desired second band (or even a 3rd band) and then added appropriate radials to the system. The would keep the SWR low on each of the chosen bands. 73

    Gary, K9ZMD/6
     
    Last edited: Nov 21, 2009
  6. N4EW

    N4EW Ham Member QRZ Page

    Thanks guys. I do not yet know the manufacturer as the thing is still way-up on a roof. I would love it if it worked for 20M. I'll consider some mods. It'll sure beat my rain gutter.
     
  7. N3XP

    N3XP Ham Member QRZ Page

    I had gotten and Antron A99 from someone who was using it for 10 meters. I worked just fine on 10,12, and pretty good on 15. Using an Mfj tuner I could tune it for 17 and 20, and could work into Europe on it. It was not idea, but it worked.
     
  8. NA0AA

    NA0AA Ham Member QRZ Page

    If you own or can borrow an antenna analyzer, run it on there and see.

    Would not be surprised that it might work OK on 12 and 10. There might be a bit of adjustment to tune it a bit lower, but 15 would be really unlikely I'd think.

    But hey, a free antenna is a free antenna.
     
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    There's a truck stop/gas station in Fairbanks that has an old school CB groundplane atop a 40 foot pole. The pole has been leaning at about a 30 degree angle for AT LEAST THE PAST 33 YEARS!

    I guess it's our version of the Leaning Tower of Pizzas. :)

    Eric
     
  10. K8JD

    K8JD Ham Member QRZ Page

    I got a CB quarterwave GP from a neighbor when I still lived in Detroit, I had to cut about 6 or 8 inches off the top to get it to 28.8 (old AM freq) and worked into Europe and South America every day back in the late 60's. Also worked great for local ragchews when the band opened up for Tech class ops.
    It is still packed up in my garage waiting for the band to come back.
    I currently have my 3 el monobander up for the rare openings that come around.
    If you want to use it on 20M you will have to splice enough Al tubing on to double its size !!!:D
     
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