You views on an off center fed 80-10m

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 2E0LPL, Jun 20, 2019.

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  1. 2E0LPL

    2E0LPL Ham Member QRZ Page

    I have spent a week trying to get an inverted L to radiate but I am just about to give up.

    Its tunes up well on all bands inc 160m and its 38m long.

    At first I grounded it via 4 copper rod spread out in a line...gets out but poorly...unhooked them and tried a 38mt counterpoint same very little getting out...still tunes well...its fed via 16mts of coax.

    So looks like I will have ditch the inverted L and forget about using 160m for now and make do with 80m...which is my second fav band after 160m.

    So I am now considering an off-center fed windom style dipole 40mtrs long for 80-10m.

    I have no experience with this type of antenna and would love to hear your views on how well they perform.

    I have a choice of bare copper wire for the elements or polyweave....my gut instinct is toward bare copper.

    So guys how does an off-center dipole perform say on 40m with a center-fed dipole cut for 40m...I have one of those up now and it does a good job....and polyweave or bare copper?

    Nick.
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    I have never been able to tell any difference between horizontal wire antennas made of uninsulated wire vs insulated wire, except that insulated wires end up slightly (~1 to 2%) shorter than bare wires to achieve resonance...

    Is the interest in OCF motivated by anything other than having the antenna work on both 80m and 40 without a tuner? The reality is that you will need a tuner to utilize the width of the 80m band; you cant escape that!

    If you use a tuner, the best place to locate the tuner is at the antenna, and then run coax from the station to the tuner... This requrires an expensive remote, weather-resistant tuner.

    If you can only have an in-shack tuner, to minimize feedline losses, it is best to use Ladder-Line between the tuner and the antenna... If that is the configuration, then just put up a "doublet" (a center-fed, ladderline-fed, dipole) which avoids being resonant on either 80m or 40m by being cut to a length about 80% of a 80m resonant dipole... That length makes the impedance that the tuner has to deal with easier to tune on both 80m and 40m, as well as on other bands.
     
    AJ5J likes this.
  3. K4SAV

    K4SAV Ham Member QRZ Page

    A 160 inverted L doesn't work very well without a bunch of radials. Also nothing works very well on 160 right now. Night times are too short. Also difficult to hear anything with all the summer time thunder storms.

    Jerry, K4SAV
     
    WB5YUZ and AJ5J like this.
  4. W5DXP

    W5DXP Ham Member QRZ Page

    Given a 40m long (130 ft) North/South dipole, here are the radiation patterns on 7.15 MHz for a center-fed vs off-center-fed.

    CFDvOCFD.png
     
  5. AA5CT

    AA5CT Ham Member QRZ Page

    There are better ways to use 120 to 130 ft of wire, Nick. Configuration-wise that is. Look to the work by G0CWT for instance ...
     
  6. AJ5J

    AJ5J Ham Member QRZ Page

    Amen to that! Radials, radials, radials and more radials are the answer for success with any inverted L. If I were in your situation I'd give it another go after installing you-know-what.

    Never used an OCF dipole but I think you'd be in for more trouble with that than with happy inverted-L camping---just my 2 dirhams.
     
    WB5YUZ likes this.
  7. AA5CT

    AA5CT Ham Member QRZ Page

    re: "Amen to that! Radials, radials, radials and more radials are the answer for success with any inverted L. "

    This breaks my heart; (and, I just have to say this :oops:) What a needless waste of materials! There are more cost-effective ways to get on 160 (and even 80.)
     
  8. KI8DJ

    KI8DJ Ham Member QRZ Page

    I have been using a bushcomm 40 through 6 meter ocf and it works great most bands do not need a tuner why mess with a bunch of radials. I have no rf in shack of course I only run 100 watts.
     
    KG7QJB likes this.
  9. AJ5J

    AJ5J Ham Member QRZ Page

    Using plenty of radials could hardly be considered a waste of materials! Anyone wishing to maximize performance out of an inverted-L will be wise to do so.

    Yes, there are plenty of other ways to get on 160 but that is not the point here---I was merely pointing out the reason the OP was not pleased with his L.
     
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    I think that 'WPA's point is that a 160m antenna only requires ~250 ft of wire if it is a dipole or even less if it is a vertical loop. A decent inverted-L will require 127ft of wire for the driven element and over 2000ft of wire to have a decent (not great) radial field.

    I add, the inverted-L will waste more than half the transmitter's power heating the dirt around the antenna (regardless of how many radials you have), and pick up much more noise than a dipole or loop...
     

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