Icom AH4 tuner and 500' longwire

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N7CPM, Jul 28, 2015.

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  1. N7CPM

    N7CPM Premium Subscriber QRZ Page

    Hey guys, I'm still pretty new to the fun but frustrating world of random wire antennas. Last month, I purchased a 500' spool of 14 gauge shielded stranded wire and have that up in my trees in the back forest connected to an Icom AH4 tuner mounted to the side of my house. Right now I have the tuner connected to a series of ground radials I have at various lengths all connected together over a grounding rod.

    Here is my question. I have not be having the best luck with this antenna, it works, but not as well as I would expect. The area where my radials are located is not a big space at all, so I only have about 8 radials. Would it be better to run a single, long counterpoise back into the forest? Is there a certain length I should look to use?

    Thanks guys! I always appreciate the helpful info on this forum!
     
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    Is the shield connected to the 14 Ga wire? If not, that may be your problem.

    Ed
     
  3. N7CPM

    N7CPM Premium Subscriber QRZ Page

    Oh man, my mistake. I meant insulated wire, not shielded. Totally different thing :oops:
     
  4. KJ3N

    KJ3N Ham Member QRZ Page

    If there is actually 500 feet of wire attached to the ceramic "knob" end of the AH-4, I'd say that's WAY too much wire. I'd cut it back by at least half. The alternative would be to take the 500 feet and arrange it in a loop configuration, attaching the other end to the ground side of the AH-4. If that's not practical, then an major increase in radials would probably be in order. Eight radials isn't much, IMO.

    You don't mention how the 500 feet is run, at what height, and in what sort of configuration (straight, zig-zag, etc). Without further information, it's difficult to give advice.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    How high above ground is the wire along its path from start to finish?

    What kind of "end" insulator are you using at the far end of the wire antenna?

    500 feet may be a difficult length for the AH-4, as it is 1WL long at 1.87 MHz (160m), 2WL long at 3.74 MHz (80m), 4WL long at 7.48 MHz (just above 40m), etc. Trying to match an end-fed wire that is 1/2-WL or any multiple of 1/2-WL long can be difficult and may be impossible for the tuner.

    When tuning an end-fed to be used on multiple bands, I try to avoid resonant lengths entirely.

    By "shielded," I'm guessing you mean "insulated," and not really "shielded."
     
  6. N7CPM

    N7CPM Premium Subscriber QRZ Page

    KJ3N, thanks for the info and followup questions. So the wire is up in the trees at approx 30-40ft high. It goes back mostly straight, but does zig zag a little bit. Here is an approx. graphic of the run:
    antennarun.PNG
     
  7. N7CPM

    N7CPM Premium Subscriber QRZ Page

    So I don't currently have an end insulator on the run. It wouldn't be a big deal to install one where it terminates.

    Thanks for the info regarding the length, I will look at trimming the line. I just found a site (http://www.hamuniverse.com/randomwireantennalengths.html) which seems to highlight lengths to avoid. Does this look pretty accurate to you?
     
  8. KJ3N

    KJ3N Ham Member QRZ Page

    I'd lose the last 300 feet at a minimum. Running the above configuration through EZNEC shows way too many peaks and nulls to be effective, even on 80m.
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Probably. Note that 495' and 496' length are on the list, as they should be.

    Use an end insulator that's a few inches long and make sure the end of the wire doesn't touch any tree branches or leaves.

    That is a high voltage point on the antenna, no matter what frequency you use to operate.
     
  10. K5VV

    K5VV Ham Member QRZ Page

    It's very difficult to predict the performance of a random wire antenna. There is no magic length (although there are lengths to avoid) and the rule of thumb for the ground/radial system is "the bigger the better". You can expect the tuner to get a good match and you can expect to work a few stations.

    It's impossible to say whether shortening the wire from 500' to 450', or changing the radial system from 8 radials to one counterpoise will make an improvement.

    I like random wires because they're so simple and easy to setup. But this is one part of the hobby where "try it and see" is often your best friend.
     
    W9WQA likes this.

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