New Comet GP-3 worse than Slim Jim??

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N8SAN, Mar 17, 2018.

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  1. N8SAN

    N8SAN Ham Member QRZ Page

    OK. What's wrong?
    I have a brand new GP-3, flying at 30'. I also have a slim jim at 25' or so.

    The GP-3 is by far 10x worse than the slim jim.
    I can hear the local repeater and the airport perfectly, but when I talk to my buddy, 9miles away simplex it's downright atrocious.
    At 50 watts he said I'm in the mud, and he barely breaks my squelch. I connect back up the slim jim, full quieting both ways at 15-20 watts.

    OK full disclosure time, I'm using RG6 with F connectors and PL259 adapters. BUT I'm using them on the slim jim too. I'm not looking for absolute 100% best of the best no loss performance.
    Any thoughts on this issue? If the slim jim and comet were the same I'd buy into the coax issue. But seeing as the slim jim works so well, I don't know.
    I don't want to order up 120$ worth of coax and have it be the same.
    I COULD swap the slim jim coax with the comet, but I'll have to pull the comet back down, for the 3rd time. But might as well as it's not operational in it's current state.

    SWR on 2m 147.4700 1.2 @50watts forward.

    Photo for reference.

    Last edited: Mar 17, 2018
  2. AI6AK

    AI6AK Ham Member QRZ Page

    Might be an issue with the antenna itself. When I first got my GP-15 the SWR was through the roof. I loosened the allen screw at the base and slide the cover off. The internal joint holding the base and antenna was missing the small screw and the pieces were barely touching. Simple fix and worked perfectly after that. Something to check.
    AK5B likes this.
  3. N8SAN

    N8SAN Ham Member QRZ Page

    Oh ok. Something to check for sure.
    My SWR is perfect however. Stranger things have happened.
  4. AK5B

    AK5B Ham Member QRZ Page

    If you're worried about the slight impedance mismatch by using RG-6 all you need to do is cut the coax multiples of half-wave lengths long and it will repeat the impedance seen at the antenna feed point. That's what I did with a 6M antenna fed with Amphenol RG-6 that I put up recently and the match is 1.1:1.
    No need for new coax---just factor in the velocity factor when computing the length. this makes it a piece of cake and is the calculator I used



    PS: I suspect something like the screw or a bad connection is at the root of your problem, too. That Comet should outshine that J-pole 7 days a week.
    AJ6O, KG7QJB, W6KCS and 2 others like this.
  5. N8SAN

    N8SAN Ham Member QRZ Page

    You would think so!!! But wouldn't it show up with SWR?

    Forgot to add.
    Another anomaly. I had pulled it back down to check my connections, and it was about 10' above the ground. Significantly better, NOT GREAT by any means but better. Once I raised it back to 30' same results. The feed line IS paralleling the rotor control wire. But obviously it wasn't running the rotor at that time. Anything to that? I should be able to just pull power from the rotor box completely and confirm.
  6. N8SAN

    N8SAN Ham Member QRZ Page

    No issues with rotor wire.
  7. AK5B

    AK5B Ham Member QRZ Page

    The rotor wire, tower and all other cables nearby should not have the slightest bearing on this since RG-6 is well shielded and is coaxial to begin with---but perhaps there's a problem with those adapters you're using. Certainly another place to check.

    I avoided the F-to PL259 adapters altogether by soldering the RG6 center conductor (only) and relying on physical contact of the aluminum shield to the UG-176 for both ends of my 83-foot run (thanks to KC8VWM for coming up with this method).

    It is also odd that your Comet performs well at 10' but not at 30'---maybe ther's something off with your feedline or adapters somewhere along the line. Hope you can figure it out---good luck.


    WZ7U likes this.
  8. KD6RF

    KD6RF Ham Member QRZ Page

    Try it on a few other stations - it is possible (but probably not all that likely) that you have a destructive multi-path null at that antenna height for a particular direction.
    N3AB, AG5DB, AK5B and 1 other person like this.
  9. WZ7U

    WZ7U Ham Member QRZ Page

    I was thinking a similar thing. My thought was either a null or the antennas pattern was going over the other station at that height. I've never modeled that antenna (well, any antenna) so I don't know the take off angle and the only other thing I noticed was the apparent proximity to the HF beam. At that camera angle it looks kinda close; maybe move the yard arm down about 10' and recheck?
    AK5B likes this.
  10. N8SAN

    N8SAN Ham Member QRZ Page

    Oh interesting! I'll try it.

    The takeoff angle is very interesting. But wouldn't my receive from him be fine? My receive from him is also degraded. But certainly not as bad as my signal to him.
    He's using the same J pole slim jim FYI.

    It is interesting that my local repeaters and airport receive fine.

    The distance form the top of the Comet to the Mosley is approx 5'.

    I pulled it down again and took it apart. The set screw was a touch loose, but not falling out.
    The connections look pretty good to me.
    comet 1.jpg comet 2.jpg

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