Comet GP6

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KN6OYS, May 31, 2021.

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  1. KN6OYS

    KN6OYS Ham Member QRZ Page

    I have a Comet GP6NC and want to convert to GP6 which would entail lowering the frequency bands which as far as I know means lengthening. Would like some advice. Thanks. KN6OYH Phil
    Last edited: May 31, 2021
  2. K1LH

    K1LH XML Subscriber QRZ Page

    Ideally you'd want to find someone with a regular GP-6 who is willing to take it apart and make a careful set of measurements of lengths between the coils and the coil sizes (diameter/turns, cap values etc) from which you can compare the NC version to see if the element lengths are different, or if the difference in tuning is done with-in the matching network.

    If the element lengths are different (distances between the coils etc) then it might be as simple as modifying yours to match.

    These are phased as:
    144MHz: 6.5dBi 5/8 wave x 2
    440MHz: 9.0dBi 5/8 wave x 5

    If you look at the antenna element you should be-able to recognize the 2 longer 5/8 sections on VHF, and the 5 shorter 5/8 sections on UHF - it will likely involve lengthening each of those sections the right amount to move each band down, keep in mind the shorter UHF sections make up the overall lengths of the longer VHF sections.

    The NC covers 153-157 and 460-470, VHF needs to be lowered around 9 MHz, and UHF around 20 MHz.

    With out another GP-6 as a reference it might be advisable to create a copy of the element to experiment with first, or create a drawing of it we can look at to help identify whats what.

    An antenna analyzer that covers VHF/UHF would also be useful when attempting to re-tune it.
    KN6OYS and AK5B like this.
  3. KI8DJ

    KI8DJ Ham Member QRZ Page

    Probably too much trouble to do it, housing might be too short. Just buy the right antenna. One of the knockoffs like Tram or jetstream will save you some bucks.
    KN6OYS and AK5B like this.
  4. K8JD

    K8JD Ham Member QRZ Page

    Converting a U/VHF GP vert to 80 M requires another 65 ft of radiating element !
  5. W4EAE

    W4EAE XML Subscriber QRZ Page

    The fiberglass shell for both the GP-6 and GP-6 NC are the same, so it would be possible to fit the radiating element inside it. As already stated, it might be more trouble than its worth.
    KN6OYS likes this.
  6. KN6OYS

    KN6OYS Ham Member QRZ Page

    Thank you all!!!

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