Comet GP1 vs GP3

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI4POT, Feb 22, 2021 at 11:34 PM.

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  1. KI4POT

    KI4POT Ham Member QRZ Page

    Between those two antennas, is there any appreciable difference in performance if both are mounted so that their tops are at the same elevation (ie the mounts would be a different heights).

    I live in an HOA, but can have an antenna in my backyard as long as it's not visible from the street out front. I have a mast that is about 1.5' taller than my gutter. I could mount the Gp-3 right above the gutter or the GP-1 at the top of the mast (1.5' higher). The GP-3 would put more antenna in the air, but because it would still be behind the roof, would it perform any better (the backyard has similar townhomes facing us, so I have essentially the same barrier on that side, just further away). The tops of either antenna would be at roughly the same height.

    I'm looking to work SOTA activators in the Blue Ridge Mountains, Skyline Drive, etc about 30-80 miles away. I'd also use it for general simplex operation as far out as I can "reach".

    A beam or yagi is not in the cards, it can only be a vertical.

  2. K3XR

    K3XR Ham Member QRZ Page

    Go to one of the dealer sites like DX Engineering they have the specs (gain figures) for both models. Not surprisingly the GP-3 has higher gain.
  3. KI4POT

    KI4POT Ham Member QRZ Page

    I've read all that. Hence my question.

    I'm wondering if the lower gain antenna will out perform the higher gain version if mounted slightly higher (1' higher). Both would be behind my roof and the tops of either would be at the same elevation. The difference would be the base elevation.

    Or maybe I'm overthinking this. I'd prefer to go with the GP-3, but I also don't want it to be a magnet for the HOA's attention.

  4. W4EAE

    W4EAE Premium Subscriber QRZ Page

    A one foot change in height is not going to make any appreciable difference--unless that one foot gets you clear of an obstruction--so the higher gain antenna should perform better than the lower gain antenna if mounted a foot lower.

    Also consider that the 'height' of a vertical is not dependent upon the height of the top of the antenna, but the height of the center of the antenna.

    None of this will matter much if there are structures in the path in every direction. If your mounting position is only 1.5 feet above the gutter and you have a pitched roof, your signal will have to travel through the structure whichever antenna you choose. If you are trying to reach stations 80 miles away--even if they are several thousand feet higher than you--the actual pitch from your location to theirs is quite shallow.

    If townhouses are surrounding you, and all are of similar height and spec; your best bet for an antenna not seem from the street might be to put it in your attic. The signal will have to pass through your structure at the height you indicated even if it is outside. It will have to travel through less structure if it is in your attic. Alternatively, mounting it as high as possible in the center of your back yard would probably yield the best results.

    All that said, 80 miles will probably be a challenge with any antenna in the situation you describe. At a bare minimum, getting the antenna above the roof line would be necessary; and that is out for you.

    In terms of which antenna would be better, I would get the tallest one I could fit in my attic if I were you. I think 80 miles is probably out without some tropospheric assistance (luckily, that should become quite common in Spring and Summer in your locale). Thirty miles is probably workable, depending upon the other station or repeater.
  5. KI4POT

    KI4POT Ham Member QRZ Page

    Thanks. 80 miles is the longest distance, more likely is 30-50 miles (lots of summits in that range).

    If I were to go with an antenna in the attic, I would have to go with the shorter one and the middle will still be about the same elevation. However, I would then have to route coax to my operating position, which is non-trivial. Basically this house stinks for radio, every option includes some annoying compromises, which is why I have been a portable op since the beginning. :rolleyes:

    Putting the antenna in the middle of the backyard is a nonstarter. Not only do *I* not want it there, my wife would object. Also, the space between the townhome rows acts as a wind tunnel, so any tall structure (and this would be nearly 30' tall to get the antenna over my house) would need significant bracing and guying to withstand the wind. That's just too much effort and expense.


  6. KO4HFX

    KO4HFX Ham Member QRZ Page

    I had the same decision to make a month ago and went with the GP-3. Got mine from DX Engineering and spoke with one of their tech support folks. The reason for my decision was the increase in gain--pretty significant. I'm in a situation to be able to take advantage of the increase.
  7. KM3F

    KM3F Ham Member QRZ Page

    An increase in Gain is the flatening of the Omni pattern.
    It dosn't just roll off the top end of an antenna.
    I use a 19 foot Co-Linear and it's pattern is nearly flat toward the horizon with about 10db of gain on 2m..
    I work into northern repeaters over the Pa. Pocono mountains from the Lehigh Valley and a lot of others all around in Pa, NJ. and southern NY. state.
    I have to uses a 10 or more element beam to beat it.
  8. K6GBW

    K6GBW Ham Member QRZ Page

    People have a tendency to think that gain is always better. But the truth is that if you are primarily working repeaters then having too much gain can be a detriment. Both the GP-1 and 3 are good antennas. I use the GP-1 on a 25 foot mast here in the Los Angeles area where we have repeaters at very high elevations on several different mountain ranges (Hollywood Hills, San Gabriels, Verdugo) as well as Catalina Island. I routinely use that same antenna to talk to mobiles at about fifteen miles distance in the San Gabriel Valley and the Los Angeles Basin. For VHF and UHF you would have to go to extreme measures to do much better. My advice is to pick the antenna that is easer to mount and run good coax to it (LMR400) and then don't give it another thought.
  9. KH6AQ

    KH6AQ Ham Member QRZ Page

    144-148 MHz, 3.0 dBi
    442-450 MHz, 6.0 dBi

    144-148 MHz, 4.5 dBi
    440-450 MHz, 7.2 dBi
  10. KI4POT

    KI4POT Ham Member QRZ Page

    I'm mainly (entirely?) interested in simplex. While I understand the benefit of LMR400 (have used it in the past), the run from the base of the antenna to my radio will be less than 20' and pass through one of those flat Comet window-feed-through jumpers, so I don't think LMR400 will provide much benefit over the RG-8x I have already.


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