Comet GP-9 VHF SWR Issue

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LakeMan2

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I have a new Comet GP-9 dual band antenna. When I put it up and checked it out with my analyzer I found that the VHF/2M bandwidth is very, very narrow. It has an SWR of 1.18 about 500kHz below center but the edge of band SWR was 2.6 on the low edge and 4.2 on the high edge (the difference between high and low edge is partially due to being a little off center). The SWR plot is a sharp V with a slightly steeper rise on the upper band half.

The UHF/70cm SWR looks good being fairly flat across the band varying between 1.2 and 1.35.

Just to make sure it was not a coax or other system problem, I replaced the GP-9 with a GP-6 I had and everything looked good. VHF with the GP-6 (everything else the same) was below 1.5 across the band.

The high side VHF is the problem. I read about cold solder joints. I took all three sections apart tugged on all the joints, and nothing felt "loose". Unfortunately the foam spacers are attached at every solder joint so I can't inspect them without ripping the foam off. I have been reluctant to do that as I am considering sending the antenna in for warranty repair. I would prefer to fix it at home but I am really wondering if a solder joint would cause what I am seeing (since the center freq has very good SWR) or if it is more likely that the antenna is simply not tuned well. Given that for the VHF it is a 5/8th X 3 (and the UHF is 5/8th X 8) I currently don't know enough on how to tune that.

So if it is really likely that it is just a solder joint, I will tear all the foam off, see if I can find a cold joint and re-solder it. If it is more likely to be poor tuning, I will send it in for warranty (unless I find info that suggests that re-tuning it is relatively straightforwards, which I doubt).

Obviously I am hoping to get some opinions here if it is likely a cold solder joint or a tuning issue?

Thanks
 

LakeMan2

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Feb 21, 2014
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Are you looking at this website from K3DAV that refers to the GP-9 SWR problem (and fix)?
Comet GP-9 VHF/UHF Ant. - K3DAV.com - Amateur Radio Operator
Regardless, the Comet manual does show a low SWR in a pretty wide swath near the tuning point, so it appears something is not right with yours....
Yes I saw that site, amoung others that mention the cold solder joints. When people talk about that I get the sense that the VSWR goes bad across the board, not just at the band edges. But again I am not sure...
 

popnokick

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The mfr spec sheet shows SWR to be no higher than 1.3 from 144.5 to 147.5, centered on 146 mHz. If you're measuring something different then you have an issue with the mfr. They may contest it and ask you to perform some other tests. But all you're asking is that they meet their advertised spec, which is in some places required by law. However, if you attempt your own repair without their authorization, it could result in them saying they cannot accept the return of it for exchange or credit.
 
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