New GP-15 Antenna and The Undead GP-1

During some testing a couple of weeks ago, it became clear that something was up with my trusty old Comet GP-1 VHF/UHF antenna.  The SWR was way off, a little above 3:1 in the 2m and 70cm bands, which is to say that, rather than radiating RF energy, a lot of it was being bounced back into my transceiver and getting turned into heat.[1]

Now, I'd had my eyes on an antenna that would add the 6m band as well[2], and the Comet GP-15 checked all those boxes, as well as adding about 3 dB more gain on 2m and 70cm.  The only real downsides are at 8 feet length it's twice as long as that discrete little GP-1, and it has a somewhat lower wind speed rating, 112 vs. 135 mph.  That lower wind speed rating turns matters from "set it and forget it" to "another item on the hurricane checklist to bring inside."

The GP-15 is kind of an odd antenna.  It relies on one extra-long, tunable radial (see inset pic) to adjust its resonant frequency.  The instructions have a helpful chart showing radial length setting vs. resonant frequency.  I'm really only interested in the 50 to 51 MHz part of the band, where the SSB voice, various beacons, and allegedly some digital traffic hangs out.  (see chart linked below)  The rest of the band, 51 thru 54 MHz, is primarily set aside for repeaters and local FM use.  Not so interesting where there are no local repeaters or users.  Also, the instruction sheet flatly indicates that it has a useable bandwidth of 1 MHz, so choose which quarter of the band allocation you want wisely.  Accordingly, I set things up while still on the ground for my region of interest, mounted it on the roof[3] and.... it was resonant smack in the middle of the band, useable across the entire 4 MHz of the band.[4]  So I tweaked it a little lower to optimize for my interests and called it a day.

Still haven't gotten any 6m band openings[5], but in the wake of the cold front currently blowing through, some tropoducting is in the cards for early next week.  Contacts on 2m & 70cm however report that my signal is much stronger, so there is that. 

Finally, with the new antenna installed, it was time to dig into what went wrong with the 5 year old GP-1 and that 15 year old length of LMR-400 coax.  On the bench both tested out as working perfectly, so your guess is as good as mine.  Maybe I'll have something to sell on the Monday night net, though I'll test them all again before trying to offload them.

Anyway, here's a link to a good set of pdf charts showing what's where on the commonly used VHF & UHF ham bands.  Get your GP-15 (or GP-1, or any number of other interesting and useful items) here.

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[1] No wonder the fan was running so much!  I could barely get through a Monday evening net session without it topping 140 degrees.

[2] Why?  Because it's there, that's why!  Stop asking foolish questions.

[3] A process akin to conducting an EVA on the ISS.

[4] Yes, of course I hauled an SWR meter and LiFePO4 battery up on the roof with me, along with many other potentially useful items – wrenches, vice-grips, multi-tool, drill & driver bits, etc.  And of course an FRS radio to stay in contact with my safety man on the ground.

[5] and hence no contacts, though there is one guy over in Carrabelle who can do 6m I ought to call.