ARRL-SECTION: CT
CALLSIGN: N8RA
CONTEST: ARRL-UHF-AUG
CATEGORY: SINGLE-OP ALL LOW MIXED
Band Mode QSOs Pts Grd
420 CW 2 6 1
420 USB 1 3 0
Total Both 3 9 1
Score: 9
I cannot tell you great tales of working awesome contacts, so instead
decided to bore you with my contest prep. I'd been meaning for some time now
to put up an antenna for 432 and get a toe in the water there. The
approaching contest weekend was a good incentive for moving that project
along. For contesting, I had wanted an antenna that did not have a very
narrow horizontal beamwidth. Many of the products out there had just too
many elements for me. I know, I know, a shorter antenna will not have as
much gain, but I figured if it works out I could stack one or two more with
it to make up for that. Cushcraft has a 6 element FM band antenna that
looked close to what I was hoping to find; and I noticed that at one time
they were selling a cousin of it for the lower portion of the band, so I was
encouraged that I could easily get that to work. A comparison of their two
assembly manuals indicated that the parts were the same and the only
difference was in the adjustment of the gamma match. That seemed a bit
troublesome, but I had bought one anyway, figuring it would be an easy
matter to modify it myself. Boy was I wrong. When the antenna arrived, I
measured the element spacing dimensions (they were not in the manual) and
proceeded to model it in EZNEC. This design seemed to be a bit high in freq,
even for the FM band, and down at 432 it was close to a figure eight
pattern; not what I wanted. This result then led me down a long road of
looking at various other designs, and trying to second guess what the
original antenna was all about. Eventually, I settled on converting the
Cushcraft to a 6 element ARRL Ant Book OWA, modified slightly to fit the
Cushcraft boom and 3 of its original element mounting holes. My reasoning
was that an OWA's wide freq range would be tolerant of any of my minor
mistakes in construction and perhaps hold its performance better under rain
or ice conditions. At the same time, I decided to use ¼" rod for the
elements, something the local Home Depot had a good supply of, as well as
amateur vendors like Texas Towers. For my playing around, the Cushcraft
antenna was a good choice. It has a nice set of SS hardware, and I really
like their element mounting: getting it up away from the boom helps minimize
the effect of the boom on their length, and minimizes my errors in
correcting for that. Second, their gamma match parts are nice and it is easy
to adjust. Building a matching device that worked has always been a big
frustration for me in past antenna projects.
But other things took priority and this paper design was shelved for months
and now was reactivated the day before the contest. After finding all the
parts, I set about constructing the antenna. Getting the boom drilled and
the elements cut to length was more difficult than I thought. Building these
tiny antennas is a lot harder than the HF yagis I've built. After it was all
together, the best match I could get was centered at 418 Mhz, and it was
only a few MHz wide. Something is wrong here. Went back to the analysis
again that night and I realized my mistake was in not believing the results
I had modeled earlier and instead trying to fudge for the element mounting.
Back to the garage the next morning, I needed to cut 0.2" off the tips of
some elements, 0.16" off others, etc. It really gave me a good appreciation
for what a wonderful service K1WHS's well-equipped shop does in providing
antennas to amateurs.
This time, after a little bit more touch up, the match centered on 431 Mhz
and the 2:1 bandwidth was about 12 Mhz. And this time the match was fairly
easy to find, and I took that as a good sign. Now, how to put this up for
the contest? Where I want to put it is not ready (another long tale) and I
wanted it within reach for more measuring and fiddling. Besides, I am out of
time. So 2 hours after the contest started, the pouring rain had stopped,
and I put the antenna on a 5 foot piece of Al tubing and suspend it from the
gutter on my second level front porch. In order to be close to it to turn it
by hand, I decided to set up my 432 transceiver (FT-897) ?plein air? style
on the table on that porch and operate from there. When all was plugged
together, I heard a few weak signals. I tried to call them, and what's this?
The 897 goes nuts every time I try to transmit! I try some ferrites on the
cables, rerouting them, and finally conclude that I am just too close to the
antenna. The radio seems to transmit OK into a dummy load. $%^&#$@!! I quit
for the evening.
Sunday morning I decide to put the 897 back into the basement hamshack,
where it will be farther away from the antenna, and tied into the grounding
scheme down there. But now I need another length of coax to go out the shack
window and across the side of the house and up to the porch. All I have with
connectors on it is an old 25? piece of 72 ohm RG-11. What the heck, connect
it up, the SWR at the shack end is now about 2:1 but the 897 is able to
transmit. The received signals are still pretty weak and nobody hears me
call them. Possible reasons: 1) they are pointing away from my direction and
running considerably more power than my puny 5 watts, 2) an antenna only 11'
off the ground close to the house and pointing into wet trees is not really
too good, or 3) the antenna itself is NG. Maybe all of the above, well I
tried, and later when I can get it in the clear, maybe I can learn more.
Later in the day, with only an hour to go, I hear no one on the band. I
decide to park on the calling freq and call CQs on CW. After the first few
calls I nearly fall off the chair when a rover answers back. A few minutes
later, a weak local calls me on SSB, and when he turns his antenna toward me
he goes WAY up in S reading. Wow. Then a bit later, I get an answer from
another station 35 miles away off the back side of the antenna, in my worst
direction, uphill, and thru the house. So something is working, and progress
was made this weekend. I hope to have this antenna up higher (and rotatable)
for Sept, but we will see how that goes.
Chet, N8RA
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