Spent today putting back up all the antennas I took down for the hurricane
which passed us by (Thank you Lord). Decided to see what I could do about
getting the 402CD SWR below 2. since it has always been high but always
worked OK. Here's the scenario:
My house is oceanfront, about 150 yd. to the ocean. House is at 18'
elevation, three stories with flat roof at 45 ft. 10' Glen Martin tower
with 18 ft of mast, 4 ft into the tower turned by a T2X. The 402CD was
about 2ft from the top of mast and either a A4S or TH-7 just above the mast
bearing. The tribanders always worked great with very broad and low SWR's
on their bands. The best SWR on the 402CD was 1.9 at 7040 which was OK with
me. I put up the 402CD by its lonesome today at 2ft above the mast bearing
after taking it apart for a good cleaning, replaced all the hardware that
showed rust and replaced the coax since it was showing some evidence of salt
penetration. Re-measured and set it halfway between the CW and low-fone
setting per K7LXC's "secret setting." Measurements were taken with a
MFJ-259 and with my Daiwa SWR bridge which is fairly accurate.
Beam pointed North SWR is:
7.000 3.0
7.070 2.5 (Best)
7.180 3.0
Best SWR is at 18.800 1.1 (!!!)
Beam pointed West:
7.000 2.8
7.070 2.0
7.180 3.0
Obviously I have some interaction with something since the SWR changes for
direction, but what? The house is concrete and steel and I have some
aluminum railing directly under and behind the tower but it is only about 10
ft long. Has anyone experienced a similar high SWR with their 402CD? I
moved the 402CD up about 5 ft on the mast and it made no difference at all.
I then installed the A4S just above the mast bearing and it had its usual
flat SWR except now on 15 there is some interaction because the SWR there is
now 1.9 to 2.0 from 21.000 to 21.250. With only 4 ft of spacing I would
have expected even more of an interaction.
On the air checks with the 402CD shows it has good F/B and plays quite well
but I would like to get the SWR down. On the air tests with the A4S and it
performs super as always. Sure would like to get the 402CD tamed while I
have all this antenna energy and before contest season in a couple of weeks.
I just bought an Alpha 87A and I understand they like fairly flat antennas.
Suggestions, comments, troubleshooting tips? This one has me buffaloed.
Jon Hamlet, W4ZW
Casey Key Island, Florida
"A little bit of paradise in the Gulf of Mexico"
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