On occasion I have had similar problems with one of my 40-2cd's at 123'.
I believe that it is because I did not originally open up the traps, replace
the (most likely) rusted aluminum screws and reseal. I had significant
RF problems in 2 contests with fluctuating SWR and audio, RF in the shack,
etc.
I am only 20 miles from Long Island Sound (a very, very large body of salt
water)
and you can see it from the top of my tower. I have found significant
corrosion on many relay
boxes outside - no doubt from the rain/snow in coastal storms which comes in
from the
Atlantic and LI Sound.
I am sure that corrosion is that problem here and with your QTH on salt
water, that
makes it even more likely as your culprit too.
However, before you assume that it is the feedpoint, check the PL259 and
where it is connected
on the end of the coax coming down from the tower.
In another contest, I had an intermittent with the same 40-2cd and it turned
out that the
large temperature changes over a few months caused the PL259 to loosen
slightly
and then arc with 1500 watts going through it. This caused the intermittent
and there was
a black carbon buildup on the PL259 and the SO239 where it was connected.
Cleaning off the carbon and screwing the PL259 on with a large wrench
cleared up
that problem.
Try the simple (and not so obvious) fixes first.
GL!
Bob KQ2M
> On 40M, which is usually my best band here on the ocean, I started
> having intermittent spells of signal masking. All signals would
> suddenly drop about 3-4 S units with a slight noise mask and then
> reappear normally after an interval of 45 seconds to several minutes. I
> decided the FT1000MP was the culprit, so took it out of the line and
> replaced it with the FT-1000D. Problem persisted. Took the ATR-30
> antenna tuner out of the line thinking perhaps the antenna switch was
> the problem (Use the tuner to reach the SSB part of 40M). Still
> persisted. Then I noticed that the SWR on the 402CD was fluctuating
> from 1:1 up to 3:1 that appeared totally random. No wind, so the 402CD
> was perfectly still. I Run the radios barefoot on 40 and 80. Too much
> RF in the media room next to the shack to run HP, not to mention setting
> my alarm system off every few minutes.
>
> Background. I recently rebuilt the 402CD after a tropical storm took it
> down last fall. Mostly new aluminum, applied the Leesom upgrades, and
> installed new coax (9913) feed line. I suspect a corroded feed point
> connection even though I just put the antenna up several months ago with
> liberal applications of coax seal, etc. I did put in a few
> strategically placed aluminum rivets in the elements, and four SS screws
> in the tips. (High winds here sometimes blow the tips out of the
> elements.)
>
> Any suggestions or ideas before I tackle rebuilding the feed point on
> the 402CD which is way out there. I did put it up with an extra TH-7DXX
> mast to boom clamp which will let me tilt the boom down so I can reach
> it.
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