>From your message:
> I don't think it's in the switching relays (SO2R box.)
I sort of suspect the relay box is the problem. I have seen 'lazy' relays in
non radio applications do exactly what you are describing, that is, poor
continuity until hit with a current load. It should be easy enough to
eliminate the SO2R box as the problem, try putting the antenna circuit in
question on a new port or swap ports with another antenna. Also try
manually selecting the antenna via the SO2R box a few times before hitting
the transmit switch and see if there is a change.
I am not familiar with your antenna so if someone has knowledge on it, now
is the time to chime in.
> -----Original Message-----
> From: Dick Green WC1M
> Sent: February 10, 2008 8:37 PM
> To: Tower
> Subject: [TowerTalk] 40-2CD SWR problem
> Hi All,
> I have a strange problem with my Cushcraft 40-2CD. The symptoms are:
> - The first time I select the antenna and transmit, say at
> 50W, the SWR is very high -- somewhere between 10:1 and infinite.
> - Depending on which radio I use, sometimes if I send a dit
> at about 100W, the SWR returns to normal, about 1.5:1.
> - The reason it depends on the radio is that one (FT-1000D)
> folds back power dramatically when SWR is high, while the
> other (Orion) doesn't. Usually have to use the Orion.
> - Sometimes even 100W isn't enough, and I have to transmit at
> slightly higher power with a linear to clear the high SWR --
> perhaps up to 200W or so.
> - I use an Acom 2000A amp, and it never trips due to the high
> SWR during this procedure, presumably because the reflected
> power is relatively low at 100W-200W.
> - If I keep transmitting, the SWR stays low.
> - After 20-30 minutes of inactivity, high SWR returns. If I
> give it a shot of power, SWR returns to normal.
> - This *seems* to happen more often when the temperature is
> cold, but I'm not sure there's a definite correlation.
> I've experienced the opposite of this problem: SWR low at
> low power and high at high power, when I've had contaminated
> or damaged coax or a carbon path inside a connector. But the
> symptom here suggests that something is shorting the circuit
> until just enough power is sent down the line to interrupt
> and/or vaporize it. I've thought maybe there's water in the
> cable, but that seems unlikely -- the waterproofing is good.
> I don't think it's in the switching relays (SO2R box.) The
> only explanation I can imagine is that something is shorting
> the two tubing halves inside the ceramic insulator of the
> driven element, like water (turning to ice), or frozen carbon
> or something. Maybe insect bodies? Before I put the antenna
> up, I reinforced the center tubes with smaller diameter
> tubes. I thought I was careful not to let them extend beyond
> the outer tubes inside the insulator, but maybe I
> inadvertently reduced the size of the gap between the
> elements, and it's so close that frozen moisture mixed with
> carbon is making a circuit t between the element halves.
> I've seen something like this problem once before, on a delta
> loop. High SWR and dead receive, hit it with a quick dit of
> low power and everything is OK. But it never took high power.
> I wasn't able to track that one down, and it seems to have
> disappeared after I replaced the wire (insulated before and
> after) and restrung the antenna (same balun, same coax, same relays.)
> Has anybody seen symptoms like this? Any theories?
> 73, Dick WC1M
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