High SWR after a few seconds of TX -- rain?

Hello,

Today I noticed that, after transmitting for a few seconds, the high SWR warning would come on and my signal would drop off the transponder. It has been raining all day. I have the TX feed to the dish covered with a plastic bag. I did have a high SWR issue in the past but the bag cured it, at least until today. What seemed odd was that the SWR was low and my signal on the downlink strong for the first few seconds, then the SWR spike. I hope it is just rain that is causing the spike, but why would there be a few seconds of low SWR at the start of a transmission? Any ideas?

Setup: FT-817ND, SG Lab upconverter and 20w amp, BamaTech feed, 80cm dish

73, Bill OM3BD

Quote from HB9SKA

Is water in the plastic bag ? I'm not sure if a plastic bag is a good solution.

There does not appear to be any water inside the bag, but there is water on the outside of the bag. It is also foggy and damp. If water is the issue, what accounts for the few seconds of low SWR at the start of each transmission?

Sunny today and all is back to normal, guess the problem was weather related. Any ideas for better weatherproofing of the feed?

Quote from DD4YR

What SWR warning?

Really measured SWR with what equpipment?

Try same procedure on a dummy load instead the antenna to find the real reason.

The FT-817ND gives a high SWR warning on the main screen. Yes, I know this is only the SWR to the upconverter input, not the SWR to the antenna, but they seem to be related.

Can we use a regular dummy load at 2.4 ghz or is something special needed?

73, Bill

Quote from DD4YR

Bill,

I think there is absolutely no relationship between the SWR shown on the FT-817 and the SWR from the 2,4 GHz PA output.

Your problem seems to be between the FT-817 and the transverter input.

Cable connection flooded or something.

The dummy instead of the 2.4 GHz antenna must of course be suitable for the frequency and power.

But, as you write this, you have to look for the error between the FT-817 and the transverter anyway.

You can also connect a dummy instead of the transverter and watch the VSWR when it is wet.

73 de Robert

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Thanks, Robert. Any suggestion where to buy or how to build a 2.4 ghz dummy load?

Makes sense that the problem was between the FT-817 and the transverter input, but all is working fine now. The cable connection between the FT-817 and the transverter is indoors and has not changed. The only thing that has changed is the weather -- sunny today, rain yesterday. If I can get a dummy load and it happens again, I'll do more testing and checking.