Topband: Problems with inv L on pier over salt water

[Cecil]

I’m far from an expert but if you were over salt water I would have placed the counterpoise in the water.

I’d be curious what others think.

Great experience though...

Cecil
K5DL



> On Jan 8, 2020, at 11:07 AM, Ignacy Misztal <no9e at arrl.net> wrote:
> 
> I would like to share my experiences with 160m operations during the SP
> contest last December.
> 
> My rental house in St George Isl FL had a 140 ft pier over the bay. Also a
> power line to the end of the pier raising questions about RFI.
> 
> I set inv L at the end of the pier with 40ft Spiderpole, 70ft horizontal
> and 70ft radial on the pier.  Horizontal with 24 gauge enameled wire for
> low weight, and the rest with 18 ga THHN. Matching was with a transformer
> on FT140-61 and coil on T200-2. Minimal SWR at 1.84.
> 
> One hr before the sunset the EU was booming. RFI was pretty high but the
> signals even stronger. I tried to use KX3 and Expert 1.3k combination, but
> SWR become very unstable causing the Expert to turn off. I was looking for
> culprits but could not find anything. Frustrated, I was forced to use
> FT-891 at 100W.
> 
> The setup was still pretty good as several EU answered my CQ.
> 
> The next day I noticed that the radial on the pier that was touching
> underneath (salt water sprayed) had melted insulation. Apparently this
> caused sparcing and then variations in SWR.
> 
> I relocated the radial away from the pier, over the bay. The resonance
> moved from 1.84 to 1.96, and the impedance at resonance reduced from 40 to
> 25 ohms. So the pier (or power line) was loading the antenna, surely
> generating losses.  Operating with a KW was no longer a problem.
> 
> Here are my lessons:
> 1. 40ft Spiderpole is enough for highly efficient inv L over salt water.
> 2. Beware of insulated wire touching anything and especially wet and salty
> at high power.
> 3. Even with problems, the performance of an antenna over salt water is
> terrific.
> 4. Matching units do not have to be big.
> 5. With good antenna, $550 FT-891 is OK.
> 
> Ignacy, NO9E
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