Topband: Problems with inv L on pier over salt water

[Grant Saviers]

Important facts about salt water are the attenuation of a wire submerged 
10" at 1MHz is -87db and at 4S/m the conductivity is 10,000,000 times 
less than copper wire.

Putting a single radial in a lossy medium doesn't work very well, 
whether it is dirt or saltwater.  Radials elevated in low loss air work 
very well, especially over salt water.  They should not connect to the 
water just as elevated radials over land should not be grounded.

Modeling shows that one elevated radial over salt water has a few db 
skew in the pattern but with 5 to 6 dbi very low angle peak gain. With 
two radials the pattern is nearly perfectly symmetric.


These are the far field benefits of the ~1000x higher than earth 
conductivity of salt water, so the salt water needs to extend out 5 or 
so wavelengths.

Grant KZ1W



On 1/8/2020 12:41, Ignacy Misztal wrote:
> There was a report from an expedition where the radials in water did not
> work well but over water did. Over salt water, one radial (counterpoise) is
> enough and more do not add performance.
> I used Expert 1.3k with a tuner. The amp turned itself off hundreds of
> times over the past few years due to wrong antenna or something going
> wrong, with no consequence. The way it should be.
> 
> Ignacy, NO9E
> 
> On Wed, Jan 8, 2020 at 2:35 PM Rik van Riel <riel at surriel.com> wrote:
> 
>> On Wed, 2020-01-08 at 12:01 -0600, Cecil wrote:
>>> I’m far from an expert but if you were over salt water I would have
>>> placed the counterpoise in the water.
>>
>> Word of the day: skin depth
>>
>> Having the counterpoise over the water means the antenna
>> current goes through the (copper) counterpoise, of known
>> resistance.
>>
>> Dropping the counterpoise into the water might mean that
>> the current will be split between the counterpoise and the
>> water, at an unknown (and changing with the waves and tides)
>> proportion.
>>
>> That could be better.
>> It could also be worse.
>>
>> Could it damage the antenna tuner, if it changed
>> too quickly? Who knows?
>>
>> Now what might make some sense is to have a few
>> shorter wires come down from the feedpoint and
>> into the water, to add additional paths for the
>> current, without impeding the path through the
>> counterpoise.
>>
>> I have no idea how much that could help, though.
>>
>> --
>> All Rights Reversed.
>>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
>