[TowerTalk] Vertical in pond

[Michael Tope]

Dan Zimmerman N3OX wrote:

>"Could a fresh water pond have sufficient minerals dissolved in it to
>be helpful?    Even if not salt in the water, I think it could be useful
>in the same way."
>
>I can tell you that water that's been corroding some steel and brass for a
>few months doesn't make a very good coaxial transmission line dielectric at
>VHF/UHF... but it's not exactly a dead short either.
>
>I filled up a three foot long slotted line with such water today and
>measured transmission through it (in fact, with the intention of measuring
>the RF conductivity of this water) and got about 17dB loss in 88cm of line
>at 315MHz.
>
>So I think i'm calculating this right:
>
> line attenuation  in dB/m = 8.686 * pi * sqrt(permittivity) * loss tangent
>/ free space wavelength
>
>I know I was in the ballpark of 19dB/m, and have dielectric constant = 80,
>so I get an effective loss tangent of about 0.07...
>
>I find elsewhere that loss tangent = 2*conductivity / (permittivity *
>frequency)
>
>Backing out the conductivity from that gives about 0.007 S/m... a tad higher
>than EZNEC "Average Ground"
>
>Seawater is 4S/m
>
>Errors may abound given the hour.
>
>For a totally different perspective on fresh water, the stream near my house
>over the last week seems to have  fluctuated from 0.08S/m to 0.18 S/m.
>
>http://waterdata.usgs.gov/md/nwis/uv?cb_00095=on&format=gif_default&period=7&site_no=01649500
>
>Seems like maybe my tank's water is a lot fresher than the stream , but
>neither is quite seawater.   I don't know how USGS measures conductance or
>at what frequency.
>
>73
>Dan
>  
>
That water station data is interesting, Dan. There seems to be at least 
some correlation between that big conductance spike and the turbidity. 
Perhaps it depends on who is flushing their toilet upstream :-)

73, Mike W4EF.............................