Michael Tope wrote:
> 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 think it'd be comparable or better than a normal earth ground close to
the antenna system and give a more predictable elevation pattern.
73
Roger (K8RI)
>> 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.............................
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|