Topband
[Top] [All Lists]

Re: Topband: Ground Conductivity

To: topband@contesting.com
Subject: Re: Topband: Ground Conductivity
From: K4SAV <RadioXX@charter.net>
Date: Wed, 25 Mar 2020 09:19:45 -0500
List-post: <mailto:topband@contesting.com>
W4EF said: Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible.

You are not the only one wondering about that Mike. Those are some pretty weird measurements. I have no explanation. That's the reason I continued to take measurements over a one month period and continued to get those big variations from one measurement to the next.

It's also the reason I am repeating the measurements again now, although I moved the dipole about 50 feet away from where it was before. The readings now seem to be much more reasonable and not so much variation between each measurement. I see the resonant point moving around with ground moisture content and the whole curve shifting as well but no big changes like the first time I did this. I may try to move the dipole back where it was before to see if any of the weirdness returns.

I still can't fit any of the measured curves to a NEC2 analysis by varying ground parameters and height above ground in NEC2. Note that attempting to do this also violates the NEC2 guidelines for wire heights above ground. So why should I expect to be able to do this? I have duplicated NEC4 patterns for a BOG in NEC2 to an insignificant difference. If NEC2 is wrong, so is NEC4. That doesn't leave any tools for simulating BOGs.

I have previously done other simulations for a BOG in NEC2 and the results never agree with measurements. I keep looking for model patches that may allow some useful information to be obtained from simulations.

Jerry, K4SAV


On 3/24/2020 9:46 PM, Michael Tope wrote:
Dan,

Reading that QRZ.com thread you linked to and reflecting on K4SAV's measurements and how much they appeared to vary over a fairly short period of time, got me wondering about what could be responsible. I am fairly certain that at least part of the radial system for my 160 meter vertical is over the drain field of the septic system for my cabin. Who knows, maybe a properly timed toilet flush could make the difference between working a new one and coming up empty :-)

Okay, the toilet aided pileup busting is a stretch, but seriously, I am not sure if I can think of any better explanations than septic discharge for why ground characteristics could change that quickly. I do know in some cases there can be water table very close to the surface, but I don't know how much that typically varies over the short term. My only other thought is that maybe in K4SAV's case the lay of the grass under the wire is changing slightly over time and the impedance is super-sensitive to the gap between the antenna and the ground (although I think K4SAV said that his grass was all dead).

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

On 3/23/2020 10:18 PM, Dan Maguire via Topband wrote:
Grant wrote:
If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring.
Turns out that very subject was being kicked around on a recent qrz.com thread:

https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/

Dan, AC6LA
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

<Prev in Thread] Current Thread [Next in Thread>