Ground Probe Calculator - Page 1
Forum section: electronics / rf-microwave

author: k6sti
author_rank: Contributor
timestamp: January 07, 2024, 12:02:25 pm
content: You can measure your local ground permittivity and conductivity with a ground probe. Realistic values let you accurately model antennas with vertical and low horizontal conductors. The probe uses two metal rods a foot long spaced a few inches apart. You insert it in the ground and connect it to a VNA. This program extracts ground permittivity and conductivity from the VNA measurements:http://ham-radio.com/k6sti/gnd.htmYour antivirus software may inhibit downloading the file. Pass its URL (http://ham-radio.com/k6sti/gnd.zip) to VirusTotal (https://www.virustotal.com) to check it with dozens of antivirus programs. When you're satisfied the file is safe, temporarily disable your antivirus software, download the file, and then reenable it.Brian

author: coppercone2
author_rank: Super Contributor
timestamp: January 11, 2024, 07:42:43 am
content: I would love to see a setup with pictures that shows the physical side of the measurement to show what is considered a reasonable setup

author: k6sti
author_rank: Contributor
timestamp: January 15, 2024, 10:48:52 am
content: From the program documentation:https://www.antennasbyn6lf.com/files/ground_parameter_measurements_2.pdfhttps://www.dl1glh.de/groundconductivity.htmlhttp://www.oe1cgs.at/wp-content/uploads/2023/11/Soil_Parameters.pdfBrian

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2024, 03:01:29 pm
content: for measuring conductivity the probe looks like the correct diameter (I just glanced). I worked those formulas out before for water conductivity testers, you want long thin rods.For measuring tap water I got something like 6 inch rods spaced 1.25 inches apart IIRC.

author: k6sti
author_rank: Contributor
timestamp: January 15, 2024, 03:28:11 pm
content: The purpose of the probe is to measure ground permittivity and conductivity for use in antenna analysis software. The program can handle any probe dimensions. The only real constraints are that very short rods sample little ground while very long rods can be difficult to fully insert. The program can handle that case, too, by cascading two transmission lines. See ReadMe.txt for details.Brian

author: coppercone2
author_rank: Super Contributor
timestamp: January 15, 2024, 03:42:40 pm
content: With water, the diameter and separation and length of rods is used in a formula that kinda like ensures some linearity after a calibration. its pretty specificnot sure how it works for dirt, but I am just saying it looks generally in the ball park for reliable conductivity testing. At least I got within poland spring bottled water spec sheet 10% with a DIY probe.

author: k6sti
author_rank: Contributor
timestamp: January 15, 2024, 03:49:05 pm
content: Download the program and run it on the included file that was made with a probe immersed in water.Brian

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 19, 2024, 10:55:52 am
content: Quote from: k6sti on January 07, 2024, 12:02:25 pmBrian, I have a commercial earth test meter that uses 3 connections, one to the earth rod being tested, and the other two to probes are spaced up to 10 metres away, not a "few inches". The probes are about 10mm diameter and 250mm long.While the earth test meter is measuring only Ohms for electrical installations, I have used it to also check grounding for vertical antennas, etc.Should your tests be done with the probes further apart than a few inches?73 SJ

author: coppercone2
author_rank: Super Contributor
timestamp: January 19, 2024, 10:49:21 pm
content: I think the linearity improves the longer and more separated they are. I forgot what rod width did to the equation.

author: k6sti
author_rank: Contributor
timestamp: January 25, 2024, 05:50:46 pm
content: Quote from: Solder_Junkie on January 19, 2024, 10:55:52 amA few inches is sufficient. The software models the inductance of the wire connecting the probes, but it does not model its interaction with ground. I'd worry about that with widely spaced rods. ReadMe.txt contains several references for building and using ground probes:http://ham-radio.com/k6sti/gnd.htmBrian