{"id":14259,"date":"2026-10-23T08:52:32","date_gmt":"2026-10-23T12:52:32","guid":{"rendered":"https:\/\/www.engineeringradio.us\/blog\/?p=14259"},"modified":"2026-10-23T08:52:34","modified_gmt":"2026-10-23T12:52:34","slug":"ground-conductivity","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2026\/10\/ground-conductivity\/","title":{"rendered":"Ground Conductivity"},"content":{"rendered":"\n

An important part of any medium-frequency and high-frequency antenna system is the nature of the ground immediately around the antenna system. The reason for the complex and expensive AM ground system is to create a return path for the portion of the RF wave that is not radiating from the tower. Higher ground conductivity helps this process greatly. The higher the ground conductivity, the more efficient the antenna will be.<\/p>\n\n\n\n

Ground permittivity is relative to that of free space which is 1. In general, it is a measurement of how much polarization of the ground material occurs in the presence of an electric field. Relative permittivity is a unit-less number indicating the dielectric constant. It is an important factor in ground wave propagation modes like daytime AM radio. Lower frequencies have greater depth of ground penetration and permittivity goes up. That is why low dial position AM stations have better daytime ground wave coverage per kilowatt then the high dial position stations. <\/p>\n\n\n\n

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Estimated relative ground permittivity by composition, Courtesy of em.geosci<\/figcaption><\/figure>\n\n\n\n

According to the FCC M3 map, the ground in this general area is supposed to average 4 milliMhos per meter (milliMho is equivalent to a milliSiemen). This is a very rough estimate as conductivity can vary greatly within short distances and can change depending on soil moisture. This is the reason why many AM transmitter sites were built in swamp land. Wet soil has higher conductivity and permittivity. Plus, the land was cheaper.<\/p>\n\n\n\n

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Estimated ground conductivity by frequency and moisture, ITU recommendation P.527.3<\/figcaption><\/figure>\n\n\n\n

When modeling antennas with NEC, particularly vertical antennas, the ground conductivity plays a significant part in the antenna performance. At lower frequencies, the permittivity (aka dielectric constant) also plays a role. Having actual numbers instead of the FCC estimate gives a better overall model of the antenna.<\/p>\n\n\n\n

All of this made me think about how to obtain better data. Fortunately, a radio amateur (Rudy Severns, N6LF<\/a>, Hardy Lau, DL1GLH<\/a> and Tobias Wellnitz, DH1TW<\/a>) have thoroughly documented a good procedure. This is termed “Open Wire Line<\/a>” method, which uses two metal probes that are the end of an Open Wire transmission line. A VNA is then connected to the probes and the complex impedance is measured. The resistance and reactance are then plotted along with the physical aspects of the probes to calculate conductivity and permittivity. More information can be found at How to measure Ground Conductivity<\/a> by Tobias, DH1TW.<\/p>\n\n\n\n

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Ground conductivity probe parts<\/figcaption><\/figure>\n\n\n\n

Once again, I took stock of what I had laying around and found a pretty good way to make a ground conductivity probe. The first thing is to make an insulated holder\/handle for the two metal probes. I have a large selection of oak planks, which have been used for many projects in the past. In this case, a small piece of 1 x 2 was cut down to 16 inches. I then used the router to round off the edges and laid out the holes for the probes and N connector. I finished the oak with several coats of polyurethane<\/a> to keep moisture out of the wood grain. I purchased a three foot piece of 1\/4 inch (6.35 mm) mild steel round stock, which I cut in half. Using a 1\/4 28 die, I threaded one end of each piece so I could attach it to the oak handle. The probes are spaced 50 mm apart and are 300 mm long. The steel probes were connected to the N connector with two pieces of copper strap.<\/p>\n\n\n\n

Name<\/td>Quantity<\/td>Use<\/td>Cost<\/td>Comment<\/td><\/tr>
Oak 1 x 2″<\/td>`1<\/td>Handle<\/td>$0<\/td>Left over<\/td><\/tr>
1\/4 x 36″ steel round stock<\/td>1<\/td>300 mm probes<\/td>$6.99<\/td>Home Depot<\/td><\/tr>
1\/4 28 nuts<\/td>4<\/td>Attach probe to handle<\/td>$3.99<\/td>Home Depot<\/td><\/tr>
N Female Connector<\/td>1<\/td>RF input<\/td>$0<\/td>Salvaged<\/td><\/tr>
Copper Strap<\/td>5 inches<\/td>Connect probes to RF input<\/td>$0<\/td>Left Over<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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Ground conductivity measuring probe<\/figcaption><\/figure>\n\n\n\n

The land around my house was farm land for a long time. First field crops then a grazing pasture for a dairy farm. The last farming activity was about 65 years ago, since then the trees have grown in. The soil itself is mostly glacial till; rocks, sand and clay. I do not expect much.<\/p>\n\n\n\n

I headed into the woods with my Siglent network analyzer and measure the ground conductance. I then saved that information as a .csv. <\/p>\n\n\n\n

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Amateur Bands OWL measurements<\/figcaption><\/figure>\n\n\n\n

I have since saved my ground conductivity sweep profile in the analyzer. I reduced the points down to 180, which gives at least one point in every amateur band from 630 through 10 meters. That makes the marker settings redundant and .csv output much more manageable. I have another sweep profile for just the AM Broadcast band, this one runs from 530 – 1,710 KHz and has 118 points, which provides a measurement on every carrier frequency.<\/p>\n\n\n\n

I sent the .csv into ChatGPT and had it analyze the data. When it comes to AI, it is all about the prompt. The more information and instruction provided, the better the output will be, usually.<\/p>\n\n\n\n

The ChatGPT prompt:<\/p>\n\n\n\n

Calculate the ground RF conductivity and permittivity using the open wire line method. Measurements are made with a Vector Network Analyzer using S11, data is Real\/Imaginary, ground measurement probe consists of two steel rods, 6.35 mm in diameter, 300 mm long, spaced 50 mm. The rods are fully inserted into the ground. Include probe end fringing and steel conductor losses. Show all math and proof for the first frequency only. Use this data: cgmfhf1.csv
<\/pre>\n\n\n\n
I have found a need to be careful with any AI. ChatGPT tends to be over optimistic. My first attempt, the output had a ground conductivity of 12 mS\/m which looked great until I dug a little deeper. It seems ChatGPT copied the answers from DH1TW’s blog post. When I ran the numbers myself, it was more like 1 mS\/m. I scolded that lazy AI and told it to do it again, this time with the proof. That is why I want to see the math for the first frequency. Here is a chart with the ground conductivity and permittivity in my antenna field for the MF and HF amateur frequencies:<\/p>\n\n\n\n
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Here is the math for the first frequency:<\/p>\n\n\n\n
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I always ask to see the math for the first frequency so I can check the AI’s work and make sure that it is not being lazy again.<\/p>\n\n\n\n
Running some models in MANNA-GAL and I feel like the results are much more similar to what I am seeing WSPR beacon.<\/p>\n","protected":false},"excerpt":{"rendered":"
An important part of any medium-frequency and high-frequency antenna system is the nature of the ground immediately around the antenna system. The reason for the complex and expensive AM ground system is to create a return path for the portion of the RF wave that is not radiating from the tower. Higher ground conductivity helps … Continue reading Ground Conductivity<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":14267,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[87,222,231,343,50],"class_list":["post-14259","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tech-stuff","tag-am","tag-antennas","tag-hf","tag-mf","tag-shortwave"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/14259","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/comments?post=14259"}],"version-history":[{"count":48,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/14259\/revisions"}],"predecessor-version":[{"id":14330,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/14259\/revisions\/14330"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media\/14267"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=14259"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=14259"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=14259"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}