Our Prairie Amplifier
by Ron Chester ★ Saturday, January 16, 2021

The previous posting about the R3 vertical was just the background posting for this one. I had started looking at a lot of possible vertical antennas, but then I always had backoff because of the need for radials and that always seems like SO much work! So I have never in my life installed radials. But then I realized I had had very good results with a vertical in LA, so verticals can really have some advantages.

Being on a mini vertical binge in my reading lately, my Google Spy helped me out again with a helpful link, about verticals and radials, from an active general purpose ham radio club of about 100 members in Nashua, NH, the Nashua Area Radio Society. Google noticed that they had a 2019 article about verticals and radials. So I read it, another of many in my vertical binge reading.

Ground Conductivity

The article does a great job of discussing ground conductivity, as related to half-wave verticals. As pointed out in the sole comment on this piece, this topic is the key to how AM broadcast stations work! We live in the heart of central Illinois, which has some of the most valuable farmland in the country; rich, black, loam that is great for growing corn and soybeans, a major source of income to our part of the country, which is in the heart of the Corn Belt, in 1956 declared by Vice President Henry A. Wallace to be the "most productive agricultural civilization the world has ever seen." Drive outside our city and you see farmland in all directions, very flat prairie as far as the eye can see, but dotted with tall towers, vertical antennas for broadcast radio stations. Our local ham clubs have VHF and UHF repeaters on some of these towers, often up 100 feet or more above the rich farmland below, no yagis or rhombics needed for these signals.

The article links to a map of the US, downloadable from the FCC, that shows the conductivity of the soil all over the country, but it also shows a small map in the article of the same thing. Conductivity is measured in mhos, which is ohms spelled backwards, as conductance is the reciprocal of resistance. Is that neat, or what? Looking at this map, to the north, south and east of us, nearly all the conductance readings are in the single digits. But we are located in a band of land with conductance of 15 millimhos per meter, far higher than the rest of the country to our north, south and east.  Wow, all that flat land around us began to look much different to me. Looking to our west across the Great Plains, we see conductance similar to ours and some even higher at 30 millimhos per meter. Call it flyover country if you want, but I now prefer to think of it as the part of the country with the best ground conductance. As for RF, the higher the current in the soil, the stronger the signal radiated from the vertical antenna, which translates to better DX! Then again seawater has conductance of 5,000 millimhos per meter. In California my RF take-off to the west was across the Pacific Ocean, which is why it was so easy to work VK, ZL and other Pacific rim destinations from there. 

The radial system taps in to that conductive soil for the half-wave verticals, completing the key second half of such antennas.  All that hard work in building a good radial system could pay big dividends in harnessing the power of our rich conductive soil. Operating QRP should be far more successful from here if we take advantage of our Prairie Amplifier; that rich, conductive soil. 

REF: All about loam and how to fine tune it to be more like you want it.