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My station: microBitx putting out about 8W max into an inverted-vee with the apex around 20ft above the ground. Surrounded by trees.

His station: iCOM (one of the older classic rigs dating back to the 1980s) putting about 50W into either a dipole, or a Yagi on a rotator beaming generally in my direction.

dX between the two stations: About 3mi (6KM) with minor hill perhaps 50ft elevation at one place

Noise floor is high: Perhaps a 5

Band: 20m

The problem: At this close range I expect to receive his Tx over ground wave. Regardless of where his yagi is pointed he should be audible to me 59, and/or better. Conversely, he should hear my Tx atleast 55. This does not happen; I can not hear him at all on the Yagi except when he runs his linear putting out around 200W. On his dipole I can hear him slightly better but no better than 58. He can hear me at best returning a 44. This was not the case some years ago.

What has changed in this duration ; I use a different set of patch cords to link the SWR meter to the rig. My coaxial is still an rg58u albeit newer as the dielectric on the previous one was cracking. Oh, and our streets - earlier made of tar/bitumen - have largely been remodelled to concrete.

Does the iron in the concrete roads attenuate the ground-wave ?

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    $\begingroup$ What band? Frequency affects propagation distance. $\endgroup$
    – user10489
    Dec 5, 2021 at 2:32
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    $\begingroup$ There is no serious ground wave from a dipole or inverted V. The explanation is solely found in polarisation. $\endgroup$
    – user16925
    Dec 5, 2021 at 14:55
  • $\begingroup$ Attenuation, especially by trees, is affected by frequency. Not so much for 20m, so this is important. Also fresnel zone and edge propagation would be affected by both polarization and frequency. $\endgroup$
    – user10489
    Dec 5, 2021 at 20:30

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You're both horizontally polarized, so you weren't getting any significant "groundwave" in any case, especially not on 20m. Only vertically polarized signals propagate in the groundwave mode.

You're probably thinking about line-of-sight, which is affected by anything in the space between you and the other station, or in your Fresnel zone. Steel rebar is apparently a pretty good conductor, so yes, it's possible that it reflects horizontally-polarized signals causing substantial cancellation at low angles (this isn't attenuation, but it means that the signal isn't going to the place you want it to).

Another possibility is that due to terrain, you never had a good line-of-sight path, but that "some years ago" you were able to do NVIS on 20 meters, but currently (we're just starting to climb out of solar minimum) the ionospheric conditions don't support that.

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