Over the years I have talked a lot about ground systems for HF verticals. Most of what I have said comes from modeling and calculations of my own and experimental work of others most of which was for LF or MF broadcast applications. Other than the QST articles by Sevick many years ago and the CQ articles by Arch Doty, there has been little experimental work reported in amateur literature which could be used to judge the validity of NEC modeling and whether it can actually tell us something that's real for HF verticals. Beginning about a year ago I set up a test range in my pasture and began a series of careful experiments on HF verticals with various ground systems including some with elevated radials. Two results stand out. First the NEC prediction that a few elevated radials can be as efficient as a large number of ground radials seems to be correct at least at my site with the test antennas I used. See experiment 3.
The second interesting item is that using only a few long radials can result in much higher ground losses than the same radials shortened. In the past I have often said that a few long radials might be a waste of copper but were harmless. Not so! Experiments 4 and 5 are related to this.
I also ran some experiments with the 40m+ version of the SteppIR vertical. My particular interest was developing a ground system that was effective from 40m through 10m. That work is reported in experiment 6. Some obvious ground systems don't work all that well.
I have written up my experiments in a series of reports. Nothing formal just a review of the experiment, the results and some comments.
Separate from the reports I have written up a detailed description of the test arrangments and instrumentation: Download antenna_ground_system_test_setup.pdf
I suggest you read the test setup description first so you can follow the experiment reports which do not contain all the test setup details.
On Saturday, August first, I gave a talk to the NW DX convention on this work. The following is the PowerPoint presentation file for that talk: Download ground_system_tests.pps