Yea I scared myself with the range I got using a bunch of old 50' extension cords laid out on the ground hooked to the bottom of the tower. Work.. At one point when fooling around with this I tried aluminum foil cut up into 1"strips (Costco heavy duty 200' long) reinforced with packing tape. That worked really well too. I never got around to making the magic 120 ea 1/4 wave system to try. I found the longer ones seemed to work better even though this is counter to testing done by others. I should note that here in the Northwest the ground number is "2" if I remember correctly. I've always wondered if that would be the equivalent of elevating an antenna over a better ground. If so would attaching a 100mw tx to say a 100' deep well pipe give a longer hidden radiater. Then put the radials 100' below ground. Now that would be "work" Phil! 🙂 Dave
Ben Tongue is one of the few people I believe simply because he has said something. He is a co-founder of Blonder-Tongue Laboratories, which is among the most heavily RF design-oriented companies that exist. After he retired, he decided to apply his considerable RF design expertise to the humble crystal radio. There is simply no money to be earned in crystal radio design, and so no significant improvements had been made for many years. Anybody who has owned a crystal radio knows that it has very poor selectivity. The poor selectivity is because of the low loaded-Q of the tuning coil. The low loaded-Q is because of the load produced by the crystal detector and the earphone, and also because of the low unloaded-Q of the tuning coil.
On his website, www.bentongue.com , Ben Tongue offers many articles about crystal radio design. He specifically warns against using PVC for the tuning coil form, recommending high-impact styrene instead. He also explains how to measure the unloaded Q of a coil. Ben's crystal radios have sufficient selectivity, which such radios had not had before.
Part 15 AM today is a lot like the crystal radio before Ben Tongue. Like the crystal radio, Part 15 AM does not have the market to justify a huge engineering expenditure to improve performance. If Ben Tounge had decided to work on Part 15 AM during his retirement, maybe it would be possible to transmit a mile with a 3 m monopole at ground level. Like the tuning coil of the crystal radio, one of the things that restricts Part 15 AM range is the unloaded-Q of the loading coil.
Prof. Valentin Trainotti, the world's foremost expert on short antennas for licensed stations on the AM broadcast band, had consented to analyze Part 15 AM performance, and his contributions were reported on the following thread:
http://www.part15.us/node/1390
Trainotti found that, with modest ground screens, the losses in the loading coil dominate the losses that limit Part 15 AM range. So, the range is mostly limited by the Q of the loading coil.
Trainotti's data covers loading coils up to a Q of 400. It is really tough to get a loading coil Q this high, and an even higher Q is desirable. Ben Tongue was trying to get very high Qs for his crystal radio tuning coils, and this effort included using low-loss coil forms.
I do not use coil design software. From what I have seen by actual measurements, they tend to greatly overestimate the Q of a coil.