Total posts : 45366
Ok, so if I’m understanding correctly, at least part of the reason why a long ground wire would result in more range is because it would represent more of a fraction of a wavelength that is an easy/good conductor for the rf current radiated from the short antenna to return through.
I was just reading an interesting page by G4NSJ where he has the circuit for a simple RF ammeter and mentions that he finds it of more use in tuning his “top band” (160 meter bend, the amateur band closest to AM BCB frequencies) system than most swr meters. What particularly came to mind when reading your post, Rich, was where G4NSJ had said:
“I tune the aerial matching until for maximum earth current. This, as I have checked, corresponds exactly to the minimum reflected power and maximum power into the aerial. I borrowed a decent SWR meter from a friend of mine to check this.”
I may be missing something, but at least to my layman’s sensibilities, that statement sounds supportive of what Rich is saying in this topic.
It’s a short page, and can be found at:
However, what had caught my attention is that the circuit is extremely simple and if one already owns a simple multimeter, then calibrating the circuit to give a reasonably accurate readout wouldn’t be very difficult.
Now, if the measure of the current on the wire leading to the ground system can be taken as a fairly reliable indicator of the efficiency of an antenna system (including the antenna, ground wire, and lossy earth), then a simple rf ammeter might be a better tool for comparing part15 AM antenna systems than an FSM. The topic of field strength meters has come up a number of times and it seems to always boil down to the difficulties in calibration to get any sort of a consistent standard of measurement if they were being built by different individuals or possibly with slightly different parts. But measuring current with a multimeter is part of any beginner’s usual activities when learning Ohm’s law, and adjusting a pot on a homebrew rf ammeter (or making tick marks on a piece of masking tape on the meter face) so it can be used to give at least reasonably consistent readings of the current shouldn’t be too hard for most here with an interest in their antenna systems.
Then if one tries a different sort of coil or a different diameter of wire or pipe for the vertical element or whatever sorts of change one might make to attempt to improve an antenna system, the difference from the reading in milliamps before the modification would give a reasonable indicator that would be consistent enough to perhaps be of more use in discussions of designs here.
Tracking things like the differences between the rf current into the ground system (whether it’s a buried radial system or the infamous “cold water pipe”) during different weather conditions could be interesting, like comparing readings with the same system made after several days with rainfall compared to drought conditions, or when trees and other plants in the area are in full foliage compared to winter and etc.
Just kind of brainstorming the idea here at the moment, since comparison of antenna systems tends to be a recurrent topic of conversation/interest.
Here’s another rf ammeter design that was apparently developed for LOWfer and MEDfer use.
(For those unfamiliar with those hobby distinctions, part15 AM would fall under “MEDfer”). Now, I don’t know as either of these designs would be ideal for part15 AM hobby use, but perhaps with some thought and discussion it would be possible to come up with a simple design that would be?
My thought is that if we can come up with even one antenna system parameter that can be tracked as simply as “100 milliwatts input power to the final rf stage”, then discussing diameters of antennas or ground wires or number and length of radials and if they’re buried or not could be less subjective than “seems to work better”. If the design is inexpensive enough and easy enough to build that a number of people could make one and get involved, then we could perhaps get some interesting experiments going from the data collected.