The content following in this post was included in a recent thread on Part15.us, and now re-posted so as to make it easier to search for, and find.
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Below is a chart showing the fields produced for various distances and soil conductivities from a Part 15 AM system installed and operated in full compliance with FCC §15.219.
A very good receive system in an area of very low radio noise level and no co- or adjacent-channel interference might produce listenable/useful (but noisy) output audio from an arriving field intensity of 50 µV/m.
The chart shows that at 2 miles, 50 µV/m is met or exceeded only for 15 and 30 mS/m earth conductivity.
Field intensities at distances of 3 miles and beyond are significantly below 50 µV/m for all values of soil conductivity.
thanks Rich this is a chart that I can easily understand I wish all your charts are laid out that way. Thanks once again for an easy-to-understand Chart.
There are many factors which affect AM Part 15 range so how useful is a table such as Rich has created?
My "station" is comprised of a ground mounted over radials antenna system with approximately 30 ohms coil and ground system resistance, 8 mS soil conductivity (according to the FCC), and a transmitter producing 85 mW at the antenna feedpoint. The chart indicates a field strength of 103 uV/m at 1 mile and 44 uV/m at 2 miles and using Rich's guidance regarding receiver performance the expected range of my station should be slightly greater than one mile and slightly less than two miles.
So, how accurate is this? A range check performed using a car radio and a drive away test yielded a listenable signal at one mile (crow flies) from the antenna and a noisy but recognizable signal at 1.3 miles out.
Deapite the many factors which can affect this range, the table is a reasonably good estimator of station performance according to my test..
Thanks for posting this, Rich.
Neil
Thanks for your feedback, gents.
I've always looked at charts as more of a ballpark estimate to help base your results off of.