Total posts : 45366
If the goal is to be a community broadcaster, the goal appears to me to be an elusive one for Part 15 AM. The estimates of radiated power in Rich’s post seem high. Based on discussions on another recent thread, the estimate of about 20 uW is about right for a fairly good installation at the upper end of the band, but not at 540 kHz. About all 540 kHz has going for it is the larger near field radius. One of the things that would reduce radiated power at 540 kHz, in addition to the smaller radiation resistance, is appreciably increased loading coil loss resistance.
What is lacking is good data. Field strength readings are needed for knowing what the actual radiated power of a Part 15 AM installation is. About all we have now is an FCC field strength reading in an enforcement action for a transmiiter and antenna combination for which the input power to the final transmitter stage was measured. The cost of a field strengt meter that can be used for FCC qualification testing would be prohibitive. However, WEAK AM’s blog has a link to plans for a field strength meter that might be used for troubleshooting a transmitter and antenna system. The author’s suggestion of using an AM station of known power with a quarter wave antenna as the calibrating signal source seems a little crude, and has already been commented on by Rich. However, this might be good enough for using the field strength meter for rough performance testing.