This apparently originated from the antiqueradio forum and Boomer told TheDood who posted about it at https://www.hfunderground.com/board/index.php?topic=149519.0 and I'm posted here because I've never seen this PDF before and it's really cool. I think it's recent. It's called THE LOW POWER MW AM TRANSMITTER-ANTENNA Did you know they call them "Pantry Transmitters" in the UK?. I'm a little puzzled over his perspectives concerning 15.219, but it's definitely worth the read
https://worldphaco.com/uploads/THE%20LOW%20POWER%20MW%20AM%20TRANSMITTER-ANTENNA.pdf
No one at all found it interesting?
@richpowers I saw but had no comment to make. The antenna set up there is exactly what the Procaster, Rangemaster, has incorporated into the circuit with the loading coil and tuning capacitor on board.
@richpowers I saw but had no comment to make. The antenna set up there is exactly what the Procaster, Rangemaster, has incorporated into the circuit with the loading coil and tuning capacitor on board.
I wasn't really referring to the transmitter nor his antenna design itself, but more on his presentation of technicalities as well as his perspective on 15.219 in which he seems to imply it's "obviously" still governed by field strength:
".. Obviously any MW band AM transmitter circuits, regardless of their RF amplifier design, combined with some design of Antenna structure, must never be allowed to transmit a higher actual electromagnetic (EM) wave power than the “FCC’s regulation transmitter-antenna arrangement”
He's in the UK so his perspective can be forgiven (if that is indeed what he meant), Evidently they call part15AM xmtrs "Pantry transmitters" in the UK, signifying it's reach usually doesn't make it past the kitchen! But there really is a lot of interesting stuff he addresses, not all of which I understand. One thing that jumped out at me is that his transmitter design is neither Class C nor Class E, but Class A ... I didn't even realize there was such thing, he also makes some comparison on efficiency between the classes. It's that and more, it's just an interesting read altogether.
"... In this article, the maximum EM wave power (units Watts) that the Part 15.219 compliant Transmitter-Antenna arrangement can emit and also the Electric Field intensity E (units Volts per meter) generated away from the antenna are calculated. ...
.. Most Pantry transmitter designs use Class C output stages and Class-C, or a switching style class E radio frequency output amplifiers are such that their DC power consumption is closely correlated with their RF output power. Typically, if the Class-C or E output stage consumes 100mW DC power, the RF power output is in the order of 90mW ..... ... However, a Class-A RF amplifier is not this way at all and it consumes the same power from the power supply regardless whether its output RF level is 1mW or 100mW. Therefore the metric of “100mW DC power consumption” used in the Part 15.219 specifications is inapplicable to the Class-A RF output stage.
From the design perspective, for low modulation distortion, it is much better to have a linear modulator and linear output stage and modulating the carrier wave, prior to a Class-A RF output stage. This is much less efficient, wasting power as heat, but it is better for linearity than a Class-C stage with the modulation applied to its power supply which in most cases results in more modulation distortion.
In any case, regardless of the efficiency merits, it is very easy to ensure that a Class-A output stage’s RF power output is exactly 90mW... .. In essence this makes the Class-A stage just as technically and ethically compliant and practically equivalent to a Class C stage consuming 100mW from its power supply.
As will be shown here, any small differences in the power levels at the RF output stage are shrunk into relative insignificance, because even for the perfectly implemented Part 15.219 setup only about 0.56mW (560uW) of power appears as radiated EM waves. And typically, for many hobby Pantry Transmitter setups, is only in the order of 1/500th of that in the region of 1uW or less radiated EM wave power. ...
Summary of losses in a practical compliant Part 15.219 transmitter-antenna system:
1) As indicated by equ. 2, when the antenna height h is reduced, the radiation resistance drops with the square of that change. If we had a 10 foot antenna (with a very short earth wire) and altered that to a 5 foot earth wire and a 5 foot high antenna, we halve the antenna height. The Rrad drops by a factor of 4 and all else equal, the radiated EM wave power drops by a scale factor of 0.25.
2) Without the ground radials, a more realistic figure for the earth resistance and losses there would be in the order of 60 Ohms or more. When the loss resistance increases by a factor of 4 it lowers the antennas efficiency by a factor of close to ¼ because of the very small value of Rrad, as seen by equation 3. Therefore, another scale factor of 0.25 applies. This assumes of course that despite the higher resistive losses, the RF output amplifier remains with an impedance match to the tank circuit and is still managing to deliver the 90mW power to it. ...