Part 15 Legal/Mental gymnastics

[Tom Wells]

Some "legal" methods I'd like to try:

1. Make the output tuned circuit very, very large, and experiment with orientation of C and L.
A three-meter whip may be irrelevant.

2. Make upstream RF circuits generate considerably more power, but then couple to output stage with only resistance coupling.
Resistance coupling, BY DEFINITION, cannot couple power into a subsequent stage.
Final RF stage is regulated at 99 mw input.
I'd like to see what happens.
If the previous stage is dissapating 1 watt into the load resistance, wouldn't the RF current still have to flow in the ground circuit?

Then I'd like to combine the two.

Engineers/lawyers opinions?

 

[rfry]

1. Make the output tuned circuit very, very large, and experiment with orientation of C and L. A three-meter whip may be irrelevant.

Not sure of the concept here, but coils and capacitors are not very good radiators compared to a straight length of wire. The wires connecting them to each other and to the transmitter, and the conductor to r-f ground probably would do most of the radiation (as in the E-H / CFA antennas).

2. Make upstream RF circuits generate considerably more power, but then couple to output stage with only resistance coupling.... Final RF stage is regulated at 99 mw input

Even if the output stage was 100% efficient, the field strength produced by that output power is still subject to the radiation efficiency of the antenna system. Most of the efficiency of the antenna system depends on the ratio of the radiation resistance of the antenna to losses in the r-f ground connection.

The radiation resistance of the antenna depends on its electrical length at the operating frequency, which even in the best case barely exceeds 1/10 of an ohm when using a total radiating length of 3 meters.

Typical r-f ground loss maybe is around 25 ohms for many Part 15 AM setups, so even if the r-f loss in the loading coil was zero, the antenna system radiation efficiency would be 25.1/25, or about 1%. About 1 mW is radiated, the rest of the 99 mW tx output is dissipated as heat in system losses.
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[rfry]

the antenna system radiation efficiency would be 25.1/25, or about 1%.

My apologies. Antenna system efficiency for those parameters would be 0.1/25.1, which is about 0.4 %. Posted too early in the morning, I guess.
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[Neil E.]

2. Make upstream RF circuits generate considerably more power, but then couple to output stage with only resistance coupling.

Resistance coupling, BY DEFINITION, cannot couple power into a subsequent stage.

Engineers/lawyers opinions?

You contradict yourself with these two statements. You suggest having a stage generate power and then you propose to couple this power to the output stage with resistance coupling which you then claim couples no power.

Resistive coupling is used extensively in circuits. As an Analog Engineer you certainly know this. Perhaps you can help me if I misunderstood what you wrote.

Neil

 

[Tom Wells]

I am indeed suggesting I may, in my dense-packed brick-house neighborhood, secure better radiation from the currents in the tank
circuit. I know the cross field antenna seems to act like a "remote tank circuit", and the best minds say it is worse than a proper monopole.
I am still intrigued as to whether a huge distributed L and C would be accepted as part of the circuit, and not be regarded as the
radiating element.

MY lot is 30' by 125' and there is no place for any proper antenna.

In the case of the resistive coupling, the subsequent stage becomes a voltage amplifier.

In order to couple RF power from previous stage, we must use L or C somehow.

So if we couple in the RF with a resistor, we can define exactly 100 mw input power by (thinking in tubes ) input voltage/current
to plate.

Now imagine that the preceding stage is 100 watts, into a dummy load, with some output tapped to run the output stage.
Wouldn't the 100 watts into the dummy load also induce RF currents into the ground circuit?
And might not incidental radition from such a circuit be unaddressed by law, as it is an intermediate stage?

 

[rfry]

Now imagine that the preceding stage is 100 watts, into a dummy load, with some output tapped to run the output stage. Wouldn't the 100 watts into the dummy load also induce RF currents into the ground circuit? And might not incidental radition from such a circuit be unaddressed by law, as it is an intermediate stage?

Probably any "Part 15 AM" system design that produced much more field strength at a defined distance than can be shown by physics and field experience to be producible by a single, 3-meter vertical monopole radiator (including the exposed feedline, and the complete length of the conducting path to an r-f ground) when driven by a source of 100 mW input power would be subject to FCC notice and possible citation.

This might be worth considering if the goal of this concept is to greatly enhance the coverage provided by a station defined in 15.219.
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[Timewarp]

Part 15 AM is like Lincoln Logs, Tinker Toys, and electric trains. Kind of fun for a kid.
When the FCC finds an adult doing this, all the agent can say is Wowwwwwwwwww!

There is no way with all of todays electronic noise on medium wave that your signal
will be clean 1 block away indoors with 100 mw. Even if your antenna is 200 feet long.