"Denny" wrote
You need a flat top to pull the current node higher from the ground...
Our NDB at KHYX is less than 100 feet tall, has a series fed vertical
wire with a long, multiwire flat top and is easily copied from 80
miles away at night and 40 miles in the day...
______________

Your NDB might have been in a location with much better ground conductivity
than this one.

I was attempting to analyze the hardware described in the OP, and used
rather pessimistic assumptions in doing so.

But even then, the FCC MW propagation curves for this power, radiator
efficiency, frequency and assumed earth conductivity (2 mS/m) show a
groundwave field of about 35 µV/m at 40 miles.

I don't know if that would be called "easy copy" in the daytime using the
receivers intended for this application. Does anyone know?

I assumed an r-f ground loss of 25 ohms. That loss for an AM broadcast
station is around 2 ohms. Reducing the loss in the r-f ground would help
here, at the penalty of reducing the r-f bandwidth.

RF