In response to recent emails about the requirement for more RF out on 500
khz I am of the opinion that ERP is the way forward.
10W erp would be a realistic start and preferably 20W erp, this approach
would encourage amplifier and antenna design and research on 500 khz.
At present we have reached stalemate with the 0.1w erp restriction, limiting
communications to the UK during daytime and during the dark hours to a few
countries in near EU. There is virtually no hope at present to research
propagation or work DX on a more international scale.
To justify my ERP argument and keep the maths simple, look at examples
below.

1. 10W rf output to the antenna and an efficiency of the average antenna 1%
the ERP would be 0.1W erp, this would be no improvement from the current
position, increase it to 20W and we get 0.2W again this would be
insignificent. You would need a lot of Watts to get any real change.

2. 10W ERP and the same 1% efficiency would require 1Kw output to the
antenna and this is the sort of increase that is required for meaningfull
international communications and propagation studies.
This power level is modest compared to the commercial users of the past like
ships and costal stations. Most ships installations were running  1000 watts
give or take a little and more with good antennas especially on the larger
ships. Even with this power during daytime the coverage was only in the
region of a few hundred miles, even sorrounded by the ideal salt water
earth. Night time was different with longer range but required these powers
to work back to the appropriate shore stations.
The transmitter PA tube installations that I encountered were 2 x 4-400, 1 x
4cx 1500 b, 4 x 4c250b or 1 x 4-1000a, these seemed to be the norm.
There were some /MM with less power but this was rare except for emergency
transmitters.
The above is an example of my experience and opinion, although from what I
have read so far on this reflector the ERP approach is the favourite.

73 de Mal/G3KEV