LF: Calculating ERP from measured field strength

["Dick Rollema" <d.w.rollema@freeler.nl>]

To All from PA0SE

Today at 0800 UTC I measured the field strength of Jim, M0BMU on
137.4kHz,  at 11 microvolt/metre.

The distance between M0BMU and PA0SE is 329km.

Using the curves for ground wave propagation in CCIR recommendation 368-7
those for "Sea water, average salinity" (epsilon 70,
conductivity 5S/m) and "Land" (epsilon 40,  conductivity
30mS/m) produce the same result for Jim's ERP: 460mW (252mW EMRP) . Jim
reported his ERP being 400mW (218mW EMRP); a difference of 0.6dB. Almost
too good to be true!

But when I apply the graph for "Land" to the signal from 
DCF 39 (distance 500km, field strength 2mV/m) I find an EMRP of 50kW and
that is what is officially stated for its power. So that confirms the
"Land" curve is pretty useful for distances and paths involved
in my case.

Reg Edwards, G4FGQ, has a free  program called "Grndwav3"
on his web site:
www.btinternet.com/~g4fgq.regp/page3.html#S301.

Entering Jim's EMRP=218mW and distance 329km the program predicts for the
field strength at PA0SE the following:

Sea water: 10.35 microvolt/m
average:       8.18 microvolt/m
pastoral:       9.50 microvolt/m.

I measured 11 microvolt/m so Reg's program can also be used when the CCIR
curves are not available.  

Warning: These methods only apply to ground wave propagation, so as long
no sky wave is present. For distances up to a few hundred km this is true
during daytime.  

73, Dick, PA0SE