Hello Dick,
great that you also made your field strength measurements.
we find at Puckeridge 45W was fed to the aerial on 136kHz and 7.5W on
73kHz.
The difference between your findings and mine (16 W ERP on 73 kHz, measured
at nearly twice the distance using a very basic and rough "rule of thump"
measurment) is only about 3 dB.
Dick, PA0SE wrote:
This is EIRP and not ERP of course.
Well, kind of. What I thought was a silly question seems seems always to
have been a point of discussion betwen the experts. Let me quote from an
e-mail that Vaino, OH2LX has send me as an answer to my question:
We have not been using the "paper curves" for some time.
Many computer GW programmes have been developed but none of
them seem to serve us the way we all should expect them to do.
Hardly no one was serious with either ERP or EIRP when the
"Conditions of validity" for the family of curves were being
formulated. There were some 6 or 7 candidates icluding CMF,
EMRP and some others. EIRP is rather "fuzzy" and ERP refers
to a dipole, so the choice was to be called EMRP:
- The radiating element is a short vertical monopole
(The equivalent dipole moment is 5(lambda)/2(pii)). Assuming
such a vertical antenna to be on the surface of a perfectly
conducting plane earth and excited so as to radiate 1 kW,
the fiels at a distance of 1 km would be 300 mV/m;
this corresponds to a cymomotive force of 300 V.
Personally I don't know anyone who wants to make practical
field work or reporting in terms of CMF. As you know from
practice, the problems are hiding elsewhere. Usually it is
most useful to discover a lump sigma value for a ground path
with potential adjustments according to seasonal etc conditions.
Without reliable looking long term measurements with supporting
occasional flight measurements there would be no brain twisting,
at least we could not explain all what happens on measurements.
Best 73
Geri, DK8KW (W1KW)
| 