Date: Mon, 17 Apr 2000 03:08:22 -0400
From: "Holger 'Geri', DK8KW" <DK8KW@compuserve.com>
Subject: LF: Operation from ex-Decca station at Puckeridge
To: rsgb_lf_group@blacksheep.org
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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)