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Re: LF: Radiated powers ...

To: [email protected]
Subject: Re: LF: Radiated powers ...
From: Väinö Lehtoranta <[email protected]>
Date: Mon, 17 Apr 2000 15:24:31 +0300
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
For those interested on the history of LF/MF coverage planning:

(An excerpt from a report of
EBU Working Party A, Hamburg, April 1971)

DEFINITIONS OF RADIATED TRANSMITTER POWER
-- (5 proposals received) --

a)  Effective radiated power (ERP) - by ORF (J. Burgstaller)
It is proposed to apply the same definition as the one
used in the VHF and UHF bands.

b)  Equivalent monopole radiated power (EMRP) - BBC (Dr Phillips)

This definition is based on a short vertical reference aerial,
giving horizontally the same radiation as the actual aerial,
both being assumed to be located on a perfectly-conducting
horizontal plane. The advantage would be that in the present
CCIR Report, the curves would correspond to 1 kW EMRP (!!!)

c)  Equivalent power at a distance of 10 km (EP) - RTE (Mr Curley)

For MF propagation it would be reasonable to consider the
surrounding countryside up to a radial distance of approximately
10 km as being part of the aerial system. A practical suggestion
to define the radiated power may be as follows: the equivalent
power required to produce the same field strength at 10 km when
applied at the base of a vertical aerial of one quarter wavelength
equipped with a perfect earth system and moderate conductivity
(3*10E-3 mhos/m) around that aerial up to a distance of 10 km.

d) Cymomotive force (CMF) - ORTF
The cymomotive force is defined at any point in the space around
an aerial, for which the fed-in energy is known, related to the
distance of that point from the aerial. The gain of the aerial
must be considered when the field strength is calculated at that
point. The product of the field strength and the distance
is defined as the cymomotive force.

e)  Operative radiated power (ORP) - ARD/ZDF

This term is defined as follows: "The power supplied to the
antenna multiplied by the gain of the antenna in a given direction
when the reference antenna, placed on the surface of a perfectly
conducting plane earth, produces an unattenuated field strength
of 300 mV/m at a distance of 1 km at any angle of departure
above the plane earth.
----------------------------------------------------------------
Note by Vaino:  ERP also was there but it was not supported...




At 03:08 17.4.2000 -0400, Geri wrote:----------------------
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)
----------------------------------------------------------
V.K.Lehtoranta, OH2LX, POBox 50, FIN-05401 Jokela, Finland
------ Tel: +358-9-4173965 ---- Fax: +358-9-4173961 ------
E-mail: [email protected] - alias: [email protected] & [email protected]


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