Mal, G3KEV wrote:
So you are saying that 1W
erp from a dummy load radiates just as efficiently as 1W from a 200 ft
vertical for instance.<
... no, surely not! But 1000 Watt from a - 30 dB 'gain' Antenna (that's
approximately the 'gain' my 59 ft backyard antenna provides) will produce
exactly the same ERP (definition see below) as 1 Watt radiated from a
full-size vertical dipole (about 1100m high, which might be difficult to
build for most amateurs due to most local communities authoritie's strange
attitude ...).
Please see below the relevant definitions as they are recommended by the
ITU.
Best 73, a peaceful time 'between the years' as we say in Germany ...
Geri, DK8KW (W1KW)
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"DEFINITIONS OF RADIATION IN LF, MF AND HF BROADCASTING BANDS
(1978-1982-1986)
Rec. 561-2
The CCIR UNANIMOUSLY RECOMMENDS
that the following terminology should be used to define and determine the
radiation from sound-broadcasting
transmitters:
1. Cymomotive force (c.m.f.) (in a given direction)
The product formed by multiplying the electric field strength at a given
point in space, due to a transmitting
station, by the distance of the point from the antenna. This distance must
be sufficient for the reactive components of the
field to be negligible; moreover, the finite conductivity of the ground is
supposed to have no effect on propagation.
The cymomotive force (c.m.f.) is a vector; when necessary it may be
expressed in terms of components along
axes perpendicular to the direction of propagation.
The c.m.f. is expressed in volts; it corresponds numerically to the field
strength in mV/m at a distance of 1 km.
2. Effective monopole-radiated power (e.m.r.p.) (in a given direction)
The product of the power supplied to the antenna and its gain relative to a
short vertical antenna in the given
direction. (Radio Regulations, No. 157.)
Radio Regulations No. 154 (c) defines the gain of an antenna in a given
direction relative to a short vertical
antenna G v as the gain relative to a loss-free reference antenna
consisting of a linear conductor, much shorter than one
quarter of a wavelength, normal to the surface of a perfectly conducting
plane which contains the given direction.
The reference antenna, when fed with a power of 1 kW, is considered to
radiate an e.m.r.p. of 1 kW in any
direction in the perfectly conducting plane and produces a field strength
of 300 mV/m at 1 km distance (equivalent to a
c.m.f. of 300 V).
An e.m.r.p. of 1 kW is assumed in the derivation of the ground-wave
propagation curves of Recommen-dation
368. An e.m.r.p. of 1 kW at all angles of elevation is assumed in the
presentation of the sky-wave curves of
Recommendation 435.
Note 1 Definitions 1 and 2 are mainly used in LF and MF broadcasting.
3. Equivalent isotropically radiated power (e.i.r.p.)
The product of the power supplied to the antenna and the antenna gain G i
in a given direction relative to an
isotropic antenna (absolute or isotropic gain) (Radio Regulations, No.
155).
The idealized reference antenna, when fed with a power of 1 kW, is
considered to provide an e.i.r.p. of 1 kW
in all directions and to produce a field strength of 173 mV/m at 1 km
distance.
4. Effective radiated power (e.r.p.) (in a given direction)
The product of the power supplied to the antenna and its gain relative to a
half-wave dipole in a given direction
(Radio Regulations, No. 156).
Radio Regulations No. 154 (b) defines the gain of an antenna in a given
direction relative to a half-wave
dipole G d , as the gain relative to a loss-free reference antenna isolated
in space whose equatorial plane contains the
given direction.
The reference antenna, when fed with a power of 1 kW, is considered to
radiate an e.r.p. of 1 kW in any
direction in the equatorial plane and produces a field strength of 222 mV/m
at 1 km distance."
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