Dear Markus, Rik,
I think Rik's description is a variant of Markus' method - both using the
principle of reciprocity to evaluate the properties of a transmitting
antenna by measuring the received signal level produced by a known field
strength. So this is indeed a third method.
It is interesting that this does not actually require the field strength to
be measured in order to get the effective height/radiation
resistance/efficiency - just the ratio between the TX antenna output level
and the measuring antenna output level. However, to get the ERP when
actually transmitting, an absolute measurement of antenna current or TX
power would be needed.
So in summary, methods to determine ERP:
Method 1 - requires "calibrated" TX antenna (i.e. antenna effective
height/radiation resistance calculated from dimensions), with calibrated
antenna current measurement (or power and impedance).
Simplest in terms of equipment needed and measurement , but least reliable
because environmental losses only partly included.
Method 2 - requires calibrated receive antenna (loop) and calibrated
measuring receiver to measure receive antenna output voltage/power etc.
Most difficult to do due to equipment needed and (multiple) far-field FS
measurements. Includes effect of environmental losses. Requires no knowledge
of transmitter/antenna, apart from where it is - most useful for Ofcom/FCC
etc.
Method 3 - requires calibrated receive antenna (loop) and calibrated antenna
current (power/impedance etc.) measurement, plus ratio of received signal
levels.
Intermediate equipment requirement (Also a suitable signal is required, e.g.
DCF39). Includes effect of environmental losses.
Cheers, Jim Moritz
73 de M0BMU
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