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Message-ID: <865A6F2FC37344A4825C5068AA8ED091@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <1034F871DB99454AB819054B51F39B19@IBM7FFA209F07C> <C60A421BC61F4935A7EEE0B506AD140E@JimPC>
In-Reply-To: <C60A421BC61F4935A7EEE0B506AD140E@JimPC>
Date: Thu, 8 Oct 2009 18:59:29 +0100
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Subject: LF: Re: ERP at LF - Method 3
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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