Content-Transfer-Encoding: 8bit
Message-ID: <5.1.0.14.0.20020720155223.00ae8e80@gemini.herts.ac.uk>
Date: Sat, 20 Jul 2002 16:34:24 +0100
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: Re: LF: Calculating ERP from measured field strength
In-reply-to: <5.1.0.14.0.20020720130356.009eb780@POP3.freeler.nl>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Dear LF Group,

I'm pleased to see PA0SE's FS measurements agree well with my own - it 
looks like we are getting quite good at this now!. I measured my ERP a 
couple of weeks ago, after making some slight improvements to my antenna; 
it is still an inverted L, but it now has an average height of around 9.5m, 
and the same 40m length as before. The 400mW figure was derived from an 
average of 11 field strength measurements at distances between about 1.5 
and 3km. Comparing these to measurements I did last year at the same 
locations, it is interesting to see that the variations in calculated ERP 
between different locations are very consistent - ie. if one location gave 
a measurement 1dB above the average last year, it was also 1dB above the 
average this year, so whatever causes the variation is stable over quite 
long periods of time. All the ERPs  were within about 1.5dB of the average ERP.

The antenna current of 4.6A is well down on what I get on a cold winter's 
day, so I think this antenna should give 500-600mW ERP under good conditions

I used a "Jason" mode test signal when performing the measurements - this 
is ideal for FS measurement, because it is practically a continuous 
carrier, and makes it easy to measure the amplitude.

Cheers, Jim Moritz
73 de M0BMU