LF: RE: Field Strength Meter

["John W Gould" <jwgould@iee.org.uk>]

Chris,  your experiments of measuring ERP are interesting.  How close is the result that you obtained with that derived from aerial modelling and aerial current measurement?  To what extent do you think that local environmental factors can explain any differences?

 

I wouldn't be too concerned about leaving a 6dB margin.  My off-the-cuff feeling is that so long as we make reasonable efforts in terms of accuracy and can demonstrate an intent to operate within the -10dBW limit that this should be acceptable to Ofcom. 

 

73 John, G3WKL

 

 

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of CHRISTOPHER OSBORN
Sent: 29 May 2007 21:05
To: LF group
Subject: LF: Field Strength Meter

This bank holiday I finished PA0SE's field strength 
meter (LF Experimenter's Handbook) duly modified for 500 kc/s.

I knocked 
up Helmholtz coils of almost identical proportions to those in Dick's published 
design and with these calibrated the F/S meter.
Initial results look very 
promising and the meter seems quite linear up to my calibrated maximum of  
6 mV/m.

This evening I trudged around the fields in Biggleswade making 
sundry readings, while my PC/TX  put out a test signal every 3 
minutes.
If (?) my calculations are correct then I have an ERP of 40 mW 
averaged over 3 (1 km distant) readings.
I know this is not much of a sample 
but initial results are satisfactory and fairly consistent.

Apparently I 
am told that field strength measurement uncertainties are notoriously high - one 
RadCom informed letter suggests by as much as 6 dB.
If I wanted to be 
pedantic then presumably we should ensure that we measure no more than 25 mW ERP 
to allow for the worst case uncertainty (tongue in cheek!)

73 Chris 
G3XIZ

---

Copy addresses and emails from any email account to Yahoo! Mail - quick, easy 
and free. Do 
it now...