At 18:24 20/07/2002 +0200, you wrote:
Hi Jim,
you measured field strength at distances between about 1.5 and 3km.
did you ever measure at distances >3xlambda, p.e. abt 7km?
if you did, did you notice different results caculating the ERP?
regards
Uwe/dj8wx
Dear Uwe, LF Group,
Yes, last year I measured field strength at distances between a few 100
metres and about 10km - The ERP calculated was reasonably constant provided
the distance was greater than about 600m. Dick's measurements seem to show
that this is also true at 329km, provided you take ground loss into
account. Distances < 600m gave higher apparent ERP, which is consistent
with being in the near field of the antenna.
The text books say, with various qualifications, that the far-field region
with FS proportional to 1/distance starts at about lambda/2pi, ie 350m at
136k. The limiting factor for long distances would seem to be the presence
of skywave, especially at night. I used distances between 1.5 and 3km
partly because I knew these would give consistent measurements with good
SNR, and partly to reduce the amount of petrol I needed to put in my car!
Cheers, Jim Moritz
73 de M0BMU
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