Hi Mauro,
this is a single turn loop, around 3.5 m wide and
3 m high, now consisting of the braid of a piece of RG-216 coax cable.
Required capacitance for 475 kHz is 7.1 nF, made from five 33nF FKP capacitors
from the junk box, plus a couple of styroflex for fine tuning. It's fed
through a small ferrite toroid, 32 turns primary, 4 secondary. Loop
resistance at MF is about 0.57 ohm (Q~83), presumably largely affected
by losses from the nearfield environment (reinforced walls, house
wiring, etc). Using 35 W RF the loop current is 7.8 A. Some pics of the former LF loop tests (32 A, 250 uW)
are at http://df6nm.bplaced.net/LF/Indoor_Loop/ .
The purpose of this experiment is mainly to
be able to provide a signal for receiver testing, which (unlike my
Marconi) can be left on air during unfavourable weather. But
it's really inefficient: An old ENI broadband linear amplifier
converts 140 W DC into 35 W of RF, of which only ~ 2 mW
are radiated.
Yes it works also for WSPR - a couple of
nights ago I did get spotted by DK7FC, F59706 and SP5XSB. During the
daytime the range would be much shorter, and the signal is definitely too weak
for a decode in Heidelberg.
Best 73,
Markus (DF6NM)
Sent: Wednesday, June 24, 2015 7:30 PM
Subject: Re: LF: 476.181 kHz from indoor loop
very interesting for WSPR tests !
few
questions:
- mono-turn or multi-turn ??
- what are you using for
match to TX ???
many thanks and
73 de Mauro IK1WVQ
At
12:11 24/06/2015, Markus Vester wrote:
>I am currently running a DFCW-60
beacon on 476.181 kHz, using the
>same 10m^2 indoor transmit loop as
previously on LF. With 35 Watts
>of RF input, estimated radiated power
is around 2 mW, with lobes
>pointing west and east.
>
>The
daytime groundwave signal is visible in the bottom panel of the
>DK7FC
MF grabber. Going by the CCIR plots for 3 mS/m conductivity,
>the
groundwave attenuation for this distance would be about 23 dB in
>excess off lossless 1/r propagation, resulting in approximately 0.2
>uV/m in Heidelberg.
>
>Best 73,
>Markus
(DF6NM)
>
>
