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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)
>
>
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