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Re: LF: 476.181 kHz from indoor loop

To: <[email protected]>
Subject: Re: LF: 476.181 kHz from indoor loop
From: "Markus Vester" <[email protected]>
Date: Wed, 24 Jun 2015 21:07:56 +0200
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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 .
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)

Attachment: Indoor_Loop_Matching_MF.jpg
Description: JPEG image

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