Hi Markus,
very nice experiment! I did something similar some time ago:
http://people.physics.anu.edu.au/~dxt103/472/small_loop/
I would like now to make a larger loop using a 20m thick coaxial cable
and try to get that impedance as low as possible to increase the
efficiency. I will be setting this up out in the open in order to
avoid the influence of nearby object. Good to know that the FKP-1 caps
did not have any problems with the 7.8 A current. I am planning to use
either the FKP-1 in series as you have done, or some large broadcast
type silver mika (5 kV rated).
Good fun!
73, Dimitris VK2COW/VK1SV
2015-06-25 5:07 GMT+10:00 Markus Vester <[email protected]>:
> 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)
>
> From: IK1WVQ Mauro
> Sent: Wednesday, June 24, 2015 7:30 PM
> To: [email protected] ; [email protected]
> 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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