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Date: Wed, 14 Jul 2010 23:10:44 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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In-Reply-To: <BF4A524700075746A6467658DFC7102C51094D0E45@ICTS-S-EXC2-CA.luna.kuleuven.be>
Subject: Re: LF: RE: RE: DLF passive received with earth antenna
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Hello Rik and the group,

Agreed! But i think it is rather easy to make a comparison measurement 
with a samller loop (to the same time). This, i did today in the evening :-)

Riding my bike to the earth antenna means passing 400m altitude 
difference and i become faster each day, currently 40 min :-))). So i 
used a 1m*1m single turn loop and the OP AMP circuit i built yesterday. 
The signal level of DHO38 was as usual -20 dB (changing abt +- 1 dB, 
maybe due to modulation). Sadly the background noise is determined by 
the OP AMP, means no signal of DHO38 when using the small loop.
This background noise is -80 dB or less. So, this means that DHO38 is at 
least 60 dB stronger on the earth antenna (we regard only the signal 
levels, not the S/N). This means that the effective antenna area is at 
least 1000 m^2 which is not surprising since the average height of the 
wire above gnd GND is 4m and the distance between the two earth 
electrodes is 280m :-(
So, nothing is won with this test. I have to do it again. Maybe tomorrow ;-)

Since the OP AMP is not really a low noise type (TLC271), i will change 
it (to OP27 or LT1028) and hope for better reception. Of course i can 
reduce the FFT time as well (was not possible today since upcoming 
thunderstorms forced me to make QRT ;-) ).

73, Stefan/DK7FC

Am 14.07.2010 18:06, schrieb Rik Strobbe:
> Stefan, Jim, LF group,
>
> I agree with Jim that an earth antenna most likely will not act completely as a loop antenna.
> But as an engineer it doesn't matter to me too much, I am more interested in the efficiency of the antenna rather than how it works exactly.
> To know the efficiency you would need to measure the power you can get out af the antenna from the DLF signal.
> Knowing the ERP of DLF, the path attenuation and the antenna RX power you can calculate the antenna "gain".
> To measure the antenna RX power properly you would have to cancel out any reactive component of the antenna and terminate it properly.
>
> 73, Rik  ON7YD
>
>
>