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
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