FFT -> excise hum lines -> IFFT, before blanking?
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Friday, January 19, 2018 11:14 AM
To: [email protected]
Subject: Re: VLF: 300 mA on 4470 Hz, 67 km band
> Wouldn't it be possible to place the loop antenna > (at least for a test)
> high on the mountain,
The location here is bad for VLF, so many power lines. If I posted a sample of
the raw signal from the antennas, you would be horrified and wonder how
anything could be received through that.
I have tried with a portable rx on the local hills but the situation is no
better, usually worse! There are some large grid lines crossing the country
nearby.
As I get better with building reliable receivers I begin to think about a
remote site. Perhaps further north in the Yorkshire Dales. Only a 90 minute
drive - 60 minutes if I
take the Evo. I'm often up there climbing and rarely see any
power lines. Too far for a direct radio link but some other arrangement could
be made. I could rent a corner of a field from a farmer (just as I do here)
plus internet and power.
Or perhaps I will move up there, or to North Wales or the Lake District. Then
I could do astronomy again and the mountains would be nearer too.
Meanwhile, I might try moving the H antenna. The hum seems especially high
where it is for some reason. An underground stream runs beneath the antenna,
only a couple of metres down.
It drains water off the moors and I often wonder if it forms a channel for
ground currents too. When the weather improves I will take a portable rx to
survey the H hum in that field
and try to prove that. It is complicated to hum-survey the
H field because the level changes all the time anyway. You must record hum
(orthogonal components) plus some reference signal, eg GBZ, and at the same
time record hum and reference
on a fixed antenna to normalise the readings. This ought to
be easier now with an Rpi, 2-channel Audioinjector card and a GPS module -
another construction project on my to-do list.
--
Paul Nicholson
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