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Edgar,
this sounds like a very interesting
concept, though perhaps not easy to realize.
In principle, the two reference frequencies would
allow you to measure and track both the samplerate ratio and the
LO difference between the receivers. By interpolating and frequency
shifting of one of the data streams, you will generate phase-coherent
channels, allowing you to create a two-element steerable array. Maximum ratio
combining for HGA could then be used maximize the gain towards Europe
while minimizing noise pickup from other directions.
However there may be some limitations in that
approach. Due to the large receiver baseline (26
lambda), you cannot avoid creating a feathered-up antenna diagram
with many narrow lobes. The largest benefit could arise from the ability to
place a null on interference, which won't work so well with a
narrow null versus a distributed noise source like a thunderstorm field.
Also, due to the distances within Europe, maximizing the gain for HGA will not
always necessarily peak the signal from DK7FC. And with changing
propagation, there may also be some variation in direction of
arrival, which would have to be followed by some slow adaptation of
the weighting factor. By these aspects, a simple E-H cardioid in one of the
sites, or a pair of more closely spaced elements might be an easier
choice.
I have been following your experiments with
interest. Looking at the two grabbers, Stefan was sometimes visible in
Moonah but not (or at least not much) in Orford. Not sure whether that's due to
some intrinsic noise in the Orford setup (then you might end up making
things worse by adding in Orford data), or Stefan being weakened by the extra
distance (then Orford data would still be useful to partially null
QRN).
As far as I know, Paul Nicholson is using a
somewhat reminiscent setup on VLF: He has two loops and one E-field probe, whose
data streams are synchronized a posteriori using GPS-derived second ticks.
He then combines the loop signals using adaptive weighting for minimum
QRN level.
Best 73,
Markus (DF6NM)
Sent: Tuesday, October 08, 2013 2:26
AM
Subject: LF: Signal detection
question
Hi Group,
I have recorded signals from
HGA22, DCF39 and DK7FC from two antenna/receivers at different
locations.
The locations are 58 km apart. Recordings are 16 bits, mono,
22050 Hz, and 1.5 hours long.
The "space" signal from HGA22, (135430 Hz)
is usually stronger than from DCF39 (138830 Hz).
Is the a method that can
use the signals of HGA22 (or DCF39) as a clock (reference) to look for the weak
DK7FC signal in the recording?
I am wondering if the two wave files could
be synchronised in some way to and then added together to cancel out the noise
and highlight the DK7FC signal frequency.
Regards, Edgar
Moonah,
Tasmania.
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