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Re: VLF: E-field receivers in Todmorden

To: [email protected]
Subject: Re: VLF: E-field receivers in Todmorden
From: Jacek Lipkowski <[email protected]>
Date: Sun, 10 Sep 2017 20:06:30 +0200 (CEST)
In-reply-to: <[email protected]>
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On Sun, 10 Sep 2017, Paul Nicholson wrote:

Merging the currents from multiple front-end devices is a
conventional way to achieve ultra low noise and this looks
like a good implementation.

I tried this technique with two devices but the doubling of the
input capacitance reduced the signal by as much as the noise
was lowered, no overall benefit (in fact slightly worse).
This kind of thing shows up when you refer the system noise
to field strength V/m instead of just input voltage.
you would also need to have a proportionally bigger antenna (2x
capacitance for 2 fets etc), OR you can use multiple e-probes, each with
it's own fet :)
the latter can be easier to implement in some situations, for example
using 8 beer cans for eprobes each with it's own fet might be simpler than
a beer keg and 8 fets in parallel, both configurations should
theoretically give 9dB less noise (assuming that the capacitance of 8 beer
cans is equivalent to that of a keg of course). the added benefit is that
50Hz noise isn't in-phase in different locations near homes (unless
everything is fed from the same phase), some some of it will cancel out.
it's a concept i've been thinking about for some time now, but never got
around to implement it. even it you have the antennas quite far apart, you
don't need to care about phasing at kHz frequencies.
VY 73

Jacek / SQ5BPF


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