Thanks Roelof - Im the same - Ive tried countless revisions of isolations and earth points and probably close to optimum within local site conditions (overhead power to my left about 300ft away)
The large standard 1ohm 1mH 10m sided VLF loop is the same design we used for VLF research in Antarctica/North Pole on the transglobe expedition back in 79/82, but for the life of me I couldn't recall the transformer details; but having been given a prod by Jim/Edgar/Luis et al Ive figured out what it was using some of the pictures of the AWESOME receiver and when it gets light Ill try this new winding ratio and thicker primary wire.
We ended up not being able to use the VLF receiver up in the Arctic as we were located in small huts just near the end of the runway at CFS Alert in 81/82 and the runway lighting noise was awful - the VLF array was moved onto fast sea ice but still the noise was too bad for whistlers etc.
> From:
[email protected]> To:
[email protected]> Date: Tue, 9 Feb 2016 12:24:14 +0100
> Subject: Re: LF: RE: Vlf ot Penguins and awesomes - More
>
> Hello Laurence,
>
> For your interest.
>
> I do not know how you couple the E-probe to your receiver.
> For years, I have been using a rf - isolating transformer to
> separate antenna and receiver ground.
>
> This is a home made transmission line transformer, consisting of 11
> bifilar turns on a small high mu toroid (AL=8300). The inductance is
> 1.2 mH. The measured -3dB bandwidth in a 50 ohm system covers 4 kHz
> - 200 MHz.
>
> It appeared that the isolation was not perfect, due to the
> inter-winding capacitance. I have made a new transformer on the same
> core with two windings of each tree turns. The windings are opposite
> each other on the core. The bandwidth is now 45 kHz - 50 MHz. The
> loss is 1.3 dB.
>
> Despite the raise in the lower -3dB point, reception at VLF is much
> improved due to lower noise ingress. See attachment.
> The screen runs from 1 kHz - 13 kHz. At the right hand the dashes
> from the Russian Alpha system can be seen. The white band is with
> common ground. Harmonics of the 50 Hz mains can be easily spotted.
> In reality the picture will be better,as the sensitivity of the
> PERSEUS drops considerable below 10 kHz.
>
> The level of interference on 380 kHz caused by a plasma TV in the
> neighbourhood is also much reduced.
>
> Like you, I found that local noise on a loop is much worse.
>
> 73,
> Roelof, pa0rdt
>
>
