Date: Sat, 4 Apr 2015 23:22:05 -0230 (NDT)
From: jcraig@mun.ca
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: VLF in Canada/ G3XDV Traces
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Hi Markus,

That was exactly the quantitative info that I was seeking for 
further progress.  Thank-you very much for this and your advice.

Mike -- I saw some smudges, an "X"  but little else since 0100 just
a bit above 136.172 kHz.

73
Joe VO1NA

On Sun, 5 Apr 2015, Markus Vester wrote:

> Hi Joe,
>
> sounds good! At 1.25 km you're still in the reactive nearfield, where signal transfer occurs by capacitive coupling rather than Hertzian wave propagation. In that regime, electric field strength is governed by an inverse cube law, falling off rather steeply at 60 dB per range decade.
>
> The SNR of your audible CW signal would probably have been on the order of 10 dB in 50 Hz. If you went to QRSS-3 you'd gain around 20 dB, which would get you to 2.7 km. To reach the radiation field boundary (lambda/2pi = 5.77 km), you'd need another 20 dB, or 100-fold symbol length (ie 300 s dots). The good news is that beyond that point, it gets much easier to go further at 20 dB/decade.
>
> For the very slow modes, it would probably be better to do away with the receiver and connect the antenna directly to a laptop soundcard. Then you can use SpecLab's sophisticated samplerate tracking functions and achieve ultimate frequency stability.
>
> On the transmit side, it's more important to design the antenna and coil for voltage capability than for highest Q factor. It's relatively easy to overcome losses by a stronger power amplifier. Maximum achievable ERP from a small electrical antenna scales with (voltage withstanding * antenna capacitance * effective height)^2 * frequency^4.
>
> All the best,
> Markus (DF6NM)
>
>
> From: jcraig@mun.ca
> Sent: Sunday, April 05, 2015 12:33 AM
> To: rsgb_lf_group@blacksheep.org
> Subject: LF: VLF in Canada
>
>
> Dear Group,
>
> Last summer, my VLF CW signals were copied outside my back yard. Today,
> using a Marconi XH-100 with a SRA-8 mixer & AD9850/Arduino LO and a
> National LF-10 preselector, the sigs could be clearly heard outside my town
> with a 20 metre wire aerial strung between the car and a road sign.  For
> TX, the 100m wire (~15 m high) was coupled with 425 mH to a variac (2:1) in
> series with a 5:1 ferrite xfmr to the keyboard amp with the volume control
> set to 5 (about 30 watts).
>
> This is DX record on 8.277 kHz for this station -- 1.25 km! I wonder how
> far away it could be copied with QRSS?  Any TA attempt will have to wait
> until a higher Q tuning coil appears.  The DC resistance of the current one
> is almost 1k and I think it has much series capacitance. It gets warm
> and emits an stench of ozone when in use.
>
> 73
> Joe VO1NA
>
>