Date: Wed, 24 Mar 2010 11:51:25 +0100
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
In-Reply-To: <E1NuNdW-000602-PV@www20.emo.freenet-rz.de>
References: <E1NuNdW-000602-PV@www20.emo.freenet-rz.de>
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Message-Id: <20100324105125.4F2CC31E703@smtps01.kuleuven.be>
Subject: Re: Re: LF: Re: DK7FC's 3rd VLF transmission
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Hello Wolf,

I will have a look at the SDR-IQ.

About the frequency drift problem:
at QRL we frequently use lock-in technique to "receive" very weak signals=
 .
Receive is between brackets as "transmitting" and=20
"receiving" all happen on a 1 by 3 meter table=20
and the frequency is between 180THz and 1.1PHz.=20
TX (pulsed laser) and RX (with photomultiplier=20
serving as "active antenna") use a common=20
reference frequency what cancels out any drift problem.
For VLF a signal like DCF77 is available as=20
reference: 77.5 kHz divided by 26 and then=20
multiplied by 3 gives 8942.3 Hz (what will ensure=20
that none of the TX harmonics will block the reception of DCF77).
I would expect that during daytime and in a range=20
of 500 to 1000 km around Frankfurt the DCF77=20
signal will be phase stable and thus suited as a=20
reference for a PSK link on VLF.

73,

Rik  ON7YD

At 11:16 24/03/2010, you wrote:
>Hi Rik,
>
>I prefer the SDR-IQ for VLF - it's less=20
>expensive than the Perseus, and more important,=20
>it goes down in frequency to "almost zero"=20
>(unlike Perseus, as mentioned here before).=20
>Don't get this wrong, Perseus is a superb radio=20
>too, but there's no easy way to bypass the input=20
>bandpass (highpass). I use Perseus on HF, and=20
>SDR-IQ on LF, VLF, and to listen for bats(!) .
>
>Most soundcard's are fine too, and for the next=20
>experiment, you will be able to use the ALPHA=20
>signals to permanently calibrate the soundcard's=20
>frequency drift (when extremely high FFT resolution is required).
>
>Cheers,
>   Wolf DL4YHF .
>
>----- original Nachricht --------
>
>Betreff: Re: LF: Re: DK7FC's 3rd VLF transmission
>Gesendet: Mi 24 M=E4r 2010 09:50:19 CET
>Von: "Rik Strobbe"<rik.strobbe@fys.kuleuven.be>
>
> > Hello Roelof,
> >
> > thanks for the circuit diagram. It looks pretty simple.
> > If I "read" the circuit diagram correct it is a buffer amplifier (the
> > voltage gain maybe even less than 1, however due to the impedance
> > transformation the power gain is huge).
> > It seems a bit of overshoot to me to buy a perseus (just checked,
> > they ask 850 Euro for it), so my first option would be to go to the
> > PC soundcard.
> > Do you (or others) have any experience with that ?
> >
> > 73, Rik ON7YD
> >
> >
> > At 19:29 23/03/2010, you wrote:
> > >Hello Rick,
> > >
> > >Michael Oexner has had good results with a mini-whip E-field probe I=
 build
> > >for him.
> > >The circuit diagram is in the attachment.
> > >The feedline is CAT5 network cable.
> > >
> > >Note that the RF-isolating transformers in the signal path are not
> > correct.
> > >I have used MCL TT 1-6 parts, rated for 0.004 - 300 MHz at the -3 dB
> > >points.
> > >The common mode chokes are not optimum, as I used the parts I had on=
 hand.
> > >Type 75 or 77 ferrite should be better.
> > >
> > >Michael used a PERSEUS SDR, which has a noise figure of about 25 dB=
 at 9
> > >kHz.
> > >This is due to the fact that there is also a RF-isolating transformer=
 in
> > >the signal path.
> > >
> > >It is amazing that with this not optimized set up it was possible to=
 have
> > >good reception over a 72 km path.
> > >The actual capture area of the antenna is 30 x 40 mm single sided cop=
per
> > >clad PCB.
> > >
> > >There are quite a few people around with a PERSEUS SDR, who are proba=
bly
> > >interested in receiving Stefan's signal.
> > >So a simple antenna design might help.
> > >
> > >I have the parts for an optical link active E-field antenna, as sugge=
sted
> > >by Stefan.
> > >Due to other more pressing matters, I have not yet put them to good=
 use.
> > >
> > >I hope this helps,
> > >
> > >Best regards,
> > >Roelof, pa0rdt
> > >
> > >
> > >
> > >
> >
> >
> >
>
>--- original Nachricht Ende ----
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