Jim,
Thanks for the updated preamp schematic. What would you recommend as a suitable alternative to the ZTX690B device in your 8.97kHz preamp as I don't think these are available nowadays?
All,
Thanks for the latest data on the VLF experiments. I'd been away for a week, so missed the thread until yesterday. Sounds like Stefan's signal was received all over the place. Quite remarkable work by all concerned.
73s
Roger G3XBM
On 24 March 2010 11:51, Rik Strobbe <[email protected]> wrote:
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 "receiving" all happen on a 1 by 3 meter table and the frequency is between 180THz and 1.1PHz. TX (pulsed laser) and RX (with photomultiplier serving as "active antenna") use a common reference frequency what cancels out any drift problem.
For VLF a signal like DCF77 is available as reference: 77.5 kHz divided by 26 and then multiplied by 3 gives 8942.3 Hz (what will ensure that none of the TX harmonics will block the reception of DCF77).
I would expect that during daytime and in a range of 500 to 1000 km around Frankfurt the DCF77 signal will be phase stable and thus suited as a 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 expensive than the Perseus, and more important, it goes down in frequency to "almost zero" (unlike Perseus, as mentioned here before). Don't get this wrong, Perseus is a superb radio too, but there's no easy way to bypass the input bandpass (highpass). I use Perseus on HF, and SDR-IQ on LF, VLF, and to listen for bats(!) .
Most soundcard's are fine too, and for the next experiment, you will be able to use the ALPHA signals to permanently calibrate the soundcard's 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 Mär 2010 09:50:19 CET
Von: "Rik Strobbe"<[email protected]>
> 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 copper
> >clad PCB.
> >
> >There are quite a few people around with a PERSEUS SDR, who are probably
> >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 suggested
> >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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