G3XBM online grabber

This evening I've been setting up my on-line grabber again so that I can monitor VLF, LF or MF activity and upload what I am receiving to the internet for others to see. The grabber is, at this stage, only on intermittently as I experiment. The plan is to have a dedicated VLF or LF receiver and PC for this purpose, so the grabber can be run almost 24/7.

The main weak signal detection is done using Argo software running on my PC connected from my RX via the SignaLink USB interface. The captured signal is then uploaded to a location in my public Dropbox which is then linked to from my webpage. So, what appears on the G3XBM online grabber page is what I am seeing with Argo. The direct link to the Dropbox image is http://dl.dropbox.com/u/15047843/g3xbm.gif .

G3XBM online grabber

PC based LF/MF receivers

There are some very neat ideas for simple LF receivers around that make use of programs like Spectran or Argo effectively as the second IF and detector stages.

DK7FC's simple 137kHz receiver

DK7FC recently posted his schematic for his 137kHz receiver which used a 4MHz crystal divided down to 125kHz using a 4060 IC with the IF at 12kHz (corresponding to 137kHz) being fed straight into the PC software. With programs like Argo the scale can be offset so that the correct frequency is displayed. Of course, there needs to be some front end filtering to remove the image, in this case at 113kHz. Using this approach one can make a very simple "stand alone" LF receiver for 137kHz weak signal reception. Such an approach is ideal for grabbers which are permanently connected to a PC anyway, uploading the received signals to the internet.

Argo plot of OK0EMW tonight on 505kHz

This is the Argo waterfall plot showing the Czech 505kHz beacon OK0EMW on QRSS3 (slow CW, 3 sec dots) coming in well tonight at 1700z. It was not audible by ear though. Note the QSB in the middle when the number 0 was being sent.