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| DK7FC's simple 137kHz receiver |
14 Aug 2012
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 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.
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For a fairly small amount of added complexity (and a fairly significant reduction in component cost and availability), this receiver could provide direct conversion quadrature output - which would make a world of difference when it comes to the the software capability.
Even with the advent of low-cost DC SDR's, there still seems to be a severe lack of understanding in the Ham community about the advantages (and, yes - disadvantages) inherent in quadrature receiver hardware. Sigh... 73's WB4ONA
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