Are you doing DGPS? An an alterative to the roll-your-own SDR, tou can build a direct conversion small receiver or IF converter with a SA602 chip, which contains a Gilbert cell mixer and a local oscillator.
Here is a board that will do most of what you want, if you're willing to live with the SA602 limitation. http://home.att.net/~jacksonharbor/lfconv.htm You will get out of this board LO + (0 to 500 Khz), which you can the receive with an existing receiver that can receive the LO frequency. It comes with 4.0 and 10.0 MHz crystals. Here's an article about better input filtering against AM broadcast band interference, which will be useful for you no matter what route you take for LF and VLF reception. http://www.cliftonlaboratories.com/jackson_harbor_press_vlf_converter.htm There are many ham and non-hams who are using very low bit-rate signals in LF and VLF at micro power levels. As a result, they care about frequency stability, and some are building their own RX equipment. Here's a random sample: http://www.qrss.thersgb.net/Receiving-QRSS.html . Murray Greenman who is a member of this group did some pioneering work in VLF TX using the FE5680A as a transmitter, and he may have something to contribute on RX as well. If you need better phase noise and frequency stability, you won't get that from a product like the SA602, not the least because of its internal oscillator. You can build a receiver or IF converter yourself out of discrete mixers from Mini-Circuits, but you'll likely need a preamp as well as they generally require higher drive points (more loss), and output filters as well to deal with the image rejection. Leigh. > Hi > > I want to build a small, cheap, yet precise long-wave receiver which > can be > tuned from the computer in the 2KHz - 200 KHz range (the intended use > is to receive various time signal stations). > > Does a chip for such a receiver exist? Should I take the SDR route? > I designed a DCF77 receivers some years ago, but I need something > more flexible (and a bit more modern...) > > - Marc Balmer > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.