Re: LF: My LF /p RX...

[Roger Lapthorn <rogerlapthorn@gmail.com>]

That is neat Stefan.

Presumably one could use a 10MHz GPS locked source and divide this down as the LO and produce an output directly for SL. Then the converter could be used for extremely narrowband modes too? 

Maybe you need both a GPS derived 10kHz signal to calibrate SL and GPS derived 10MHz for the converter.

73s
Roger G3XBM

2011/9/8 Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>

LF,

Some OMs asked me to show them my /p LF receiver circuit. So i took some time and draw another ugly schematic ;-) A colleague took a photo which is far better as of my mobile phone camera...

It was a grown project and some things could be done different but the RX works well and seems to be sensitive. The CW QSOs with M0BMU, G3KEV, DF6NM, PA0A and HB9ASB were done with this RX.

The RX has a 50 Ohm input and uses a SBL-3 DBM. The circuit just uses a single BF862 amplification stage (about 20 dB gain), the rest is passive. LO frequency is 125 kHz which is achieved from down dividing 4 MHz (xtal) by a CMOS4060. So the IF is at 12 kHz for a 137 kHz signal. 12 kHz can be sampled by the soundcard and so it can be processed by SpecLab. In SpecLab, further band limiting, noise blanking, a auto notch filter, a frequency shift to a 700 Hz CW sidetone and a narrow CW filter can be realised.
It is a wideband receiver that displays 125...149 kHz if a sample rate of 48 kS/s is used. Some internal filter are focusing on the LF amateur band and provide a limiting of strog outside BCD stations such as DLF, DCF39 and so...

The circuit consumes just about 12 mA at 12 VDC! Thus it is possible to run it in combination with a 1W 5VDC->12VDC converter supplies by the USB port of a netbook. I found that this causes NO further QRM in the frequency range of interest! It rather can be an advantage since the system can run completely floating. So no additional battery is needed in /p operation. The box size is 83mm x 66mm x 28mm, so about like a cigarette box.

A photo is here: http://dl.dropbox.com/u/19882028/LF/DK7FC-p%20LF%20RX.jpg

And the homedrawn schematic is here: http://dl.dropbox.com/u/19882028/LF/DK7FC%20LF-p%20RX%20converter.jpg


Thanks to Markus/DF6NM and Ha-Jo/DJ1ZB for suggestions, advice and the discussion! Thanks to Marco/IK1ODO for the SBL-3!!

73, Stefan/DK7FC

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