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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