Message-ID: <4E68988D.40108@iup.uni-heidelberg.de>
Date: Thu, 08 Sep 2011 12:27:25 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org,
        Alejandro D Alvarez LU8YD <alex2003@infovia.com.ar>
Subject: LF: My LF /p RX...
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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