Hi Roger,
Am 08.09.2011 13:37, schrieb Roger Lapthorn:
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?
Yes this is of course possible too. What i have not drawn in that
circuit is a PLL stage that lockes the LO frequency. I use a 10 kHz ref
frequency for that but just used that a few times and think about
throwing it out again.
Last weekend in France i received OE5ODL's "5" in QRSS-60 too. Just a
very slow drift, no problem. But my RX was inside the car and so
temperatures change when opening and closing the door. At home this is
even less critical i assume.
Maybe you need both a GPS derived 10kHz signal to calibrate SL and GPS
derived 10MHz for the converter.
Well if you use 10 MHz ref frequency and down divide that by a 4060
(you will need HC or HCT types then) you will get even lower
frequencies than needed. If one of these (e.g. 10000 kHz / 64 = 156.25
kHz for the LO and then 10000 kHz / 512 = 19.53125 kHz for the
soundcard drift correction) frequencies are further down divided, you
can use the 10 MHz ref for soundcard locking as well. You can then
simply inject that frequency to the converted signal (say using a 100
pF cap or so) or run the PC in stereo mode and use the 2nd channel...
73, Stefan
73s
Roger G3XBM
2011/9/8 Stefan Schäfer <[email protected]>
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
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
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