Hi Ron,
Although al bit late I may have some suggestions for PSK. I also
build a BITX20 for PSK. Last weekend I completed the interface from
the TRCV to the soundcard. The schema is uploaded as a PDF file in
the file-box.
Some remarks:
- To avoid "earthloops" effects I used two tr's 1:1 from an old
computerswitchingsupply. I also used an optocopler from the same
supply. You can recognize the optcoplers by the DIL6 package. (pin 1
Anode D, pin 2 Cathode D, pin 3 NC, pin 4 Emitter T, pin 5 Collector
T, pin 6 Base T).
- You can easily check for low frequency sounds (earthloop and
others, special lower than 500 Hz!!) by using the waterfalldiagram in
HamScope. No lines no sound. To avoid every possibility I used 3u3
capacitors between the stages of LF. The low frequency's below 500Hz
are almost blocked. (See picture HamScope in picture box).
- The signal send to the computer by Line in comes back by Line out.
To my suprise came peaks of the signal through T6 and T5 to T4.
Oscillation was the result. T3 was added as a switch.
- When I used SpectrumAnalyzer I saw a peak in the signal I first
could not explain (see picture in the picture box). After a while I
discovered that the output impedance of the LM386 did not match with
Tr2. First I added a variable resistance. The value had great affect
on the frequency spectrum! Check with SpectrumAnalyzer. R18=33 ohm
was the best in my situation.
- The oscilator in my BITX20 will (if possible) be a VXO on 24MHz.
The reason for this is simple: lots of cristals in the junkbox and a
good supression of the signal by the Pi-filter. I can vary tot 5 kHz
when I use three crystals. But the frequency of the oscilator also
goes about 5 Kc up when a crystal is added!
The VXO is not ready yet. I still have to work for enough output for
the balance mixer.
With CWGet it is possible to decode CW in the first part of the band.
When everything is working well iI wil order a special crystal for
PSK.
73,
Ruud
PE2BS
--- In BITX20@..., Ron Brink <pa2rf@y...> wrote:
Dear bitx20 homebrewers,
I intend to build the BITX for the 17m WARC band (18.068-18.168
MHz). My ultimate goal will be to work psk31 with this splendid rig.
Has anyone suggestions to convert bitx20 to bitx17. VFO must be
changed of course and RF filters... I intend to keep my progress
updated on my website (see below).
73 de Ron
PA2RF
pa2rf@y...
---------------------------------
Do you Yahoo!?
Yahoo! Search presents - Jib Jab's 'Second Term'
