Revision 1: Nov 30th 2007. Added 2 protection diodes
January 1st 2008. Added new pictures
What the graph obtained is:
This is a picture of the 0 ray, at middle of the screen, 10 MHz/Div, with the 141T's internal marker 30 MHz@-30 dBm connected at input, but graph is inverted, not like on 141T screen...
What the graph should be...
To capture screen pictures, you can use the very handy freeware MWSnap, available to download at: http://www.mirekw.com/winfreeware/index.html, or any other, among your favorite similar softwares.
Synchro signal on a Sound Blaster PC128
Synchro signal on a C-media wave device
With different sound cards results can be slightly different.
This design, very simple: no PIC, no supply, no hard to find parts. It is made for inversion of vertical output signal coming from the analyser (0 to -0.8 V), and convert it to 0 to +0.5 V. Protection of the sound card is made at two levels, at input and output of the op amp. If obtained levels are too low, replace the 1N4148's (output protection) by LED's.
Power supply is taken out of Pen Lift output 0 to +18 V pulses.
Use only LM358N op amps, as they include ground in their common mode range. Use shielded cables between interface and sound card, preferably with independant shielding for each wire to avoid "crosstalk".
Layout and PCB
View & 3D simulations of the board
Reference line -80 dB is now at lower part of the screen, like on spectrum analyser display. That's All Fox !!!!!!
You can download this page, and files necessary to make the PCB:
Dominique - firstname.lastname@example.org OR