30 July 2009

The word of experience

Finally I put my Tek 7603 oscilloscope into service. A friend (the one from optical experiments) needed to verify a circuit he's building. Those were routine tests, not troubleshooting.

While probing for a couple of signals (ca 3 kHz, 15Vpeak) I noticed a strange random behavior: either the signal was as expected, or was passing through a high-pass filter (only spikes instead of edges).

The first problem was easily tracked down to a cold solder joint since it showed properly when touching the generating IC.

The second ghost was trickier: all joints were ok. It was a digital signal... where was the high-pass effect coming from? While checking for continuity with an ohm-meter backwards from target to source pins (with ICs removed!) I came to a homebrew connector with 2.54mm (1") pin headers ... on the corresponding pin tip I could not get a proper contact, while at the pin base it worked alright. Very suspicious. I touched the pin and asked right away: "what did you do to it? Glue?"

He admitted that the building instructions showed a way to hold the strip while soldering: put it into a roll of packing tape. !!!!!!!!!!!!!!!!

21 July 2009


After shooting the long wave NDB (non-directional beacon) CAS, I happened to have the chance to shoot another NDB in Croatia.

It is NDB ZAG, whose coordinates can be found on Internet. Unfortunately I had forgotten to plan in advance the road to get close to it, so I asked my brother back home to send me some info via SMS. It turned out that Internet is far more detailed than any other paper map I could locate and I failed to reach the NDB location.

I had to blind shoot it while driving at 90 km/h on the high speed road going to Vrbovec. It sits North of that road. The digital SLR helped to get the antenna into the frame.

This second picture is cropped from a 10Mpixel image and digitally zoomed 3 times.

After these shots I tried without success to get close to the beacon site, but nothing. Village names on Internet are not written anywhere in the real world! Now I've checked through a web service with satellite pictures how to get there, so perhaps I'll try a second approach on our next trip to Zagreb.