Thursday, April 25, 2013

Looking for the Square Law region (III)

... and all I can say is I found it!

Last weekend I assisted to a small ham radio flea market surprisingly with a lot of microwave hardware. Thanks to Andrés EB4FJV, I was able to get a DC to 18GHz Narda crystal detector. My idea was to use it as a relative measurement device, just to peak circuits at maximum output.

Sunday, April 21, 2013

DRSB-01 Geiger counter failure

My DRSB-01 ( ДРСБ-01 ) geiger counter has gone mad. Far from any source it gives up to some counts per second, when the normal rate for it in my home is around 20 counts per minute.

Once opened was easy to spot the failure: The high voltage applied to the tube was around 800 volts. The normal working voltage of the SBM-20 tube is around 400 volts, so 800 volts produces self-triggering, and therefore, the extra counts.

Monday, April 15, 2013

Counterfeit batteries

Some days ago I was given a dual SIM chinese Android phone. The LCD screen was broken and the battery was noticeably swollen, so nothing could be usable. I noticed the battery was a Nokia-like battery, even with the same prints on it, but obviously a counterfeit battery.

Friday, April 5, 2013

WiFi antennas on 2320 MHz

In the ham radio community is quite common the first experiences in the 2.3 GHz band are made using WiFi antennas. In most parts of the world the 13cm ham band is (still) 2300-2450 MHz, and the WiFi band is 2400-2484.5 MHz, so both bands overlap in a extension of 50 MHz.

But unfortunately in this area of the world narrow band work in the 13cm band is done around 2320.2 MHz, and in this frequency most WiFi antennas simply suck.

Wednesday, April 3, 2013

Singing capacitors

Today I have been repairing a 12 year old 15" LCD monitor. It had no apparent fault, everything worked nicely, but the monitor produced a extremely strong high pitched tone (around 18 kHz) enough to produce headache in only two minutes.

Usually high pitched noises come from the switched power supply. In the past I have found switched power supplies with loosen transformer cores that produced noise just like an speaker.