[time-nuts] Measuring power supply noise

Nic McLean mcleannb at bigpond.com
Sat Sep 4 10:14:51 UTC 2010

Kewl idea,
I have used TIMS's for 30 years or so and owned one for the last 10 years.
Inever thought of using one to measure power supply noise.
Well done.

There was a thread about power supply noise a while ago and the difficulty
of measurement. I've just got hold of a piece of test equipment that I've
been after for a while that is good for comparative checks. It's an HP 3552A
Transmission Test Set. Designed for testing telephone lines, its basically
an AF signal generator, level meter, frequency meter, monitor amplifier and
line iterface in a portable box. Ignoring the generator, the line interface
will allow direct connection to supplies of up to 75V and the level
meter measures noise down to -90dBm (600ohm) with low pass filters
available. The frequency meter is PLL based and locks on to the predominent
frequency. Its specified for 40Hz to 60kHz but responds down to 10Hz. The
line interface also has a switchable constant current "hold" circuit that
lets you add a 28mA load. The speaker allows you to listen to the noise. A
quick check of a switching supply gave -42dBm at 450Hz off load and -45dBm
at 1.5KHz at 28mA. A nice general purpose audio tester that is not well
known. Cost was less than $40.
Robert G8RPI.

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