Hi Alberto and all,
I can't explain the blurb, but IMO the rest is mostly
noise from an SMPS. This power supply has a full wave
bridge rectifier from the mains, feeding a large
capacitor. Across the ESR of the capacitor is noise
at the switching frequency of approximately 20870 Hz.
The bridge conducts for about 2 ms each half mains cycle.
When it is off, the noise source is effectively
disconnected. On alternate half cycles, the noise
is connected to the mains with opposite polarity.
In effect, the input bridge is a balanced mixer,
multiplying the 20870 Hz carrier by the distorted mains
current waveform.
So the noise conducted to the mains is primarily
20870 Hz +/- odd multiples of the mains frequency.
The balance is imperfect, so you can see faint lines
at the carrier frequency, and at offsets of even
multiples of 50 Hz.
73,
Stewart KK7KA
----- Original Message -----
From: "Alberto di Bene" <[email protected]>
To: "LF Mailing List" <[email protected]>
Sent: Wednesday, March 26, 2003 9:27 AM
Subject: LF: VLF signals
Hi all,
I have just built a small indoor loop, and have connected
it to the sound card. No preamp, just a step-up transformer.
I see the signals visible in the attached picture. Is anybody
able to recognize them ?
Some of the signals seem to be spaced 100 Hz, but going
to higher resolution, the spacing is just a bit short of 100 Hz...
And the blurb at 20200 - 20300, is it an RTTY ?
TNX
73 Alberto I2PHD
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