They may also be modulating it to spread out the peak energy to meet EMI
requirements.
Tom
----- Original Message -----
From: "Chuck Harris" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Sunday, December 07, 2014 8:41 PM
Subject: Re: [time-nuts] 1900kHz radiolcation testing on east coast US?
Hi Tim,
Look for a switching power supply that is fairly new, and is
of the sort that doesn't need to be messed with to cover the full
120V to 240V range.
That sort of switcher is also known as a power factor correcting
switcher. It has a PWM switched pre-regulator that takes the
unfiltered ripple straight from a full wave bridge rectifier, and
PWM's it so that it can charge the filter capacitor, without the
power line seeing anything but a resistive load. It also controls
the inrush current.
PWM pre filters, because they quickly shift the pwm signal at a
120Hz rate, are capable of producing lots of broadband 120Hz
modulated garbage if their shields, or filters are compromised.
-Chuck Harris
Tim Shoppa wrote:
Would any time-nuts know of radiolocation-type testing going on, on east
coast of US, maybe around Maine? There is a very strong wideband signal
on
1900-1920kHz, with a 120Hz substructure and a 4Hz rep-rate, likely
megawatt
power range.
Sound sample (recorded with 2400Hz receiver bandwidth, although the whole
signal is far far wider bandwidth) at
http://www.trailing-edge.com/1910-intruder.wav
Pics of the waveform at http://www.trailing-edge.com/1910-intruder-1.png
and
zoomed in at http://www.trailing-edge.com/1910-intruder-2.png
Tim N3QE
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