Hi Bruce,
Switcher, yes. But with a fair bit of filtering on it. See page 18 of
http://www.thinksrs.com/downloads/PDFs/Manuals/FS730m.pdf
Switcher to get +24 V, LC-filtering with two serial 1,28 kHz filters.
Then an LDO (LM1086CS-ADJ) to drop it to +22 V which is actually used.
700 Hz and 2 kHz doesn't sound like modern switching rates.
FLL/PLL? No.
Cheers,
Magnus
On 03/22/2013 10:01 PM, Bruce Griffiths wrote:
Switch mode power supply ?
FLL or PLL loop?
Bruce
Magnus Danielson wrote:
Fellow time-nuts,
I got the oppertunity to measure a cesium with my TimePod, I hooked up
on the FS 730/1 and noticed a bump in the phase-noise. I by-passed it
and the bump was not there. Turns out that it had a 20 dB increased
phase-noise at 700 Hz. So, we tried the other FS 730/1 they had, and
it showed the same 20 dB increase, but at 2 kHz. It was not changing
with load. There was a fair amount of 50 Hz and 150 Hz in the spectrum
too.
It was a fairly wideband rise of noise, rather than the spikes.
I did look in the schematic, but did not have the time to measure
inside them.
Have people seen this before? A fair idea of what aspect in the design
which is to blame? Let's learn from this, right?
My ideas so far:
The input has a low-Q LC filter, could it be the noise shaped as it
goes into the input limiter, considering that the LC filter might be a
little detuned from 10 MHz.
Another theory would be a resonance in the power, but I have not found
an obvious place in power design that would be a give-away.
So, thoughts? Bob? Bruce?
Cheers,
Magnus
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