[time-nuts] Phase noise measurement (was - no subject)
bruce.griffiths at xtra.co.nz
Sat Aug 21 20:03:48 UTC 2010
Poul-Henning Kamp wrote:
> In message<7c37.12cdef25.39a12f3e at aol.com>, EWKehren at aol.com writes:
>> I am not seeing it, what should I use to measure it 3561 and 70000 spec
>> analyzer do not show it?
> It is probably the 3561 not the 70k that has the best chance.
> I am not aware of the precise characteristics of the noise, but it
> sounds somewhat like a boiling pot.
> I became aware of it first time when I ran a small class-A audio
> amplifier from a couple of, probably too, small VRLA's some years
> ago, just for the fun of it.
> With no input signal, the speakers would gurgle faintly and it took
> me some time to locate the source of the noise to the batteries.
> I would guess its amplitude correlates with the ratio of discharge
> current to plate area, since it is chemical/mechanical in nature.
> These days, I would build a super-cap battery instead if I needed
> a low-power PSU with low noise.
> PS: also be aware that almost all VRLA's have a very nasty resonance
> frequency somewhere in the low MHz band. If you are after low noise,
> you should always decouple the battery good poly/plastic caps right
> at the terminals.
NIST found that NiCd cells are very quiet at least for low load currents:
Thus batteries are useful as low noise voltage references or for
providing the relatively low base current of a BJT in a low phase noise
Perhaps its the gelled electrolyte that is the source of the noise
problem with VLRA batteries??
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