Bob Camp wrote:
Hi
Since the LPRO has a "noisy" 3 terminal regulator inside it, making the
outside voltage quiet (as in noise density) probably will not help much.
I've seen people insist on a low noise regulator ahead of a fluxgate
magnetometer that used an LM7805 regulator.
The plastic enclosure was sealed with acetoxy grade silicon and buried
in the ground at the end of 50m of cable with the predictable result.
Keeping the voltage *stable* will indeed help things. I think you need a
high stability linear regulator rather than a low noise one.
One other thing to think about is line isolation at both audio and RF. Most
regulators have poor isolation above a few 10's of KHz.
At least the line isolation can be improved substantially at audio
frequencies by adding active filtering (eg Wenzel style albeit with a
few extra parts to prevent zenering transistor junctions or excessive
base current on startup) at the regulator input. Cascade 2 or more if
you need higher rejection.
RF rejection requires passive filtering.
Bruce
Bob
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Neville Michie
Sent: Wednesday, February 24, 2010 4:57 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Low noise voltage regulators
Hi,
I remember a reference, probably by Bruce, that LEDS provide a low
noise voltage reference.
I am proposing to build a voltage regulator for a thermally
controlled LPRO rubidium oscillator,
with the voltage regulator being mounted on the 0.5 inch thick
aluminium heat sink plate.
The LEDS would also be mounted on the plate, which has controlled
temperature.
The LPRO has internal voltage regulation, and by running it at ~40C
and 18Volts, the thermal
flux within the unit is minimised as is the power demand.
What I want to know is if a LM317 running on a stack of LEDs driven
by the LM317 output
would provide a low noise power source? What would be better?
cheers, Neville Michie
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