[time-nuts] Z3801A Internal A/C Supply ??

[Charles Steinmetz]

Dave wrote:

>Should I be concerned about.....
>
>1) Noise from the supply or the A/C lines now inside the box

Yes, you should always be concerned about both radiated and conducted 
noise generated by switching supplies, inside or outside the 
enclosure.  Personally, I would never run the output of a switcher 
directly into (or inside) any electronic equipment that receives, 
processes, or generates precision signals.  At the very least, I 
would package the switcher in a separate metal enclosure with a 
linear cleanup regulator and appropriate RF filtering, and feed the 
cleaned-up DC through a shielded cable to the instrument (allowing 
the supply to be located a meter or more away from the 
instrument).  NB: the shield should NOT be the power supply common 
conductor.  It should be connected directly to chassis at the 
instrument, and either floating or bypassed (0.1uF) to the chassis of 
the power supply.

I like the Philmore "multi-pin mobile connectors" for this (see 
below).  I hard-wire the cable at the power supply end, and use a 
male chassis socket on the instrument and an in-line female plug on 
the instrument end of the cable.

The power supply "hot" and common should be bypassed (0.1uF) to the 
instrument chassis right at the socket, then they should pass through 
a common-mode filter, before being fed to internal circuitry.

>2) Heat from the supplies, as I said they are hardly warm to the 
>touch after running for two day.

I doubt you need to worry about this, if they are cooler to the touch 
than the OCXO.

Best regards,

Charles

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