[RFI] FW: Quiet Switching Power Supply?,

[Jim Brown]

On Fri,8/5/2016 3:19 AM, Rob Atkinson wrote:
> Balanced line operators need a pair of identical thermocouple amp
> meters arranged so as to be easily inserted in the line to measure the
> current on each side simultaneously.

Identical is the key word here. Remember that the coupling of noise in a 
system is due to the imbalance, which is the DIFFERENCE of two currents 
that are quite close in amplitude. Thus, very small errors in the 
measurements of the two currents result in a large error in the common 
mode current in dB. Those errors include the precision of the match 
between the two ammeters, the precision to which they can be read, the 
difference, at the measurement frequency, of any stray L and C in the 
coupling to the two thermocouples.

73, Jim K9YC