[Lowfer] 600MRG> Question about parallel diodes

[ToddRoberts2001 at aol.com]

In a message dated 6/6/2010 1:53:39 A.M. Eastern Daylight Time,  
ku4xr at yahoo.com writes:

The article I read, ( and saved ), was about the noise generated
in the  power supply used for an active antenna. The writer 
mentioned adding .1µF  caps across the diodes to lower the noise 
generated at LF, and VLF. The  article was from 2006, so relatively
new. I am curious there now. It might  fall into the catagory of
" it won't hurt " BUT; would there be any real  world benefit in
adding the capacitors across the diodes, specifically for  receivers?
A sidebar thought; at LF and below, Mother Natures noise is  probably
by far worse than any noise generated by the power supply  diodes,
with the exception of switch mode supplies maybe.
 
 
Hi Andy,
It is always good practice to place a .1uF cap across each diode
in a power supply to suppress the square-wave switching noise  from
the diode. This is especially important for a power supply used  with
an LF Active Antenna of LF Converter.
 
The switching noise from the diodes can sound like a buzz in  your
LF receiver, just like the buzz you can get from a light dimmer.
Sometimes the noise is 'tunable' , that is it will seem to peak in a 
certain part of the band. 
 
I have had this happen with an AMRAD VLF clone converter I built
a while back. I tried using one of those plug in Wal-Wart power  supplies
with it and I would hear a loud buzz from about 200-400KHz,
just like I might hear from a noisy light dimmer. 
 
I cut open the Wal-Wart and installed a .1uF disc capacitor  across
each diode and after that reception was dead quiet all the way down
to VLF.
 
73 - Todd WD4NGG