[Premium-Rx] RA6830 digital noise source

[Carcia, Frank A. HS]

	Hi All,
	I was bringing a dead processor module back from hanger queen mode
this weekend
	and found the digital noise source while testing it. I have 1
chassis that has always
	been a problem with digital noise and has become a test box. I
bought some modules
	from the famous Racal man in Md. and picked up a couple dead units. 
	I added the extra ground on A11 which helped a little but the noise
was hurting the
	MDS at 6 KHz. bandwidth. 
	The 6830 modules are sitting on a ground plane mother board and the
shield plates
	for each module are sitting in metal guides attached to the sides of
the chassis.
	There is a vertical divider at the digital section around the
synthesizer module. 
	The radio is well shielded on 3 sides but the top is open.  I
grabbed a piece of sheet
	metal and laid it across the tops of the modules A6 to A13 inside
the chassis
	side rails and pressed it so it contacted all the module top
shields. The two lit bars
	on the s meter display went out and the noise went away. The CPU
module has
	two test points that can be shorted to throw it into reset holding
the last settings.
	I tried it and there was only a slight change in noise between
running and reset.
	The metal sleeve that is the radio cover does not contact the
modules if they are
	pressed all the way in. There is about .05 inch between the top of
the modules and
	the cover. The processor section  is about 1/8 inch. 
	I'm thinking of a couple possible solutions for this problem and
would love suggestions.
	1. Make 3 shield plates to shield all the tops of the modules in the
digital, synthesizer
	and RF sections. This could cause thermal problems if it is solid
metal.
	2. Shield the digital section. Then set the height of the RF modules
..05 inch higher
	    to contact the chassis sleeve. A number of holes could drilled
into the sleeve
	and module shields. The modules could be tapped to accept small
screws.
	
	I don't care if it takes a little more time to service the radio but
there must have been
	a system spec Racal was stuck with that hurt the shielding. 
	I've been chasing this one for a while and seem to have found the
source. Now
	for a simple fix. Any ideas out there. Yup digital return currents
on the chassis.
								fc
	    shields and