There has been extensive discussion on the Ten-Tec Reflector over the years about remedying the birdy problem
on the Omni 6.  Piotr Tomczak LA9HFA did much of the initial work and later, Warren Walsh K2BM and Glenn 
WA4AOS contributed. Finally the Ten-Tec service department has aided the effort.  I've gathered some of the 
information from emails and the reflector and present it here, as well as a picture of Piotr's modified Omni 6.  


From Piotr Tomczak, LA9HFA:

I added a SERIES chokes to the +12v for digital board. The same chokes the TT use on the
final board.

I added additional screen cover of the digital compartment, to be sure to reduce the noise
out of that board. The whole Logic compartment should be like a Faraday cage, closed for RF.
I talked to RF people at work and they support that view but it will require me to use more
tape and put an extra shilding plate as well...I already have copper tape on the front hole
where two coax cables are going out of the logical compartment as well and on the hole between
Logic and Low Level board.

Decoupling capacitors were soldered to the following IC's
U1, U3, U4, U5, U21

The Ferrites are put on following cables:

2 pcs of ferrite clamps are on 
94, 95, 68, D

one ferrite clip in
63, 52, 87, 97

one on 
2

Try to find on the market the ferrites which have higher attenuation on the 30Mhz. One can use
more turns but the cables at OMNI are too short to make more turns..

The dc cables from regulator are taped by a copper tape into the chassis, to help decouple noise.


From Warren Walsh, K2BM: 
This past weekend I removed the Logic Control 
board from my OMNI-VI+ and looked it over.  What a surprise, being a 
digital designer, I was very concerned by the quality of this board.  I 
cannot believe there were so few de-coupling capacitors on the digital 
section of this board, and the size of the power/ground traces is 
appalling.  I also cannot believe it would have increased the cost that 
much to have had a power and ground plane.  I did find that there is 
approximately a 5 Ohm resistance between VCC pin 26 and VCC pin 57 of 
the DSP chip, this is NOT good.  I soldered a jumper between these two 
pins.  I would suggest that anyone who has an OMNI-VI check this out.

I have had several people ask about the actual modifications I 
performed on my OMNI-VI+ (Option 3 Upgrade).  I really did not do anything 
extraordinary.  I basically followed the suggestions listed by Piotr 
Tomczak in his posts about the OMNI synthesizer noise.  This board 
lacks sufficient de-coupling caps, and the POWER (+5V) and GROUND connections 
to the IC's are made with SIGNAL size traces are what I consider to be a 
problem.  The second part of the last sentence is what I feel causes 
the ~5 Ohm resistance between pin 26 and pin 57 of the DSP chip.  I added 
de-coupling caps between the POWER (+5V) and GROUND pins on all the 
digital IC's.  The value of these caps is NOT critical you can use .1uF, .01uF 
or .001uF 50V CERAMIC caps.  I did not have enough of any one value, so I 
used some of each of the previous values.  I also soldered a piece of 24ga. 
Teflon wire between pin 26 and pin 57 of the DSP, this eliminated the 
~5 Ohm resistance.  I did NOT add any ferrite beads to any of the 
interconnecting cables other then the incoming +12V line, for that I 
used a small snap on ferrite I had handy wrapping the +12V wire twice through 
this ferrite.  As I said in my previous post, I CANNOT say for sure which 
mod made the difference, but I have a SIGNIFICANT reduction in birdies 
across the bands


From Glenn, WA4AOS: 
With some research and testing, I was able to do some shielding with a material called "TI Shield" 
and replaced several audio lines with shielded cable. I design and build audio equipment including 
high gain pre amps where noise can be a very big problem. I have played with various shielding 
material but TI Shield is cheap, effective and reasonably easy to work with. First, I cut out a 
piece with a stout paper cutter and made a lid for the microprocessor box. This helped considerably. 
Next, I cut out pieces to fit around the processor board with better results. Later I cut a piece to 
fit under the processor with slightly better results. This material looks like copper foil and comes 
in various thickness sheets. I applied it with thin double sided adhesive tape. I ran several ground 
lines which were soldered to the TI shield pieces and tied them to ground. The material can be found 
at Percy Audio.  Cutting the pieces does take some time especially to fit around the processor board
but I believe it is worth the time and effort. 
 


2007 Update:
Dave K1FK reported this tidbit to the TenTec reflector:
When my rig was back to the factory for the Opt 3 upgrade I asked TT to take care of the 
original birdie problems, and they did so by soldering the shields of the inductors on the 
BPW/Front End Board to the ground plane.  You can do this yourself ... very easy to do. Just 
tag the shield to the gnd plane on opposite sides of the can to the gnd plane ... 
Click here to view K1FK's picture 1   picture 2

This jibes well with a comment from TT's service dept reported in Nov 2006:
"Some spurii, but not all, can be reduced by making sure that the mounting
screws for the boards and ALL chassis screws are tight. You may have to move
some cables and or put a twist in them. Also on the Band Pass Filter board, any
part that passes through the top ground plane to ground or earth, should be
soldered on the TOP side of the board. No two rigs are the same, some it is
cables, others it is grounds or a combination of both."