I got my TenTec Omni VI+ transceiver directly from the factory and even if the radio is great I did not liked following things.
The heat sink was wrongly designed.
Some PCB boards had a lousy manufacturing quality
There has been lots of digital syntheses noise on the higher bands.
I have contacted the factory at once and discovered that they cannot do any thing with this situation. The solution was to make the fixes by myself an here is the story.
The heat sink modification
The problems with the original heat sink is that the ribs are constructed horizontally which block air circulation and additionally the heat sink is under dimensioned.
First of all I recalculated the needed heat sink based on the power dissipation of the final as it stands in the books. Then I have chosen an industrial standard heat sink that has been laying about 10% below the calculated value. (We do not use AM at full power). The chosen heat sink has ribs that are running vertically which easy the air to transport away the heat out of the surface.
Picture of the new Heat Sink.
There is not much one can do with this problem, just take a soldering equipment and do the job.
The problem has been solved by resoldering and cleaning of several small boards. I addionally added several 22nF capacitors to decouple the boards. Seems like the TenTec did not bothered to think about it.
Removing the syntheses and digital noise
To start with I would like to thank you some of the RF friends from Nera Satelite Communications A/S that I had a pleasure to work with. They supported me with my noise reduction strougle. The process has taken around two months but it was worth it.
I added a SERIES chokes to the +12v for digitial 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:Two ferrite clips around cables: 94, 95, 68, D
One ferrite clip around cables : 63, 52, 87, 97
One on cable: 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 remov some of the noise.
In order to subpress the noise even more I added additional copper screening of the compartment where the processor board is located.
