K3:VFO Noise any suggestions?


Hi Group

I am having a issue with VFO noise on 40 meters after the K3SYN3A upgrade.


    1. Its not noise in my shack

    2.  I do have the VFO noise mod installed with the correct SPI settings and firmware

    3. I have had some suggestion from support.

    4. Its a very very old serial K3(below 300 serial)

    5. All mods and upgrades have been done.

    6. I did not have this issue using the old synthesizer

    7. Its only on 40 meters.

I am told and have read that its SPI bus noise. I have read  everything on SPI bus noise and  it seems that its a common EMC problem that has many  design and installation variables.

I have access to EMC equipment and can pin point the noise.  I was wondering if anyone has gone down the road of trying Kapton Tape and something like stick on foil tape to minimise radiated bus noise. I have not entirely worked out  if its conducted or radiated noise. I will be probing with a very expensive FET amplified probe soon.

I have a rural QTH with a low noise floor. I also use a beverage antenna and I can hear a pin drop.  I dont have the typical S5 to S7 city band noise! During the night the noise floor is high enough so I  cant hear the noise on the main TX antenna when tuning. During the day I can hear the noise on the main TX because the band noise is low . If I terminate the antenna ports with good loads the noise is very evident.

I have rebuilt my K3 with all the mods and upgrades. I Swapped out the TMP cables as well as cleaned all the interconnects etc. 

Any suggestions would be welcome. The K3SYNA was a worthwhile upgrade in terms of eliminating birdies/spurious products for me on the higher bands.



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