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.