K3 Receiver - spurious responses


John Lemay
 

Hi all

I was delighted to pick up a second-hand K3 recently, almost fully loaded
including the second receiver.

However, the receiver(s) have a large number of fast tuning spurious
responses. One of the worst, on the main receiver is at 28.134MHz and using
Spectran I can measure it as 50dB above the background noise. Clearly this
can't be right.

I have re-run the synthesiser calibration procedures for main and sub, but
to no effect. I've tried re-routing the tmp cables, which does have some
effect but I can't find any positions which provide a cure, or close to a
cure.

I have an earlier K3 which I built from a kit (serial 15xx) which is totally
without these spurious responses, so I know it can be achieved.

Any ideas please - before I drop a line to Elecraft support on Monday ?

Many thanks

John G4ZTR


Steve
 

Let the group know what you find out.  I have a signal on 28.134 also.


vk3od@...
 

Hi  Group

I am having  a problem with spurious products  after the K3SYNA upgrade. I am  using a very early K3(less than Serial 300)   model, that has been upgraded with all mods including the VFO noise mod.

The K3SYNA was major improvement  in eliminating most of the birdies  that I encountered. I did not have the noise issue with the older synthesizer. I am considering down grading back to the older synthesizer if I cant fix this problem.

I did check for grounding and poor solder joints.  I did actually find some dry joints  by touching  the caps with a insulated tool while monitoring with a EMC probe.  I had some spare TMP cables switch I swapped as well.

I have the ability to pinpoint the noise source and I was wondering if anyone has tried   something like Kapton tape and copper foil to  try and eliminate some of these issues. I have read all that I can about SPI  buses and interference however I am not confident about cutting signal lines to place in  lumped filters and capacitors etc. I have also re-seated all the interconnects and cleaned the pins with alcohol and Deoxit etc.

I am planning on using a  active  FET probe to try and isolate the exact pins of  the noise source

I am still having issues with VFO noise on 40 meters that is very evident when spinning the VFO
I have adjusted the SP1/SPI2 settings. 

I use a beverage antenna for RX so when tuning the band the noise is a very annoying problem During the night when 40 meters is firing the  band noise is well above  the internal noise when using the main antenna for RX.  During the day on the main TX antenna the noise is obvious because of the lower noise floor. I am in a  rural area so I dont have S7 city noise that most hams have. If I use the Beverage the noise is very evident. The spurious noise is evident on  the P3 when spinning the VFO.

Its not noise from shack or switch mode power supplies. I have terminated all the ports  on the k3 with loads and I have access to EMC probes  and other EMC equipment that  clearly shows that my shack is clean.

Has anyone found  a solution to this issue? I have been in contact with support and I have had some suggestions to try and  help mitigate the problem. Any suggestions would be appreciated. 40 meters is a critical band right now because 20 meters and the other higher bands  are in a really shocking state at the moment in my area.

73
Craig


repair@...
 

I had a similar issue with my K3 transmitting spurs.  I found a missing screw on the main board. When I was building it, I guess I missed that step.