Strange. Slice B signal bleading over to Slice A signal?

  • 1
  • Problem
  • Updated 5 months ago
I think I may have found a real issue with my new 6600M or with DAX. I am running CW skimmer on two bands and the strongest signals are being spotted at the 2nd harmonic frequency.  This is happening for the strongest stations. See image:



Setup:
- 6600M running SmartSDR on the radio
- Slice A sitting at 14.024 kHz using ANT 1 (which is my SteppIR)
- Slice B sitting at 7.005 kHz using ANT 2 (which is a vertical for 40 m)
- DAX 1 for Slice A, DAX 2 for Slice B
- slice master to launch CW skimmer automatically for each band
- RBN to connect to slice master aggregated feed

I am sitting and watching the panadapters right now with 20m totally dead and 40m having a few signals. I will need to wait till signals are strong again, at least 50 db to see if I can see this issue in the panadapter also.

I will keep it running without changing anything in case anyone has any ideas what to try next, but will stop RBN aggregator from publishing these bad spots...

73
Andy
KU7T
Photo of Andy - KU7T

Andy - KU7T

  • 144 Posts
  • 10 Reply Likes

Posted 5 months ago

  • 1
Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

  • 9148 Posts
  • 3467 Reply Likes
It is very possible that you have a very sensitive radio and that the station transmitting on 40m is overdriving his transmitter and his 2nd harmonic is strong enough for the radio to receive on 20m with the StepIR.

DAX isn't the issue because it is sending the demodulated audio bitstream form the slice (DAX) or the IQ data from the panadapter (DAXIQ).
(Edited)
Photo of Andy - KU7T

Andy - KU7T

  • 144 Posts
  • 10 Reply Likes
Thanks for the (possible) explanation. I have been running skimmer for years and not noticed this with other SDRs. Maybe the Flex is more sensitive, maybe conditions were just weird or by accident both stations were just overdriving their amps yesterday (or a combination of these)...

Thanks
Andy
KU7T
Photo of Andy - KU7T

Andy - KU7T

  • 144 Posts
  • 10 Reply Likes
I contacted the spotted stations with the harmonics. I now believe that this is not possible. The 20m band was dead, they have good antenna isolation and do not overdrive their rigs. Also, there has been no other skimmer in north America that spotted these harmonics.  Only me.

So, this must be an issue on my side. I guess, it must be the 6600M or CW skimmer.  I will have to wait till this happens again and then see if I can hear the harmonic signal in the second slice or not.

73
Andy
KU7T
Photo of Andy - KU7T

Andy - KU7T

  • 144 Posts
  • 10 Reply Likes
Is there a way to record my 2 DAX streams?  If I could let my system run as it is and find out when this happens again, it would be good to go back and see if the harmonics where there or a product of later processing(Skimmer?).

Andy
KU7T
Photo of Stan - VA7NF

Stan - VA7NF

  • 416 Posts
  • 92 Reply Likes
Not covered so far, and I see it on strong stations. 
In your examples the strong station is on 40M and the "image" on 20M is 33db or more quieter.

Simple things like a rusty tower bolt or section join, a poor telephone wire connection, or similar diode junction, will CREATE a second/third harmonic signal that appears as real.  

If you have any DFing equipment see if the 2nd signal is coming from the same direction or is originating near your station.  I have used this method to find faulty coax connections and tower rust.