One of the rules of Continuous Improvement is that you don't know if you improved something if you can't measure it. I'm still fighting an occasional "Jumping SWR" (from 1.75 to 6 with power cutting back) when using PSK-31 at 35 watts on my ICOM 718 to my new Hex Beam on 10 and 12 Meters. The Hex Beam has 4 MFJ Ferrites on the COAX right at the connection point per manufacturer recommendation. Next time I get out the ladder I'll go up on the roof and add some more Ferrites. My shack is in the basement.
Getting rid of one Power Strip in the shack reduced the frequency of the problem. Using a MFJ 949E manual antenna tuner to take the SWR from 1.75 to 1.5 usually stops the problem. Adding ground wires in the shack usually increases the problem. I don't think there is anything wrong with the coax or connectors. Everything was tested individually, temporarily replaced with known good, or eliminated. I also did a full end to end test with Dummy Load up on the roof. I can also reproduce the problem on a Hustler Vertical Antenna (totally rebuilt this spring)
I don't think the problem is the Hex Beam or Vertical Antenna as they work fine on a steady signal (Key down or Tuner button) with SWR being 100% steady. On PSK, the ICOM-718 SWR meter jumps around "two ticks" (I.e. from 1.75 to 2.0 and back). I believe the problem is some kind of Ground Loop and or RF in the Shack. Alternately, the 8 year old ICOM-718 has gotten extra fussy about SWR of 1.75. Thus, is there any way to measure RF in the shack?
I have a Rigol 100mhz digital oscilloscope, but an a newbie using it. I also have a dip meter, field strength meter, plus an assortment of regular digital multimeters, and RF and Audio signal generators. Any suggestions on how to take some actual measurements? Random problems are *^($#%@#.