Re: P6021 Noise Problem?

Jim Ford

Nearby FM radio station, maybe?                   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chappy <sb.chadwick@...> Date: 2/27/21 8:07 AM (GMT-08:00) To: Subject: Re: [TekScopes] P6021 Noise Problem? I finally had a chance to get back to this yesterday. Thanks again to all who provided suggestions, and especially Dennis with his detailed reply.  I have been a longtime lurker on this site and I have learned a lot about Tek equipment and troubleshooting in the process. Tests performed:1. I attached a normal Tek 100Mhz probe to two separate power supplies that were powered OFF. On a 2mv/div scale I was able to see a few cycles of a decaying signal that appeared to be approx 100Mhz.  Visible on both my Tek and Keysight scopes.2. I attached a 10ft loop of wire to my scope. I did not have a microwave diode but I think the wire alone is providing a clue. The wire picked up a 93Mhz signal with varying amplitudes from 4 to 6mVpp!3.  I hooked up the 6201 probe to my Keysight 1102G scope, injected a 1Mhz 5mVpp square wave.  The square wave had both noise and an additional signal riding on the square wave.  Using the single shot capture I was able to break out a 93Mhz signal riding on the square wave from the noise.4. I tested my 6201 probe following the procedure that Dennis suggested by shorting the tip to the ground sleeve and then shorting that to the scope. I am still able to see the 93Mhz signal under the noise.  Both the noise and the signal had an amplitude of less than 1mVpp. I suspect that the 93Mhz signal is getting into the circuitry of the 6201 probe either through the the power cable, or the probe cable. For now I am going to leave the probe as is. Most of the hobby work that I do right now is below 1Mhz, and if I need to use the probe, I will run it through my 7A13 plugin with the 5Mhz BW limit enabled. I will check this issue again when I move to a new location. Reference the 93Mhz signal, could this be a sub harmonic of a surveillance radar working in the GHz range?  Could it also be a sub harmonic of wireless routers that can be as low as 900Mhz?  I turned off all of the other potential noise sources in my house while performing these tests, to include fluorescent lights, and all SMPS wallwarts.Sincerely,Steve

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