I deal currently with an EMI issue using a 1GHz Cal Test CT4121 FET probe. 50E input was selected on used scope.
1. I liked to measure the noise of a switched power supply as 12V battery to +5V & +/- 15V for audio as using in the 100mA range.
- it showed some noise even without powering the switcher
2. Then simple shorting the FET probes (using shorted given connections) showed similar frequency burst at about 650kHz
- switched other gear as in addition WiFi & LAN/WAN & lamps off >> no influences
- added a EMI blocker (black part on picture) what lowered the bursts about 30% only
3. Then put the probe into a metallic case & top shielding all grounded to scope GND pin
- it did not help
- not grounding the shield picked additional hum
4. Even using TEK 2465B shows equal burst behavior at 650kHz
5. Using ordinary probes did not show equal signals
The beef questions: does someone have some Keysight or TEK or LeCroy FET probes with similar experiences?
Or and help how to get ride as may using symmetric probes?
While it looks like the probe cable detects any surrounding EMI
So now