Trouble in measuring gate and drain voltage of transistor at 120 MHz

Hi,

I have to measure drain and gate voltages of power transistors at around 120 MHz. The transistors' casing are soldered on PCB and the PCB has other circuitry also which is causing great trouble in measuring the drain and gate voltages at the time of transistors' functioning. As expected the gate and drain voltages appear in rectangular pulses which have both dc bias and rf component. However, the oscilloscope shows the magnitude of drain voltage pulse varying if the wires (which are soldered on one end at drain and gate of transistor and at the other end are connected to oscilloscope) are moved or contacted or if you make a hole with your hand (see picture below) and let that wire pass through that hole.

https://4.bp.blogspot.com/-6RCRiJaVJs4/TjIy-6WczZI/AAAAAAAAAAM/icwzHbG5ano/s1600/igloo+001.JPG

Please share your ideas or suggestions or experiences in this regard. Also, please provide material in as much detail as possible.

The yellow pulse is of gate voltage and green one of drain voltage.
**broken link removed**

Hi,
In the following, the yellow pulse is of gate voltage and green one of drain voltage.

View attachment 74003

I cannot see you edaboard page or the Attachment 74003.


To look at high frequencies you need an appropriate scope probe, not wires running from the circuit to the scope.

JimB