On Thu, May 8, 2025 at 8:59?PM Jason B via groups.io <sydbowen=
[email protected]> wrote:
I've tried DC balance. I was mistaken on the channel 2 waveform on GND.
It's on AC. I have it set right now at 2 mVAC and 2 nS on channel 2 with no
probes connected and readout on frequency is 850 MHz with a perfect sine
wave at 3.55 mV. Lol, I think I acquired a basket case maybe?
Interesting.
Below 50mV/DIV the preamp amplifies the incoming signal, so it's perhaps
within reason that it's amplifying something at the BNC. I guess it might
also be oscillating.
Have you measured the DC resistance of your inputs? It should be as near to
1MOhm as makes no difference in DC coupling and infinite in AC coupling.
What happens:
- In 50Ohm coupling?
- In DC coupling?
- When you connect a probe?
- When you connect coaxes of different lengths?
- At other attenuation settings?
The CH1/CH2 preamp hybrids should be interchangeable (though the
calibration is preamp specific, so keep track of which is which), so you
might see whether this oddness follows the preamp.
It's also possible that the hybrid contacts are oxidized, leading to
weirdness, so before you swap them, try just re-seating them and/or
cleaning their contacts.
