Forums › SA Series Discussions › SA44B change amplitude with Ref Lev
- This topic has 2 replies, 2 voices, and was last updated 3 years, 5 months ago by yo3fff.
yo3fffParticipantyo3fff October 10, 2019 at 12:28 pm
When I set the SA44B to Auto Gain/Atten the measured amplitude is all right down to Ref Level -40dBm.
When Ref Level is set to -50dBm or less (when the preamplifier is ON) almost no signal go into the graph. Is like the input is disconnected from the signal source (see attached pictures).
This is happen in Sweep and Real Time mode.
The self test is passed. The preamplifier it is working just fine on the manual mode.
This behavior does not been from the beginning but with a software upgrade but I cannot recall which version was.
Right now I update Spike to ver 3.4.1 (the latest) but the issue is the same.
What is wrong?
Please advise how to get rid of this problem.
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Justin CrooksModeratorJustin Crooks October 10, 2019 at 3:46 pm
Around 2016 we started adding a resistor to provide a weak return path to ground because some units would develop this condition you described over time. I think the problem stems from the fact that there’s no return path to ground when the attenuator is 0 dB, and a tiny leakage current from the attenuator can essentially blind the RF switch until a ground path exists.
If you can set the attenuator to 5 dB, or add a 1 dB external attenuator, this problem should clear up. Otherwise, you can get an RMA, send it in, and we can add the resistor.
yo3fffParticipantyo3fff October 11, 2019 at 11:47 am
Thank you for the answer. The external attenuator it fix the problem.
Because the unit is not in the 1year guarantee I think I can fix it if you can send me the detailed rework to be applied.
I’m a professional Electronic Engineer being able to solder 0201 components.
Thank you for your support.
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