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| DC coupled 2.7 GHz Active Probe Project - Now Available! |
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| hpw:
--- Quote from: lasmux on May 28, 2024, 02:23:47 pm ---The 60MHz low frequency? It's not shown on your plots that only go up to 10MHz. --- End quote --- 60MHz, may some IM or simple GND connection pickups.... as I had on an 1GHz active Cal Test :palm: The simple solution went as for xGHz differential probes :phew: |
| joeqsmith:
With probe leads shorted, wrapped in foil, placed in shielded box with ferrite at feed, sweeping from 9k to 9GHz with probe turned on. Output appears very clean but of course, it would be difficult to use it to take a measurement like this. *** Also, I normally keep a 10dB attenuator on the spectrum analyzer. This data was collected with attenuator removed and in peak mode. |
| joeqsmith:
Showing the range you are interested in (15 to 100MHz) with same setup. |
| joeqsmith:
Looking at the probe attached to the SA, without any shielding and leaving the two tips isolated. The probe was not connected to anything but hanging in the air. For all images, baseline is with the probe attached but turned off. I know it is sensitive to my hand placement on the body. I wonder if this is part of the same problem. |
| lasmux:
Did you remove a 10db attenuator for the 100MHz-1GHz test? And was the signal tip floating or grounded? So I guess it's fairly clear from all the testing that the probe amplifier input is picking up RF noise from your lab surroundings, given the earlier shielded test you did. This is kinda expected to a degree due to the input impedance of the amplifier, however I'd say the amplitude of this noise is higher than ideal. It looks like your lab has a fair amount more RF noise than mine. I think the amplitude of the actual noise in the oscilloscope traces you've captured is still acceptable, given the probes low price. If it was a $4k probe from Tektronix it definitely wouldn't be acceptable. I'll have a look at reducing the input impedance of the probe this weekend to 100kOhm or 200kOhm, and potentially upgrading the remainder of this batch if it makes an improvement. I now just need to find/make some suitable radiators to test the changes. Also I'd need another batch of stickers for the probe ::) |
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