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Old 24th Jul 2017, 4:55 pm   #1
Skywave
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Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Question Home-brew 100:1 'scope probe.

Occasionally I have a need for a 100:1 'scope probe. The max. voltage it will ever see at the tip will be about 50 v. RMS. Based on an idea I found on the 'Net, I came up with the following drawing. The 'scope it will be used with is a Tek. 2465; 1MΩ input resistance + 15 pF. A few Qs. have arisen about this probe, so I'm asking for advice here, please.

1. What would be a suitable choice of coax cable and a suitable length for it? I'm thinking in terms of about 4 feet. I anticipate that the capacitance of that cable will be the predominant factor determining the B/W of the probe. What -3 dB B/W am I likely to achieve?

2. Should the probe body have a metal or a plastic case? Metal will provide screening but also introduce capacitance.

Your thoughts and comments will be appreciated: thank you.

Al.
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