[time-nuts] semi-OT: comparison of two 10x scope probes (cost $7 vs. $406)
beale at bealecorner.com
Thu Mar 17 18:41:30 UTC 2011
I am always loosing the little hook adaptor on the end of my scope probes so I went looking for replacements. I noticed that I could buy a pair of complete "100 MHz" probes including tip and ground clip online for $13 shipped from Shenzen China. Didn't expect much, but this application was for low speed signals anyway and I got some. Couldn't loose at that price. I figured the hook tip adaptor alone was worth it.
They arrived the next week and just for fun I compared my new $6.50 probe with a 500 MHz Tek P6139A probe, using a not terribly fast scope, the 100 MHz Tek TDS 220, and a signal of unknown risetime, the output of a 26 MHz Pletronics OCXO in a 14DIP can (by the way these go for $2 online, the cheapest OCXO I've seen). This was just a quick casual comparison, not to be taken too seriously.
I was somewhat surprised to see the cheap probe presented the same 3.8 ns risetime as the Tek probe on this scope, although it comes with some ringing also whereas the Tek probe did not show ringing. Both probes were used in the same place, ground directly to probe shield without flying ground leads (although the circuit itself was casually constructed and had about 1" length of ground return). If you had a simple 1-pole 100 MHz lowpass you'd expect 3.5 nsec risetime so this is in the right ballpark for scope rated at 100 MHz (and my source signal may be no faster than that anyway- I haven't built an avalanche pulse generator yet :-).
Scope photo showing the comparison below. The cheap probe trace is shown as RefA (light grey) and the Tek probe is CH1 (dark grey/black). https://picasaweb.google.com/lh/photo/1_SVMQ3ajYJUARc51BXnzw?feat=directlink
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