EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: rwgast_lowlevellogicdesin on September 05, 2015, 11:04:00 pm
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So I know you can use some 50ohm resistors and caps with coax to make a 1x probe, I also know this technique will load your circuit and draw alot of current.
Some american companies offer 1x probes at 25mhz bandwidth, I.E Probemaster and Avex. I bought the Avex 100mhz monolithic probes, now im lookin for a good way to do 1x, what is it these 1x probes do over coax? Do they still load your circuit, like coax?
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What frequency response and impedance do you want/need?
1x probes work by having a lossy transmission line, of relatively high impedance (90 ohms maybe?). The total series resistance for the (2m?) cable is somewhat higher.
The impact on circuit is equivalent to an RC circuit having losses varying with frequency. The DC resistance is 1M, the capacitance is on the order of 200pF (check a datasheet to be sure), with an ESR of perhaps 100 ohms but depending on frequency (transmission line effects). Likewise, the frequency response (what gets to the scope) is strongly attenuated above 10MHz or so (check datasheet).
Tim