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This scope specs mention the following inputs: enter image description here

I don't understand what meant by channel to channel isolation here. I made a continuity test and the input grounds of two channels are connected. I thought Ch-Ch isolation meant the input channels' grounds are isolated but obviously that's not the case. But then what could be meant by Ch-Ch isolation here?

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I don't understand what meant by channel to channel isolation here

"Isolation" means that a signal on channel 1 won't appear on the trace for channel 2 or vice versa. It doesn't mean that the signal input connections for channel 1 and channel 2 are isolated (although on some equipment this may be so).

An isolation of 100:1 likely means that a 1 volt signal on channel 1 might produce a 10 mV signal on the trace of channel 2.

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  • \$\begingroup\$ "An isolation of 100:1 likely means that a 1 volt signal on channel 1 might produce a 10 mV signal on the trace of channel 2." Is that the same thing with the term cross-talk? And is that due to multiplexing? \$\endgroup\$ – floppy380 Oct 1 '19 at 12:47
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    \$\begingroup\$ @HelpMee yes, it's cross-talk but it could be due to several things and is not necessarily caused by multiplexing although multiplexers are quite poor at isolation at high frequencies. I'm not going to guess the mechanism. \$\endgroup\$ – Andy aka Oct 1 '19 at 12:50
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It means that (for instance) if you set both A and B input channels to 1V/div, and apply 1V at the specified frequency to channel A, you should not see more than 1% (i.e. 10mV) of that voltage on the other channel (which you probably wouldn't be able to see). It doesn't say whether the other input should be open or short circuit which might affect things - should be better s/c.

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  • \$\begingroup\$ I see, what prevents such ch to ch coupling? \$\endgroup\$ – floppy380 Oct 1 '19 at 13:32
  • \$\begingroup\$ A better scope. I don't know what type this is, but if you look inside the old Tek models (which you now pick up at bargain prices) you see a lot of attention was paid to screening and layout. Of course things get worse as f goes up, which is one reason that scope costs rise a lot with BW. kerrywong.com/2013/08/11/tektronix-2213-teardown-pictures \$\endgroup\$ – danmcb Oct 1 '19 at 14:08
  • \$\begingroup\$ in this pic you see that they put a lot of iron around the input attenuators - which makes sense, your smallest and most vulnerable signals are there, and the fact that the input needs to go through this big and bulky switched attenuator (in order to deal with signals from mV to 10's of V) means that it is hard to keep the signal paths really short. These old analogue scopes are impressive pieces of design. kerrywong.com/blog/wp-content/uploads/2013/08/2213internal2.jpg \$\endgroup\$ – danmcb Oct 1 '19 at 14:11
  • \$\begingroup\$ How about isolation amplifiers across each channels? \$\endgroup\$ – floppy380 Oct 1 '19 at 16:05
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    \$\begingroup\$ Isolation typically means galvanic isolation - i.e. how much potential you can apply between two conductors before you get breakdown - conduction you don't want. (Usually this is arcing across the gap.) An isolation amplifier is just an amp that gives this up to some potential - say a few kV. But there is no such "isolation" between the inputs of a scope. (They share a common ground.) What we are talking about here is crosstalk, unwanted coupling between channels. The mechanism is L/C and generally rises with frequency. (The same thing happens between channels on an audio power amp.) \$\endgroup\$ – danmcb Oct 2 '19 at 7:27

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