am I hooking up Oscope correctly

Question

Hi,I just bought a mini-circuits zx60-8008 amplifier and am experimenting wth it a little.I need to find out if I am  hooking it up to my Oscope correctly to measure what is coming out of it. Here is what I am currently doing.I hook the GND peg to the GND of my power-supply, then the +12 peg to the +12 of the power-supply.Then I input a signal into the IN coax jack of the amplifier.Then I have a short (maybe 2" long) coax cable attached to the OUT jack of the amplifier, with the insulation scraped off the end so I can attach an Oscope probe to it.Then I hook the + probe of my scope the bare center wire in the short coax attached to the OUT jack of the amp.And then I attach the GROUND clip of probe to the GND peg of the amplifier.Then I measure the signal coming out of the amplifier.So is this the correct setup to do measurements with an oscilloscope?Maybe I shoud be connecting the GROUND clip of the scope probe to the outside grounding sheath of the coax attached to the OUT jack of the amp instead? Does it matter, maybe this is actuall the same as attaching to the GND peg of the amp - like I am already doing.This is a basic question about measurement, but I could not find a diagram anywhere quickly that shows the correct way to do this.--thx, jw

Phil Allison · Accepted Answer

"john w"**  The only such device I can find refernece to is the  ZX66-8008E -   a 20MHz to 8GHz lo-noise amp.   That the one ??** Not really.Forget the probe.You need to make up a lead with 50 ohm co-ax and terminate it with a BNC plug and a 50 ohm load at the scope end.Most wide band scopes have a switch setting on the front for 50 ohms input   -  this is the only way to avoid standing wave effects on the connecting cable.I hope your scope and generator have a more than 20MHz bandwidth or they are useless........   Phil

ehsjr · Answer

In general, you want the ground clip of the scope probeattached to ground as near to the signal you are probingas you can get it.Ed

Charles Schuler · Answer

Is this an RF amplifier? If yes, is your scope up to the task? Generally, it is good idea to load RF amplifiers to 50 ohms or 72 ohms and keep the scope ground leads as short as possible. The coax ground is a better choice.

redbelly · Answer

As others said, at these frequencies (> 20 MHz) you'll need a 50 ohm termination, if you're using 50 ohm coax.

If you're scope doesn't have a 50 ohm setting on the input, you can get a convenient 50 ohm BNC in-line terminator from Thorlabs for 35 $US. It's part # T4119 here:

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Mark

john w · Answer

Thanks - I have got this going now.  --jw

am I hooking up Oscope correctly

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