Products > Test Equipment

Show us your square wave

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modrobert:
HP 1660AS with cheap passive probe, signal from Spartan-3 XC3S400 FPGA, using DCM to generate pulses.

Howardlong:
I did a new video yesterday on measuring rise times of external signals with an HP 54121T sampling scope setup (comprises of a 54120B mainframe, 54121A four channel 20GHz test set and an umbilical) plus some external plumbing. Unlike sampling scopes that use a random sampling approach, the 54121T requires a delay line to be able to see the trigger. Sorry the focus wasn't quite the best but hopefully it's good enough.



An earlier video I did on this scope here:



TheSteve:
First pic is 15 MHz from Agilent 81104A pulse/pattern generator top, Agilent 33120A middle and Rigol DS1074Z-S bottom.

Second pic is the 81104A at 40 MHz
Third is 81104A at 60 MHz
Forth is 81104A at 80 MHz
Fifth is 81104A at 85 Mhz(this is technically over range as the 81104A is only spec'd to 80 MHz

All shots are from TDS7104 terminated with 50 ohms.
Poor Agilent 33120A probably shouldn't be spec'd to 15 MHz for a square wave...

EV:
Here are pictures of100 MHz and 250 MHz square waves from Tektronix PG502 pulse generator. The scope is Tek R7633 with 7S12, S-6 and s-53 plug ins.

tggzzz:
I picked up a couple of Tektronix 1502 TDRs for £20 each at an auction, not expecting them to work, but hoping that I would be able to make a frankenmachine. After creating a fake battery one did work, and the results are shown below.

So, what's the risetime? The manual state the tunnel diode output should have a risetime of "around 50ps" and a "system reflected risetime of 140ps or less". Another source states the TD risetime is 35ps. The amplitude is around 225mV.

The display is nominally 0.025m/div for a "solid poly" dielectric velocity factor 0.66, so 1 div ~= 125ps. The measured risetime is about 0.5div, or 60ps. Note that no tweaking nor calibration has been done, but comparing the display with measurements of a cable's length, it looks pretty accurate.

Not bad for a £20 instrument first introduced in 1975.

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