Agilent 33120A pissy square wave?

[echen1024]

I was playing around with my 33120A function generator, and holy hell that is a shit square wave. I think even the MHS2300 in the other thread does a bit better than this.
Look at this 1MHz square


Pretty decent at 500Hz


And you do NOT need to see 4MHz


Others with a function gen, can you verify that that yours does the same as well? And 10MHz, near the 15MHz limit is just a sine wave.

[sync]

Do you have it proper terminated? 50 ohm BNC cable and 50 ohm terminator at the scope.

[echen1024]

Yes I believe I do.

[RRobot]

Hooked up to a MSO7034B my 33120A produces virtually no overshoot even at 4 MHz, provided I have the scope set to 50 Ohm impedance. Setting it to 1 Meg impedance the output looks similar to yours, although not quite as exaggerated. So basically you have not setup your impedance matching correctly.

[AndyC_772]

I see results almost identical to yours if I connect a probe to the the output of my function generator but don't connect the ground lead.

If I use a BNC cable, I get a nice clean square wave whether I have the scope set to 50 Ohm or 1M.

I think your problem is poor grounding, not impedance matching.

[TiN]

Captured output on mine HP 33120A (was bought broken, replaced bunch of chips in it).
Tektronix CSA7404 with TCA-BNC adapter on input (50 ohm only)
1m BNC-BNC cable from front panel output on 33120A (tried also Tektronix SMA-SMA cable with BNC-SMA adapter on gen output and TCA-292MM adapter on scope)

2.5 Vpp, 500Hz



1 Vpp, 1MHz square wave mode



2.5 Vpp, 1MHz square wave mode



2.5 Vpp, 4MHz square wave mode



2.5 Vpp, 15MHz square wave mode



5 Vpp, 15MHz square wave mode



 

[BravoV]

Yes I believe I do.

Dunno why, I have doubt if you're not doing that properly, take a photo of your scope's coax cable connection picture right at the bnc and post it here.

You are not using the scope probe, right ?

[echen1024]

I am using a BNC cable I bought from weirdstuff.

[rdl]

Doesn't that Rigol scope have 1 M ohm input? Are you using a 50 ohm adapter?

[echen1024]

Godddamn it!  I need a 50 Ohm adaptor now.

[BravoV]

Godddamn it!  I need a 50 Ohm adaptor now.

LOL ... I knew it, trap for young player as Dave says.

Ideally you need a feed thru 50 ohm adapter, but a bnc T connector and a ordinary 50 ohm terminator should be fine since its easier to source and cheaper too.

[linux-works]

since you're local to the bay area, go over to halted (hsc) and grab a tee and a 50ohm term.

we know what the problem was.  we all have done this before, not to worry

[BravoV]

we know what the problem was.  we all have done this before, not to worry

+1 


Just to make sure you understand and not buying wrong stuffs, get one of this terminator with value of 50 Ohm, beware not the one with 75 Ohm termination, usually it has the number 50 Ohm printed at the cap like below example.



Plug the 50 Ohm terminator at one end of that bnc T connector, while the middle male connector goes to your scope's BNC input, and connect the other end through the BNC cable to your fun-gen bnc output.

[echen1024]

since you're local to the bay area, go over to halted (hsc) and grab a tee and a 50ohm term.

we know what the problem was.  we all have done this before, not to worry

I'm not. I was visiting. I'm in Texas. I will buy one off of Digikey or eBay then.

[bingo600]

I saved some old T's and terminators from my first home cheapernet "10-Base 2"
They come in handy now ....

https://en.wikipedia.org/wiki/10BASE2

If i see a couple of feed throughs for a nice price i'l grab some.
But until then , this works ok.

/Bingo

[linux-works]

yes, the old DEC thin-net (10base2) tee and terminator finally come in handy again, after all those years

[RRobot]

If i see a couple of feed throughs for a nice price i'l grab some.
But until then , this works ok.

Yes I've been looking for a few of these (specifically the Pomona 4119-50) on ebay as I can't bring my self to pay $50 for a new one. So far no luck.