Scoping Tiny Signals ~250uV

_If_ they sell one to you, that is. Else they'll gladly do it for you, for a repair fee that will make your stomach churn.

Maybe, but risky. Imagine: You are testing gear for the European market, meaning at 240VAC plus 6% or so. Now with some bad luck you happen to cut power at the peak and a 360V transient roars into you coax. Ok, your

17dB attenuator will cut that to around 50V. Will your analyzer like it? Who knows ...

Diode mixers don't always break, sometimes they get a "ding". Gradual damage. When your analyzer suddenly shows a slight drop in sensitivity remember this thread ;-)

Now it is, of course, possible to protect an input. But simple back-to-back diodes aren't going to cut it because those produce harmonics, and you can't have that in pre-compliance sessions.

--
Regards, Joerg

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Agilent says it is out-of-support so I suppose they are not going to sell me new RF assembly nor are they going to repair it. And I somehow suppose that those mixer diodes are not available off-the-shelf from Digikey...

So it is better to but in another attenuator and get a good preamplifier? I am mainly trying to get some clue about emi compliance so it needs amplifier anyway I think. (and I'm not RF guy)

And how easy it is to break RF signal generator output? I suppose it is more robust. (I installed 9dB attenuator there just to be sure).

I compared it just few weeks ago with signal generator and they agreed within 1 dBm and noise level is about where it should be. So I think it is not damaged...yet ;-)

-ek

Not necessarily. Also, there are shops specializing in boat anchor repair.

It all depends on whether or not you can open the can in there. This is one reason why I declined to purchase a used Tektronix insert. A little research turned out that the whole mixer area was almost welded shut. No idea why they did that, but it made the unit worthless to me. It had the telltale sign of the usually pre-compliance fender bender, sensitivity down by 30-40dB. Nearly always means a shot 1st mixer.

A "disposable" preamp is what I often use. Or rather, a buffer. Simple BFS17 stage where I have a whole vial full of those. They cost less than a fuse at the hardware store.

I grew up in medical ultrasound where pulse amplitudes can reach 200V. We have killed numerous generator outputs. Which is why I always liked my old tube generator, it is bullet proof. Still have it but sits in the garage because the oscillator tube finally wore out and the whole thing is too freaking heavy.

Well, that's the magic word, "yet" :-)

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

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[...]

A DC block is a good idea as well. Some spectrum analyzers won't take any DC at all without damage.

Need to check that if I someday change that dead clock battery in there... But drawings in the manual indicate that there is more than enought shielding in there indeed, might be big project just to see there.

Maybe I really need to try learn some RF design. All the preamplifiers I found on Ebay were quite expensive. I think I have some RF transistors in a drawer somewhere...

-ek

The output of an LISN, for standard conducted compliance testing above

150KHz (or 10KHz), is AC coupled.

I was aware that most SA inputs are rated at

The HP 859X series max DC input is 0VDC. There may be others as well.