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 Post subject: HP/ Agilent 41800A Active Probe Question
PostPosted: Mar Fri 09, 2018 3:26 am 
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Joined: Jul Fri 07, 2006 6:09 pm
Posts: 1438
Location: Charlotte, NC
I've gotten more interested in lab grade test equipment recently and so far have a few pieces of Tektronix and Hewlett Packard including an HP-3585A Spectrum Analyzer. I was recently offered an HP 41800A Active Probe for a very attractive price and so I have a couple of questions. What was its original purpose and would it have some usefulness for a hobbiest? It appears it was designed to work with the 3585A also.

Thanks in advance,
Greg


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 Post subject: Re: HP/ Agilent 41800A Active Probe Question
PostPosted: Mar Fri 09, 2018 3:18 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1178
Location: Santa Rosa, CA
Greg,
I was involved in the design, testing and production of an earlier
version of this probe at HP. Its purpose is to provide a very
high, broadband impedance to the circuit under test while providing
a low impedance (usually 50 ohms) to the measuring instrument
which could be a spectrum or network analzyer, amplifier or 'scope.
These usually have unity (or close) gain.

I would NEVER, EVER use one of these in high voltage circuits. The
damage level for DC and even AC is very low. On the order of 3 volts
(AC) for the one I was involved with. Maybe someone improved
this on later versions but I doubt it.

These always came with probe tip attenuators which should always
be used.

I'd be very wary of buying a used active probe without being
certain it works properly. Too easy to damage them.
Steve

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 Post subject: Re: HP/ Agilent 41800A Active Probe Question
PostPosted: Mar Sat 10, 2018 11:58 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4716
Location: NJ, 07645
Greg G wrote:
I've gotten more interested in lab grade test equipment recently and so far have a few pieces of Tektronix and Hewlett Packard including an HP-3585A Spectrum Analyzer. I was recently offered an HP 41800A Active Probe for a very attractive price and so I have a couple of questions. What was its original purpose and would it have some usefulness for a hobbiest? It appears it was designed to work with the 3585A also.

Thanks in advance,
Greg

You might want to consider building this for your 3585A as you already have a 1 meg input on it.
https://www.youtube.com/watch?v=ETKyKC2Zj-M


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 Post subject: Re: HP/ Agilent 41800A Active Probe Question
PostPosted: Mar Sun 11, 2018 12:26 pm 
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Joined: Jul Fri 07, 2006 6:09 pm
Posts: 1438
Location: Charlotte, NC
Many thanks for the replies! I was hoping the HP-41800A active probe would suit my needs but with the low threshold voltage limit would not be suitable for vacuum tube work. I would like to pick the high frequency RF off the top of vacuum tube plate circuits and need about 300VDC capability.

Also, thanks Scott! I've seen a few of the excellent Mr. Carlson instructional videos but not this one yet.

All the best,
Greg


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