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Old 5th December 2004, 01:14 AM   #1
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Default Oscilloscope question

I have recently purchased an HP 183a oscilloscope with 1830a and 1840a plugins. First, I was wondering if anyone has had any experience with this set-up? Also, I haven't received the scope yet (I purchased it off Ebay), but I found a spec sheet saying it has an input resistance of 50 ohms. I can not for the life of me find any probes that will match its 250 mhz bandwidth and input resistance. The only 50 ohm probes I can find are in the ghz bandwidth. I don't care if they are 100 mhz, but can someone please help me find some probes for this scope. If I can use 1 megaohm probes, please let me know that also. Thanks.
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Old 7th December 2004, 12:10 AM   #2
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Does anyone know if I can use a 50 ohm bnc feedthru termination adapter to accomplish this? If so are all adapters compatible with all scopes as long as they are bnc connectors? For example, can I use a tektronix 50 ohm bnc feedthru termination adapter with an HP scope?
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Old 7th December 2004, 01:41 AM   #3
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I'm a 3rd year computer engineering student, and I dont claim to be an expert in oscilloscopes but I would suggest buying an attenuator (or making one). Get a probe with the required bandwidth, and simply attenuate the signal by however much is required. (If that's what you're asking)

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Old 7th December 2004, 02:26 AM   #4
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I don't have much experience with H-P scopes but I do with Tektronix. The best place to watch for 50 ohm/250 mhz probes is on E-bay. Some scopes actually had special probes made specifically for them and some probes BNC connector activated certain other features on a given vert. amplifier module.

My preference has always been for Tektronix equipment (not that the H-P is bad) but because Tektronix specialized primarily in o'scopes and there are alot of really great classic TEK scopes available inexpensively on the used market, parts and plug ins are also far more available. A Tektronix scope is actually a work of art on the inside. You can only appreciate one if you like fine electronic design work and get to view the insides.

There is a really good TEK Scopes forum at Yahoo.....

When I was a young tech at Midwest Hi-Fi back in 1973 I couldn't afford any decent test gear... now that they are all obsolete I have them all.

I have these TEK scopes in my collection.........

315D - vacuum tube.

465B - 100 mhz dual trace, integral DVM on top.

7623A - Storage - 100 mhz - Really neat scope!

7904A - 500 mhz mainframe - 250 mhz vert. amp plug ins, quad trace.

SC504 - 80 mhz dual trace... TM-500 series.

SC501 - One of the smallest O'scopes ever made, TM-500)

H-P 3580 Spectrum analyzer All have either been restord or have always continued to meet their specs.

One thing for sure... I have way too much test equipment. The above list is only a small part of it, but I do enjoy using them.

Mark
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Old 7th December 2004, 03:10 AM   #5
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Default 50 ohm inputs

This low impedance will hamper some of your attempts to measure, but there's ways around it.

Unfortunately, a 50 ohm load will kill most any signal you apply to it. The exception would be an Amp's output. But an amp's output can likely blow up the scope. Read the input, You're likely limited to about 5 Volts.

You can make a 100x passive probe. A 4.95kohm resistor at the probe tip, connected to 50 ohm coax, will form a 100 to one divider. Input Z is 5kohms.

You can make an active probe yourself. Use an op amp with more bandwidth than you need. I would suggest at least 10MHz bandwidth. Too much bandwidth could be hard to stabilize though.

The op amp's output should have at least 100 ohms in series before driving the coax cable.
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