On Wed, 14 Dec 2011, Mark Wendt wrote:
> Date: Wed, 14 Dec 2011 12:09:55 -0500
> From: Mark Wendt <mark.we...@nrl.navy.mil>
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] Scopes
>
> On 12/14/2011 11:58 AM, gene heskett wrote:
>> On Wednesday, December 14, 2011 11:47:19 AM Mark Wendt did opine:
>>
>>
>>> On 12/14/2011 11:10 AM, gene heskett wrote:
>>>
>>>> That's great news Peter, but what does a fully stuffed 7623 weigh? My
>>>> Hitachi, which of course is not a storage type, weighs maybe 10
>>>> pounds, goes anywhere. Probes won't reach? Stick an upside down 5
>>>> gallon paint bucket under it. :)
>>>>
>>> That's why the good Lord allowed Tek to invent scope carts. And 9' long
>>> probe leads. ;-)
>>>
>>
>> Scope carts are ok but we haven't used the one we have in 15 years, too big
>> to get between the rows of racks.
>>
>> 9' leads? Those are transmission lines and there is no way to make them
>> flat and high impedance w/o echos. You have to mentally subtract the
>> echo's because they aren't terminated with the cables actual impedance.
>> Even 30"ers can do that to you at the frequencies I play with. A 9 footer
>> would have to have active electronics (power hungry and hot) in the hand
>> piece to drive the low impedance cable, and probably a cable terminator
>> hidden in the connector at the scope end of the cable. Last time I looked
>> at active probes they weren't too far from a 4 digit asking price. Now,
>> check ebay& expect to fix it.
>>
> All depends on the kind of lead you're looking for. Your typical
> passive probe isn't dealing with that kind of stuff. Not sure if this
> would work in the situation you're talking about but here's a Tek 1.5
> GHz active probe that's currently set at $115: #380392358070.
For high speed digital stuff a home made passive 100-1 probe is trivial to
make and has better than a GHz bandwith (5K 1/8W R into 50 Ohm Coax). This
type of probe has much better fidelity than normal high impedance passive
probes, and when you get above 20 MHz or so the 5K Ohm input impedance causes
much less trouble than the passive probes relativly massive input capacitance.
Peter Wallace
Mesa Electronics
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