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From: Robert Baer <robertb...@localnet.com>
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Subject: Re: Homebrew HV hiZ scope probe
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josephkk wrote:
> On Sat, 03 Nov 2012 18:25:19 -0800, Robert Baer<robertb...@localnet.com>
> wrote:
>
>> Fred Abse wrote:
>>> On Tue, 30 Oct 2012 20:33:39 -0800, Robert Baer wrote:
>>>
>>>> Sorry...mistype... cable is about 50 ohms per foot.
>>>
>>> Says so on the schematic in the probe manual.
>>>
>>> Probe cables, at least modern ones, use foam dielectric, hence lower
>>> capacitance per foot.
>>>
>>> I've got some probes with removable cables, I'll TDR one when I get the
>>> time. I'll have a go at open and shorted measurements, too, and calculate
>>> the complex Zo. With a resistive center, Zo will be significantly complex
>>> at higher frequencies than "regular" coax.
>>>
>>    Thought of a way to (perhaps) make resistive coax with element in the
>> 50 ohm per foot region.
>>    Find some Nichrome or other resistive (heater) wire,and use Teflon
>> sleeving in successive layers or use shrink tubing in successive layers.
>>    Slip braid around that.
>
> Nicrhome is ok for heater uses, but i prefer constantan for electronic
> purposes.  Check out the properties differences, it will be worth it.
>
> ?-)
   I vaguely remember that one can be soldered; which one is that?