At 21:05 1/10/2007, herbs@surfvi.com wrote:
>Topbanders:
>
>I have a few TDK large diameter 3" Ferrite Toroids and would like to convert
>them into decoupling common mode chokes for my Beverage feed points to
>decouple RG6 runs. I have wrapped several with RG-6 but noticed I could make a
>neater coil with more turns if I used some rugged plenum cable which I have.(I
>got several surplus 50 footers with BNC connectors already attached from a
>Video Camera installation.)
>
>The only problem is that I have no idea what the impedance could be, even
>though most video installs in the past I know about use 75 ohm cable. The
>cable is marked as Montrose CBL6719 #26 gauge AWB. I have made several trips
>to the search engine but have come up empty with any spec on this cable. I
>looks and dress well on the large ferrite circular cores...so if there is any
>information out there on this cable please let me know.
>
>Thanks,
>
>Herb Scheonbohm, KV4FZ
Hi Herb.
You can get an idea of the impedance if you have access to a TDR
(Time Domain Reflectometer) or an oscilloscope that has a gating pulse output.
If you have an oscilloscope that matches the bill do the following.
Run the gating pulse to a T-adapter at the input of the scope, swamp
the input with a 50ohm or 75 ohm resister (depending on your
normal/known system), attach to the T-adapter a length of 50 ohm
coax, and after that (serially) attach the unknown coax. If the pulse
goes up in value at the junction of the coaxes, the unknown coax is
larger than 50 ohms. Then use a known value of 75 ohm coax and see if
the unknown still goes up or goes down. If you have some RG62 (90
ohm), try that too.
This isn't exact, but it will give you an idea of the unknown
impedance value relative to a known value.
73, Richard - K5NA
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