Re: [amsat-bb] Coaxial's "Z" request

[Sil - ZL2CIA <zl2cia@xxxxxxxxx>]

Hi,

I have a similar question.

Like Mak, I have a coil of unidentified coax. I believe it to be 92 ohm. 
It was offered to me for free and seems to be in good condition. I have 
used RG62 to make matching sections in the past, so it seemed like a 
good idea to accept it (= how your attic fills up with junk).

It seems to me that if I carefully measure the diameter of the centre 
conductor and the braid diameter (using, say, a micrometer), I should 
then be able to calculate the characteristic impedance using the formula
Zo=(138Log10(Dshield/dcentre))/SQRT(K)?

(from Radio Data Reference Book - G. R. Jessop)

The dielectric constant K can be obtained by making an "educated guess" 
about the insulating material.

Will this work?

Accurately measuring the diameter of the centre conductor (dcentre) 
would seem (to me) to be the problem. Small errors here will 
significantly change the result.


Sil - ZL2CIA.


SV1BSX wrote:

 > Hi all,
 >
 >  I bought a Coaxial-cable that mentioned  Z=120 Ohms.
 > (I thought that they will be very useful for "stubs").
 >
 > The type of coaxial (written on plastic cover) is:
 > 2002  HCE  02 0798
 > Unfortunately, looking for specifications ( VF etc) is impossible to
 > find anything about it. Seems to be completely unknown coaxial
 > cable. So now I'm wondering also about the impedance of it !
 >
 > Is it possible to measure the "Z" into an unknown coaxial with simple 
instruments which are available in our Shacks in order to confirm if the 
impedance is 120 Ohms?
 > Any suggestion or idea is welcome.
 >
 > Thanks in advance.
 >
 > 73, Mak SV1BSX
----
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