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

[Cliff Buttschardt <k7rr@xxxxxxxx>]

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

Yes, Mak, it is very easy to approximate the surge impedance of any
transmission line with a simple L-C meter, even the battery powered
portable ones.  An old fashion Q meter is best but not necessary.
      Note the the characteristic impedance is equal to the square root
of the inductance divided by the capacitance.
      Take a reasonable length of line say two, three wavelengths and
measure the capacitance with the other end open.  Then short the coax
with very short leads and measure the inductance.
      Be sure and convert these to fundamental units:  microfarads and
microhenries.  Divide and take the square root.  Probably the best
accuracy is only ten percent but good enough to determine just what
kind of cable you have on hand.  73   Cliff Buttschardt  K7RR  LM 1606
----
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