[time-nuts] Non-impedance matched antenna cables

Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Jun 13 10:03:33 EDT 2008


Chris Cheney wrote:
>> Before you do this find out what the reflection coefficient is for the
>> Thunderbolt input and the active antenna output when using a 50 ohm cable.
>> The active antenna may not be that well matched to 50 ohm cable.
>>
>> Then adjust the cable length to an odd multiple of half the signal 
>> wavelength in the cable.
>> If done well this should reduce the effect of such reflections by more
>> than 30dB. This of course only works with a single frequency antenna.
>>     
>
> FWIW whether even or odd makes no difference for HALF-wavelength 
> multiples - both provide a 1:1 impedance transformation.
>
> Chris
> G3RSE
>
>   
Nothing to do with impedance transformation.
Just the phase shift associated with propagation down the cable and back 
is then 0.

Bruce



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