[time-nuts] Non-impedance matched antenna cables
bruce.griffiths at xtra.co.nz
Fri Jun 13 04:37:12 EDT 2008
Magnus Danielson wrote:
> Hi fellow time-nuts,
> For those of you that isn't aware of it, using 75 Ohm antenna cables rather
> than 50 Ohm cables is a bad move, as the antenna cable itself will create a
> multi-path system. This article elaborate on reflections i cables:
> http://tycho.usno.navy.mil/ptti/1998/Vol 30_39.pdf
> Nothing new, but needs to be said, especially with Thunderbolts getting more
> popular, as the manual clearly recommends 75 Ohm cable as I recall it. Do not
> listen to that.
If one uses cheap cable with relatively high attenuation at L1 this may
not be a problem.
However the active antenna may need higher gain to compensate.
The question is just how much one way cable attenuation is required?
A considerable reduction in this effect can be obtained by making the
cable length close to an odd multiple
of one-half the signal wavelength (½λ) in the cable.
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