[time-nuts] Re; Do reflections up/down the antenna cable cause a problem with GPS
jimlux at earthlink.net
Tue Nov 22 21:08:57 EST 2016
On 11/22/16 4:36 AM, John Ponsonby wrote:
> Remember that for a microwave LNA the condition for optimum noise figure is not the same as the condition for the input to be matched. Thus one doesn't expect the input of a good LNA to be matched to 50Ω. (Dr John Ponsonby)
this is also true for virtually any amplifier.
For lower frequency (say, <100MHz) you might find a current noise and
voltage noise spec, from which one could figure out an optimum source
resistance. But when it comes to the reactive component? Good luck.
It's also something that doesn't seem to show up on data sheets for RF
components - you *might* get a "input Z for lowest noise" curve on a
Smith chart, but you'd be lucky.
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