[Moon-net] Réf. : Re: additional cable loss in front of LNA

[Marko Cebokli]

Hello,

the confusion here arises because people mix two things:

1. Transmission loss = (power delivered to load)/(power available from 
generator)

and

2. Cable loss = amount of power converted to heat on the cable

They will be the same only under matched conditions.

The second quantity will certainly increase with mismatch - it is easy to see 
why: both the forward and reflected wave currents will heat the cable. (And 
the voltage stress on the cable will also increase)

On receive, you are interested only in (1), and (2) is not important - but if 
you run your TX cable close to melting, some mismatch might just push it over 
the precipice...

73, Marko S57UUU



On Sunday 11 May 2008 16:07, DEHAYS Dominique wrote:
> Hello ,
>
>
> I have always found those curves extremely misleading , and
> they crept into many persons brain ( hams and non hams) the idea that
> cable losses increase with SWR , which is absolutely wrong.
>
>
> These " additionnal line losses" have simply nothing to do
> with transmission lines , you can exactly find the same results with no
> lines at all ( generator directly connected to the load.
>
> It simply means that the generator cannot transfer maximum power to the
> load because impedance is not matched.
>
> It is not really a loss , but simply says that power transfer could
> be x.xx dB better if the impedances were matched. So , as it is not
> power loss , this has absolutely no influence on noise figure.
>
>
> 73
>
> Dom/F6DRO
>
>
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