> -----Original Message-----
> From: Jim Brown [mailto:jim@audiosystemsgroup.com]
> Sent: Tuesday, May 05, 2009 4:29 PM
> To: Tower Talk List; garyschafer@comcast.net
> Subject: RE: [TowerTalk] Hardline ?
>
> On Mon, 20 Apr 2009 18:08:39 -0400, Gary Schafer wrote:
>
> >I hate to start something here,, but where does the "0.18 dB additional
> loss
> >come from with any length of line"?
>
> There's an equation in the ARRL Handbook and in the ARRL Antenna Book, and
> there
> are graphical plots of that equation for various values of mismatch and
> matched
> loss.
>
> 73,
>
> Jim Brown K9YC
>
That is not applicable to this situation:
"Mismatch loss is the ratio of power delivered, to power available"
That (mismatch loss) is speaking of a load impedance not matching the source
impedance so as to not allow all available power to be coupled into the
load.
With two different impedance transmission lines connected together there is
indeed a mismatch at the junction just as there is if the impedance of an
antenna does not match that of the feedline. But that mismatch gets
transferred to the transmitter end of the line where it is corrected with a
tuner or the pi network in the amplifier, allowing the transmitter to
deliver full power.
So mismatch by itself does not cause any additional loss. In this case as
there is none.
Once the source (transmitter) sees a load impedance that allows it to
deliver all its available power, then there is no longer a mismatch as far
as power delivered.
The transmitter is delivering "all available power". The only loss is due to
line loss and any additional line loss due to reflected power loss. For
these losses to be calculated line loss must be first known.
73
Gary K4FMX
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