Load matching puzzle
 

(Food for thought for the relatively new folk here...and perhaps even
some old-timers.)

Consider a system (linear, time-invariant, steady-state excitation and
all that jazz) in which a source delivers 1 watt to a load composed of
a uniform transmission line terminated in a load. Further, this line
has some loss and the frequency is low enough that its characteristic
impedance is noticably reactive, just as Reg has pointed out. Call it
Ro-jXo. What should the impedance of the load be to maximize power
dissipated in the load? Is the answer a function of anything else not
yet stated?

Cheers,
Tom

Tom, I do hope you will tell us what the correct answer is.

Perhaps we shall then be able to deduce what question you intended to ask
rather than the ambiguous mix-up you actually asked.
---
Reg.

Maximum power is dissipated in the load when the length of the line is 0
metres.

Am I right, Helmut ?

On Tue, 19 Aug 2003 17:43:39 +0000 (UTC), "Reg Edwards"
wrote:

Maximum power is dissipated in the load when the length of the line is 0
metres.

Am I right, Helmut ?


Right, if the question we
how to optimize the cable length,
Let me suggest the following answer:

************************************************** ********
The correct length of a feed line is from
the antenna jack of your transceiver straight up
to the connector at the antenna feedpoint or balun,
no more no less.

************************************************** ********

Imagine an antenna cable 1 meter too short,
the tranceiver hanging in mid-air above your desk,
otherwise, too long cables tend to cause unecessary
losses and comprise man-traps.



Hope that settles the never ending dispute about
length-of-feedline.
Add some grain of salt :-)


w.

"Tom Bruhns" wrote in message
m...
I'm sorry, Reg, but that is not a correct answer for the question as
it's stated. I hope others will jump in. Actually, had you gotten
the right answer, I'd have scolded you for posting it so quickly and
not letting some of the more novice folk have a try at it.

I see no one has taken up the challenge in a while so here goes. If I
interpret Tom's question correctly:

100 feet of 50 ohm line with 1 megahertz loss of 2 dB/100 feet and 10 watts
fed into it must have a load of 69+j107 ohms for maximum power in the load
of 8.418 watts. Line Zo is 50-j17.301 ohms.

Is this correct or shall I join Reg in the 'I ain't got it right' box? :-)

73, AL