On Tue, 28 Jun 2005 22:52:51 GMT, Lancer wrote in
gtk3c11b9q6nhs69mr9r6rftv1rkur1v70@2355323778:

On Tue, 28 Jun 2005 15:40:40 -0700, Frank Gilliland
wrote:

On Tue, 28 Jun 2005 19:13:35 GMT, james wrote
in :

snip
The "Magic" of an electrical halfwave transmission line is at a
precise frequency, the reflection of the load to the transmistter is
equal to the characteristic impedance of the transmission line
irregardless of what impedance it is terminated with.


I think you have that a little misconstrued..... reflection of the
load to the transmitter by a half-wavelength coax is equal to the
-load- regardless of the characteristic impedance of the -coax-.

Thanks Frank;
I missed that, so if I have a 100 ohm load and and feed it with a
1/2 wave of 50 ohm coax, I'll see 100 ohms at the radio, not 50 ohms?


Yep. And I should add that 18' of coax is recommended not because of
it's propogation characteristics -inside- the coax, but because of
it's velocity factor on the -outside- of the shield which is nearly 1.
IOW, when the shield of an 18' length of coax is grounded only at one
end, that ground will be reflected at the other end of the coax. At
least that's the theory. In practical use it's not perfect, but it's
still better than a fully ungrounded radio or antenna.






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