[Antennas] Re: Hairpin monopoles

[Wes Stewart]

--- James Duffer <dufferjames@hotmail.com> wrote:
[snip]

George's explanation is of course right on.

> 
> An interesting analogy but leaves some questions. 
> If the transmission line 
> is terminated in a load that is equal to the
> transmission lines 
> characteristic impedance, then what has frequency
> got to do with 
> characteristic impedance????  The charateristic
> impedance is dependent on 
> the physcial construction
> conductor diameter and distance of the conductors. 

Characteristic impedance is dependent on R, L and C
per unit length.  R, L and sometimes C are frequency
dependent.

As George told you, the characteristic impedance is
reactive, especially at audio frequencies. 
Terminating a reactive line with a real resistance
causes the line to be mismatched.  The mismatch is
frequency dependent.

If you want a simple way to explore this, I suggest
that you go to:

http://www.qsl.net/ac6la/tldetails.html

and download the program.

Once you install it, select Belden 9913 line and set
the frequency to 0.001 MHz.  Make the load R=50, X=0
and then look at the SWR.  You should see that it is
1.77:1.

If you terminate the line in its characteristic
impedance; 50 -j28.8, then the line is matched, but
you have a 1.77:1 mismatch at the input. (Assuming
realitively short lengths)



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