[Antennas] Re: Hairpin monopoles

Thu, 8 May 2003 11:04:49 -0500

I am sure that Wes and I would interested in knowing what you find out in
your investigation. I don't know about Wes, but I feel that my contribution
is to provide accurate information about topics with which I am familiar.

Whether or not you choose to accept it is your choice - not my job!  <:}

For the record, however,

1. the characteristic impedance of any transmission line is a complex
quantity of the form Zo = Ro+jXo

2. depending upon the frequency range involved, the reactive component Xo of
Zo may or may not be of importance

3. coax cable manufacturers *do* provide the complex Zo values for their
cables; the TLDetails program Wes referenced will show you what it is for
each of many commercial cables, and the calculations within the program use
the complex Zo values;

4. your geometric interpretation is a useful approximation, within certain
frequency ranges, but is not universally applicable nor is it a formal
definition of Zo

5. characteristic impedance is a complex quantity.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
<mailto:[email protected]>

----- Original Message -----
From: "James Duffer" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Thursday, May 08, 2003 10:09 AM
Subject: Re: [Antennas] Re: Hairpin monopoles

>
>
>
> >From: Wes Stewart <[email protected]>
> >To: James Duffer <[email protected]>, [email protected]
> >Subject: Re: [Antennas] Re: Hairpin monopoles
> >Date: Wed, 7 May 2003 17:10:50 -0700 (PDT)
> >
> >
> >--- James Duffer <[email protected]> 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.
>
> Which is dependent on the physical construction of the transmission line.
> Refer to the formulas for Zo of parallel or coaxial lines (Zo= 276 Log
2S/d
> where S is center to center distance between the conducior and d is
diameter
> of conductor[same units], Zo= 138 log (b/a) where b is inside diameter of
> outer conductor and a is outside diameter of inner conductor.
>
> Wouldn't manufacturers of coaxial cable state that the characteristic
> impedance Zo is for example 50 Ohms at 100 Mhz if it was indeed dependent
on
> operating frequency.  Sorry but I am from Missouri and you have to "show
> me".
>
> In that line, I am going to visit the URL you referenced and ponder this
> some more, cause if I am wrong I want to know why and I will change my
> thinking when convinced.
>
> 73, Jim, wd4air
>
>
>
>
>
>
> >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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