[Antennas] ladder line questions

Mon, 17 Nov 2003 11:03:22 -0600

Well, I am sorry that you disagree because although there are special cases
in which the rig will see a 25 ohm load with a 100 ohm dual coax line, in
general your statement is without merit.

The input impedance of any line is a function of its type and construction,
its length, its Zo and the load on "the other end." If you know the load and
the electrical length of the line, you can determine the input impedance
seen by the rig or tuner. The Smith Chart is the older means for this
calculation, or the equations can be handled, although with difficulty, on a
calculator, or there are computer programs that handle this with great ease
of use. I recommend TLDetails.

If you are somehow thinking that the two 50 ohm coaxes look to the tuner to
be in parallel and thereby present a load of 25 ohms, I must politely
comment that you are entirely incorrect.

I highly recommend that you review the ARRL Antenna Book and, best of all,
"Reflections II" by my good friend Walt Maxwell, W2DU.

Thanks for your comments and I mean no disrespect, but you are completely
wrong with your statement. I would hate for anyone reading the reflector to
go away with that information thinking that it was correct.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"Starting the 58th year and it just keeps getting better!"
[email protected]

----- Original Message ----- 
From: "KZ5V" <[email protected]>
To: "George, W5YR" <[email protected]>
Cc: <[email protected]>
Sent: Monday, November 17, 2003 2:53 AM
Subject: Re: [Antennas] ladder line questions

> George,   Thanks...  yup, two 50 ohm coax cables do form a 100 ohm
balenced
> feedline, of sorts.  But also form a 25 ohm impedance load to the
> transmitter.This can be handled with most mfj tuners, if you hook them up
> backwards. But still a bad idea...  Granted there are a lot of ways to
solve
> a problem, but only one best way.  .. and this isnt it.
>   Usually  I agree with you, but this is an exception.
> KZ5V
> ----- Original Message ----- 
> From: "George, W5YR" <[email protected]>
> To: "Hue Miller" <[email protected]>; <[email protected]>
> Sent: Sunday, November 16, 2003 8:06 PM
> Subject: Re: [Antennas] ladder line questions
>
>
> > Two 50-ohm coaxes form a shielded 100-ohm balanced line.
> >
> > 73/72, George
> > Amateur Radio W5YR -  the Yellow Rose of Texas
> > Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
> > "Starting the 58th year and it just keeps getting better!"
> > [email protected]
> >
> >
> >
> >
> >
> > ----- Original Message ----- 
> > From: "Hue Miller" <[email protected]>
> > To: <[email protected]>
> > Sent: Sunday, November 16, 2003 4:43 PM
> > Subject: Re: [Antennas] ladder line questions
> >
> >
> > >
> > > ----- Original Message ----- 
> > > From: "HSHK" <[email protected]>
> > >
> > > "....Besides using a 4:1 balun and then running coax, you can
> > > do away with the balun and use balanced coax.
> > >
> > > If you'd like to make some ladder line, the attached pics will
> > > show...
> > >  Bill KA8VIT"
> > >
> > > Bill, attachments don't make it thru the list reflector.  Are the
> > > photos up somewhere else where i could have a look?
> > >
> > > Also- is this correct: the 2 coaxes run this way, as a balanced
> > > coax, 4x the impedance of the single coax?
> > >
> > > And if so- let's say we do this, raising the impedance, let's say
> > > we then want to retain the balanced coax idea ( more for noise
> > > suppression and ground independence ) but want to have the
> > > line impedance the same as for a single coax span. How many
> > > "balanced coax" pairs do we need in parallel? 2 or 4? Just
> > > curious.
> > > Tnx, Hue Miller
> > >
> > > - - -
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