[ICOM] Pro II Antenna Tuner question

[D C Macdonald]

Then that makes the situation even worse for the
transformation of impedance on the quarter wave
transmission lines!!  The impedances become really
extreme!!

Of course losses are much lower with the parallel line

73  ---  Mac, K2GKK/5


----Original Message Follows----
From: "David J. Ring, Jr." <n1ea at arrl.net>
Reply-To: ICOM Reflector <icom at mailman.qth.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Subject: Re: [ICOM] Pro II Antenna Tuner question
Date: Sat, 10 Jul 2004 20:12:04 -0400

Mac, you're right on the money about the transforms, but
the fellow was using 600 (or other) high impedance line.

Right info, wrong question!

73
DR


----- Original Message -----
From: "D C Macdonald" <k2gkk at hotmail.com>
To: <icom at mailman.qth.net>
Sent: Saturday, July 10, 2004 7:01 PM
Subject: Re: [ICOM] Pro II Antenna Tuner question

Don't forget the Velocity Factor of the feedline!
If you are using "normal" coax, the VF is .66,
which means 1/4 wavelength on 80 meters
is around 40 feet!

Use of 1/2  ELECTRICAL  wavelength of feedline of  ANY
impedance gives you exactly the same impedance at both
ends.  This  MAY  give you an  EASY  mismatch to deal
with if your antenna is close to resonance.  It should be
no problem, for example, to TUNE a 75/80 meter dipole
antenna SYSTEM with reasonable ease in the matching if
you use 1/2 wave (electrical) of feedline.

Quarter wavelength feedlines act as impedance transformers.
For example (assuming use of 50 Ohm coax), if your antenna
impedance is 100 Ohms and you use 1/4 wave of feedline,
the impedance at the transmitter end will be 25 Ohms.
If your antenna (loaded mobile whip) is 4 Ohms, transmitter
will see over 600 Ohm as a load.


TX Z     FL Z
----  =  ----
FL Z     ANT Z


73  ---  Mac, K2GKK/5