David,
I think the best and quickest way to understand and observe line impedance
transformations is to model it using software. Two popular programs are TLW
and TLDetails. TLW is bundled with the ARRL Antenna Book. TLDetails can be
downloaded here:
http://www.ac6la.com/tldetails1.html
It won't take you long to perform several "what if" impedance
transformations by varying line length and type.
Paul, W9AC
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of D Rodman
MD
Sent: Sunday, November 20, 2016 8:01 PM
To: topband@contesting.com
Subject: Topband: Ladder line + tuner
I designed a loop for 100 ohm impedance and fed with coax and 1/4 wave
transformer. It has worked well for years. I got the bright idea to
replace the coaxial feed with 35' of 450 ohm ladder line and a Bliss remote
tuner. This combination would not match. I experimented. A nice dip in
VSWR was noted about 400kHz lower than the bottom of the band where that
combination of antenna plus ladder line was almost perfectly resonant. A
versa tuner WOULD tune it but I needed to add about 90' of ladder line for
the remote tuner to produce a reasonable lower complex impedance inside the
band (actually it was reduced to about 58 + j6). The impedance with 35' of
line was over 1K and this is too large of a value for that tuner to accept.
(That is a previously made tuner with vacuum capacitor and large roller
inductor.) Does anyone have knowledge or experience with impedance
transformation on ladder lines that might be able to teach me something here
about the effects I noted??? Thanks.
--
David J Rodman MD
Assistant Clinical Professor
Department of Ophthalmology
SUNY/Buffalo
Office 716-857-8654
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