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:[email protected]] On Behalf Of D Rodman MD Sent: Sunday, November 20, 2016 8:01 PM To: [email protected] 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 _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
