This antenna is based on articles "A Parasitic Lindenblad Antenna for 70cm" and "An EZ-Lindenblad Antenna for 2 Meters" by AA2TX, published in QST magazine. I have made some changes so it could be better weather protected.
While I was building it, I got the idea to add 6M J-pole by feeding the whole 70cm Lindenblad antenna, and feed the line with ¼ lambda stub made of TV twin cable.
Painter’s poles are used for the main structure, 3 sections of 4ft. military fiberglass mast, and 12ft. telescoping fiberglass.
The 70cm radiator is changed to coaxial antenna design. Coax cable is routed through the bottom ¼ lambda element, thus no balun is needed – the sleeve is actually the balun.
1/2 and 5/8 Al pipe sizes are used. Because of the small sleeve/coax diameter ratio, only the sleeve must be shortened with pipe cutter to tune the antenna. Keep the LMR240 coax cable centered with electrical tape.PVC fittings, ¼ fiberglass rod and Epoxy Putty are used to finish it.
145MHz Dipole construction. 1/2 Al tube. Center insulator 3/8 Derlin rod. LMR240 coax with balun core. PVC fitting was split and glued back after assembly.
All dipoles assembled. Coax cable routed thru cross members, 4ft section of fiberglass mast and soldered to SO-239 round connector. Upside-down view.
View of 6m 1/4 lamda stub, soldered to 70cm coax (upper) braid and core baluns (type 43).
Determining the length of 1/4 lambda stub is easy and precise with an Antenna analyzer. Start with 1.40m long piece, leaving one side open and connect the other end to your analyzer. Ladder line should be hanging in "free space", away from metal objects. Swipe and find the frequency with "zero" impedance. Trim both wires until the desired operating frequency is reached. Make it short on one end and solder the 6m coax 70mm "up". Balun is made of 2 type 43 cores. Water seal all joint with "Electrical Liquid Tape"
Finally, very small changes can be made by trimming the ladder line open end.
- "The Lindenblad: The Ultimate Satellite Omni Antenna" by W6SHP
- "A Parasitic Lindenblad Antenna for 70cm" by AA2TX
- "An EZ-Lindenblad Antenna for 2 Meters" by AA2TX in QST 08'2007