I mentioned in my article WIA 4:1 current balun that the use of a single toroidal core in the above graphic compromises the balun. This article gives a simple, but more detailed explanation for the technically minded of why the shared magnetic circuit ruins the thing.
I had a contact with a newcomer recently, and struggling to hear him, I learned that he was using the 3030 antenna described in the WIA’s “Your entry to amateur radio” 2nd ed, the Foundation licence training manual.
Eric Nichols, KL7AJ, published a manifesto entitled “SWR Meters Make You Stupid” announced on eHam in March 2010. Eric is clearly a disciple of Walt Maxwell (W2DU SK), his first announcement states
By popular demand, my complete treatise on transmission lines. Approved by Walt Maxwell, W2DU as if Walt’s blessing was an imprimatur from the ham radio church.
From time to time, correspondents have asked how the Cobwebb antenna works, and particularly how the impedance matching scheme works.
Firstly, what is the Cobwebb?
It is an innovative antenna for small spaces, quite compact and as I recall originally intended to cover five amateur bands from 20-10m.
In Common mode current and coaxial feed lines, I mentioned that common mode current is easily measured,
An antenna feed line is intended to convey energy from the transmitter to the antenna, and usually without giving rise to radiation itself.
The term “common mode” comes from consideration of the currents on an open two wire line, and it refers to the net or unbalance current, ie the current that would give rise to external fields, to radiation.
This article looks at the equivalent common mode current in a coaxial transmission line.
There are frequent recommendations of RG174 for portable stations (eg SOTA), usually running QRP, principally because it is light and easy to wind up into a small package to fit into a pack. RG174 commonly uses silver coated steel (SCS) centre conductor, sometimes copper clad steel (CCS), sometimes copper.
The LG LCD television failed after less than 10 years, the LCD backlight would not always start and it became a bigger problem each winter.
Discussion with a correspondent recently ranged onto the effect of some conductor materials in antennas. This posting reports the feed point impedance and internal efficiency (meaning power not turned into heat in the structure divided by power input at the feed point) of a 160m half wave dipole (80m long, centre fed, 20m above average ground and using 2.6mm diameter single core wire).
Robert Nickels, W9RAN shows a design for an “8 element colinear vertical” for 1090MHz ADSB in QST Jan 2014 in his article Virtual Radar From a TV Dongle.