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.
Continue reading Cobwebb antenna impedance matching scheme
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.
Continue reading Common mode current and coaxial feed lines
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.
Continue reading RG174 for portable HF operation
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.
Continue reading TV upgrade
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).
Continue reading Wire dipole on 160m
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.
Continue reading Yet another dodgy coax collinear
An extended test comparing signals received in Florida from three nearby stations in Australia was conducted 21/12/13, a low elevation path of more than 14,000km.
The A/B comparisons were performed on statistics gathered from the W4HBK grabber, in this case measurements of the noise and each of two transmissions of 1min of steady carrier every 5min over a half hour.
Continue reading A/B comparison test on 40m