Readers of my article Galvanised steel wire OCF dipole have asked whether the analysis applies to an ordinary centre fed half wave dipole, and this answer is no, not exactly, but very close. The current distribution on the OCF is very slightly different to a CF dipole, and this causes a very slight change in … Continue reading Galvanised steel wire CF dipole
There is little doubt that overall, hams have dumbed down as technology has raced ahead. An interesting result of this is the appearance of new antenna analysers aimed at the dumb ham. What is the dumb ham in this context? Last update: 14th October, 2017, 7:36 PM
Off centre fed (OCF) dipoles are very popular with Hams on HF. Many claims are made for variations of the theme, but the essential common feature is that the offset feed point provides a feed point impedance that is not too unsuited to 50Ω coaxial feed line at the fundamental resonance of the dipole and … Continue reading OCF dipoles
G5RV antenna figure prominently in many online forums. At (eHam 2014) W6OGC describes his G5RV antenna system. 102′ center feed point at 32′ drooping off on each side to 12-15′, 31′ of 450 ohm twin lead, fed with ~130′ or so of RG-8X through a 1:1 current balun at the base of the mast, aligned … Continue reading G5RV woes – W6OGC
The G5RV Inverted V antenna system at VK2OMD is fed with 9m of home made open wire transmission line using 2mm diameter copper wires spaced 50mm giving a line with characteristic impedance of 450Ω. (Varney 1958) described the tuned feeder configuration of his popular G5RV antenna system. Last update: 27th February, 2014, 4:36 AM
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. Last update: 1st April, 2016, 10:59 AM
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. Last update: 16th February, 2014, 7:53 PM
Speaker cable and similar Figure-8 twin in various sizes is popular as RF transmission line, particularly with QRP operators, especially those operating portable in the field (eg SOTA activators). Indeed, SOTA seems to have triggered a revival in the use of these cables. With the large number of online recommendations, one could be forgiven for … Continue reading Speaker cable as RF transmission line
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 … Continue reading Wire dipole on 160m