I saw a recent ‘maker’ video describing a small transmitting loop for 40m.
The loop used a 3m length of 19mm copper pipe formed into a circle, and at the gap where the ends almost meet, a tuning capacitance is synthesised using coaxial cable.
Above is a screen shot from Reg Edwards loop design program. It calculates the radiation resistance at 0.005Ω, loss resistance of the loop at 0.035Ω, capacitance to resonate it of 206pF (Xc=108Ω), and a bandwidth of 3.2kHz.
I described a method for designing antenna systems to avoid excessive voltages in baluns and ATUs at (Duffy 2011) .
This article reports post implementation measurements of an antenna system designed using that method and using a G5RV Inverted V with tuned feeder and ATR-30 ATU with integral 1:1 current balun. The tuned feeder is a home-made line section of 2mm diameter copper conductors spaced 50mm, and 9m in length. An additional 0.5m of 135Ω line connects from the antenna entrance panel to the ATU.
This article explores the loss that may be encountered in an ATU in a practical setting.
The load is a G5RV with tuned feeders operating at 3.6MHz. The tuned feeder is 9m of open wire line of characteristic impedance 450Ω, and the impedance seen by the ATU is around 40-j150Ω, this is not a particularly onerous load.
This is a project to design and build a Guanella 1:1 (current) balun suited for up to 100W on HF with wire antennas and an ATU.
For use with a tuner, the most important design criteria are:
Continue reading An inexpensive medium power tuner current balun for HF using Jaycar parts
Third part in the series..
Direct measurement of common mode current in an antenna system is the best indicator or whether there is a common mode current problem.
In Common mode current and coaxial feed lines, I mentioned that common mode current is easily measured.
Continue reading Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #3
Second part in the series…
When baluns are used with open wire feed lines to wire antennas on HF, most commonly the main purpose is to suppress common mode current, to ensure that the current in one wire of the feed line is equal but opposite in direction to the other wire at that point.
Continue reading Design / build project: Guanella 1:1 ‘tuner balun’ for HF – #2
This is a project to design and build a Guanella 1:1 (current) balun for use on HF with wire antennas and an ATU.
First part in the series…
For use with a tuner, the most important design criteria are:
Continue reading Design / build project: Guanella 1:1 ‘tuner balun’ for HF – #1
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.
Continue reading WIA 4:1 current balun – further explanation
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.
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.