AMATEUR RADIO FOR THE GREAT OUTDOORS
Antennas including linked dipoles, telescopic poles also ham radio kits - everything you need.
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Antenna Centre + 1:1 Balun
AVAILABLE AS A KIT OR READY-BUILT AND TESTED
An antenna centre with built in 1:1 common mode current balun.
Much nonsense is talked about baluns. The purpose of a balun is to isolate the antenna from the feeder. Baluns are not always necessary. One indication that a balun is needed is when the VSWR of an antenna varies if the feeders is touched or moved. However, this is by no means a comprehensive test and the only real way to tell is to measure the common mode currents on the feedline and then to decide what is acceptable in your own situation. Baluns are especially important where;
Radio amateurs often coil a few turns of feeder up at the feedpoint of the antenna to act as a feedline choke. Sometimes this seems to work. This has given rise to an impression that such an approach is adequate in all situations - it is not. The common mode rejection ratio of a balun depends on the impedance of the system at the point that the balun is used. Note that the impedance is not related to the impedance of the feeder itself (it's not usually 50 Ohms). The impedance where the balun is located can be just about anything. If it is very low, a few turns of co-ax "scramble wound" might act as a viable balun. If it is very high even a well designed balun might struggle to help.
The graph below compares the SOTAbeams balun (green trace) with 7 turns of cable "scramble wound" (pink trace). The red trace is a 680 Ohm resistor used for calibration and checking. The markers have been set in the amateur bands.
First note that the calibration resistor is measured at about 680 Ohms across the entire frequency range - this indicates that the mesurement system is working well.
The scramble wound "balun" (pink trace) shows a low impedance (less than 680 Ohms) up to 12MHz. From there the impedance peaks at 19.5MHz before falling rapidly to 30MHz where it is nearly back to 680 ohms. The peak is caused by the "balun" resonating. The resonant frequency will likely change depending on how the balun is located and with rain/moisture; not good.
The scramble wound balun used in testing
The SOTAbeams balun (green trace) shows a very different characteristic. It is designed to act as an effective feedline choke from 1.8-30MHz. It shows an impedance of over 1,000 Ohms across the virtually the entire range from 1.8-30MHz. Its performance will not change significantly - it's stable and predictable.
Very few other manufacturers show the results of this sort of testing. One can only wonder why?
Click graph to enlarge
The following graph shows the Common Mode Rejection Ration (expressed in dB) of a scramble wound "balun" compared to a SOTAbeams balun.
Clearly the SOTAbeams balun is always better than a scramble wound "balun" in the amateur bands. The SOTAbeams balun provides predictable performance across its range; that's because it has been designed and properly tested!
Showing reviews 1-10 of 14 | Next
Posted by Chris VK3PAT on 8th Nov 2016
I bought two of these balun kits and assembled them both in under an hour. The kit is very well made and cleverly designed. Price is also very reasonable for Aussie buyers as we don't pay the 20% VAT which just about covers the postage. Another great product from Sotabeams. You guys really do understand portable amateur radio.
Posted by David Fairchild on 17th Sep 2016
Nice kit and a good addition to my portable antenna kit. Simple to build and good quality parts.
Posted by Pete on 18th Aug 2016
The kit is complete and nicely engineered. Very strong plastic and very light-weight.
Posted by craig gwillym on 12th Apr 2016
Advice from Richard was excellent on my first dip
Into antenna building . Balun is constructed very well with quality parts and works extremely well
Posted by Rienus PA0RBA on 31st Mar 2016
Compact, easy to build and high quality
Posted by Paul 2E0MIY on 8th Feb 2016
I like making antennas and want to build as much as I can. The Balun is a nice straightforward kit with excellent components which was fun to build. I fitted it in my loft having soldered up a BNC plug to connect it,(which was a first for me). The antenna works very well without needing a tuner and i have since made up a fantail antenna connected to the 1:1 Balun and found can work 10/20/40 without a tuner and with very modest VSWR levels with surprisingly little trimming.
Posted by Per R. Pilkvam on 20th Dec 2015
Easy to make from the kit. Very lightwight, so this is a very good product. I love it. Many thanks, Richard!
Posted by Paul W. on 24th Feb 2015
Purchased this 1.1 balun in kit form. Downloaded the instructions and put the whole lot together in just over 30 minutes. Very easy to construct and works great. Would I purchase another? You bet I would.
Posted by Steve Milner on 10th Jan 2015
Bought this ready-built after seeking advice from Richard on its suitability for a fan dipole in the attic. Works a treat.
Posted by Rene - ON7FR on 20th Dec 2014
I bought the kit, very easy to make ,it's small ,cheap and lightweight compared with other brands.Will use it in the field as an inverted V . Waiting the good weather to use it.I'm very happy .
Showing reviews 1-10 of 14 | Next
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