Antenna Centre + 1:1 Balun

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Antenna Centre + 1:1 Balun


An antenna centre with built in 1:1 common mode current balun. 

  • Feeder strain-relief built in
  • BNC socket
  • Water-resistant construction
  • Antenna wire strain-relief built in
  • Fixing for centre support
  • Lightweight 86g (3 oz.)
  • High performance by design
  • Loss < 0.2dB @ 14MHz
  • 125 Watt power rating.
  • Note: the balun is designed with a lip that can be sealed using a silicone sealant if required for use in more permanent installations. We do not supply the balun sealed as this allows users to gain access to the enclosure.

The technical stuff

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;

  • the radiation pattern of an antenna needs to be carefully controlled and made predictable
  • sources of electrical noise can be induced onto the feeder
  • RF at the transmitter end of the feeder needs to be reduced - for example if your radio is connected to a computer for data modes
  • the Q of the antenna is high. In such cases uncontrolled common mode currents can cause all sorts of problems

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

What does this mean?

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!

20 Reviews Hide Reviews Show Reviews

  • 5
    first dipole build

    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

  • 5
    Great value for money

    Posted by Rienus PA0RBA on 31st Mar 2016

    Compact, easy to build and high quality

  • 5
    1:1 125 WATT BALUN

    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.

  • 5

    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!

  • 5
    Works brilliantly

    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.

  • 5
    Works very well

    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.

  • 5
    Great Balun

    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 .

  • 5
    Lightweight 1:1 Balun that is Great

    Posted by Craig Simmons on 11th Feb 2014

    Balun works great, very light weight and easy to hook up. Adds to the ability to create several types of antennas for use.

  • 5

    Posted by Rolf on 7th Feb 2014

    Good item to construct wireantennas in the field without soldering.