Antenna Centre + 1:1 Balun

¥2,135
(Inc. Tax)
¥1,779
(Ex. Tax)

NOTE Customers outside the Eu pay the lower (Ex. Tax) prices!

(20 reviews) Write a Review
SKU:
ACB-101
Shipping:
Calculated at Checkout

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. 

  • 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.

img-2624-1-.jpg

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?

sotabeams-balun.png

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.

cmrr-85-ohm.jpg

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
    great little kit, all parts present and assembled easily, works just great

    Posted by Bob Harwood on 11th Oct 2018

    can recommend highly

  • 5
    1-1 balun

    Posted by Werner on 29th Jul 2018

    Nice light weight and easy to use.

  • 5
    Easy assembly - Top Quality

    Posted by Tom on 11th Apr 2018

    The 1:1 balun went together as advertised and performs equally well.
    Top quality material and easy instructions (online) so you will never
    misplace them.

  • 5
    nice et easy to build

    Posted by Nicolas F4EGX on 29th Nov 2017

    built 2 in less than an hour. Very easy.

  • 5
    Easy construction and does the job

    Posted by Neil on 16th May 2017

    Used on holiday to make up a portable 40m dipole - strong construction and works well (I worked VK from roof terrace in Tenerife)

  • 5
    Excellent

    Posted by Jonathan Kempster on 10th Mar 2017

    An excellent balun. Very small and lightweight. Totally practical and suited to portable ops.
    Don't accidentally order the kit version by mistake, like I did, unless you want to build it yourself!

  • 5
    Easy to build and it works

    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.

  • 5
    Simple and lightweight

    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.

  • 4
    Light-weight, functional balan

    Posted by Pete on 18th Aug 2016

    The kit is complete and nicely engineered. Very strong plastic and very light-weight.