A balun (from "balanced to unbalanced", originally, is an electrical device that allows balanced and unbalanced lines to be interfaced without disturbing the impedance arrangement of either line.
 
This is a handy device for portable or temporary antenna installations - This is a Ruthroff voltage matching version excellent for matching balanced ladder line fed antennas such as dipoles, inverted 'v's etc to 50 Ohms coax.  Or to construct a dipole without a feed line.  If the antenna is not resonant at the frequency required you'll still require an antenna matching unit but this little balun will help a lot.
 
To test I rigged up a quick 6m (50.323MHz) dipole of approx 1.5m per element and transmitted 10w FT8 for a short period and looked at PSKreporter to find I'd been received in Northern Ireland from the North East of England.  Very pleased with that considering how simple the antenna was.
 
You'll need two lengths of wire that attach on the nut & bolts. Or ladder line feeding a dipole - I also tested across all the amatuer bands using my balanced fed outside wire dipole - and left the unit in place - I do alot of data but only 20-30w so in short bursts the balun can cope - Ideal for QRP NOT QRO as this little balun will get rather warm if you feed 100w FT8 into it!!   You'll now if you have heating problems as the SWR will shoot up quite quickly.
 
 Balun operating power up to 100W SSB Suitable HF Shortwave Antennas between frequency of 3-30mhz ideal for outdoor activations / Portable QRP Stations/Homebrew antenna experiments.
 
Good for matching antenna to receiver only equipment as well - may improve received signal as it will allow maximum power transfer (maximum received signal) to be transferred from the antenna to the receiving equipment and can help reduce noise from the antenna feedline.
 
This little Balun is light -  only 39g and case is accessible for modification or repair if required.  Also allows for waterproofing if required.
 
Product size: 91x36x26MM/3.58x1.42x1.02inch including terminal
housing size: 61x36x26MM/2.4x1.42x1.02inch
 
I will ship this with the lid off the package - to reduce height for shipping - just clip it back on when you receive it.
 
See the link in the information section for more information and design notes.