A New BALUN
RF Engineering | Keith Rawlings
A Work in Progress
Many of our regular RadioUser columnists are also engaged in making radios, accessories and components.
One example of such activity is our Aerials Now columnist and reviewer Keith Rawlings, the driving force behind the company R.E.C. Electronics.
Keith has written about ‘Magnetic Long Wire Baluns’ here before – in RadioUser, September 2016: 58-63, to be precise. Some of Keith’s work has now taken a more concrete shape, and he recently contacted me again.
Keith also kindly sent me a ‘pre-production’ model of his new BALUN (Balancing Transformer).
The acronym BALUN stands for ‘Balanced-Unbalanced’. These are devices used to couple a balanced impedance, such as an aerial, to an unbalanced transmission line, such as a coaxial cable.
The BALUN is needed to prevent asymmetrical loading of the balanced impedance and the induction of currents on the exterior of the unbalanced transmission line (Oxford Dictionary of Electronics and Electrical Engineering, 5th ed.: 36)
Keith said about his device: “This is an MLB [Magnetic Longwire Balun] for a ‘random wire’ end-fed. It has been optimised for frequencies down to 100kHz. It is useable over the entire High Frequency (HF) range, but the performance drops off above approximately 20MHz [...]
“Attach 30ft or more of wire to it and let me know how you find it. I will be making another ‘low-noise’ version that has a ground connection – which should minimise electrical noise below 2MHz.
Naturally, I took Keith at his word and dug out that aerial flex wire for a short test, about which I will write more at a later stage.
The images on this page show the BALUN, and my initial results on short wave have been extremely promising.
This BALUN could be just the thing for short wave radio enthusiasts and DXpeditionists this summer. It will go in my travel bag, for sure, for some global radio listening.
I shall move on to some more challenging signals and some SW DXing this week and next - Watch this space.
In the meantime, if you have any questions for Keith, you can contact him at the email, below: