It's a bit of an animal - A 1:1 Balun for use on HF (1.8-30MHz) that easily handles 400w RF power (full-duty cycle). Ideal for Dipoles at the home QTH. We don't cut corners: This balun is wound using RG142 coax and the ferrite core is an FT240-31 offering resistive performance 3.5MHz up to 30MHz so a perfect companion for your resonant HF aerial or fan-dipole. At resonance, this balun is good for around 1kW CW/Datamodes.
We also have a Doublet/G5RV Choke, using the same internal configuration, but with the terminals at the top of the box.
Made (and used) by us - Be weary of any supplier who can't (or won't) tell you what's inside the box you buy!
Baluns - What/Why?
It's good practice to put a Bal(anced)Un(balanced) where coax meets aerial or balanced-feeder. A Balun will help prevent "common-mode current" on the outer of the coaxial braid - This is vital to ensure that RF does not flow down the coax, turn it into part of the antenna system and give you "RF in the Shack". Using a 1:1 Current Balun at the junction of balanced-feeder+coax is also recommended.
We do not advise the use of "ugly chokes" (air-cored coils of coax) for use at HF - these do not offer a consistent choking impedance and, in some cases, can actually increase common-mode current! Simply put - Use a 43 or 31 mix ferrite toroid and a coax of a suitable power rating. At VHF, a few turns of coax is perfectly adequate - for 50MHz/70MHz, Aerial Parts of Colchester offer a ready-made choke for a yagi.