What Balun / Ferrite ?
We're often asked what type of Balun or UnUn is required for a given situation along with questions about Ferrite Toroids, their mix-types and how many turns are needed.
This page is designed with the new Ham in mind - or one that wishes to expand on their Balun/Ferrite wisdom!

Ferrites - Do you need one/them?
The use of a ferrite has become common practice almost to the point of "I must have one on every cable".  This isn't the case in 99 out of 100 situations.  The purpose of the ferrite is to form a high-resistance path to stray RF that flows along a cable - We're used to seeing those little lumps on USB+VGA cables, and they've been there for years... That's a single "turn" and often more than enough for a typical domestic environment that may have a broadcast transmitter nearby.

With Amateur Radio setups, the RF is much closer so a more robust solution is often required to attenuate the RF before it has an adverse effect on equipment.  Symptoms may include: Keyboard/mouse lockups, buzzing in powered speakers, monitor flickering or devices with touch-sensitive buttons behaving erratically.  Often, in a Ham Shack - the solution is as simple as re-arranging wires on the desk.

The general solution (and every situation is different), is to wrap a few turns of cable as close to the equipment as possible.  Snap-on ferrites are great for non-invasive tests, and additional ferrites can be used where the cable is too thick to support more turns.  You may need to reduce power and gently increase it, making ferrite adjustments as you go.  Experimentation is key.

Build vs Buy - Why?
Amateur Radio is, after all, a technical hobby that encourages construction where possible - but this isn't always practical with some projects.  You may have to purchase more materials than you need to make it cost-effective, you may not have the suitable tools, space or equipment required to build+test.  Winding 8-12 turns (especially RG142 coax) around a toroid is more of a physical skill than a technical one - and you'll know exactly how after you try it for the first time!

Just what is inside that box?  Does it say?  Does the seller know?  One size doesn't always fit all solutions - and this is why we have several Balun options plus this page to help you decide.

Baluns and UnUns

• My aerial is a coax-fed Dipole for a single band (but I might use an ATU on other bands) with up to 100-watts
  100-watt 1:1 Balun
   

• My aerial is a coax-fed Dipole for a single band (but I might use an ATU on other bands) and I'm using more than 100-watts
  400-watt/QRO Dipole Balun  
   

• My aerial is a Doublet (fed with balanced line) or is a G5RV - I'll be using up to 100-watts across the whole of HF
  100-watt 1:1 Balun
   

• My aerial is a Doublet (fed with balanced line) or is a G5RV - I'll be using up to 1000-watts and/or operating mostly below 15MHz
  400-watt/QRO Choke Balun for ATU/G5RV  
   

• My aerial is a Doublet but not long enough for 160m/80m, so I might want to convert it to a Marconi-T
  Doublet Choke with Switch 400w
   

• My aerial is an off-centre-fed Dipole
  4:1 Current Balun  
   

• My aerial is a full-wave loop
  2:1 Loop Balun  /  4:1 Current Balun
   

• My aerial is a random end-fed wire which I'll use an ATU to deal with
  9:1 UnUn 250w  /  9:1 UnUn 400w
   

• My aerial is a half-wave wire or I have a 20m/40m garden
  End-Fed Half-Wave Coupler 250w  /  End-Fed Half-Wave Coupler 400w

Ferrite Toroids

Home-brew is a great way to get exactly what you want from a project as well as learning along the way.
We sell a range of ferrite toroids than can be wound with either RG316, RG142, RG58, Mini8 etc to form a Choke Balun.

Our Ferrite Toroid comparison chart may also help you decide:

Here's a line-graph we made using data from Fair-Rite based on a single ferrite bead.  This outlines the typical Resistance of each type of Ferrite mix over a range of frequencies.  This data serves as a simple visual guide rather than a definitive answer to "What type do I need?"...

Although this is quite a basic plot, a longer look will show that a 31-mix offers the best "all-round" solution unless you have a specific frequency range in mind. Bear in mind that with 2.4" ferrites, the Resistance will (hopefully) be >1500-ohms and differences between ferrite types will be greater than the few Ohms you see here!

[this page was last updated Thursday December 12, 2024]