Baluns, ununs and chokes: a complete mess in ham practice.

How to choose the right balun for the antenna?

(Informal, but professional!)

End of confusion – a guide to selection and application

If you’ve ever scratched your head, wondering when to use a 1:1 balun, when a 49:1 unun, and why the hell you need a „choke,“ you’ve come to the right place. In fact, there’s no magic involved – it’s all about mode matching and impedance transformation.

Here I’ll add that I’m the self-proclaimed godfather of ununs and chokes (they sound even cooler to me in Bulgarian than the originals) – there are still no suitable words in Bulgarian. The genealogy of ununs is similar to that of baluns, and a choke is a choke.

Part 1: Modes and Roles – Balanced vs. Unbalanced

It all starts with what kind of antenna you are feeding and what kind of cable you are using.

Balun vs. Unun – what is the difference?

Baluns and unununs are transformers that serve to match the power mode (balanced/unbalanced) and/or impedance matching.

Part 2: The coefficient – ​​which one is for where?

Each transformation coefficient has a specific and different purpose depending on the antenna for which it is used.

A brief overview of the most common transformers

Tip: The standard choice for EFHW is 49:1, and 64:1 is for installations where the antenna is mounted lower or near objects that increase the impedance. The difference is often insignificant and can be corrected by the built-in tuner. For POTA/SOTA activation, 64:1 seems to be a better choice because in most cases the situation is not known in advance. But even then we can never be sure – a great place to deploy the antenna may be found.

Part 3: The Choke – the Shadow Hero (HF Choke)

A Coaxial Choke or Shortwave Choke Coil (HF Choke) is a simple but extremely important device whose purpose is to block unwanted currents flowing on the outside of the braid (screen) of the coaxial cable.

Where is it most effective?

The most effective location for the choke is as close to the antenna as possible.

• At the antenna: It isolates the antenna from the feed line, ensuring that the coaxial does not radiate. A critical and essential choice.
• At the transceiver: It acts as a secondary line of protection. Filters residual currents and prevents radio frequency interference (RFI) in the station as a whole (transceiver, computers, audio and USB cables).

The myth of the additional choke: There are legends that if your 1:1 balun is a high-quality current balun, there is no need for an additional choke to improve the efficiency of the antenna. But if you have RFI problems, a secondary choke before the transceiver will probably do an excellent job. If not the neighbors, at least the transceiver will thank you.

Part 4: Power and Materials

We can’t help but touch on the topic of ferrite cores – a favorite topic of every radio amateur!

Ferrite and power

The size of the ferrite core is directly related to how much power the balun/unun can handle before it saturates or overheats.

• Saturation: If the power is too high, the ferrite saturates, its permeability μ drops sharply, which leads to a sharp increase in SWR and overheating.
• The solution: A larger core volume (e.g. FT-240) raises the saturation threshold and allows operation at higher power. Two or three smaller toroids can also be glued together for the same purpose.

Ferrite Selection (Type 43 vs. Type 61)

Conclusion and conclusions:

1. Calculations are extremely necessary and important, but never rely on them too much – check what kind of antenna and balun you have created using a suitable device or, in extreme cases, even the SWR meter of the transceiver. Adjust the antenna in place.

2. The most important thing is to choose the device according to the type of antenna and the purpose:

• for isolation – balun 1:1,
• for reducing unpredictable impedance to the impedance of the cable or transceiver, or for multi-band vertical antennas – unun 9:1 or 4:1 (it is best to test with a device);
• for direct matching of a resonant unbalanced antenna to the transceiver – unun 49:1.
• for direct matching of a resonant unbalanced antenna to the transceiver under adverse conditions (presence of nearby objects, inability to raise the antenna high, etc.) – unun 64:1.
• so that both neighbors and equipment love you – you add Choke!

3. Leave the antenna slightly longer than calculated – it is always easier to cut than to splice during the setup on site.

4. I recommend testing the baluns and chokes on site with suitable resistors, a substitute for the corresponding antenna – 50, 200, 450, 2450 and 3200 (I am sure you will find what resistors to connect in series for the tests).

5. Last but not least: I am sure that many hams will say “I work with resonant antennas and I don’t need baluns, chokes and chokes!” and whatever else. True, everyone makes the choice for themselves. In my antennas I use. Always! I try to squeeze out maximum efficiency, to work with low powers at long distances. And despite the low power, I don’t want my neighbors to know when I’m on the air!

With this knowledge, you are armed to successfully select and construct your baluns, ununs, chokes, and antennas!

Материалът Balluns, ununs and chokes: complete nonsense in ham practice. е публикуван за пръв път на Галя и Тони - Галанто.