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Re: [Amps] Ferrite Core for 160M PI Output

Subject: Re: [Amps] Ferrite Core for 160M PI Output
From: Jim Brown <>
Date: Thu, 15 Jun 2017 11:04:58 -0700
List-post: <>
On Thu,6/15/2017 10:20 AM, Manfred Mornhinweg wrote:

##     #61 ferrite is  UHF material and semi useless for an HF balun.

Not right. 61 is good for absorption in the UHF range, and for relatively low loss applications on HF. It works great as balun, for example in the form of an FT-240-61 core with 12 turns of RG400 on it. Instead it's not good for a bead balun, because its permeability is too low for that.

You are mistaken, Manfred. I've measured chokes like that wound on #61. They are NOT effective at MF or HF. #61 is FAR too high Q at HF.

#77  ferrite is out of vogue these days for HF baluns.....even though
Hy-hain still uses it on their BN-4000 balun.

That's their design error.

Both have been replaced with type 31 ferrite.

Yes. And I was the guy who did the research, and published it, that caused Fair-Rite to use it in that way.

77 is low frequency, high flux density ferrite for power supply applications. It can be pressed into HF balun applications, but is far from optimal. Many people have used old TV flyback transformer cores and even TV yokes for winding baluns - that's much the same material.

31 is formulated for absorption in the HF range, not for transformers. It can be used in baluns only if enough turns (or beads) are used to provide a really high impedance, because the impedance it provides is almost purely resistive. It makes for a VERY lossy balun if used to provide a moderate impedance.

You clearly don't understand how common mode chokes work. You need to study my tutorial on the topic.

A good common mode choke MUST BE resistive at the operating frequency, and achieves that by making it self-resonant in that range, and the best materials yield a circuit Q for that resonance on the order of 0.5, making it a very broad resonance. The circuit Q of an HF choke wound on #61 is on the order of 10, making it effective on a single frequency. And since the parastic C that forms that resonance is so small, it's quite difficult to measure accurately.

61 provides a lower impedance than 31 or 77, but it's mainly inductive in the low and mid HF range. So its far less lossy. If used in a way that provides too little impedance, though, it can detune an antenna.

The problem with being primarily inductive is NOT that it detunes the antenna, but rather that the inductance combines with the common mode impedance of the feedline (it's simply a wire connected to the antenna at one end and usually the TX at the other).

So, it all boils down to selecting the material best suited for the balun on intends to build, and then design it correctly.

And it helps to NOT use the word "balun," which is used to describe at least ten different things that are completely different from each other. #61 is a great material for use as the core of a TRANSFORMER below 10 MHz, but useless as the core of a CHOKE below about 200 MHz.

31 cannot fully replace 61 nor 77, nor can 61 fully replace 31 nor 77, etc.

#77 is NOT a suitable material for a transformer NOR a choke above 100 kHz.

#31 does NOT replace #61 or #77 or #78. Rather, it supplements #43, which is slightly better as the core of a CHOKE above 20 MHz, and good down to about 5 MHz. I've used both #31 and #43 as the cores of TRANSFORMERS for RX antennas that I use on 160, 80, and 40M.

Each has its applications.


Some companies offer several dozen different ferrite mixes, so that designers can select the optimal material for a given application.

Yes, but the designer must first understand how they work. Again, study the link I posted. Or buy a recent version of the ARRL Handbook and read it there.

73, Jim K9YC
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