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Author Topic: Good website or book for homebrew chokes?  (Read 365 times)

KD0VE

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Good website or book for homebrew chokes?
« on: March 22, 2023, 08:05:18 PM »

Starting to make antennas for spring.  Got a couple verticals in the pipeline and want to make feedpoint chokes.

I have made chokes in the past but want to make high power tolerant stacked toroids for the 1st time.  What are good options for the tape used to wrap the toroids?

I'd be very interested in a good website or book with lots of detail.

thx to anyone tasking the time to offer advice or links.
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WB6BYU

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Re: Good website or book for homebrew chokes?
« Reply #1 on: March 22, 2023, 09:22:54 PM »

NA6O

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Re: Good website or book for homebrew chokes?
« Reply #2 on: March 22, 2023, 09:57:34 PM »

Here's a good place to start.

YES. That is the premier source for modern information on choke design and applications. There’s much to learn here and by all means do some experimenting and see for yourself how performance varies with parameters such as core type and number of turns. A VNA is very helpful.

As for “high-power” chokes, a preferred design approach is to provide sufficient choking impedance such that the power dissipation is small. This is accomplished by winding an optimum choke, perhaps using Jim’s cookbook (http://www.k9yc.com/2018Cookbook.pdf), and by placing additional chokes in series to increase bandwidth and/or total impedance when required.

Gary NA6O
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W9IQ

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Re: Good website or book for homebrew chokes?
« Reply #3 on: March 23, 2023, 12:09:56 AM »

What are good options for the tape used to wrap the toroids?

The best option is to not wrap the toroid with any type of tape or insulator. It is completely unnecessary and only serves to trap heat in the core.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

G4AON

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Re: Good website or book for homebrew chokes?
« Reply #4 on: March 23, 2023, 04:13:22 AM »

In addition to the useful info already given, don't forget that a feeder can pick up RF and bring it into the house/shack. I have measured significant RF on the outer of a spare feeder laid across the back lawn, it was picked up from a nearby horizontal dipole.

You can check how effective your choke(s) really are with a simple clamp on meter, yet very few seem to bother. Why guess when you can measure? I have one of these meters, it is built into an old home brew transistor tester case and took a matter of a few minutes to make. Building details are on this site: http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

My meter has the 1A/100mA switch and a type 43 clamp on core that slides nicely on RG213 size coax. It is fixed to the plastic case with hot melt glue. Measured accuracy is +/-20% from 1.8 to 70 MHz (our 4m band).

You might find it isn't necessary to use additional chokes at the house end of your feeders, but with the the above meter it is easy enough to measure.

73 Dave
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W9IQ

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Re: Good website or book for homebrew chokes?
« Reply #5 on: March 23, 2023, 04:29:49 AM »

If you prefer a simple graphical representation of an FT240-31 toroid choke implementation, see the chart below. The idea is to maximize the RS for the bands of interest. You can use two different cores in series and the RS values will add for each band.

- Glenn W9IQ

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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W4HRL

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Re: Good website or book for homebrew chokes?
« Reply #6 on: March 23, 2023, 07:17:44 AM »

The aforementioned K9YC.com website is a great resource, as is W9IQ's compiled chart.

Another website that is full of good reading and various test results is that of DJ0IP (D-J-zero,,,)  www.dj0ip.de/rf-cmc-chokes/

W4HRL
Mike in PoquosonVA
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WA3SKN

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Re: Good website or book for homebrew chokes?
« Reply #7 on: March 23, 2023, 09:01:57 AM »

I will mention that this subject has been well covered in the ARRL Handbooks lately.  If  you don't have one I can recommend getting one... and if you do have one, check it out!

-Mike.
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KD6VXI

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Re: Good website or book for homebrew chokes?
« Reply #8 on: March 23, 2023, 10:37:12 AM »

I will mention that this subject has been well covered in the ARRL Handbooks lately.  If  you don't have one I can recommend getting one... and if you do have one, check it out!

-Mike.

And the guy that wrote the section in the ARRL handbook is...

K9YC, Jim Brown.  Of Audio Systems Group.

He and Ward Silver also did some extensive updating on the grounding and bonding section of the handbook.

--Shane
WP2ASS / ex KD6VXI
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AD7VO

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Re: Good website or book for homebrew chokes?
« Reply #9 on: March 23, 2023, 07:35:28 PM »

Check out this website.

http://www.karinya.net/g3txq/chokes/

He presents actual measured data for many configurations.
He also explains how to measure them.
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W1VT

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Re: Good website or book for homebrew chokes?
« Reply #10 on: March 24, 2023, 05:15:57 AM »

When Steve G3TXQ (SK) made his measurements Vector Network Analyzers (VNAs) were too expensive for most hams, but now there are cheap
Chinese versions that are quite affordable for hams who want to measure their RF chokes.
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VE7RF

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Re: Good website or book for homebrew chokes?
« Reply #11 on: March 25, 2023, 08:53:20 AM »

The 4" NanoVNA and the deluxe version of the MFJ clamp on RF ammeter is what's really required.  If the idea is to minimize CM current, then just measure the actual CM current in several places.  Without the ability to measure CM current,  you are just assuming the cook book CM choke works.   As G4AON pointed out, you can still measure CM current in places you thought not possible.
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