Topics

Common Mode Chokes

Everett N4CY
 

Below is some work that I did looking at some Common Mode Choke options. The 2 most common toroids that are used are FT240-31 and FT240-75 for Common Mode Chokes. However, there is another good on which is a TDK N30 (Part Number TDK B64290L0040X830). 


Using My Array Solutions VNA2180 I looked at each of the three toroids mentioned above.
However, the best way to get much better results than using only one toroid is to cascade two, or more chokes in series, as can be seen in the below sweep.
Everett N4CY

Paul Cianciolo
 

Hello Everett,

Nice work!  I do not have a VNA .. just scalar so I cannot do the fine graphs that you put up. Maybe someday..  I am glad you did it.
My CMC's are probably not optimized, but I wanted to show what was possible with junk box parts.
Your work here gives accurate results. Thank you for posting it!!

PauLC

W1VLF

Jos Stevens
 

You might look at NanoVNA on the web, its very  cheap for a VNA.

Jos (pa3cce)

Op 13-11-2019 om 17:45 schreef Paul Cianciolo:

Hello Everett,

Nice work!  I do not have a VNA .. just scalar so I cannot do the fine graphs that you put up. Maybe someday..  I am glad you did it.
My CMC's are probably not optimized, but I wanted to show what was possible with junk box parts.
Your work here gives accurate results. Thank you for posting it!!

PauLC

W1VLF

Everett N4CY
 

Hi Paul,

A VNA takes all of the guess work out designing a Common Mode Choke. There are a lot of very low cost VNAs now on the market. They may not give exact results, but would certainly give you workable data.

Everett N4CY

In a message dated 11/13/2019 10:47:29 AM Central Standard Time, paulc@... writes:

Hello Everett,

Nice work!  I do not have a VNA .. just scalar so I cannot do the fine graphs that you put up. Maybe someday..  I am glad you did it.
My CMC's are probably not optimized, but I wanted to show what was possible with junk box parts.
Your work here gives accurate results. Thank you for posting it!!

PauLC

W1VLF

n2msqrp
 

Paul.

I enjoyed the video. It's an incentive for me to place chokes on my active whips. What types of cores did you use for the LF common mode chokes?

Mike N2MS

On November 13, 2019 at 11:45 AM Paul Cianciolo <paulc@...> wrote:

Hello Everett,

Nice work!  I do not have a VNA .. just scalar so I cannot do the fine graphs that you put up. Maybe someday..  I am glad you did it.
My CMC's are probably not optimized, but I wanted to show what was possible with junk box parts.
Your work here gives accurate results. Thank you for posting it!!

PauLC

W1VLF


 

Paul Cianciolo
 

Hi Mike,

I plan to build one and show a video of it.  The core I will be using  1.25" material 75 core.
Mostly because I have some of these cores available.  For VLF and LF  material 75 or 77 works well. 
 
Here is a link to the cores I will be using  2675821502 by Fair-Rite Products | Ferrite Core | Arrow.com
 

Kriss Kliegle
 

Al Scanandoah <k2znqrp@...>
 

Do a search on "clifton labs z5100a" for some good construction info.

Al, K2ZN

On Wed, Nov 13, 2019, 3:56 PM Kriss Kliegle <kliegle@...> wrote:
Some good data on cores and mixes:

https://palomar-engineers.com/ferrite-ring-toroid-specs



Attachments:

jdow
 

Back in the 70s Indiana General (RIP) had a WONDERFUL core material CN-20 as I recall. I still have a very small number of 3/8" diameter 3/8" thick cores. I used a pair of cores to make myself a very interesting directional coupler that worked from about 1.8 MHz (funny I should pick that frequency for testing {^_-}) to the 2 meter range with 30 dB coupling and 20 dB (at the extremes) to 50 dB directivity. God but I loved that wonderful stuff. I could make an 1:32 turn autotransformer using simple enameled wire and expect it to work over amazing frequency ranges. Er, I had time on my hands at work and fiddled around with some materials on hand and....

{^_^}

Kenneth Sejkora
 

Thank you Paul and Everett for sharing your work with the common mode chokes.  I'm certainly planning on constructing a couple to reduce the noise propagated through the coax shield.

Everett, you recommended the TDK B64290L0040X830 core for winding the choke.  You also specified that your design used 35 turns of RG-316.  I checked out the specs of the TDK core, and it is considerably larger than the stacked toroids that Paul used.  In Paul's configuration, he used two "stacks" of four each of somewhat smaller toroids wound in a "binocular" fashion.  My question to you Everett is whether you also used multiple cores in each single choke, or if you just wound all 35 turns of RG-316 through a single TDK core?

Again, thanks to both of you for the excellent work.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro

Everett N4CY
 

Hi Ken,

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

Your best bet for the RG316 coax is eBay...

Everett

In a message dated 11/14/2019 6:03:19 AM Central Standard Time, quickhatch44@... writes:

Thank you Paul and Everett for sharing your work with the common mode chokes.  I'm certainly planning on constructing a couple to reduce the noise propagated through the coax shield.

Everett, you recommended the TDK B64290L0040X830 core for winding the choke.  You also specified that your design used 35 turns of RG-316.  I checked out the specs of the TDK core, and it is considerably larger than the stacked toroids that Paul used.  In Paul's configuration, he used two "stacks" of four each of somewhat smaller toroids wound in a "binocular" fashion.  My question to you Everett is whether you also used multiple cores in each single choke, or if you just wound all 35 turns of RG-316 through a single TDK core?

Again, thanks to both of you for the excellent work.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


Kenneth Sejkora
 

Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


On Thursday, November 14, 2019, 08:55:20 AM EST, Everett N4CY via Groups.Io <everettsharp@...> wrote:


Hi Ken,

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

Your best bet for the RG316 coax is eBay...

Everett

Martin - G8JNJ
 

Hi Everett,

A couple of other points to note for those who may not be aware.

The S21 measurement (Insertion gain) dB values are only valid for a 50 Ohm circuit. Although this can provide some guidance, it should be used with caution.

The common mode impedance on a line varies with wavelength and can be anything from a few tens of Ohms to several thousand Ohms.

The exact amount of choking depends upon its placement along the feedline and its effectiveness will vary with frequency.

The S21 measurement also does not indicate the resitistive choking impedance (which is the part that matters) relative to the reactive part.

When used in an actual environment the reactive component can in some cases make the situation worse.

It's best to measure the S11 resistive and reactive impedance components, and optimise the resistive part for the frequencies of interest.

In addition to adding choke baluns it's also worthwhile adding earth (ground) spikes at regular intervals, or if possible bury the coax, at least 6" (15cm) or more deep. This helps create a low impedance shunt path to ground in-between the series connected choke baluns. The combination of using both methods is very effective, and helps prevent further stray coupling between the antenna and feedline due to proximity.

Unbalanced Active antennas such as E-Probes, which have a very high value of feed point impedance, are extremely difficult to isolate from common mode noise that is carried along the feedline as it forms part of the antenna.

Unless you provide an alternative noise free 'ground' for the antenna, and somehow manage to effectively isolate unwanted noise from the feedline, you will not be able to obtain the best performance.

Nearby objects such as metal buildings and fencing can also re-radiate unwanted noise, that can easily be picked up by a receive antenna.

Regards,

Martin - G8JNJ

jdow
 

Paul has done this very well. All I could suggest is a transformer in the line to break the ground loop between his shack and the grounded antenna. Note that his design was optimized for VLF in these two recent videos. For HF YMMV.

{^_^}

On 20191114 08:51:26, Martin - G8JNJ via Groups.Io wrote:
Hi Everett,
A couple of other points to note for those who may not be aware.
The S21 measurement (Insertion gain) dB values are only valid for a 50 Ohm circuit. Although this can provide some guidance, it should be used with caution.
The common mode impedance on a line varies with wavelength and can be anything from a few tens of Ohms to several thousand Ohms.
The exact amount of choking depends upon its placement along the feedline and its effectiveness will vary with frequency.
The S21 measurement also does not indicate the resitistive choking impedance (which is the part that matters) relative to the reactive part.
When used in an actual environment the reactive component can in some cases make the situation worse.
It's best to measure the S11 resistive and reactive impedance components, and optimise the resistive part for the frequencies of interest.
In addition to adding choke baluns it's also worthwhile adding earth (ground) spikes at regular intervals, or if possible bury the coax, at least 6" (15cm) or more deep. This helps create a low impedance shunt path to ground in-between the series connected choke baluns. The combination of using both methods is very effective, and helps prevent further stray coupling between the antenna and feedline due to proximity.
Unbalanced Active antennas such as E-Probes, which have a very high value of feed point impedance, are extremely difficult to isolate from common mode noise that is carried along the feedline as it forms part of the antenna.
Unless you provide an alternative noise free 'ground' for the antenna, and somehow manage to effectively isolate unwanted noise from the feedline, you will not be able to obtain the best performance.
Nearby objects such as metal buildings and fencing can also re-radiate unwanted noise, that can easily be picked up by a receive antenna.
Regards,
Martin - G8JNJ

Everett N4CY
 

Ken

You will wind each toroid with 35 turns and they are connected in series, not stacked.

Everett

In a message dated 11/14/2019 10:54:48 AM Central Standard Time, quickhatch44@... writes:

Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


On Thursday, November 14, 2019, 08:55:20 AM EST, Everett N4CY via Groups.Io <everettsharp@...> wrote:


Hi Ken,

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

Your best bet for the RG316 coax is eBay...

Everett

Kenneth Sejkora
 

Hi Everett,

Please ignore my earlier followup question.  I looked back at your previous email and saw that you used a cascade/series configuration in your choke design.  Did you take any efforts to magnetically isolate the two toroids from each other, or does that even matter?

You also mentioned the use of a 1:1 isolation transformer using a bifilar winding through a BN73-202 binocular ferrite.  Would you recommend twisting the two wires together prior to winding, or is there any advantage/disadvantage to winding each turn separately?

Thanks for indulging my questions.

Ken, WBØOCV 


On Thursday, November 14, 2019, 09:52:21 AM EST, Ken Sejkora <quickhatch44@...> wrote:


Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro



Patrick
 

Hi there,

<< You will wind each toroid with 35 turns and they are connected in series, not stacked >>
With 35 turns, what is the "frequency coverage" ?
How many turns would be required for this setup to be effective in the range 500-1200 kHz ?

Thanks

Le ven. 15 nov. 2019 à 12:14, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> a écrit :
Ken

You will wind each toroid with 35 turns and they are connected in series, not stacked.

Everett

In a message dated 11/14/2019 10:54:48 AM Central Standard Time, quickhatch44=yahoo.com@groups.io writes:

Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


On Thursday, November 14, 2019, 08:55:20 AM EST, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> wrote:


Hi Ken,

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

Your best bet for the RG316 coax is eBay...

Everett

Everett N4CY
 

Patrick,

If you only want to use just one toroid, than use the TDK N30 with 35 turns on RG316 will cover the frequency area of interest. 

Everett N4CY

On Nov 15, 2019, at 8:02 AM, Patrick <aunumero73@...> wrote:


Hi there,

<< You will wind each toroid with 35 turns and they are connected in series, not stacked >>
With 35 turns, what is the "frequency coverage" ?
How many turns would be required for this setup to be effective in the range 500-1200 kHz ?

Thanks

Le ven. 15 nov. 2019 à 12:14, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> a écrit :
Ken

You will wind each toroid with 35 turns and they are connected in series, not stacked.

Everett

In a message dated 11/14/2019 10:54:48 AM Central Standard Time, quickhatch44=yahoo.com@groups.io writes:

Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


On Thursday, November 14, 2019, 08:55:20 AM EST, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> wrote:


Hi Ken,

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

Your best bet for the RG316 coax is eBay...

Everett

Tom Crosbie G6PZZ <tom@...>
 

Hi Everett,

You seem to be advocating the use of both the N30 and the FT240. Should one be used inside and the other outside? If so, which is which? I can’t mount one outside so could I connect the two in series just before the receiver?

 

With regard to the BN73-200, I have a query regarding the type of wire to use. Would a twisted pair removed from a CAT5 cable be suitable? I have loads!

 

Here in the UK, we never thank our service members for time in the military the way Americans do. I’ll put that right today by thanking all members of the UK’s armed services especially my son now 20 years in the RAF and my No1 project helper!

 

Everett, I hope this finds you in continued good health

 

Tom G6PZZ

 

From: airspy@groups.io <airspy@groups.io> On Behalf Of Everett N4CY via Groups.Io
Sent: 14 November 2019 17:51
To: airspy@groups.io
Subject: Re: [airspy] Common Mode Chokes

 

Ken

 

You will wind each toroid with 35 turns and they are connected in series, not stacked.

 

Everett

 

In a message dated 11/14/2019 10:54:48 AM Central Standard Time, quickhatch44@... writes:

 

Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

 

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

 

Ken, WBØOCV East Falmouth, MA USA

41.5997N, 70.5614W  FN41ro

 

 

On Thursday, November 14, 2019, 08:55:20 AM EST, Everett N4CY via Groups.Io <everettsharp@...> wrote:

 

 

Hi Ken,

 

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

 

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

 

Your best bet for the RG316 coax is eBay...

 

Everett

 

Patrick
 

Hi Everett,

Unfortunately, I have no TDK N30 on hand.
Only a FT240-31 ring and a couple of material 75 ferrite clamp on.


Le ven. 15 nov. 2019 à 17:08, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> a écrit :
Patrick,

If you only want to use just one toroid, than use the TDK N30 with 35 turns on RG316 will cover the frequency area of interest. 

Everett N4CY

On Nov 15, 2019, at 8:02 AM, Patrick <aunumero73@...> wrote:


Hi there,

<< You will wind each toroid with 35 turns and they are connected in series, not stacked >>
With 35 turns, what is the "frequency coverage" ?
How many turns would be required for this setup to be effective in the range 500-1200 kHz ?

Thanks

Le ven. 15 nov. 2019 à 12:14, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> a écrit :
Ken

You will wind each toroid with 35 turns and they are connected in series, not stacked.

Everett

In a message dated 11/14/2019 10:54:48 AM Central Standard Time, quickhatch44=yahoo.com@groups.io writes:

Thanks Everett.  Fantastic information.  However, I'm having trouble envisioning the configuration using two toroids in each individual common mode choke.  Are the TDK N30 and FT240-31 toroids 'stacked' together, with the RG-316 looped through the 'stack' to tie them together?  Do you have a simplified drawing or photo of the configuration you use?

Thanks again.  Also, a belated Veterans Day thank you for your military service in the Air Force.

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro


On Thursday, November 14, 2019, 08:55:20 AM EST, Everett N4CY via Groups.Io <everettsharp=aol.com@groups.io> wrote:


Hi Ken,

You need only one of the TDK N30 and one FT240-31 cores, each must be wound with 35 turns of RG316. Also as Paul said you will need one at the antenna and one at the receiver. Also another thing that will help is a isolation transformer between the coax and your receiver, which can be made using a BN73-202 binocular core with 6 bifilar turns. One winding will go to your coax and the other to your receiver.

You can get all of the ferrite from Mouser Electronics. You have the part number for the TDK core and the part number for the FT240-31 is 2631803802, the part number for the BN73-202 is 2873000202.. So you will need 2 of the FT240-31 and 2 of the TDK30 and you might want to get several of the BN73-200 cores as they are great for making up matching transformers.

Your best bet for the RG316 coax is eBay...

Everett