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Common mode chokes

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Gary Gregory-2

Common mode chokes

Hi,
I have an inverter generator producing S9 noise on 3.5Mhz, and S7 noise on 7Mhz. Higher frequencies are clear.
If I were to use a trifilar wound choke on the lead from the generator, what would be the best mix...43, 77 or?....
I can source ferrite cores here in VK, whether I can obtain what I will need is unknown but likely. Failing that, Mouser?
I spent a lot of time searching the web but unsure still.
If the learned group could help out with advice it will be greatly appreciated.
Regards,
Gary
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Jim Brown-10

Re: Common mode chokes

On Sat,8/6/2016 10:50 PM, Gary wrote:
> I spent a lot of time searching the web but unsure still.

k9yc.com/RFI-Ham.pdf See the Choke Cookbook and follow the guidelines
for the bands where you have noise, and for coax the size of the power
cable. Place the choke as close as possible to the generator. Also study
this slide show for a talk I did several years ago about this to our
local contest club.

http://nccc.cc/pdf/CQP-RFI2013-2.pdf

73, Jim K9YC

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NK7Z

Re: Common mode chokes

In reply to this post by Gary Gregory-2

On Sun, 2016-08-07 at 15:50 +1000, Gary wrote:

> Hi,
> I have an inverter generator producing S9 noise on 3.5Mhz, and S7
> noise on 7Mhz. Higher frequencies are clear.
> If I were to use a trifilar wound choke on the lead from the
> generator, what would be the best mix...43, 77 or?....
> I can source ferrite cores here in VK, whether I can obtain what I
> will need is unknown but likely. Failing that, Mouser?
> I spent a lot of time searching the web but unsure still.
> If the learned group could help out with advice it will be greatly
> appreciated.
>

Hello Gary,

I have had good luck using mix31 material in the FT-240-31
configuration.

See:
http://www.fair-rite.com/design-tools/materials/

For an explanation of what each mix does, also see:
http://audiosystemsgroup.com/RFI-Ham.pdf

and:
http://audiosystemsgroup.com/SAC0305Ferrites.pdf

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

for more information.
--
73's, and thanks,
Dave (NK7Z)
For software/hardware reviews see:
http://www.nk7z.net

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Cortland Richmond-2

Re: Common mode chokes

In reply to this post by Gary Gregory-2

I had a similar problem in 2005 when noise from a 2kW Honda got into my
RV on FD. Lacking any ferrites etc I borrowed a plastic "milk bottle
box" and wound about 30 feet of extension cord around it., which worked
well as a temporary fix.

Cortland
ka5s

On 8/7/2016 2:21 PM, [hidden email] wrote:
> I have an inverter generator producing S9 noise on 3.5Mhz, and S7 noise on 7Mhz. Higher frequencies are clear.
> If I were to use a trifilar wound choke on the lead from the generator, what would be the best mix...43, 77 or?....

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Elecraft mailing list

Re: Common mode chokes

Check Jim's tutorial on RFI. You will need some clip on #31 cable ferrites, I think.....
Mel, K6KBE

From: Cortland Richmond <[hidden email]>
To: [hidden email]
Sent: Sunday, August 7, 2016 2:54 PM
Subject: Re: [Elecraft] Common mode chokes

I had a similar problem in 2005 when noise from a 2kW Honda got into my
RV on FD. Lacking any ferrites etc I borrowed a plastic "milk bottle
box" and wound about 30 feet of extension cord around it., which worked
well as a temporary fix.

Cortland
ka5s

On 8/7/2016 2:21 PM, [hidden email] wrote:
> I have an inverter generator producing S9 noise on 3.5Mhz, and S7 noise on 7Mhz. Higher frequencies are clear.
> If I were to use a trifilar wound choke on the lead from the generator, what would be the best mix...43, 77 or?....

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MaverickNH

Re: Common mode chokes

In reply to this post by Jim Brown-10

Just wondering - short of +/- RF Burns and Audible Noice, can one readily detect/measure Common Mode Current on a coax antenna feedline?

MaverickNH

Re: Common mode chokes

Further (apologies, I should have thunk it through before posting):

Based on http://www.karinya.net/g3txq/chokes/ which may or may not be well-accepted, which choke configuration would you choose for "Best"? I'm actually fond of two chokes in series to address the 1.8-30MHz range, but am still pondering which two? At a hefty pre-made price, one can have 160-40m & 40-10m http://palomar-engineers.com/antenna-products/1-1-balun-kits/super-choker, albeit with no transparency of composition. What cost of of Low SNR? Thousands$$$ spent on Transceivers/Antennas and $100s on chokes?

BRET/KC1CJN

Jim Brown-10

Re: Common mode chokes

In reply to this post by MaverickNH

On Tue,8/9/2016 1:56 PM, MaverickNH wrote:
> Just wondering - short of +/- RF Burns and Audible Noice, can one readily
> detect/measure Common Mode Current on a coax antenna feedline?

Yes. A calibrated RF current probe coupled to the outside of the coax
can easily measure common mode current. Here are a couple of easy ways
to do it.

http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

Note that because the coax is acting as part of an antenna for common
mode current, the current will vary along the line just as it would for
any other antenna. For example, the coax a simple wire dipole in an
earth-based station acts as a wire connected between the shield side of
the dipole and ground, with the length of the wire equal to the physical
length of the coax, and oriented in space as the actual coax is routed.

73, Jim K9YC
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gm3sek

Re: Common mode chokes

In reply to this post by MaverickNH

>
>Just wondering - short of +/- RF Burns and Audible Noice, can one
readily
>detect/measure Common Mode Current on a coax antenna feedline?
>

Google for: clamp-on rf current meter

http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

This review of two MFJ products (one good, one awful) may also be
useful:

http://www.ifwtech.co.uk/g3sek/clamp-on/mfj-reviews.pdf

73 from Ian GM3SEK

>-----Original Message-----
>From: Elecraft [mailto:[hidden email]] On Behalf Of
>MaverickNH
>Sent: 09 August 2016 21:56
>To: [hidden email]
>Subject: Re: [Elecraft] Common mode chokes
>
>Just wondering - short of +/- RF Burns and Audible Noice, can one
readily

>detect/measure Common Mode Current on a coax antenna feedline?
>
>
>
>--
>View this message in context:
>http://elecraft.365791.n2.nabble.com/Common-mode-chokes-
>tp7621305p7621430.html
>Sent from the Elecraft mailing list archive at Nabble.com.
>______________________________________________________________
>Elecraft mailing list
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Josh Fiden

Re: Common mode chokes

In reply to this post by MaverickNH

Add another winding to a choke and it magically becomes a transformer!

73,
Josh W6XU

On 8/9/2016 1:56 PM, MaverickNH wrote:

> Just wondering - short of +/- RF Burns and Audible Noice, can one readily
> detect/measure Common Mode Current on a coax antenna feedline?
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Common-mode-chokes-tp7621305p7621430.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> This list hosted by: http://www.qsl.net
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>

Don Wilhelm

Re: Common mode chokes

In reply to this post by MaverickNH

Bret,

Refer to the K9YC (Jim Brown) paper on RFI, Ferrites, Baluns and Audio
Interfacing for "good" baluns.
http://www.audiosystemsgroup.com/RFI-Ham.pdf.
For common mode chokes (baluns), look particularly at Chapter 7 of that
document.

A stack of 5 FT240-31 cores and a length of coax sufficient to wind 5 to
7 turns through the cores is generally less expensive (and more
effective) than the cost of commercial baluns or "in-line isolators".

73,
Don W3FPR

On 8/9/2016 5:10 PM, MaverickNH wrote:

> Further (apologies, I should have thunk it through before posting):
>
> Based on http://www.karinya.net/g3txq/chokes/ which may or may not be
> well-accepted, which choke configuration would you choose for "Best"? I'm
> actually fond of two chokes in series to address the 1.8-30MHz range, but am
> still pondering which two? At a hefty pre-made price, one can have 160-40m &
> 40-10m
> http://palomar-engineers.com/antenna-products/1-1-balun-kits/super-choker,
> albeit with no transparency of composition. What cost of of Low SNR?
> Thousands$$$ spent on Transceivers/Antennas and $100s on chokes?
>
>

EricJ-2

Re: Common mode chokes

In reply to this post by Jim Brown-10

W8JI also describes one and how to calibrate it.

http://w8ji.com/building_a_current_meter.htm

Eric KE6US

On Tue,8/9/2016 1:56 PM, MaverickNH wrote:
>> Just wondering - short of +/- RF Burns and Audible Noice, can one
>> readily
>> detect/measure Common Mode Current on a coax antenna feedline?
>

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gm3sek

Re: Common mode chokes

In reply to this post by Josh Fiden

>
>Add another winding to a choke and it magically becomes a transformer!
>

Unfortunately that doesn't work for RF current measurement. The
objective for a choke is to create a high series impedance, but the
objective for an RF current transformer is exactly the opposite: to
avoid disturbing the situation that is being measured, the impedance
inserted into the main line must be as low as possible.

To achieve a low impedance in the main line, an RF current transformer
requires *ONE* pass of the primary winding (feedline) through the core
and typically about 10 turns on the secondary. The secondary must also
be terminated in a low load resistance, typically about 50 ohms. With a
1:10 turns ratio the series impedance inserted into the main line is
then about 0.5 ohms.

That is why a common-mode choke and a common-mode current transformer
are two completely different creatures. Don't confuse them.

73 from Ian GM3SEK

>-----Original Message-----
>From: Elecraft [mailto:[hidden email]] On Behalf Of
>Josh Fiden
>Sent: 09 August 2016 22:16
>To: [hidden email]
>Subject: Re: [Elecraft] Common mode chokes
>
>Add another winding to a choke and it magically becomes a transformer!
>
>73,
>Josh W6XU
>
>On 8/9/2016 1:56 PM, MaverickNH wrote:
>> Just wondering - short of +/- RF Burns and Audible Noice, can one

readily

>> detect/measure Common Mode Current on a coax antenna feedline?
>>
>>
>>
>> --
>> View this message in context:
>http://elecraft.365791.n2.nabble.com/Common-mode-chokes-
>tp7621305p7621430.html
>> Sent from the Elecraft mailing list archive at Nabble.com.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
>
>______________________________________________________________
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Vic Rosenthal

Re: Common mode chokes

In reply to this post by MaverickNH

Here is a device I made to do that:
<http://www.qsl.net/k2vco/sniffer/rfsniffer.html>

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

On 9 Aug 2016 23:56, MaverickNH wrote:
> Just wondering - short of +/- RF Burns and Audible Noice, can one readily
> detect/measure Common Mode Current on a coax antenna feedline?
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W4GRJ

Re: Common mode chokes - FS RF meter

In reply to this post by EricJ-2

FS- I have a RF current meter MFJ 854 purchased for a project
now available for sale in perfect condition $80 mailed.
Please contact me offline.
Jack
W4GRJ

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of EricJ
Sent: Tuesday, August 09, 2016 5:38 PM
To: [hidden email]
Subject: Re: [Elecraft] Common mode chokes

W8JI also describes one and how to calibrate it.

http://w8ji.com/building_a_current_meter.htm

Eric KE6US

On Tue,8/9/2016 1:56 PM, MaverickNH wrote:
>> Just wondering - short of +/- RF Burns and Audible Noice, can one
>> readily detect/measure Common Mode Current on a coax antenna
>> feedline?
>

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