Re: [Elecraft] Common Mode chokes to reduce noise

[Jim Brown]

On 11/28/2021 11:05 AM, Ed Cole wrote:
K, kind of what I was thinking.  So either go on search for noise source 
or try reducing the noise at the receiver.  K3 NB does not improve SNR 
on 6m.


The K3 NB has lots of tweaks. Depending on the modes you use, it might 
help in some situations.


On HF noise varies: 80m its S7 from an inverted-V; on 20m its S3 from a 
yagi (both have baluns).


Of course -- noise sources vary widely in their spectral content, and 
how much we hear will depend on what they are using for TX antennas and 
how those TX antennas are coupled to the noise sources. Likewise, how we 
hear them will depend on our antennas -- their location, directivity, 
and whether they are well choked at the feedpoint.


6m noise at S5-S7 is the most troublesome because I do weak-signal 
operating (eme, ms, FT8). InnovAntenna 6m baluns are many ferrite beads 
in series.  6m yagis are LFA7 from InnovAntenna (UK).


Is that S5-S7 on a well calibrated S-meter?  That's HUGE.


Shack is grounded via No. 8 wire to ground post adjacent to shack. 
Aluminum plate coax thru-wall panel is grounded by it, as well.


You need to STUDY N0AX's ARRL book on Grounding and Bonding, to which I 
contributed, and/or this slide deck pdf.

http://k9yc.com/GroundingAndAudio.pdf

Also these to chase down and kill the noise sources. The first is text, 
written for National Contest Journal, the second is a slide deck.

http://k9yc.com/KillingReceiveNoise.pdf
http://k9yc.com/KillingRXNoiseVisalia.pdf

73, Jim K9YC

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Re: [Elecraft] Common Mode chokes to reduce noise

[Ed Cole]

OK, kind of what I was thinking.  So either go on search for noise 
source or try reducing the noise at the receiver.  K3 NB does not 
improve SNR on 6m.


On HF noise varies: 80m its S7 from an inverted-V; on 20m its S3 from a 
yagi (both have baluns).


6m noise at S5-S7 is the most troublesome because I do weak-signal 
operating (eme, ms, FT8). InnovAntenna 6m baluns are many ferrite beads 
in series.  6m yagis are LFA7 from InnovAntenna (UK).


Shack is grounded via No. 8 wire to ground post adjacent to shack. 
Aluminum plate coax thru-wall panel is grounded by it, as well.


ED-KL7UW
-
If it does, something is very wrong in your shack, like bonding. What
DOES matter is having effective common mode chokes at the antenna's
feedpoint. See my recommendations at k9yc.com/publish.htm

73, Jim K9YC
--
I don't see how a common mode choke would help in that situation. If the
noise changes that dramatically depending upon where you have the
antenna pointed, that strongly suggests that the noise is being received
by the antenna and is not riding on the shield of the coax.? If it is
received by the antenna it is differential in nature and a common mode
choke won't do anything.

It sounds like you are being plagued by either a local noise source, or
the atmospheric noise is much stronger in one direction.? In my case,
the background noise during the middle of the day is always stronger
east versus west even though there isn't any significant housing or
businesses within 200 miles east of me.

73,
Dave?? AB7E
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Re: [Elecraft] Common Mode chokes to reduce noise

[Dave]

While it is unlikely to make any difference, if you can source these
ferrite sleeves in the USA they are excellent value and perhaps worth a
try. A pack of 5 cost about $1.50 plus shipping and tax (£1.15 + tax in the
UK). Two packs (10 sleeves) should make an effective choke for 6m and will
slip over RG213 size coax.

My own measurements of them with a VNA look OK with 10 used on 6m and 4m, 5
are suitable for 2m.

https://cpc.farnell.com/unbranded/559-568/emi-sleeves-10-7-x-28-5mm/dp/CBBR6937?ost=559-568

73 Dave G4AON
-- 
Sent from my iPhone SE
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Re: [Elecraft] Common Mode chokes to reduce noise

[David Gilbert]

I don't see how a common mode choke would help in that situation. If the 
noise changes that dramatically depending upon where you have the 
antenna pointed, that strongly suggests that the noise is being received 
by the antenna and is not riding on the shield of the coax.  If it is 
received by the antenna it is differential in nature and a common mode 
choke won't do anything.


It sounds like you are being plagued by either a local noise source, or 
the atmospheric noise is much stronger in one direction.  In my case, 
the background noise during the middle of the day is always stronger 
east versus west even though there isn't any significant housing or 
businesses within 200 miles east of me.


73,
Dave   AB7E



On 11/27/2021 10:21 AM, Ed Cole wrote:

I primarily work eme so band noise is a prime enemy of weak signals.

I was reading the comments about combating mic noise and wondered if 
adding some ferrite beads to my 6m coax at the shack would have any 
effect on received broad-band noise.  I definitely see the noise peak 
in one direction of the antenna S5/S7 vs S2 at 180-degrees azimuth 
rotation, and it also drops with about 13 degrees of antenna elevation.


My 6m LFA antenna use ferrite bead baluns.  Transmission coax runs 
40-foot vertical and 50-foot horizontal on the ground.  Rx comes from 
a remote preamp connected thru a TR relay with output thru LMR-240 
coax to the Rx antenna port of the K3.


73, Ed - KL7UW


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Re: [Elecraft] Common Mode chokes to reduce noise

[Jim Brown]

On 11/27/2021 9:21 AM, Ed Cole wrote:
I was reading the comments about combating mic noise and wondered if 
adding some ferrite beads to my 6m coax at the shack would have any 
effect on received broad-band noise.


If it does, something is very wrong in your shack, like bonding. What 
DOES matter is having effective common mode chokes at the antenna's 
feedpoint. See my recommendations at k9yc.com/publish.htm


73, Jim K9YC
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Re: [Elecraft] Common mode chokes - FS RF meter

[w4grj]

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:elecraft-boun...@mailman.qth.net] On Behalf Of EricJ
Sent: Tuesday, August 09, 2016 5:38 PM
To: elecraft@mailman.qth.net
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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Re: [Elecraft] Common mode chokes

[Vic Rosenthal 4X6GP]

Here is a device I made to do that:


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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Re: [Elecraft] Common mode chokes

[Ian White]

>
>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:elecraft-boun...@mailman.qth.net] On Behalf Of
>Josh Fiden
>Sent: 09 August 2016 22:16
>To: elecraft@mailman.qth.net
>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.
>> __
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>> Message delivered to j...@voodoolab.com
>>
>
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Re: [Elecraft] Common mode chokes

[EricJ]

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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Re: [Elecraft] Common mode chokes

[Don Wilhelm]

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?




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Re: [Elecraft] Common mode chokes

[Josh Fiden]

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.
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Re: [Elecraft] Common mode chokes

[Ian White]

>
>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:elecraft-boun...@mailman.qth.net] On Behalf Of
>MaverickNH
>Sent: 09 August 2016 21:56
>To: elecraft@mailman.qth.net
>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.
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Re: [Elecraft] Common mode chokes

[Jim Brown]

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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Re: [Elecraft] Common mode chokes

[MaverickNH]

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



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Re: [Elecraft] Common mode chokes

[MaverickNH]

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.
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Re: [Elecraft] Common mode chokes

[Mel Farrer via Elecraft]

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


  From: Cortland Richmond <k...@earthlink.net>
 To: elecraft@mailman.qth.net 
 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, elecraft-requ...@mailman.qth.net 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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Re: [Elecraft] Common mode chokes

[Cortland Richmond]

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, elecraft-requ...@mailman.qth.net 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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Re: [Elecraft] Common mode chokes

[Dave Cole]

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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Re: [Elecraft] Common mode chokes

[Jim Brown]

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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