Common mode choke criteria

I'm installing a active antenna, part of the low noise protocol is keep noise out of the system. I want to install a common mode choke, I'm using the one here as a starting point.

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I don't have that toroid but I have many potcores. The recommended core is Amidon 75 (J) material. I have Ferroxcube 3C81, 3B7, 3D3, 4C6 and Magnetics K material. I don't know what characteristics are desirable for a common mode choke. Just want to have a clean DC line with no ingress. Any helpful thoughts?

Mikek

Reply to
amdx
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btw, that should be FT50-75, not FT-500-75. Mikek

Reply to
amdx

Here you'd have to mention what kind of noise, mostly which frequency range.

IF you want to keep out low frequency noise from LED lights, CFLs, switchers and such then J-material is good. If your intent is to block VHF or higher frequency stuff then it's not, then you need other core material and almost be coaxial in the power input.

If the noise is the neighbor's loud stereo it won't work at all :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

The antenna design is 10kHz to 30MHz. I need to choke the antenna feed line also. As a start, to much buzzing to pick up anything below 500kHz. OK two beacons, but covered with buzzing. So far running on batteries, the input power is not causing the problem.

Mikek

Reply to
amdx

Some years ago I built a simple little box to try to hear the local Loran C transmitter on 100KHz. It just seems to be a fact that there's more noise down there. I never heard it with any kind of probe antenna, but ultimately was able to hear it using a loop.

Reply to
Wond

77 material works best for that but the J material is suitable as well, especially since you said further below that stuff I need to choke the antenna feed line also.

Same core type then.

Afraid it's plain coming into the antenna and a CM choke might do ... nothing. The man-made noise nowadays is so bad that my hopes of resurrecting my ham radio hobby when my body won't tolerate mountain biking anymore might be just a dream. Most of it is coming from our own house but next to impossible to fix or would be a Herculean tast. Myriad CFL, LED, switchers et cetera.

I remember the days when the only noise on shortwave and below was the ignition of the occasional two-cycle moped buzzing by. Oh, those were the days.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I was hoping that getting it 40 ft away from the house and 25ft in the air would help. Could I have caused a problem by running the coax in side of the steel mast? Next step is to battery power the radio to see if that removes any buzz. Dallas Lankford did a lot of research on receiving AMBCB , his noise and ingress prevention was to use twisted speaker wire as a feedline and a matching transformer at each end. This helped when phasing antennas also because the feedline didn't add signal and degrade the null. Mikek

Reply to
amdx

That does help but depends on what neighbors are spewing around in EMI and whether the local power grid is above ground. If it is then it'll be a tough job.

No, it's actually best in there for various reasons.

Highly doubtful that it would make a difference but winding the DC cable through J material as many times as possible would take care of that. Plus good bypassing inside the box, right at the metal.

Transformers work similar to CM chokes for common mode noise. What I am saying is not to get the hopes up too high that the EMI won't come in via the antenna.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Lucky, we do have underground electric, but I do have one above ground pole with wires about 100ft away.

I hooked the radio (Icom R71A) to dc and that lowered the noise 2.5 S units.

Yep, most houses are EMI emitters, to many electronic devices are noisy. Mikek

Reply to
amdx

Unfortunately that's all it takes to spew noise.

Then you still have an imbalance on the antenna side. I don't know the R71A but Icom normally does a good job of filtering the power side. Try a very thin coax for the antenna connection and wrapping it through a J-code as many times as possible.

Especially CFL and LED lighting where every penny must vbe sahved from a design. "Do we need that much bypass cap? Nah, we can lower than to

0.01uF, save three milli-Dollars and still be two decibels under".

Below 150kHz nothing much gets measures in EMC tests so the spectrum down there looks like a Tokyo subway at rush hour.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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