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Author Topic: Which RFI filters  (Read 2579 times)
9H1FQ
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Posts: 177




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« on: November 28, 2017, 06:15:42 AM »

I want to filter every cable I have in the shack and other cables close to my antenna!

Which are the best, effective clipons ferrites, rings, beads, whatever. Also those that do not need to cut , but, insert on a wire? Possibly, sets for various wire diameters.

Also, I have a cabletv cable running nearby, can I filter, without affecting the signal?

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AE5GT
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Posts: 79




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« Reply #1 on: November 28, 2017, 07:43:12 PM »

The absoulte best "ferrite" suppressor that i have seen is the type thats solld in most DIY and home centers , They come in 4, 8,16 and there may even be a 24l pound model . They all come with a long wood handle attached ,and you apply them liberally to any switch mode power supply in sight"  Grin  .  The "suppresson" from these is excellent 200 db + and its one size fits all.


Your probably not going to do that. But i did , it works. I changed as many SMPSs to regulated/non regulated(class 2)   as possible.  

The best non destructive suppression is going to be to use shielded  cables where ever possible the tighter the braid the better.  I think you'll get 70-90 db depending on the braid , get clear cables for indoor that way you can tell its shielded.

Ferrites : 43 material fo 10 Mhz and up . 31 material   10 Mhz and down  .  You can use either one for general wideband HF suppression . 28 material will also work .


 Generally speaking the bigger the ferrite the more suppression.  Use large dia clip ons and multiple turns for max suppression. FT 240  cores for lots of turns or big connectors that cant be removed. Remember nomenclature is Diameter - material    ,,,an FT 240 - 43  core => 2.4 inch diameter 43 material.  


If cost is factor you can simply coil up the offending cable like a coax balun and get some suppression that way.

For cable TV make sure its Quad shielded RG6.

One of the best things to do is to bury any exposed cables , the soil tends to suppess RF.



« Last Edit: November 28, 2017, 07:49:52 PM by AE5GT » Logged
WB4SPT
Member

Posts: 502




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« Reply #2 on: December 01, 2017, 02:56:30 PM »

The absoulte best "ferrite" suppressor that i have seen is the type thats solld in most DIY and home centers , They come in 4, 8,16 and there may even be a 24l pound model . They all come with a long wood handle attached ,and you apply them liberally to any switch mode power supply in sight"  Grin  .  The "suppresson" from these is excellent 200 db + and its one size fits all.


Your probably not going to do that. But i did , it works. I changed as many SMPSs to regulated/non regulated(class 2)   as possible.  

The best non destructive suppression is going to be to use shielded  cables where ever possible the tighter the braid the better.  I think you'll get 70-90 db depending on the braid , get clear cables for indoor that way you can tell its shielded.

Ferrites : 43 material fo 10 Mhz and up . 31 material   10 Mhz and down  .  You can use either one for general wideband HF suppression . 28 material will also work .


 Generally speaking the bigger the ferrite the more suppression.  Use large dia clip ons and multiple turns for max suppression. FT 240  cores for lots of turns or big connectors that cant be removed. Remember nomenclature is Diameter - material    ,,,an FT 240 - 43  core => 2.4 inch diameter 43 material.  


If cost is factor you can simply coil up the offending cable like a coax balun and get some suppression that way.

For cable TV make sure its Quad shielded RG6.

One of the best things to do is to bury any exposed cables , the soil tends to suppess RF.





yeah,   pretty good.   mix 31 does fail at UHF, gota go with mix 61 up there.   And at the very low end, for 160meters, go with mix 73/78.   Sledge is the good fix!
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K0UA
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Posts: 1468




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« Reply #3 on: December 06, 2017, 03:55:37 PM »

Of course all switch mode power supplies are not built the same.  Some are pretty quiet, and I had one that I am pretty sure with a proper antenna stuck on it could have been used for worldwide "spark" contacts by keying it on and off.  It is hard to believe the amount of RF energy some of these things can radiate.  Yes the sledgehammer would be a sure way to eliminate the problem. Smiley
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K8BYP
Member

Posts: 55




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« Reply #4 on: December 11, 2017, 02:59:39 PM »

Laird 28 series snap on ferrite, very high rejection at HF:

https://www.digikey.com/products/en?keywords=28A0592-0A2

I used one of these to make a parallel tuned circuit BCB trap, got 55 dB rejection from a simple tank!

The critical thing besides attenuation at some frequency  is WIRE DIAMETER (wire, not the plastic around the wire)

A ferrite core with a 1/4" hole will NOT work well filtering 30 AWG wire wrap wires.

The wires need to be a tight fit inside the core for maximum coupling.

And for fun, try them for antenna tuning... ahem
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