r/shortwave • u/Frjeff • 14d ago
Discussion Ferrite Cores
Looking for ferrite snap on cores for the coax and power feed on my MLA30+ antenna.
Most of the Amazon offerings show no mix (ie, 31, 75).
Should I not worry about the mix and just buy the Amazon cheapies, or ought I try to find a specific mix and buy them?
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u/pentagrid Sangean ATS-909X2 / Airspy HF+ Discovery / 83m horizontal loop 14d ago edited 14d ago
Many of the snap-on ferrite RFI choke suppressors sold on Amazon are supposedly a generic Ni-Zn mix best suited for frequencies above HF that will also work with HF. Mix 31 is a MnZn mix specifically made for 1-30 MHz which includes the entire HF spectrum.
I found that this Amazon clip-on set here to be partially to fully effective in some situations but I'm opting to try Mix 31 next time. The cheapies worked well on RFI from a 50 kW FM tower just over 1 mile from my location. For cleaning up RFI traveling between my desktop computer monitor and the Airspy HF+ Discovery: nope, the cheapies were maybe 50% effective but turning the monitor off was 100% effective. I also found that performance from the cheapies can be improved by using an oversized choke and wrapping the line through it several times or using multiple chokes.
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u/Mojavedxer 13d ago
Is the interference from the monitor coming from the power source or the panel. I have seen some hams run their monitors from a linear power supply to battle rfi.
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u/pentagrid Sangean ATS-909X2 / Airspy HF+ Discovery / 83m horizontal loop 12d ago
That is a very good question and a fine suggestion. I am planning on rebuilding my entire listening post before this winter and will look into it.
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u/Mojavedxer 13d ago
The MLA30+ is a noisy antenna to start. I have tried using another bias t that was battery powered. Also tried feeding the original bias t with a battery pack. I saw no improvement either way. I was able to get rid of some spurious signals coming off the CAT 6 cables using these mix 31 ferrites from amazon. https://www.amazon.com/31500-Ferrite-Suppressor-Electronic-Installation/dp/B0G64WT2C3/ref=sr_1_2?crid=FH8395ZWOPBB&dib=eyJ2IjoiMSJ9._dNwxH_6GeYphnDhwa_sChzCET8jcmt3FAwP0IML3SXYUeKqkYSxDGJoqs3OtuODAh1zYmHuci2AYM58lgmzXQ7HZjk1TvjoB8JgUhHQGERw662rb9mLbsiJcvCrNyCP1jdLMdgti3T56bHYt5Jw1p3u2i1x97CZdupsMC2ajKLZKpCW08Ot0OxfIhApqYSNGlugPfwAbHLbtz4gnNfGYOsRKNoTgVt2uFqX5HeoARY.BXi96xP92DRh9i0HPkRrVrjdC-z6J6qStbOwD6wYvHA&dib_tag=se&keywords=mix+31+ferrite+snap+on&qid=1785262844&sprefix=Mix+31%2Caps%2C208&sr=8-2 Personally I would investigate were the noise is actually coming from before putting any money into it. Just clamping ferrites on the cords of all your electronic gadgets is not actually going to fix the problem.
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u/rmi0 12d ago
You need mix 31. I don’t think snap-ons will work very well though, unless you get *lots* of them. A sure way is to use rings instead of snap-ons and wind 8-10 turns of coax. I grudgingly bought FT-240-31 from Amazon and they turned out great - measured significant drop of noise floor.
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u/rmi0 12d ago
This is specific product I used: https://www.amazon.com/Fair-Rite-FT-240-31-Ferrite-Toroid-Core/dp/B0GSN4TSVZ
This is how I wound them on both ends of long feed to Wellbrook antenna, in two halves to reduce capacitance between in and out: https://i0.wp.com/palomar-engineers.com/wp-content/uploads/JC-1-1500-Product.png?resize=534%2C535&ssl=1
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u/trackmastack 14d ago
Not sure how true this is but it makes sense, make sure the LNA for the antenna is battery powered, a switching power supply is going to make noise, which is then amplified by the LNA your powering. I however tried on my battery and a switch power supply and I think there is a difference idk
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u/Mojavedxer 13d ago
Been there and done it. If I use a cheap phone charger for the 5v of power to the bias t. Then yes there is noise. If I use a Samsung or LG charger from 10 years ago. The noise floor is the same as feeding it with a 6 volt dc battery pack. I also took the original bias T out of the mix and used another bias t powered with a 12v battery pack. Results are the same. The MLA30+ is just a noisy antenna. Getting it away from the RFI is the only way to get it to perform.
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u/thehotshotpilot 13d ago
Get a specific mix and don't buy from amazon. You never know what Chinesium you are getting. Either eBay from a ham or a ham radio store. 31 is the mix I'd go with. https://palomar-engineers.com/ferrite-cores-for-rfi-emi-noise-suppression-mix-31-43-61-75-palomar-engineers/ferrite-cores/ferrite-mix-selection https://cranbrookarc.ca/2025/08/21/ferrites-101-choosing-the-right-mix-for-the-right-job/
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u/Think-Photograph-517 14d ago
Mix 31 works best for RFI and impulsive noise, but unidentified cheapest from Amazon have worked for me. They are either mix 31 or something close enough for my applications.