Ferrite Core 1, RFI 0

Once again, a giant ferrite toroid coil saves the day. I have a random wire antenna (about 100 foot long) running into the basement workshop, fed with RG-6 coax (the coax shield is left floating at the antenna end). Reception was horrible, I could barely hear anything, even SWBC stations. I considered that maybe it wasn’t a lack of signal problem so much a signal to noise problem, so I located a large ferrite toroid coil from the junkbox, wrapped as many turns of coax around it as I could (about a dozen), and placed that in series with the incoming coax, just before the radio. Voila, the noise/hash was gone. The choke helps to reduce RFI flowing as currents on the shield of the coax.

The ferrite core was a Fair-Rite 5943003801, 61 mm toroid, type 43 ferrite. I buy mine from Mouser for about $4 each: http://www.mouser.com/ProductDetail/Fair-Rite/5943003801

Here’s a photo showing how the coax is wrapped around the toroid core:

And here are some before and after video recordings. The gap about half way through each is when I disconnected the incoming coax to the radio, and inserted the choke, and then reconnected the coax:

2 thoughts on “Ferrite Core 1, RFI 0

  1. Hi Chris !

    I’m a newbie, so sorry for the silly questions and my approximate english : OK, so you wrap some coax around the toroid, and then attach it to the connector coming from the wire antenna on one end and to the RX at the other end, right ?

    I suppose the piece of coax you use for this, must not be too long, maybe just 1m or less ?
    Why not directly wrapping the RG6 coming from the antenna around the core, rather than using another piece of coax ?

    What about wrapping the USB cable between the PC to the SDR ? Mine is supposed to be shielded but …
    In other words : if I had only 3 toroids, where should I place them for maximum noise reduction ?

    You mention materiel 43 ; it seems #31 is often used. Which one is better considering my interest is LF and medium waves ? (and FM DX on summer).

    That’s all ! Thanks a lot in advance for your reply.

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