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A cautionary tale with ferrite cores

Bob-N4HY Company Adviser
Ferrite Beads on gigabit ethernet cables are sometimes a disaster.  Even though they are twisted pairs, the ferrite bead was still enough to distort the pulses and cause regular failures.  Since I removed the core, I have not had a single failure in two days.

Bob N4HY


  • Steve G1XOW
    Steve G1XOW Member ✭✭
    edited May 2020
    Bob, you may be right, but this is not my experience so far.

    I have a 10M long CAT7 (flat) Ethernet cable with FT240-31 at each end, both have 10 turns, leaving about 6 metres I guess laying on the floor.

    My radio is directly connected to the PC (no switch, no router), and is powered-up 24/7 for the past 10 months. SSDR has never reported a single dropped packet and the network shows as perfect.

  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited June 2020
    Back in the day when I was installing Ethernet networks in telco COs worldwide, the only time there were ferrite beads on Ethernet cables was when we were using shielded twisted pair.  These were custom made cables, with the shield bond broken at one end to prevent ground loops and the ferrite core molded into the cable jacket.  The mix was unknown (I asked).
  • DaveC
    DaveC Member ✭✭
    edited May 2019

     just look at specs and data sheet. What is the Ethernet spec as far as data rate?
  • EA4GLI
    EA4GLI Member ✭✭✭
    edited November 2016
    Thanks Bob for pointing this out.... I think I had a couple of ferrite cores on an ethernet cable at some point but removed them... never realizing that it could have been affecting performance in a detrimental way.
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    The issue is not the frequency that the Ethernet cable was operating at, but the stray RF frequencies the engineers wanted to attenuate getting into the telco switches.
  • Randy
    Randy Member ✭✭
    edited March 2020
    I am using shielded cables without a ferrite core with no problem.  Before I used a Cat 5 cable I made with a ferrite core an no problem either.  Remember when you wind the UTP around a core, do not do it tightly because it will cause a stagger in the pairs which can induce crosstalk.

  • DaveC
    DaveC Member ✭✭
    edited December 2016
    Not what was asking, Sorry. what is the minimum Ethernet bit rate you can use with a 6x00 radio?
    10mb, 100mb ?
  • Jay Nation
    Jay Nation Member ✭✭
    edited August 2016

    I'm not official!image

    But 100mb, ought to work ok. 
    I've been using my Maestro for a few weeks and haven't noticed the data rate ever exceeding 3mb. 
    Even with 2 active slices and the display refresh rate maxed and display averaging minimized.
    I described it as "ought" because 802.11n, and ac, both increase the data rates, and also are improvements on the older 802.11g standard.
    I don't have any 10mb/10BASE-T equipment left to try 10mb with.

    If anyone's tried it with 10mb/10BASE-T, I'd also like to know how well it worked.

    73, Jay - NO5J
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    You can run SmartSDR over 10 Mb, but you don't have a lot of headroom for streaming lots of other data, like DAXIQ, DAX and REMOTE audio.   Especially if you are running in half duplex mode.  I recommend that 100 Mb Ethernet be the minimum used.  The radio will auto-negotiate to GigE speeds and using that provides a LOT of additional headroom.
  • DaveC
    DaveC Member ✭✭
    edited December 2016
    Thanks Tim good to know. I appreciate all you do for us hacks TNX
  • Bob-N4HY
    Bob-N4HY Company Adviser
    edited September 2018
    Well it appears YMMV. Maybe I have a cheap short run of cable. At 1 Gbps, I was a numbskull for not thinking. I took it off and replace the cable with high quality shielded cat5 and I now have a Faraday cage instead of a ferro magnetic shield. Doh! I know better.
  • Patrick
    Patrick Member ✭✭✭
    edited July 2016
    Tim, right on, I was going to comment about shielding also. One added precaution is to rout the Ethernet as far as possible from RF sources and cables.
  • DaveC
    DaveC Member ✭✭
    edited December 2016

    Thanks for input!
  • k3Tim
    k3Tim Member ✭✭✭
    edited May 2020
    another data point - noticed today an army of ants marching along the ethernet cable - no effect on the signal integrity.. 

  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
    They probably were not wearing tiny little steel toed boots either :-D
  • Wayne VK4ACN
    Wayne VK4ACN Member ✭✭✭
    edited December 2016
    Tim Just be wary of ants in the shack. I had random black ants wandering on desk for months. Got tired of them so i traced them. They were going into back of Ftdx5000. So i opened it up and was a nest. Thousands of them and eggs. Took it outside lightly sprayed with Baygon. Under a metal shield i removed there were heaps more. Fortunately they hadnt done damage to the transceiver. So track them 73 Wayne Ps at least they were black ants and not white ants (termites)
  • Jim Youngquist
    edited April 2020
    We have a 140 ft tower, with a switch at the bottom and internet radios at the top.  in the middle is a low power FM repeater.  all the cables go up the center of the tower and are about 25 ft away from the fm antenna.  of the 13 shielded cat6 cables, 7 of them start out at 1G speeds and then fall off to 100M after a short while.  the other 6 stick and stay at 1G.  some techs have said it is the fm interference and that ferrite cores would resolve the problem.  opinions?

  • K1UO Larry
    K1UO Larry Member ✭✭✭
    edited April 2020
    Hi Tim,  I never ran into you here in Maine but years ago I asked the same question to the Bell Labs Engineers as to what the mix was on the rfi/emi cores.   I suspect it was material designed for the very high end of the radio spectrum where many of the variousTelco systems carrier and radio operated.
  • KD0RC
    KD0RC Member, Super Elmer Moderator
    edited April 2020
    When it comes to RFI, there is no telling...  Ferrites are a pretty cheap way to try and see.  If they don't work, you are not out much - a few bucks and a tower climb.
    Len, KD0RC
  • Stan VA7NF
    Stan VA7NF Member ✭✭✭
    edited April 2020
    At these frequencies DO NOT wrap the cable around the ferrite - The capacitance between the windings introduces problems.  Use several small unwrapped beads.  This applies to 50Mhz and above, including coax, even if double shielded

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