Noise at roughly 60 KHz intervals

I'm seeing a BUNCH of noise signals from about 11MHz to 22 Mhz (?) at roughly 60 Khz intervals.

Is this a known electronic design issue? Is it possibly a signal from one of the computers in the vicinity?  If so, is there a fix?  




  • jksjks
    edited July 2017
    Probably not a Kiwi design issue, unless you've supplied your own, older Beagle that is known to have noise problems (see What you describe is typical for one type of SMPS we've seen. 60 kHz is a common switching frequency.

    Switch off the other devices until you find the culprit. Try filtering the mains input to your Kiwi linear power supply and perhaps Ethernet and antenna feed line.

    There are plenty of Kiwis that are in very quiet noise environments with few system noise effects, e.g.

  • Thanks, will check it out.

    These seem to have appeared suddenly, well, I don't think I had them a couple of weeks ago and here they are.

    Got to move it out to the shop!



  • More
    30/60KHz spurious signals.

    have a KiwiSDR with BBG that was purchased as a set. It is supplied from a 5V
    3.5A linear psu.
    After sorting out the interfacing to the network, it worked.

    I have a choice of two antennae, a 12m longwire, or a PA0DRT copy active
    mini-whip. There were a few unwanted signals to clear up with ferrite rings but
    as I go down towards the noise floor there are spurious signals that DON'T go
    away with application of ferrites or screening.

    I can see similar unwanted signals on a selection of already wired and active KiwiSDR
    web receivers.


    chose one of the stronger spurii showing on my RX, at 23127KHz +/-3-500Hz, as a
    working point, and I
    tried and tried to reduce its level in the receiver, the spurs are about 30dB
    above the noise floor.

    Very similar spurii can be seen on several other KiwiSDR RXs accessed via the
    list and I can post the screen dumps when I’ve worked how to do that.


    the moment I have given up as I can't get rid of these signals.

    They are even still there, at reduced levels, when I have removed the antenna
    and all my peripheral circuitry, leaving just the power cable (with large
    ferrite ring), and the CAT6 cable (with FT240-31 rings at either end) with the
    antenna input shorted out.

    In fact I surmise that the unwanted signals come directly from the IP network

    anyone else seen this? 

    And better still has anyone found a way around the situation/problem??


    network switch is a Netgear Prosafe GB switch, model GS105 that is supplied
    from a linear psu; and the connecting CAT5e cable is about 5m long. 
    I am trying to find someone to lend me an
    alternative switch.


  • I'm curious to see if the different switch fixes this.
  • what happens if you connect a PC directly to the Kiwi and shut off other network stuff? (as a test)
  • Makes me wish I hadn't thrown out all those 10base-T to 10base-FL converters 15 years ago.

  • I put the KiwiSDR back into it's cabinet yesterday and was surprised to see the noise floor (at 23127) had dropped from about -120-130dB down to -150dB. Silly numbers! has anybody else noticed a similar change? And the spurious levels seem to have dropped as well
    The latest version installed is 1v14.
  • I found an awesome paper that talks specifically about wired Ethernet RFI issues (starting on page 12):
    Although it seems your use of type 31 toroids at both ends of the cat-5 is the best first step.

  • I faced the similar RFI problem with my ethernet cables inside the garage where the receiver risdes.
    The only solution (partial) I found is to keep the Ethernet cables as short as possible. That can be seen
    on the welcome photo of my SDR.
  • I have the Kiwi on my "IT Shelf" in the basement and I don't think I see this even though it is nestled up need my router etc. I have #31 ferrite on all the cables and also have it under a Faraday shield.

  • Regarding the use of a direct link KiwiSDR to PC or Laptop. It didn't work at all.

    Also no one I know has a spare switch for me to borrow, will I have to buy one??

    And I see that someone else has also commented on a very similar situation.
    See -Does someone have an idea about these birdies ?  by F1JEK/P

    here is an illustration showing that it is just my installation that has this phenomenon.


  • Sorry, I meant --- ISN'T JUST my installation
  • edited August 2017
    Hi Bill, Peter and others,

    I'm fairly sure it's originating from your ethernet cables and / or router.

    As an experiment today I connected a 1inch diameter single turn RF 'sniffer' loop to the end of a short length of coax and had a 'sniff' around my KiWi's

    Sure enough there is a very strong signal as described at 23127KHz and also at regular intervals of approx 60KHz over most of the spectrum.

    The next three screen shots were taken with the 'sniffer' loop in among all the ethernet cables going into my small 4 port Netgear network switch that sits under the desk.




    The fourth image shows the very weak interference when the KiWi is connected to my antennas.


    In my case I've added a lot of ferrite rings around the various cables going to and from my KiWi's (see next photo)


    To suppress RF radiation on cables at frequencies around 23MHz the optimum results would probably be obtained with something like 8 turns of the ethernet cable through a ferrite ring made from either type 43 or 31 material.

    Note that you need to add ferrite rings on all the ethernet cables and at each end of every cable.

    I hope this helps.


    Martin - G8JNJ


  • jksjks
    edited August 2017
    I run my Ethernet switch from a linear supply. But of course inside the switch has an on-board 3.3V SMPS to regulate the nominal 5V DC input. I've been meaning to "sniff" that to see what frequency it runs at and check if it correlates to the spurs that I see.
  • edited September 2017
    62 kHz increments of dirty but stable carriers are very common. 
    It is generated by the digital circuits inside wired LAN switches and LAN routers.
    Ferrites on all the I/O CAT-5 cables and power supply cable of the LAN can help to suppress it. 
    Getting the antenna further away from the computer and LAN helps a lot. 
    Coaxial ferrite choke isolators at the feedpoint of the antenna, and where it gets close to the LAN helps also. 
    Image of 62 kHz LAN noise:
  • It looks as if there are two threads, no.778 and no.827, dealing with these very similar conditions.
    Thanks for the info and advice Martin, I'm slowly working through cabling permutations and lots of ferrite rings.
    I've gotten another KiwiSDR with ser. no. 2050 for second installation and this is attached to a "Beagle Bone Green" with a label BBG217021961 stuck to it.  So I can do a direct comparison after the tests with different ferrite toroids attached in various places are completed. So far no real progress has been made and I haven't found or borrowed a different switch either, new ones cost money, plus I'm a little fed up with getting nowhere fast.
    Is there any data not yet published relating to the older BBGs obtained separately to a KiwiSDR so that we can check against the ser. no.s of the BBGs supplied in the sets. 

    WA2ZKD wanted to know if i'd tried a direct connection between the KiwiSDR and a PC.
    Well, I didn't get networks comms to start at all so I wonder if this is only possible with a USB connection?
    Or maybe if I had a 'crossed over' network cable, this connection might work. Does someone have any thoughts on this?

  • jksjks
    edited January 2018
    Here's a new blog post where a 20 dB reduction in Ethernet spurs on 20 meters was had by changing to a metal-case Ethernet switch and long, shielded CAT6 cables:

  • my case I have a choice of two antennae, a 12m longwire, or a PA0DRT copy active mini-whip. There were a few unwanted signals to clear up with ferrite rings butas I go down towards the noise floor there are spurious signals that do not go away with application of ferrites or screening.
  • How is your Kiwi networked? the standard repeating signal from ethernet is virtually everywhere. You could try a wireless (or fibre) bridge to the Kiwi and add distance from noise sources.
    Initially just try to turn things off see if the source is in your control, if it is, good otherwise welcom to the modern world, I can tell what PC my neighbour is using from the QRM signature.

    I find some cheap CCTV cameras are just terrible (looking at you ESCAM), broad frequency comb transmitters peaking around 20MHz, you'll need to see where the signal is getting in.
    I reduced the direct local pickup problem by using a wireless bridge, ferrite rings on everything and a metal case, grounded.

    The CCTV camera will still cause issues as that is a geniune RF signal being transmitted, reduced that mainly by CAT7 cables fibre bridge and grounding.

    My PA0RDT benefited from grounding at the base of the feed (with a low pass filter) network cable as feed (CCTV baluns) and another ground just before the RX.
    If your Kiwi is online? I'll see if it ties up with what I'm used to as local QRM here.

  • Interestingly I found that using screened CAT 5 cable actually made the noise levels on the VLF bands <50KHz much worse.

    In the end I went back to using un-screened CAT 5 with 12 turns through a FT240-31 core (Mouser part number 623-2631803802) which was just as effective on the HF as it was when used with screened CAT 5 at frequencies around 20MHz, but didn't introduce the additional noise on VLF. I think the screen adds an additional ground loop, which the transformers in the Ethernet interface and external choke baluns can't fully isolate / filter because of the very low RF frequencies involved (just my opinion).

    I also found that bonding the RF in and GPS connectors directly to the metal case at the point of entry reduced the HF noise floor by a further approx 3-6dB depending upon the exact cable configurations, but your mileage may vary.


    Martin - G8JNJ
  • Not sure I'd be able to test low down, something they do next door seems to set light to the lower end of the spectrum.
    Image below while fighting today's new raft of QRM.
    PA0RDT on the bottom, LZIAQ with bike rims top, without the ability to subtract one loop from the other the anything below 150kHz is just about blown away. I was using bendy coax loops for a week or so but QRM so bad today needed the symmetrical metal loops to properly subract.

    I see what you are saying about ground loops and shielding, I really only use the shielding on the CCTV networking as that sings, ferrite as well on a longer run but those rings are not cheap (to be honest I've not gone as far as 12 turns, normally six here).

    Fibre or radio for the Kiwi as it's easier than working with ground loops.

    I personally would wifi link the Kiwi first, so much easier to deal with injected noise if you can isolate the kiwi and antennas from the rest of the copper wiring.
  • My cat got obsessed with chewing up the 4 pair FTP cable feeding my loop antenna @ and it has been raining here, soaking the cable through the punctures, so the signals degraded and the noise increased. So of course I decided to replace it and while I was at it, I thought it would be nice to move the loop antenna 250 feet west to make my wife happier with the clutter I generate around the place. I've tried winding baluns and shielded network cables and routers, and have not had much luck getting rid of those pesky spurs up and down the band. Now that the antenna is farther away from the garage and house, those spurs are attenuated to the point of being down in the noise and not noticable over most of the band! If you compare with the 8074 address above, you will see the difference in performance. The 8075 is a dual loop setup that is still behind the garage. Both antennas are using the LZ1AQ type of amplifier.

    The new FTP cable is a shielded, direct buried, CAT 6 type cable. The shield is not grounded on either end, so only capacitance to the ground it lays on to drain the shield. I should layout a conduit for it to keep that pesky cat and other varmints from chewing holes in it.
    Ron - KA7U
  • That made me chuckle "move the loop antenna 250 feet" within that distance here - 32 other houses.

    Has made a very nice difference though, well done.
  • The worst spurs are still visible although about 20 to 30dBm down from before. So I think the spurs are actually received by the antenna and not a common mode problem that can be cured by shielding and cores, necessarily. Shielding and cores did make a difference here on most spurs, in the 5 to 15dBm range. Moving the antenna west was the dramatic improvement however. I think if the antenna is in a high density neighborhood, it will be very difficult to eliminate this interference.
    Ron - KA7U
  • In the addition to all the good points above another thing that might be worth checking is the coax cables going to your receiver. I replaced one low quality cable with poor shield and center conductor connections and noticed almost 15 dB reduction in these 62 KHz EMI signals. Mind you this was a brand new Taiwan made cable, admittedly a low cost version.

    Ben - SWLOI33
  • Yesterday I made up 6 RJ45 to BNC balun boards for my loop antenna projects. I've been using plastic RJ45 units that plug in vertical to the board. I bought a bunch of shielded RJ45 PCB sockets and used them on the 6 new boards. When I tested the new boards the noise level on the loops was very bad as compared to the existing batch using the plastic RJ45's. So I rewound a balun 3 different ways without improvement. Finally I cut the ground trace to the shield, pin 9 on the schematic, and placed hookup wire to run the ground to a new common point on the circuit board. Then the unit worked as it should, and was comparable to the plastic RJ45 sockets. The feedline is using plastic RJ45 plugs, so the shield ground was not common with the FPA cable shield anyway. I am curious why this happened. It happened on all 6 boards. It doesn't take much to upset the feedline into the receiver from the antenna and create a ton of noise.

  • It would seem the the shield is conducting noise on the "receiver" end to the antenna end in an imbalanced manner, at least partially invalidating the entire point of having a balanced feedline.

    There is probably a bit of imperfect balance on your loops making them somewhat susceptible to E-field conducted. The other possibility is that connecting the shield causes noise currents to flow between the receive and antenna ends: If this happens, all bets are off as these currents can/do get into everything! I'm somewhat surprised that the VCC and DC return connections don't cause a similar problem - unless you have significant choking inductance (say, a bifilar on a ferrite core) on these lines to decouple them at RF.

    On something like that I would wind a couple dozen turns of that flat CAT5/6 cable (I use 6'/2meter jumpers) on a large-ish 77 or 75 mix toroid and have one of these at each end to insert several millihenries of inductuctance longitudinally down the line to quash such currents. In that case, a "DC" ground on the shield at each end ("past" the choke) should have little effect at those frequencies where the added ferrites' reactance is in effect.

    Clint KA7OEI
  • Hi Ron,

    I agree with Clint.

    The screen can sometimes be a curse as it introduces low frequency ground loops that may negate the balanced lines. You need to use type 77 or 75 in order to be effective at the lower frequency end of the spectrum, although type 31 would be OK if you are not interested in VLF, and type 43 would be best if you are only interested in say 3-30MHz.

    In your circuit I'd also suggest adding a choking balun to the power and ground return and ideally a suitable decoupling capacitor between the two wires on each side of the balun in order to tie them to the same RF potential.

    I'd also add a choke to the DC supply to minimise any noise from the supply on the non-grounded +ve line. Something like 12 turns through a BN73-202 core is quite good in that respect.

    I've just been building some coax bias Tees and they have three inductors. The Bias Tee inductor itself, an inductor on the +ve DC supply rial and a choke on the incoming DC supply lines. It also has 2 lots of 2,000uF LF decoupling in addition to the normal 0.1uF & 10uF RF values. Because the DC input is carried on the coax you have to be very careful about both common mode and differential mode noise being injected directly into the RF path from the power supply.

    If you use CAT5 or a balanced feed you need to be extra careful that you don't inadvertently introduce unbalanced paths that make it end up being the same as using unbalanced coax.


    Martin - G8JNJ
  • edited December 2018
    OK, I have been experimenting to find the best configuration. I terminated the receiver end of the CAT6 FPA cable into a shielded RJ45 plug and used a balun board with a shielded RJ45 jack. The interference level dropped to a low level as compared to a non shielded RJ45 plug plugged into a shielded RJ45 jack, but there remained a significant group of spurs around 18250KHz, peaking at about -98dBm on the kiwiSDR scale. I then used a balun board with a plastic RJ45 Jack and using he shielded RJ45 plug, the level of the spurs remained the same. Then I reterminated the CAT6 FPA cable into a plastic non-shielded RJ45 plug and connected that to the non-shielded RJ45 jack on the balun board. The level of the spurs around 18250KHz dropped to -108dBm, an improvement of -10dBm on the KiwiSDR. This is actually quite good as compared to the average KiwiSDR I've listened to. At the antenna end, the CAT6 FPA cable is terminated into a plastic non-shielded RJ45 plug and the amplifier connects with a non-shielded RJ45 jack. I read on the LZ1AQ web site that grounding the shield at the receiver and leaving the shield open at the antenna would give the best common mode rejection, but I have not tried it with a shielded connection on both ends here. My new amplifier boards are configured to accept the horizontally mounted shielded jacks and I'll try terminating both ends in a shielded jack with the next amplifier build. Until then, the non-shielded jacks and plugs on both ends of the feedline is providing the best results here. I do not understand why.

    As to the DC ground configuration, you can check the schematic to see the amplifier power input circuits.

    Ron - KA7U
  • When it comes to conducted/induced currents along the length of any cable, a shield connection can be a liability as it, by definition, has no galvanic isolation.

    The other thing to consider is that the capacitance of the shield to the inner conductors - probably in the area of 10-15pF/foot. What this means is that along a 100 foot length of this stuff, noise on the shield and/or longitudinally on the twisted conductors will have 1000-1500pF of coupling which, at 1.8 MHz, has a reactance of 88-59 ohms (respectively) which can do a pretty good job of coupling garbage on the line: If the balance of the transformers is anything other than perfect, you will hear the noise.

    Many years ago I constructed a system that had galvanic isolation that used twinax and I needed to have extremely good longitudinal isolation. Constructing a Faraday-shielded transformer helped tremendously, having 60dB or so isolation, but the last little bit of isolation was aided by having a fairly high-value potentiometer (5k, I believe) across the input balanced line with the wiper to ground and adjust it for the best null - well over 80dB. Had I needed to go higher than just a few MHz I would have probably needed to include some nulling capacitors as well.

    * * *

    I see in the loop amplifier diagram that the V+ and ground leads are AC-decoupled with 470uH inductors (ideally around 5.3k at 1.8 MHz, or about 2.6k for the pair). At LF frequencies, these are probably a bit marginal - around 177 (88 for the pair) ohms at 60 kHz.

    As far as grounding the shield goes, one typically tries all of the combinations and uses the one that works best. If grounding either end of the shield (but not both) makes a difference, I would kind of suspect that one or both of the transformers lacks sufficient longitudinal isolation, typically caused by mutual capacitive coupling between windings.

    All of this indicates that the "shack" end of the cable is extremely noisy from switching power supplies, and connecting the shield at either end simply couples the noise on it, effectively bypassing part of the transformers' isolation, so whatever you can do to decouple the entire cable at RF (especially the "shack" end) will help (e.g. dozens of turns of this CAT-5 cable through a large, mix 75 or 77 toroid) . I would bet that if a large decoupling choke were put at each end of the cable, connecting the shield at either/both ends would make very little difference at RF.

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