Different Noise Thresholds

Dear All,
I tried with different antennas (same locations) but nothing. There are some thresholds of noise as in picture on 3,5MHZ, 5MHz and 14MHz. Without the antenna (I tried, hi!) there is a uniform white noise.
Any suggestions? Is it the same also for your stations?

You can check at www.iz3eaw.it

Giulio IZ3EAW



  • There are at least two problems that I can see. First, you have terrible switch-mode power supply noise in the LF band. The harmonics are very wide at LF and so will be even wider if they are present at HF which can make them appear more like broadband noise. Look at the screenshot below of 0 - 450 kHz. Almost all of that is SMPS noise. And half way through the waterfall capture these huge wide signals appeared at 65 and 98 kHz. You really need to track down and eliminate these sources of noise.


    The second screenshot has a suspicious looking abrupt left edge on the noise pedestal at 5.24 MHz. That is quite possibly interference from VDSL Internet service.


  • Yes, 5.2-8.5 MHz and 14.1-17.7 MHz are downstream bands of VDSL. Upsteam bands in between are also partially visible.
    I had the same problem and the authorities found a broken overhead line. After they fixed it, the noise was gone.
  • I thank you for the very interesting answers you gave me!

    Now all I have to do is ask you a new and very dangerous question: how can I understand what are the sources of QRM?

    I've already disconnected all the household appliances, nothing. nothing changes at all. I just inserted a mains filter on the SDR power supply, nothing. How do you advise me to proceed?
    I'm building 4 crossed loops with LZ1AQ pre-amp, maybe this setup can cancel the noise, what do you think?
    Thank you,
    Giulio IZ3EAW
  • I have an old trusty Sony ICF7600G that I can walk around with and sniff out potential noise sources.
  • edited March 2019
    Giulio if you build the magnetic loops with nulls in mind, do try to make them as symmetrical and as well aligned as possible, when subracting one loop from the other the symmetry helps (I have found).
    That does assume your interference is coming from one direction.
    I made a four-loop antenna LZ1AQ from RG 213 flexible coax loops and the noise cancelling was less efficient than two solid aluminium loops I am pretty sure that is because the loops were not held in alignment very well.

    When routers are setting up VDSL connections the signal is different, if you have houses close by it is fairly safe to assume the one rebooting is the one with lights on and someone cussing ;-).

    Here i assume every bit of copper is going to inject noise into the SDR, buy some clip on ferrite sets, make sure you have a bunch of oversize 11-13mm ones in there as a few loops through that will be more affective than a couple of small exact size clip-on's. Break up all the runs of copper with ferrite, watching the waterfall as you go. The biggest sinks are often the easist to find as they respond well to damping.
    Also it is good to have somewhere to dump the RF energy if you can, I've gone over to running the CAT5 feed inside microbore copper for a decent length so that there is an earth connection at either end and the feed is protected from burial and extra shielded, waterproof the ends with mini IP67 junction boxes with glands that take 6-10mm.
    The microbore is only for short runs obviously, most people with log runs can move the antenna away from the QRM source.
  • Thanks for solutions!
    NEWS: I went to my neighbor, with whom I have good relations. I asked him to turn off the devices and power supplies he had turned on one by one. Well ... the 68kHz problem is solved: it was a switching power supply (which I changed at my expense) of the cordless.

    The problem with the VSDL remains, which I really don't know how to solve it (especially for 14MHz noise).
    Thank you again,

  • If you can find what neighbour it is with the VDSL, and they are willing to help, ask them how long the router to wall lead has to be, then make one that long with ferrite at the router end (or both ends), E.G. if they need 1.1m take a 2m lead and wind the excess on a ferrite or two. Here most router leads are RJ11-RJ11 straight through but it would be good to check first. The leads are cheap and providing a spare means the user is less likely to question the need.
    If the VDSL is coming from overhead lines getting it on a well balanced pair should help data throughput and reduce radiation. ADSL and VDSL can sometimes work with one wire only, it radiates badly and is slow but can work so faults (plus noise) can gradually build before eventual complete failure. Here in the UK there is priority given to voice calls so if the voice service is crackly report that, data is secondary and much harder to get companies to address. Also VDSL should only be present on the socket the router is using, if there are hard wired extensions it's best to make sure VDSL filters are dropping the data frequencies where not required (also helps throughput). UK land lines have a newer master socket supplied that filter the data off and tries to reduce wiring to extensions for signal integrity but that helps us too.
  • Dear All,
    I think that the problem is on my router: https://drive.google.com/open?id=1PrXrEtvKZnQYzwzKBrEw8Hl5rYd-ZnJ0
  • Use of the small shortwave portable radio is always a quick way to zero in
  • Ehm, now...any suggestion? What should I do?
  • 1. Move the router further away from the Kiwi
    2. Put clip on ferrite on leads
    3. Get a different router
  • what devices are connected to the router and where are they located?
  • UPDATE:I connected my KIWI directly to my laptop, I switched off the router, all the electronic devices in my home, desktop ect. The noise is always the same (BTW I have reduced other little noises). So I will proceed asking to my neighbor to switch off a minute the ADSL router.
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