ad: Momobeam-1

QRO making broadband slow

Discussion in 'General Technical Questions and Answers' started by M0AGP, Nov 20, 2021.

ad: L-HROutlet
ad: l-rl
ad: L-Geochron
ad: L-MFJ
ad: abrind-2
ad: Left-3
ad: Left-2
  1. M0AGP

    M0AGP Ham Member QRZ Page

    When I transmit on 160m with QRO, the broadband speed grinds to a halt (though all electronics keeps functioning), and when I stop transmitting it springs back to life. During the ping test part of the broadband test as I transmit, the ping test fully stops receiving anything and when I stop it goes back to a reasonable set of numbers. During the "file download" part of the test, the router seems to stop receiving data when I transmit and then afterward all is fine.

    Not sure how it works in the US (probably similar) but here there is a data line management algorithm that detects errors and "resynchronization events" (resynchs). Resynchs are when there's been an issue so disruptive that the router needs to resynchronize with the main system. I've got a fair amount of info on how the algo works, but suffice it to say that if you have enough errors and/or resynchs, the assumption is that your line speed should be made extremely slow so that you can at least get some info through. And you get a permanently slow line...

    The band that has the most impact is 160m. My setup is about 160 feet of buried M&P RG8-type cable from the base of the inv L to the shack. The rig and amp are grounded to the AC mains ground.

    There has never been any RFI issue before of the type where transmitting has a negative effect on anything. There have been a few unrelated RFI issues with house electricals interfering with experimental weak-signal receive antennas.

    There is no common mode choke at the inv L feedpoint, but with 160 feet of cable directly in contact with the dirt and buried 8-9 inches deep, it seems unlikely that a CMC would make much difference.

    On the router I have four FT140-43 ferrite toroids: one on each end of the data cable with about 20 winds through the toroid, one on the power cable with about 20 winds (and cables shortened to the maximum possible extent), and I also managed to squeeze about 8 winds of the ethernet cable onto a toroid. The ethernet cable is only about 2 feet long now.

    I was thinking the next step in isolation could be to add even more ferrites, or it might be a sort of "Faraday cage" for the router. The WiFi is rarely used, but the wavelength is so much shorter, if I was to make a wire cage with like 4 inch spacing of the wires, you would think this would block 160m but let 2.4 GHz through, no?

    Any other suggestions?

    My simplest plan B is to just switch the offending router off and use the "family internet router" which is in the room next door and is fully unaffected by the transmitter.

    But I'd like to see if I can fix this QRO issue first before going to plan B.

    Mike M0AGP (ex WB9WFJ)
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Not unexpected when you are living inside your antenna :(
    UT7UX, N2UHC and KP4SX like this.
  3. M0AGP

    M0AGP Ham Member QRZ Page

    Mike are you expecting I still have common mode issues even after coax was buried (8-9 inches I think) for 160 feet? Then again the skin depth at 160m would be pretty large...

    So maybe I should add a CMC at the base of the inv L and at the shack? Sorry I expected burying the coax for such a long run would rid me of that problem...

    Also, there is a second router in the next room which enters the house at exactly the same point as the "work" router that is being interfered with. There is no impact whatsoever on that router when I transmit - if all the house wires are radiating, why is there zero impact on the other router?

    There's also zero impact on the laptop which sits 12 inches from the amp...
    Last edited: Nov 20, 2021
  4. KV6O

    KV6O Ham Member QRZ Page

    What is your ISP connection? Cable? DSL? Fiber? Satellite? Cellular? Something else? Is the interference occurring at the ISP's demark, or on your network?
  5. M0AGP

    M0AGP Ham Member QRZ Page

    The connection is described as "fiber to the cabinet" which amounts to a 38Mbs service to a server cabinet and then it is twisted pair for a bit over two miles. Not sure if that helps.

    As I say the router in the next room is absolutely fine when I transmit but the router 3 feet from the rig grinds to a halt when I transmit. Both of the lines come in via the same pathway, including via this room and the routers are identical...

    When I transmit things grind to a halt as described above - it is 100% certain that the problem is me transmitting and not a problem on the line.
  6. K8JD

    K8JD Ham Member QRZ Page

    Is there reflected power from this ant on 160M? SWR problems ?
  7. M0AGP

    M0AGP Ham Member QRZ Page

    No - the SWR is about 1.6.
  8. M0AGP

    M0AGP Ham Member QRZ Page

    OK - after working with a very experienced RSGB expert in RFI for several weeks, he has said it is the most bizarre RFI case he has ever encountered.

    Summarizing 60+ emails etc, here is the action taken.

    1) Buying 10 "big-clamp-on" type 31 ferrites (Fair rite 0431177081) and making a number of chokes as per the below.
    2) On the more distant router (15 feet away in another room, but the "master socket" is in the shack) the only cables are the data cable and the power cable.
    One "Big Clamp On" (BCO) on the power cable at the router, one BCO on the data cable at the router and one BCO right at the master socket (where the data socket on the wall is):
    3) A QRO-level common mode choke using no less than 4 BCOs with 7 turns of M&P ultraflex 7 through all the BCOs.
    According to charts, 7 turns through one BCO should produce around 3k ohms impedance at 160m, so you would expect some serious choking action with this:

    1) Impact of putting in place the big common mode choke above: no impact whatsoever.
    2) Impact of putting all of the BCOs on the power and data cables: no impact whatsoever.

    In addition, I put BCOs on every cable in the shack that had anything to do with the transmitter/amp. All the power cables, the one to the antenna switch, the laptop, and also the other identical router that is in that shack (and affected the same way) and the ethernet cable from the shack router to the laptop.

    No impact whatsoever.

    And I started decreasing power to 100w and even down to 10 watts, with all of those chokes, and the router in the next room screeches to a halt.

    So I thought, well there are two ways RF can get to the router: through the wires and through the air. I seem to have done a good job on the wires.

    I wrapped the router in aluminum foil (!) expecting that there would be no signal. Nope! Still a good signal from the router. And 10w on 160m still stops the internet.

    I then put metal baking pans on both sides of the router in addition to the aluminum foil.

    No impact whatsoever.

    I guess the router is still able to transmit/receive using the few inches of power cable and few inches of data cable that are exposed.

    After all this, the RSGB guy pretty much threw his hands up.

    My working theory: there is something in the routers that has a broadband resonance in the 1-4 MHz range and when it picks up radiation in that range something stops working.

    My solution: I will get an unlimited mobile data package and when I want to use the low bands, I will ask my family to switch to my mobile phone's hotspot.

    The mobile phone normally lives about one inch from the amp and has never had any RFI issues. It's mobile hotspot is usable in most of the house...

    Before replying to this thread and saying "have you tried X?", please read the entire original post, and please don't assume that both the RSGB guy and I are complete idiots...
  9. N1EBC

    N1EBC Ham Member QRZ Page

    Ok how long has this been an issue, how long has router been in play vs the 160m band. If it just cropped up and antenna is ok maybe something starting to fail in the router maybe a blocking LC filter.
  10. M0AGP

    M0AGP Ham Member QRZ Page

    This has been the case since I put the inverted L up - about 2 months ago I think. There may be blocking filters that failed in both the routers as this happens in both of them.

Share This Page