I recently built a vertical. It's 6M radiator, a coil, and 1.2M more of radiator. It sits on my roof, which is metal, and acts as a ground plane (GND from the feedline is connected to it). There is a choke right at the feedpoint. The impedance is matched (with a LC circuit) from 36 ohms to 50 (49.9, for a SWR of 1.02:1 according to my VNA).

But whenever I transmit more than 50W, my internet and the neighbor's, drop. Sometimes it's a small packet loss, other times is continuous over several seconds.

This doesn't happen when I use the dipole.

The dipole is located about 15M from the street (where the cable companies cables are located, overhead), and the vertical is only 5M away from it. My cable drop rests on the metal roof that acts as a ground plane (I lifted it about 50cm but nothing changed).

What can I do to avoid this situation?

I also have a problem with strange interference near 145mhz that doesn't go away even when the power goes out. I suspect it's CATV related, so I'm thinking a leaky CATV amplifier is causing interference, and I'm causing interference to it as well.

I tried choking the cable to the modem but nothing changed.

  • $\begingroup$ Can you verify (by connecting an ethernet cable) whether it's the modem/router or wifi connection dropping? Solutions will be different. $\endgroup$ – Zeiss Ikon Apr 6 '20 at 16:22
  • $\begingroup$ In a nice world, you'd be able to call the cable company. They'd dispatch a knowledgeable, helpful technician that would show up on time and work with you to identify where the RF is getting into their systems and mitigate the issue. But I don't think that will happen. $\endgroup$ – Phil Frost - W8II Apr 6 '20 at 16:23
  • $\begingroup$ @ZeissIkon it happens both on cable and over wifi. $\endgroup$ – hjf Apr 6 '20 at 16:38
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    $\begingroup$ @PhilFrost-W8II In the real world, they'll send out a "technician" who knows nothing about radio and not much more about internet, and who will swap out the modems/routers without any testing and bill the ham an outrageous amount for the hardware, mileage, and time. $\endgroup$ – Zeiss Ikon Apr 6 '20 at 16:53
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    $\begingroup$ Interesting. I'd guess it's the fact that you're using your roof as the groundplane. With enough feedline between your tx and antenna, and a probably even longer connection of your roof to ground, you might be feeding RF into the internet equipment's ground that way. My second guess is your ISPs are using unshielded twisted pair for their last mile cables and catching tons of interference that way $\endgroup$ – PrefixCactus Apr 6 '20 at 22:58

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