I have a 40M vertical on top of my roof. When I transmit at 100W, my internet drops. My neighbor's internet too (different cable company). At 50W it seems to be OK.

As an expermient, I used a smaller vertical (Hustler 40M mobile), clamped to a yagi's boom. It uses my 10-15-20M yagi as radials of sorts (gamma matched so all elements are shorted to the boom).

The "large" vertical is about 4M away from overhead power and cable wires. The smaller one is about 15M away from those. The ends of the radials of my large vertical are only 20-30cm away from the power lines:

enter image description here

I have found two things:

  1. Noise is lower (1-2 S-units) with the smaller vertical
  2. The internet doesn't drop when I transmit 100W into the smaller vertical

Could both observations be attributed to just lower performance from the small vertical? The radiator is only 1.5M long, a coil, and some more whip. The larger vertical is 6M, coil, 1.2M.

I might consider moving my larger vertical and put it on top of my yagi, if this helps me reduce noise and avoid interference to CATV. But I'm not sure how a "yagi as a groundplane" would affect performance vs "16 5m long radials" as I have now.

Another question is: will the mast act as a radiator or counterpoise too? Is it beneficial for my application, or do I now have a off-center fed vertical dipole?

If I had to choose between the ability of transmitting 50W in a vertical with plenty of radials, and 100W in a vertical with few short radials (a yagi), what would be the best choice?

Finally, a photo of the small vertical clamped to the yagi:

enter image description here

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    $\begingroup$ Both your "large" vertical and your radial wire(s) appear to pose significant electrical safety hazards. We value the welfare of our HamSE community as well as their friends, families and neighbors. I beg you: please, please, move everything away from the power lines. $\endgroup$ – Brian K1LI May 22 at 15:07
  • $\begingroup$ @BrianK1LI I'd agree, power lines are led out of reach for good reason. However, don't be too alarmed here: these aren't old-school blank metal wire conductors, these are properly PVC-insulated wires and hence don't need safety clearance. $\endgroup$ – Marcus Müller May 22 at 17:48
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    $\begingroup$ Only 30 cm clearance from power lines? Sounds like a bad time waiting to happen. $\endgroup$ – Phil Frost - W8II May 22 at 18:43
  • $\begingroup$ The metal roof of the house itself is also 30cm away from those power lines, and the antenna is attached to it anyways. Like Marcus said, these are insulated power lines (see, they're 4 conductors braided together. The insulation can't really melt without something even worse happening first) $\endgroup$ – hjf May 22 at 19:13

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