shorting a spider antenna


I managed to get a home made spider antenna onto my roof, feeding directly into an amp, powered by an injector inside the house. I realize the antenna itself is open and there is no need for a DC blocker. I am wondering what happens in winter with snow and ice. As the antenna is exposed, if there is any kind of water buildup that freezes on the antenna then there is a very good chance it will short, which won’t make the power supply too happy. Is it not therefore good practice to put a DC blocker between the antenna and the amp to mitigate this issue, or is this problem not likely to happy? Now is the time to consider this, as the roof is a no-go in winter.


Hi Stuart.

A friend of mine protected his spider for the winter with a plastic container has shown in the attached photo.


Weather/rain won’t cause a short to the extent that the power supply will become upset.
However… if connected directly to your SDR or an un-protected amp, static buildup from a spider or cantenna like this can take out the front end of your SDR or amp.
Cures for this include using a grounded antenna (collinears or diploes, grounded quarter wave), adding an RF choke across the base of the antenna to provide a DC ground while not attenuating RF at the desired frequency, or using an intermediate component (such as a filter) that provides protection.

bob k6rtm

Hi Bob

Thanks, grounding is something that I had not considered until now. I’ve just got my installation running, and I am getting great performance from my antenna and amp, so I don’t really want to go away from the spider I’ve built just yet. Do you have any links to chokes or groundable filters so I can investigate further? I assume just grounding the braided coax is not really a solution.



Effectively that is exactly what I’ve done.

I have a commercial collinear, with a satellite amp directly underneath. The braid is connected to the bracket by the antenna connectors - and I’ve grounded the mast (aluminium pole) to a 4’ long ground spike.

This serves too purposes:-

  1. In case of lightning strike hopefully most of the power from the strike wont enter the house wiring
  2. Static build-up … usually it’s not the amplifiers that die, it is the Ethernet port on the Pi that gets sacrificed (unless you are running WiFi)