Discussions about Antennas in general, building antennas, installing antennas or buying antennas.


Postby charlessenf » Wed Dec 09, 2015 1:02 am

Our OTA reception (Using Digital TV as well as Converters) of a couple of channels (TriCities, TN WCYB-DT 5.1,5.2,5.3) improved significantly after I mounted an aluminum Chimney Cap on the chimney that supported our antenna!

Now, I mentioned 'ground plane,' because I heard about something of the sort many decades ago and recall it had something to do with radio reception.

This Chimney Cap is some 78" long, 18" wide and about as tall at the highest point.

It is a 'covered wagon' style. That is, a sheet of aluminum 36" or so wide by 78" long is formed into a semi circle with 'sides' the appears as a U-shaped cover when viewed from one end as the cover of an old Conestoga wagon.

Quite an expense of metal. Mounted, in this case 'behind' the antenna. That is, as the 'front' of the antenna is aimed at the transmitters and the antenna is mounted to one of the narrow faces of the chimney with the Cap covering the chimney from the antenna mast to the other end, It seems to me the Cap is 'behind' the antenna.

I thought to post here to see if anyone knew why the reception would/should have improved - assuming it was not mere coincidence.

I thought that, if there was a correlation and I knew the theory behind the phenomenon, I might add some more metal (or move the antenna) and improve reception further.

Also, running our Dishwasher interferes with the WCYB-DT signal the Chimney Cap had improved.

I wondered if it might be worth the effort to add an 8GA copper ground wire to the antenna mast and/or to the Chimney cap and connect it to a grounding rod.
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Postby geenathegeek » Fri Jan 08, 2016 9:50 pm

It sounds like you are getting some Ground Plane effect, or, depending on the orientation, the cap could be acting as a reflector, giving some gain in a preferred direction. There is a lot of theory on antennas, but most of it is under "ideal" conditions. So many factors affect a real-world setup that antennas are often considered black magic.

As to a ground wire, since it would be many times the wavelength of the signal being received, theory says that there would be no effect, but if you already have the wire, it never hurts to try. Besides, it will drain off electrostatic charges which could damage your amplifier or TV front end. It is probably not worth the effort to buy the wire though.
The only thing impossible is that which we do not attempt.
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