[kwlug-disc] Home made indoor TV Antenna

John Johnson jvj at golden.net
Wed Apr 16 11:11:13 EDT 2014


On 2014-04-16 09:55, Colin Mackay wrote:
> I have one of these: 
> <http://cdn3.volusion.com/m5ytq.j6phj/v/vspfiles/photos/CM-3000A-2.jpg?1385029454>[ 
> edit ]
> Did try an 8-bay like in the walmart link above, to no avail.

While I do not have recent experience with RF, my experience with 
antenna technology goes back, way back. Perhaps, a decade or 2 or 3 or 4.
That said, IMHO, the basic principles remain.

Please note that I am trying not to sound pedantic. Nor write an essay. 
And I apologize for any perceived pedantry and the length.

RF is really a higher frequency of the Electro-Magnetic radiation.

And RF itself covers a wide range of frequencies, for the purposes of 
this discussion from MW (medim-wave used for AM radio) though to microwave.

Excluding the plumbing and stripline technologies of microwave, 
reception of the lower frequencies, including VHF, UHF, UHF-HD, etc. 
depend on the first principle, i.e. signal capture.

By "signal capture" I mean the capture of the RF radiation in "the 
ether", in the desired frequency band. This "signal" will include a 
multitude of channels or sources, each with its own content modulation 
methods. This "signal" will also include channels or sources from 
frequency bands outside of the desired frequency band.

Presumably one of the channels or sources is the desired source in the 
desired frequency band. After "signal capture" a variery of 
technologoies come in to play to suss out the desired channels or source 
from the "captured signal". These technologies include filters, 
amplifiers, tuners, etc. And are not the point of this discussion.

Returning to "signal capture", the first principle mentioned above, 
involves the principle of induction, i.e. the generation of an 
electrical signal in a conductor by the RF energy "in the ether". Tesla, 
Hertz, Lenz, Faraday, Maxwell and Fessenden (a Canadian in the bunch) 
and others have studied, researched and documented this process.

However, basically, the strength of the induced electrical signal in the 
conductor depends on the properties of the conductor and the strength of 
the RF radiation at the point of induction.

We cannot do much about the strength of the RF radiation at the point of 
induction.*

That leaves the conductor, and the properties of the same. One of the 
properties of the conductor is its "size" or "length" relative to the 
frequency of the RF radiation. The "size" or "length" of the conductor 
can be used to "tune" the conductor to specific frequency bands. This 
can be in a 1:1 relation (full wave) , or in 1:n where n is even 
multiples, or more common n:1 where the conductor is in even fractions 
of the frequency, e.g. half-wave, quarter-wave, etc.

Basically: more metal in the sky ==  more captured signal (YMMV)

IMO Antenna packaging like flying saucer is like that of fishing lures 
at Canadian Tire. The item must first attract the buyer and whether or 
not the  item actually works in the wild is secondary.

* Some technologies can improve the strength of the RF radiation at the 
point of induction. These include placement and orientation of the 
conductor, i.e. antenna. These also include additional elements, such as 
directors and reflectors, as seen on Yagi VHF antennas and the bow-tie 
on on the Walmart HI-DEF antenna.

/essay

Regards
John Johnson




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