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-   -   Too strange... (http://forum.tvfool.com/showthread.php?t=2249)

Maury Markowitz 29-Sep-2011 6:12 PM

Too strange...
 
I'm in Courtice, Ontario. For funzies, I made an antenna for myself using a short length of RJ59's bare copper touching the screw on a local power outlet. I got the TV to reprogram the channel list to see what would happen. I got two channels...

Channel 22 is a analog CBC repeater. The signal was just OK, which I found to my surprise was coming from an antenna only a mile or so from my house! So that one's not surprising.

Ahhh, but how about the really good reception on 23.1?! This is a station in Buffalo, miles away.

I guess the grounding length was something close to 5/8ths of that frequency?

GroundUrMast 29-Sep-2011 7:15 PM

Quote:

Originally Posted by Maury Markowitz (Post 12426)
...

I guess the grounding length was something close to 5/8ths of that frequency?

Quite unlikely... you also need to consider the length of wire in the wall.

The cover plate screw may be close enough to ground potential at DC and power line frequencies, but at VHF and higher, just a few inches changes the impedance of the wire. Achieving near zero ohm impedance connections at radio frequencies is quite challenging the moment you insert just a few inches of separation between two objects.

UHF channel 22 is 518 to 524 MHz. The wave length at that frequency is about 0.58 meters so, a 1/4 wave length would be only about 5 1/2".

WNLO, real channel 32 (virtual 23.n) is broadcast on even shorter wavelengths, 578 to 584 MHz (0.516 meters).

You've demonstrated the resilient nature of the forward error correction incorporated into the ATSC standard. Unlike analog NTSC signals that will have noise (snow) and multipath (ghosting effects) show in the display as the result of poor signal quality at the receive location, if you receive enough raw data so the receiver can recover the underlying data stream error free, the ATSC signal will display perfectly.

Maury Markowitz 29-Sep-2011 8:49 PM

Quote:

Originally Posted by GroundUrMast (Post 12427)
You've demonstrated the resilient nature of the forward error correction incorporated into the ATSC standard. Unlike analog NTSC signals that will have noise (snow) and multipath (ghosting effects) show in the display as the result of poor signal quality at the receive location, if you receive enough raw data so the receiver can recover the underlying data stream error free, the ATSC signal will display perfectly.

Sure, BUT... in addition to the channel 22 NTSC a couple of miles away, and WNLO about 70 miles away, there's the CN tower about 35 miles away. This broadcasts dozens of high power signals, mostly ATSC.

So the strange part is why can I get a perfectly good ATSC on channel 33 from 70 miles away, but nothing whatsoever from a bunch of powerful channels half that distance?

It seems the system is either *astonishing* directional, or *astonishingly* tuned to specific frequencies. Neither seems terribly likely!

Or perhaps the tuner skipped channels... I'll check that tonight.

GroundUrMast 29-Sep-2011 9:20 PM

Quote:

... *astonishingly* tuned to specific frequencies.
That would be quite likely, though quite random and unpredictable, given the random nature of selecting dimensions and placement of the 'antenna' component(s).

Practical antenna design does not often follow a "cut, try, repeat till you get lucky" process. But such a process will produce random results.


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