[mythtv-users] Attic antenna

[Tom]

At 01:58 PM 8/28/2009 -0700, you wrote:
>On Fri, August 28, 2009 1:37 pm, bhaskins at chartermi.net wrote:
> > Questions:
> > I have read that the old style 300 ohm twin lead has a lower loss
> > per foot than coax.. true/false ?
>
>True.  However, you have to keep it away from metal and other wiring -- at
>least twice the width of the line.  This is because the electromagnetic
>field extends into the air around the conductors, whereas with coax it's
>contained within the shield.
>
> > Since this will be about a sixty foot run, would the twin lead be a better
> > deal?
>
>With coax you'll probably want a preamp at the antenna to make up for the
>line loss.  You have to weigh this added expense against how difficult
>it'll be to route the twin lead.

The TV and the inputs on the TV cards are 75 ohm impedance. Twinlead is 300 
ohms and won't work. Not without a matching transformer-- another place you 
can lose signal. Most antennae for UHF are already 75 ohm F-connectors, so 
why transform the signal from 75 ohm to 300 and then back again when you 
get it into the house?

Can you support the twinlead several inches away from ALL metalic objects? 
Got any pipes in the walls, other wiring, metal ceiling hangers, metal 
corner bead on every corner where drywall meets drywall, etc etc etc etc?

I think the reference to twinlead having less loss is to 300-ohm ladder 
line, which is larger and uses better materials than the old TV-twinlead. 
Yes, coax has loss, but it's so far simpler than using twinlead that I 
never even considered using twinlead. I'm out in the exurbs here, quite a 
ways West from the city center, plus the towers for most of the local 
station are on the East side of the city. I have a $65 antenna from Radio 
Shack on a pipe strapped to my chimney, and the strong stations come 
through perfectly. Even the two low power ones come in pretty good, except 
when it's raining really hard they can be a little spotty.

Bite the bullet. Do it right.

-T


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