[mythtv-users] OT: Indoor VHF gain antenna

[David Brodbeck]

On Tue, January 26, 2010 4:26 pm, Brian Wood wrote:
> I'm also curious, I thought a half-wave dipole had a theoretical
> impedance at the center of 74 ohms, why do you need a balun to match
> it? You might also try a "folded dipole", made from 300-ohm twinlead,
> based on the "more metal more signal" theory.

That's a good point.  For some reason I was thinking it was in the 200-300
ohm range.  I probably had it conflated with a folded dipole in my head. 
I'll try making one fed directly with coax and see what happens.  It's not
like it'll cost me anything.

I've built antennas before for amateur use, but figuring out if you've
done it right is a lot more difficult on a frequency where you can't
transmit.  If this were a transmitting antenna the high SWR would have
been a big tip-off that I had a problem with my design somewhere. ;)

> I'd try a direct feed into the coax, without the balun, and see what
> happens, or a folded dipole.

I've actually got a folded dipole, but it's cut for the FM band and
performance on TV channel 9 is pretty abysmal.  Part of the problem, I
think, is it's the traditional sort with a twin-lead feedline, and the
twin-lead seems to pick up a lot of interference from the computer.  I
also find that, even when I'm only dealing with a six foot length, keeping
twin-lead away from other conducting objects is quite tricky.