Re: Kind of simple question matching impedances/resistances on twin-lead

bill.sloman_at_ieee.org
Date: 02/22/05 

Date: 22 Feb 2005 02:03:52 -0800

Treeline wrote:
> <bill.sloman@ieee.org> wrote in message
> news:1108978930.272139.206430@l41g2000cwc.googlegroups.com...
> >
> > Treeline wrote:
> > > I cut in half a twin-lead antenna wire, typical 300 ohm wire.
> > >
> > > I inserted a Balun transformer on the first cut end to make it 75
> > ohms and connect it to an old TV.
> > >
> > > So far, so good.
> > >
> > > Then I got to thinking and that was bad. How can I reconnect that
> > twin-lead that I cut in half, in
> > > case I wanted to use the other, unused end? And still keep that
Balun
> > transformer on that end?
> >
> > <snip>
> >
> > This has to be a troll.
> >
> > -------
> > Bill Sloman, Nijmegen
>
>
> Why is this a troll?

My assumption was that the 300-ohm twin-lead antenna wire lead to an
antenna. If you cut it in half to produce an ostensibly useful unused
end, you would appear to be splitting it into two separate wires, both
leading to the antenna.

300 ohm antenna wire is intended to hook up to a loop antenna, which
happens to have an output impedance of 300 ohm. It sounds as if you
think that 300 ohm antenna wire is intended to be an antenna, which it
can be if the local signal is hgh enough .....

> In any case, I did a quick test and I would reckon doubling up the
> transformers results in a very marginal loss. I noticed one spec of
0.5 dB loss on parts like this,
> and that sounds reasonable without measuring.
>
> I'll bet if Newton came to you about an apple falling on his head,
you would say, heh, you'll a
> troll.

No, I'd ask him why he was fussing about gravity after having invented
a time machine ...

> Asking questions which may be obvious to others is not trolling
unless I already know the answers.
> Here I do not. I could find out the answers if I got my equipment out
of storage but it's snowing
> again and quite cold in that unheated place. And I really don't mess
much with antennas and TVs,
> hence asking here since TV appears to be ubiquitous for most.

You need to ask the question in a way that suggests that you might
understand the answer.

---------
Bill Sloman, Nijmegen

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