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Old July 16th 09, 07:28 AM posted to rec.video.cable-tv,sci.electronics.repair,rec.radio.amateur.antenna
Robert Macy Robert Macy is offline
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First recorded activity by RadioBanter: Jul 2009
Posts: 3
Default How Can you Make a VHF TV Antenna for an Attic

On Jul 14, 9:55*pm, wrote:
Hi - I need to receive VHF TV (channels 6,7,9,13) and would like to
make a super-duper antenna for inside my attic. *I would have thought
that I could easily find (simple) instructions on the internet but
can't. *Does anybody have a simple idea that just uses wire (wire
should be easy to attach in an attic).

I've seen some instructions (mostly UHF or DTV) and some of them do
calculations for wavelength (let's say 5 feet). *And then, with no
explanation, the guy just says "I made it 10 feet for better
reception". *So I ask, can I not then just use the entire length of my
attic for super-duper reception? *Wire is cheap after all, and I only
want to crawl up there once.

I don;t have a PhD in antenna making, so a lot of the instructions/
terms don't mean much to me (dipole, balun, etc). *I'm hoping for
instructions such as:
1. Cut a piece of 18gauge coppr wire 5 feet long
2. attach one end to a rafter.
3. solder the other end to the centre wire of the coax
4 insert tab A into slot B
etc
etc.

Also, I see instructions that say you should aim the antenna without
defining "aim". *Do you allign the wire in the direction of the
transmission antenna, or should the wire by perpendicular?

Thanks


Just saw this thread and some very good suggestions.

One thought. Unless your close to the TV Transmitters, stay away from
using wire as the antenna. There is a good reason antennas are made
of tubes, not wire. At high frequency, like television transmission
frequencies, the current creates a repulsion field that pushes the
current away from the center of the conductor. In other words, all
the current travels on the outside surface of the wire. Look up the
term, "skin depth". At frequencies as low as 20MHz, more than 99% of
the current will be within 3 mils of the surface. The only easy way
to lower the losses in the antenna is to use large diameter
conductors, but since the inside of the conductor carries no current,
you don't need metal there, so it is ok to use hollow tubes.

Antenna manufacturers save themselves money by lowering material costs
and shipping weight. They use hollow tubes. If you don't care about
weight or material cost, go ahead and use solid rods, 1/4 inch, or
even 3/8, but stay away from 18 Awg, way too small.

One other thing, nature abhors sharp edges, that's why bubbles are
round, so don't use square tubes or sharp bar stock either. Use
rounded tubes or rods. Even smoothing and polishing the surface
lowers the resistance. When you're done, passivate the surface of the
conductors to prevent corrosion over time. [meaning: paint the
antenna] Over time, corrosion will deteriorate your antenna's
performance. Rounded surfaces also means make your connections smooth
with nice transitions. As in, "if it looks good, it works good." You
can use aluminum if the lengths are continuous and/or you make
connections using constant mechanical pressure, like a "lots of teeth"
star washer that has bitten down through the insulating oxide layer
held with a bolt.

All in all, it seems a lot easier to buy a fringe field antenna and
put that in your attic. But if you do it yourself, hope you're
successful, document what you built, and share it here.

Robert