Electronics Forums > Re: How Can you Make a VHF TV Antenna for an Attic

# Re: How Can you Make a VHF TV Antenna for an Attic

Sal M. Onella
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Posts: n/a

 07-15-2009, 06:28 AM

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> 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'd like the answer to be YES, but it's NO.. If you wanted to make an
antenna for just one channel, I'd say yes. I already did it for some guy
who wanted a channel 2 antenna over a year ago.
>
> I've seen some instructions (mostly UHF or DTV) and some of them do
> calculations for wavelength (let's say 5 feet).

It's a multi-step process. You have to look up the channel frequency for a
TV channel. Then, you take the number 300 and divide it by the frequency.
The result is the wavelength. The elements are then cut for approximately a
half-wavelength. More details below, if you want 'em.

Multi-channel antennas have multiple elements, all differing lengths. If
you have one element, you can expect to receive one channel well and other
channels maybe but not as well. A single channel antenna can be made of TV
twinlead and attached to a piece of wood. It's called a "folded dipole."
More below.

> 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?

Nope. He's full of it to say that. The only thing that gets longer to make
a better antenna is the boom, the center long rod of a long antenna, and it
gets longer because additional elements are added to it to improve the
performance. However, you have to know how many, how long and where to put
them. That's why we study this stuff.

> Wire is cheap after all, and I only > want to crawl up there once.

Crawl up there once and bring a TV antenna with you ... a STORE-BOUGHT TV
antenna. Hang it flat from the rafters. A balun is a little matching
transformer with side-by-side wire connections on one side and a round
coaxial cable connection on the other side. Picture here:

www.summitsource.com/images/products/COTRAN.jpg

Most antennas have two screws for attaching one side of a balun. Connect
your coaxial cable to the other side.

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

The outline of many TV antennas, viewed from above or below, resembles the
outline of an arrowhead. That's it. The smaller elements are on the end
that's nearer to the TV station. The signal arrives perpendicular to the
alignment of the elements.
an antenna which illustrates the arrowhead concept. The stations are off to
the right side in this picture. I have no idea whether the antenna in the
picture is any good.

If you make a single element antenna, you align it perpendicular with the
arriving signal. These do work pretty well, by the way.
http://www.wfu.edu/~matthews/misc/dipole.html has some step-by-step
instructions for making a folded dipole with ordinary tools.

One last thing: It's not beyond the realm of possibility to make one folded
dipole attic antenna for Channel 6 and a second folded dipole attic antenna
for Channel 9. The Channel 9 antenna just MIGHT also handle 7 and 13 if
you're in a good reception area. You can cable both of them to the TV and
switch between them.

Sal

Rich Webb
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Posts: n/a

 07-15-2009, 12:15 PM
On Tue, 14 Jul 2009 23:28:21 -0700, "Sal M. Onella"
<(E-Mail Removed)> wrote:

>

[snippety snip some good info from Sal]

Also, to the OP, if you're interested in playing with this some, even
just to the point of seeing what some of the radiation/reception
patterns look like (goes-out signal strength is the same pattern as the
goes-in sensitivity, btw) hop over to http://home.ict.nl/~arivoors/ and
d/l a copy of Arie's version of the 4nec2 antenna modeling software.

There are example files that are similar to typical TV antennas, among
others. You can get a list of channel assignments versus frequency on
Wikipedia.

--
Rich Webb Norfolk, VA

Alan Douglas
Guest
Posts: n/a

 07-18-2009, 11:15 AM
>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).

There was an article in Electronics World in December 1967 by Harold
Pruett titled "Designs for Log-Periodic FM & TV antennas". He used two
lengths of hookup wire, attached to a wooden frame in a zigzag
pattern, and gives all the dimensions needed. I built one then and it
has worked fine ever since, though now there's nothing to receive in
this area so I've switched to a UHF-only antenna in the attic. I can
mail you xeroxes of the article. I'm adouglas (at) gis.net.

Alan

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