Building TV Antenna - length chart needed

[jam...@home.com]

I've been looking at numerous websites and videos for building digital
tv antennas. I live in the country and am a long distance from all
stations. (most are at least 50 miles). The plans for the antenna are
mostly for a single, double, or 4 pole bow tie. But they all have
different whisker lengths which is for different stations (vhf, lower
uhf, middle uhf, and high uhf). They have referred to an online chart
that shows the stations frequencies and the length of these whiskers
that are most suitable for that frequency. i'm not finding such a
chart.

I'm mostly looking to improve the upper VHF, channels 8 thru 10
(actual). I have one of those small RCA amplified antennas that are
meant to mount on a wall or on a mast. I have mine on a mast, made from
several lengths of 1-1/4" EMT conduit. It sits about 5 feet above the
highest part of my roof. I'm getting a good signal for stations located
between 15 to 50 (actual), but those other ones I mentioned above dont
come in very good, or not at all.

I just want to play around with some ofthese bow tie antennas made from
scrap wire and stuff, but so far, I only know that the whiskers need to
be longer for the low uhf and upper vhf channels. I'd like to make one
that is suitable for top gain for those channels 8 thru 10 (actual).

Thanks for all help.

[dca...@krl.org]

On Thursday, January 23, 2014 3:42:38 PM UTC-5, jam...@home.com wrote:

>
> I'm mostly looking to improve the upper VHF, channels 8 thru 10
>
> (actual).

> Thanks for all help.

The first thing you need to do is find out the frequencies of the stations that you want to receive. When the conversion to digital signals occurred, they tried to make it easy for the masses. So stations that say were on channel 8 still show up as channel 8, but in actual practice the station moved to say channel 34. So you want to find the actual frequencies.

Second the bow tie antennas are generally for uhf and not for vhf.

There are several web sites that will show the direction from your house to the tv stations and the virtual and actual frequency that the station transmits. So google for tv location and frequency. When you can say exactly what frequency you are trying to receive, then we can be of more help.

Dan

[jam...@home.com]

I only used the word ACTUAL at least three times in my posting. There
was a reason for that! I charted the whole thing on tvfool.com.
I also know the exact direction of the station from that website in
degrees from compass points.

ONCE AGAIN
They ARE the >>>===--- ACTUAL---===<<<< channel frequencies in use.

Channel 8 /IS/ on the channel 8 frequency.

This is not the case for all the channels around here though.

Lets begin with channel 8.
According to
http://en.wikipedia.org/wiki/North_American_television_frequencies
Ch 8 is 180 to 186mhz. Video and sound are different. I'm not sure
which to use. But that site has them all listed.

Therefore if i want to pickup ACTUAL ch 8 thru 10, I'm looking at 180
thru 198mhz.

[whit3rd]

On Thursday, January 23, 2014 1:25:39 PM UTC-8, dca...@krl.org wrote:
> On Thursday, January 23, 2014 3:42:38 PM UTC-5, jam...@home.com wrote:
>

> > I'm mostly looking to improve the upper VHF, channels 8 thru 10

Oops! The channel numbers haven't changed, but the frequencies
were heavily reallocated when the digital conversion began; it's a real
problem trying to find those frequencies from the channel number (I've tried)
and there have been (in Seattle at least) a half dozen frequency changes
announced by my Tivo (along with instructions to re-scan so the receiver
doesn't miss channels).

> The first thing you need to do is find out the frequencies of the stations that you want to receive. When the conversion to digital signals occurred, they tried to make it easy for the masses. So stations that say were on channel 8 still show up as channel 8, but in actual practice the station moved to say channel 34. So you want to find the actual frequencies.

Bingo! Maybe, if you seek in the menus of antenna-connected TVs and converters, one
will give out this info, in an up-to-date fashion. Which might change next month.

I tried FCC and local station's websites, and was unable to locate that information
in those places. <antennaweb.org> used to be a good place to start.

[gregz]

In pittsburgh, there is only one VHF channel. Channel 13. Kinda makes it
hard to use a single UHF antenna. Don't know why FCC mad them stay on 13 ,
when they were preparing to go UHF.

Bow tie's are wideband.

Greg

[David Platt]

In article <689243948412220314.18...@news.eternal-september.org>,

gregz <ze...@comcast.net> wrote:

>> I tried FCC and local station's websites, and was unable to locate
>that information
>> in those places. <antennaweb.org> used to be a good place to
>start.

www.rabbitears.info seems like a good place to start looking today.
It looks as if they're actually pulling data from an FCC database.
Try the "TV Query" feature, and ask for a detailed listing on all
stations in a given market and city... LOTS of information there,
including the transmitter location, power, antenna height, gain, and
directional pattern!

>
>In pittsburgh, there is only one VHF channel. Channel 13. Kinda makes it
>hard to use a single UHF antenna. Don't know why FCC mad them stay on 13 ,
>when they were preparing to go UHF.

From what I recall, the usual reason for this would be that there was
no UHF frequency to which they would be moved, and which would have
allowed them to retain their current customer-footprint coverage,
which would not have caused interference problems of one sort or
another for other stations in the area.

This sort of situation cropped up a fair bit in some of the more
crowded metro areas (especially on the east coast) where each large
city had a large number of stations. "Packing" all of the stations
into the available UHF channels wasn't a trivial challenge, since some
stations were moving up from VHF, and some had to move down from the
higher-frequency UHF channels which were being reclaimed from TV
allocation and transferred to public-service allocation.

[dca...@krl.org]

On Thursday, January 23, 2014 5:07:26 PM UTC-5, jam...@home.com wrote:



> I only used the word ACTUAL at least three times in my posting. There
>
> was a reason for that! I charted the whole thing on tvfool.com.
>
> I also know the exact direction of the station from that website in
>
> degrees from compass points.
>
>
>
> ONCE AGAIN
>
> They ARE the >>>===--- ACTUAL---===<<<< channel frequencies in use.
>
>
>
> Channel 8 /IS/ on the channel 8 frequency.
>
>
>
> This is not the case for all the channels around here though.
>
>
>
> Lets begin with channel 8.
>
> According to
>
> http://en.wikipedia.org/wiki/North_American_television_frequencies
>
> Ch 8 is 180 to 186mhz. Video and sound are different. I'm not sure
>
> which to use. But that site has them all listed.
>
>
>
> Therefore if i want to pickup ACTUAL ch 8 thru 10, I'm looking at 180
>
> thru 198mhz.

Okay the speed of light and radio waves is 300,000,000 meters / second.

So if you divide that by 180,000,000 You get the wave length is 1.667 meters.
Multiply that by 39.37 inches / meter and you have the wave length is 65.62 inches. The speed of a radio wave is slower in a conductor than in a vacuum, so multiply the 65.62 by .95 and get 62.34 inches. And a half wave length is 31.17 inches. So that is the number you want for the horizontal length of each section of the antenna.


If I have screwed anything up, somebody please correct me. I have not screwed arounud with antenna's for a long time.

Dan

[Phil Allison]

<dca...@krl.org>

Okay the speed of light and radio waves is 300,000,000 meters / second.

So if you divide that by 180,000,000 You get the wave length is 1.667
meters.
Multiply that by 39.37 inches / meter and you have the wave length is 65.62
inches.

The speed of a radio wave is slower in a conductor than in a vacuum,

** Not true.

The speed of a EM wave is slower in a * medium* like plastic insulation.

> so multiply the 65.62 by .95 and get 62.34 inches.

** Accounts for the "end effect" that makes all antennas seem a little
longer then the elements .

But a "bow tie" antenna is a odd ball with a larger effect that a straight
element.

>And a half wave length is 31.17 inches. So that is the number you want for
>the horizontal length of each section of the > antenna.

** But each arm of the "bow tie" is only half that.

The OP should try using arms of about 12 inches.

OR much better BUY a real antenna ( Yagi or log periodic) cut for the bands
he need and with high gain..



... Phil

[miso]

The only wideband antenna for your application is a log periodic. The ARRL
handbook has the designs. Unless you are good with welding, this isn't
trivial. The ones I've built were done with threaded Al rods, which means
you need to use a tap and die. [There are tricks to do the Al to Cu
interface.] You do this kind of work for antennas you can't buy, i.e. for
SIGINT. For TV, you buy the damn antenna. It is cheaper.

Now if you want to build an antenna for ONE channel, it will have to be a
folded dipole due to the TV bandwidth. The folded dipole is the driven
element. You need at least one reflector and one director. These are not too
difficult to make if you use brass rods and a wooden boom.

The deal is unless you know what you are doing, these outdoor antennas will
degrade faster than commercially made antennas. It is a waste of time.

If you really insist on this project, look at this website:
http://www.george-smart.co.uk/wiki/432MHz_Yagi
The site is kind of slow. I found it by doing an image search because 90% of
the designs on the internet are wrong. This is the right approach, though I
haven't checked his math. The driven element is a folded dipole for
bandwidth. The loop balun works well. The boom has to be wood. Metal boom
design changes the math a bit, and the modeling programs like NEC do not
work well with metal booms, so most yagi designs on the internet with metal
booms are fiction.

I have one of these scaled for the federal 400MHz band and it is awesome.
[Like I said, you go through this nonsense for things you can't buy.]

[Kevin McMurtrie]

In article <otu2e9h6hgk14rap6...@4ax.com>,

You can buy single channel yagi antennas if you're willing to buy as
many antennas as you want channels. Nothing is going to beat them.
They're simple so you can also find online calculators to make them.

Single band VHF-Hi Yagi antennas can be purchased from most major
manufacturers. They're extremely long but reasonably narrow. VHF-Lo
isn't used for commercial TV in urban areas of the US so they're
becoming more common.

Bow-tie arrays that do VHF and UHF have a misaligned mixer that forms a
weak dipole for VHF. Reviews haven't been kind of them.

If you have few neighbors, a very low noise amplifier on the mast will
serve you well.

[Martin Brown]

Indeed. Unless he has stations in several different directions the best
solution by far for marginal reception is a high gain directional aerial
high up and pointed at the transmitter. Yagi or log periodic depending
on the needed bandwidth. A masthead amplifier might help too.

You can make your own DIY yagi/log periodic but it is hard work.

UK has suffered some silly problems after digital switchover because the
Welsh stations are now powerful enough and omnidirectional transmitting
that they appear in a sidelobe of many high gain antennas in Manchester
(a major city). Certain manufacturers older sets like Panasonic are
stupid enough to place the first station found in the prime position
when they retune. The result is that because the lower frequency Welsh
stations are found first they occupy the main slots!
(this is really unhelpful as hardly anyone in Manchester speaks Welsh)

The approved fix is to unplug the aerial connector until the low
channels have been scanned! Telemenders charge good money for this!!

--
Regards,
Martin Brown

[dca...@krl.org]

On Thursday, January 23, 2014 11:18:49 PM UTC-5, Phil Allison wrote:




>
>
> But a "bow tie" antenna is a odd ball with a larger effect that a straight
>
> element.
>

>

> OR much better BUY a real antenna ( Yagi or log periodic) cut for the bands
>
> he need and with high gain..
>
> ... Phil

Thanks for the corrections.

Do you know of any website that has good information on bowtie antenna's?

Dan

[Wond]

Search "Gray Hoverman"

[upsid...@downunder.com]

On Thu, 23 Jan 2014 16:07:26 -0600, jam...@home.com wrote:

>Lets begin with channel 8.
>According to
>http://en.wikipedia.org/wiki/North_American_television_frequencies
>Ch 8 is 180 to 186mhz. Video and sound are different. I'm not sure
>which to use. But that site has them all listed.
>
>Therefore if i want to pickup ACTUAL ch 8 thru 10, I'm looking at 180
>thru 198mhz.

The 18 MHz is just 10 % relative bandwidth, so Yagi would be the best
choice (no need for log periodics). The bandwidth is not a problem at
least up to 7-10 elements, for longer Yagis, use thick tubing.

At VHF frequencies, antenna amplifiers are not needed to compensate
for downlead losses, but of course, if there are multiple receivers
connected through power splitters, some amplification between the
antenna and splitter may be required.

[Mark Zenier]

In article <e3e67282-224a-4ae9...@googlegroups.com>,

whit3rd <whi...@gmail.com> wrote:
>
>I tried FCC and local station's websites, and was unable to locate that
>information
>in those places.

<http://www.fcc.gov/encyclopedia/TV-query-broadcast-station-search>

There's a entry form for "Stations within a radius" where you put in
a longitude/latitude and a radius and it returns a choice of search
results with real channel, azimuth and distance, equivalent ERP,
licensee, etc. Near the bottom of the page.

There's also links to FM and AM band search pages, too.

Mark Zenier mze...@eskimo.com
Googleproofaddress(account:mzenier provider:eskimo domain:com)

[Jon Elson]

jam...@home.com wrote:

> I've been looking at numerous websites and videos for building digital
> tv antennas.

Well, this stuff isn't that critical. Once, while living about 90 miles
(as the crow flies) from home, I decided to see if I could pick up
a home-area FM radio station. I made a folded element out of coat
hanger wire and connected it to the 300 Ohm twin-lead. Then, I
made a director and reflector also from coat hanger wire, using
Yagi formulas in "Reference Data for Radio Engineers". I then
drilled small holes in a scrap of broom handle and slipped the director
and reflector thright the holes, and taped the folded element
in the middle. It worked AMAZINGLY well! The only thing that
messed it up was aircraft flying near where the beam was being
refracted by the atmosphere.

Jon