Building TV Antenna - length chart needed

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.

Reply to
jamesw
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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 c hannel 8 still show up as channel 8, but in actual practice the station mov ed 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 tran smits. So google for tv location and frequency. When you can say exactly w hat frequency you are trying to receive, then we can be of more help.

Dan

Reply to
dcaster

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.

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.

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---===

Reply to
jamesw

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 trie d) 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).

s that you want to receive. When the conversion to digital signals occurre d, 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 m oved 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 conve rters, 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 inf ormation in those places. used to be a good place to start.

Reply to
whit3rd

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

Reply to
gregz

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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!

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.

Reply to
David Platt

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 meter s. 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 vacu um, so multiply the 65.62 by .95 and get 62.34 inches. And a half wave len gth is 31.17 inches. So that is the number you want for the horizontal len gth of each section of the antenna.

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

Dan

Reply to
dcaster

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.

** 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.

** 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

Reply to
Phil Allison

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:

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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.]

Reply to
miso

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.

Reply to
Kevin McMurtrie

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
Reply to
Martin Brown

Thanks for the corrections.

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

Dan

Reply to
dcaster

Search "Gray Hoverman"

Reply to
Wond

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.

Reply to
upsidedown

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 snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Reply to
Mark Zenier

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

Reply to
Jon Elson

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