Very Distant TV stations and Antennas

[barry martin]

A.T.:

A > I was wondering if it would be possible to get an antenna that would A > pick up a network station in a town about 140 miles from the A > transmitter. This is also in a mountainous area of Virginia. The rest A > of the channels would be arriving from a town about 50 miles to the A > north. I am trying to set up an antenna to get the networks and not A > have to get cable. Would it even be remotely possible to recieve such A > a signal? Thanks in advnace.

Maybe, maybe not. You will need a high-gain antenna pointed in the direction of the transmitter site. Note: the transmitter site is not necessarily "anywhere near" the studios. Locally KWQC-TV/Channel 6 has studios in Davenport, IA, with the transmitter at the antenna farm here in Bettendorf, IA, about 10 miles away. OTOH KLJB-TV/Ch 17 also has their studios in Davenport but their transmitter is in Orion, IL (yes, different state), about 25 miles away. The FCC website has this type of infornation.

You might want to look into a Beverage Antenna, which is primarily for Ham use but has been adapted for other bands. Good news it is rather cheap to build and is very sensitive. Bad news is mountains or other tall structures between you and the transmitter are going to block the signal no matter what kind of antenna you use.

- ¯ barry.martinþATþthesafebbs.zeppole.com ®

• Keep Using My Name in Vain And I'll Make Rush Hour Longer - God

[David Martel]

Greg,

When converting math into English sometimes the words aren't enough. "the horizon in nautical miles is the square root of 2 times the antenna height in feet.140 sm is about 122 nm." Consider that 122= 1.414X fills the bill but so does 122=(2X)**(1/2). The second equation gives Mr. Plummer's height. I do not vouch for the correctness of the second equation since I don't know this field.

Dave M.

[Jim Laumann]

Seems to me that VHF signals are line-of-sight. That being the case, if there is a mountain in the way, my guess is nothing will help. Not sure about UHF signals. If there is no mountain, etc, then an antenna on a rotor and a amplifer might help, although I think 140 miles is really pushing it.

Jim

[Tony Hwang]

Hi, Radio signal LOS is not equal to visual LOS. It's longer. Mountain in the middle? You can still catch stray, scattered signal by experiment. The higher antenna is the better is not a rule of thumb. Some times you have to aim antenna at wrong direction. Tony, VE6CGX

[William W. Plummer]

d[nm] = sqrt(2 * h[ft])

d[nm] = d[sm]* 5280 / 6080

122 = 140 * 5280 / 6080

from above, d**2 = 2 * h or, h = d**2 / 2

For d=122, you need a 7442 foot tower to have line-of-sight to the horizon. But the Earth's curvature could peak halfway between the sender and the receiver. So, with no diffraction or other effects, you might get by with an 1861 foot tower.

BTW, here's derivation of the "radar range approximation". Draw a circle of radius R with center E. This is the Earth. Draw a radius and label it S (for sender). Where S meets the circle is the horizon. Draw a second Radius and label it T (for tower). Extend T out beyond the circle by h (tower height). Draw the tangent from T (tower) to S (sender). There is a right angle at S between the tangent and the radius by definition. R+h is the hypotenuse of the right triangle. The length of the tangent is our d, distance to the horizon from the tower.

By Pythagorus, (R+h)**2 = R**2 + d**2 . We need to get every thing into feet, starting with d in nautical miles.

(6080*R + h)**2 = (6080*R)**2 + (6080*d)**2 (6080*R)**2 + 2*6080*R*h + h**2 = (6080*R)**2 + (6080*d)**2

Now, h**2 is very small compared to the other terms and can be dropped. (6080*R)**2 + 2*6080*R*h = (6080*R)**2 + (6080*d)**2

Divide by 6080**2

R**2 + 2*R*h/6080 = R**2 + d**2

Subtract R**2 from both sides

2*R*h/6080 = d**2

Now approximate the radius of the Earth R as 6080 nautical miles,

2*h = d**2

or, d = sqrt(2*h).

[Childfree Scott]

You might want to look into how far a digital TV signal can go, I think they might work better.

[James Nipper]

I can't see digital/non-digitial having anthing to do with it. TV signals are RF, whether the modulation is digital or not.

However, not being an expert, I could be wrong.

--James---

[Chet Hayes]

I agree with the previous advice as to not investing a lot of money until you figure out how you're going to transition to digital, which is under a FCC mandate to happen in the next few years. I would think this date will get pushed out, but you should at least factor in the transition to digital. In your case, it may offer some compelling advantages, as digital doesn't have issues with snow, ghosting, etc.

I'd find where the digital transmitters are located for your area. A good place to start is

[clifto]

I'm no expert on digital either, but I do recall a newspaper article a while back, from the early days of digital in Chicago; people three miles from the transmitting antennas were having a great deal of trouble getting any usable signal. I get the distinct impression that digital needs a MUCH cleaner signal than analog.

[Greg]

Dropped "bits" in analog is just snow. Dropped bits in digital, beyond what ECC can reconstruct = garbage.

[Bob in CT]

There are people receiving signals at over 60 miles (both digital and analog). See:

Then any of the HDTV forums.

[Terry]

"Bob in CT" wrote in message news: [e-mail]...

I agree; our experience with both analog and digital inspires this comment which generally agrees with the "MUCH cleaner signal" requirement. Without getting into too much detail of the different technologies to any extent I offer this; TV, especially digital has got 'better quality' over the years since it was first introduced as simple black and white, non stereo etc. So the signal now transmits more bits of information, colour, five channel sound, program schedules, text of the voice and other information! Also there is a basic difference in the nature of digital versus analog signal modulation. The simplest radio transmission of all was the dot/dash (morse Code). All that was needed was to able to 'hear' the transmission going on and just a little bit.. Even with severe noise; noise that perhaps could be stronger than the radio signal itself, it was only necessary to detect the slight change in order to be able to read the message! Very slow limited information but could often be the best or method of last resort! Next came AM (amplitude modulation) or analog, where the signal strength is modulated up and down in time with speech music or picture. Again even with noise as long as it is possible to 'hear' the variation it is usually possible to read the signal. When TV was introduced analog was used; noise due to a weak signal or otherwise can interfere with analog TV and may cause everything from a hissing noise, slipping or rolling of a TV picture or 'snow' on the picture. But in many cases as long as the picture can resynchronize itself fairly quickly the human eye and ear can tolerate the slight interruption. Airlines still use AM modulation for some frequencies because it is still considered that there will be a better chance of hearing a weak or interfered with emergency signal from a flying or downed aircraft! FM, frequency modulation was introduced especially for the sound part of TV and also for 'FM' stations. Better quality but using much more bandwidth and it has gained a reputation for 'When it works well the quality is good; very good, allowing stereo and other high quality sound transmission etc". FM also used for many VHF police, taxi and military radios systems with the channels packed much closer together than TV. Finally digital, where the signal is sort of turned on and off many millions of times per second, works very well and allows a lot of information to be transmitted provided there is good bandwidth (bandwidth has to do with speed of transmission available that's why you can't receive a TV programme over a telephone dial up on the internet!). This provided the signal is not interfered which means good clear signal from the digital transmitting TV station or from a satellite. When all the digits are received the TV receiver reconstructs the picture and sound etc. perfectly. However if digits are lost or interfered (due to noise or weak signal or interference) the receiver lacks the information to reconstruct the picture. We also have digital satellite and it very frustrating when the screen breaks up into a series of meaningless rectangles! Interference with the digital signal sometimes makes loud noises on the sound! Heavy rain with a certain size of rain drops causes more trouble with our received digital signal than does snow! Getting a clear signal path between you and various TV stations which may be in different directions from your location is important. Also your TV antenna has to cope with several different frequency channels; so most TV antenna are a compromise! The biggest current issue that is IMO worth mentioning to posters is 'interference'; it appears that the profusion of electrical devices we use today, everything from a Christmas Tree light flasher, microwave oven, light dimmer switches, our personal computers, hair dryers/shavers, blenders etc. etc are not manufactured or regulated to standards by the FCC (or other regulatory authorities in other countries) so they do emit interference or radio energy, which they should not? The most current of these is some trials of sending digital and internet signals over the power lines; commonly called BPL. BPL trials in a number of countries have been cut short because of interference with critical services such as ambulance, police and aircraft to ground communications! The problem with BPL being that the overhead wires are carrying not only the electrical energy they were designed for, which doesn't radiate to any great extent. But for these other radio/digital signals; the overhead wires are in effect a very large and very extensive transmitting antenna! So if you get 'interference' complain to your political representative for proper regulatory enforcement of electrical/radio standards! If you have a weak signal, well that's what you have to work on! Better antenna for that channel, pointing the right way (remove any hills or skyscrapers that are in the way!), don't live under a landing flight path or with a busy highway with metal vehicles whizzing by right in the sight line between you and the TV station and you should be OK analog or digital. Good luck.