OTA Antennas

Introduction

There have been many questions about the OTA reception and with the TV industry moving to DTV there will be more and more. There is no better method of getting HDTV material to your HDTV than the signal from an OTA receiver.

 

When it comes to pulling in OTA signals it can pretty much be a hit and miss situation. In reverse order of importance:

The worse thing would be to have no antenna at all.

The next best thing would be to have an indoor antenna.

The best thing would be to have an outside antenna.

There is no getting around it, size and placement matters when it comes to an OTA antenna. The difference between an indoor antenna and an out door antenna is not double or triple, it is multifold. Unless there is a situation that prevent you from installing an outdoor antenna, that is what you should do.

 

Purpose

The purpose of this essay is to provide information that will allow one to be more informed when setting up an OTA antenna system rather than to recommend particular equipment.

 

HOA Regulations

Before we get into the subject from a technical standpoint of receiving a signal, there is a matter that needs to be discussed.

 

Many people think that their HOA covenants and restrictions prohibit the installation of outdoor antennas. And many HOA documents that were created before 1996 do have such prohibition provisions in them, but the Telecommunications Act of 1996 has made these provisions invalid. For more information see: Complete FCC Fact Sheet…

 

Being on a HOA board myself, I know from first hand experience that many people just read their deed restrictions (or covenants and restrictions) and think everything in them is enforceable. Well they are not in the case of satellite dishes for TV or internet reception or antennas for OTA TV reception. The Telecommunications Act of 1996 made antenna provision in HOA documents obsolete.

 

There are circumstances that will not allow for an outdoors antenna, such as condos and apartments where the outside exclusive use areas do not face the proper direction. Then there are other people who use the HOA as an excuse to try other indoor antennas, because they don’t want an outdoor antenna on their roof or are nervous about having to deal with their HOA. Some use the HOA excuse as a ploy to try to get someone to come up with some magical antenna. That is going to be fruitless. I would just say that none of that would change the type of antenna you will need. If one is stuck on having only indoor antennas, unless you are very near the transmitter, you will have to go through a trial and error method to find an antenna that will work and it is possible that a single indoor antenna will not work for all stations and you may not be able to receive all stations.

 

Physics

Receiving a RF signal is basically a matter of physics. RF signals have a wavelength that is a factor of the frequency the signal is broadcast on and the optimum length of an antenna element is one that is equal to this wavelength or a multiple of this wavelength. Since channel 2 starts at 54 Mhz with a wavelength of 6 meters, the next best element length of ½ wavelength is normally considered the optimum for antenna design. The ½ wavelength element is called a dipole antenna and as you can see it will still represent a pretty large antenna. For channel 2 the dipole length is 3 meters or 118.11 inches. Any other element size will reduce the signal level received.

 

All antenna designs are a series of compromises to be able to cover the entire TV broadcast range and the Channel Master Crossfire a antennas all are 110” wide with differing number of elements. The more elements the better chance there is to match more channels ½ wavelength, thus the stronger overall. Other techniques include making the elements form a V shape to reduce the overall width and resulting turning radius.

 

There is a direct correlation to antenna size and the signal received. Double the antenna size and double the signal. There are some techniques can slightly extend antenna area beyond its physical size and poor designed large antennas can effectively reduce its size, the fact remains that there is no substitute for size and a large antenna is going to give you a better signal than a small antenna.

 

Miles Rating

First of all I’m one of those people that think the miles rating given by the manufacturers is only useful for relative comparison between antennas offered by a given manufacturer. There is not any standard as to how these figures are derived and each manufacturer has their own method of determining their ratings. Bottom line trying to determine which antenna would be better between two different manufacturers is not possible, in my estimation.

 

Secondary Signals

Secondary signals, also called multipath, are those that have been reflected off of a large object, such as a large building, and arrive a short time later than the primary signal. If these reflections are strong enough, they can totally confuse the DTV receiver and you will get no signal as far as the receiver is concerned. Directional antennas have a front and a rear. The front is pointed toward the transmitter. Directional antennas have elements at the rear of the antenna to shield the active elements from these signals that come in from the rear of the antenna.

 

Outdoor Antennas

These are the larger antennas usually consisting of a boom with perpendicular elements of varying lengths to cover the frequency range required. For VHF this is from channel 2 at 54 Mhz to channel 13 at 210 Mhz with FM radio between channel 6 and channel 7. FM covers 88 to 108 Mhz. UHF channels start with channel 14 at 470 Mhz with each channel being an adder of 6 Mhz up to channel 69 at 794 Mhz.

 

Smaller antennas are available like the Channel Master Stealthtenna for urban areas that work very well, but if you are very far from the transmitters these loose their effectiveness very quickly.

 

Fringe Area Reception

There is not going to be any substitute for a large outdoor antenna if you live 50 miles plus from the transmitters. Next to the size of the antenna, the height is as important. The higher the better as there is more signal strength the higher you go. The reason is pretty simple. TV signals for the most part are line of sight signals and anything that is between the transmitter and your antenna will reduce the signal. This can be trees, buildings and even the ground itself. The higher the antenna is the more chance it has not had to go through some of the obstructions.

 

Amplifiers

There are two basic types of amplifiers, indoor and outdoor. Beyond that there are four specifications that are important. Gain in db, noise, output power and distortion. Gain is the amount of signal increase where 10 db is x10, 20 db is x100, 30db is x1000 and so forth. The noise figure should be a low number, the lower the better. The output power will be rated in dbmv and distortion is how faithful the output signal is to the input signal. Too high of an input signal to an amp can cause distortion and that is why if you are very close to the transmitters an amp is probably not called for. Some of the more expensive amps will have both gain control and a tilt compensator that allows the boost of the higher frequencies only to compensate for the fact that higher frequencies will suffer more loss in the coax than the lower frequencies.

 

Indoor amplifiers are used to boost the signal due to the use of splitters needed for inside the building. Typically these will be lower gain something on the order of 6 db or so. There are distribution amplifiers that have multiple outputs, building in the distribution splitters.

 

Outdoor amplifiers are meant to be located as near the antenna as is possible, ometimes built right into the antenna. These units will be furnished with a power injector that is mounted inside the building to feed the power for the amplifier into the down lead to be fed up to the antenna. Typical gain for this type of antenna is 15 db and up. T0o much gain can be as bad as no gain if it causes the connected device to overload.  You want a high gain - low noise amplifier in this application. I read somewhere that for every 30 feet of additional height you will get an additional 3db of gain, so an amplifier can make up for quite a bit of height.  Of course the higher the better.

 

Indoor Antennas

If an indoor antenna is a must, the best bet is to try different antennas until you find the best possible. Since you are dealing with a smaller antenna that is not big enough to cover the ½ wavelength of the HDTV signals, none are going to be optimum and they will be a compromise. Get the antenna from a store that will allow you to return it. I would also get a long RG6 cable so I could move the antenna about in the house.

 

Try different locations in the attic if you have an attic. If you must put antenna in the attic, you should bear in mind that objects near (within ½ wavelength) the antenna effectively become part of the antenna and will reduce its effectiveness. Many times when the signal has to penetrate radiant barriers, it will be close to non-existent.

 

If you don’t have an attic, try different places in the house or apartment. Also try different windows so the signal doesn’t have to go through foil on insulation or brick. Once you find the optimum location for the indoor antenna, then address how to get the wire to it. The chances that the antenna placement on top of your TV will be the best place is not likely. Partly due to the interference that will come from your TV and digital receivers themselves as well the probability that the signal has to pass through more walls. Computers and other digital processors will interfere with HDTV reception in many cases.

 

HDTV Antennas

There is not any difference between an analog TV antenna and a HDTV antenna. Many manufacturers have come out with so called "HDTV" antennas, but that is just a marketing ploy.  Most digital stations are in the UHF band with a few in the upper VHF band.  There are always exceptions to every rule with channel 2 in Chicago being a notable exception.  Because of the fact that most locations will have stations in the UHF and upper VHF bands an antenna like the Channel Master 4228 is a good all around antenna for HDTV use.

 

Bottom Line

If you seriously want good OTA reception there is no substitute for a big well made antenna mounted as high as is possible. Normally a single antenna will do the trick with a motorized rotator if stations are located in different directions. The alternative could be poor reception or cable.

 

Many people have asked for suggestions for deep fringe locations. A highdefforum member, tigerbangs, who is very knowledgeable suggests this:

OK, once again, for clarity: the deep-fringe perscription is as follows,

1 Channel Master 4228 UHF antenna
1 Wade-Delhi VIP-306 VHF antenna
1 Channel Master Titan 7777 preamp
1 Channel Master 9521a rotator
30′+ antenna height from the ground

install carefully, avoid bodily injury

Links

These websites contributed to the information presented:

http://www.kyes.com/antenna/antennadex.html

http://www.tvantenna.com/support/tutorials/uhf.html

 

Other Useful Links

These websites contain various information that you may require in the installation of your antenna:

 

www.antennaweb.org
Television Station Data

The definitive site for choosing installing an antenna.  Entering your address in the form (or just your zip if you prefer) will return a list of television stations you can be expected to receive.  Other valuable data including the color antenna suggested for each station, the compass orientation and distance for each station.  Selections to show all stations, analog stations or digital stations are available.  Start here.

 

http://www.2150.com/broadcast/default.asp
Broadcast Television Station Search
A great site for letting the reader know what stations are available to them in analog and/or digital. A bit more cumbersome to use than antennaweb.org in that you need to know your latitude and longitude, but far more useful for seeing digital stations beyond 35 miles. You can use the site http://www.lyngsat.com/tracker/america.html to get the approximate latitude and longitude of your location. Use any satellite selection to get to the US map.

 

http://www.channelmaster.com/pdf/AntInstallGuide.pdf
Antenna Installation Guide
This guide is often reprinted in other websites, but it remains the definitive how-to guide for installing an antenna. Very worthwhile!

 

http://www.hdtvmagazine.com/programming/broadcast.php
HDTV Magazine - Broadcast HDTV Programming
Digital stations listed on a market-by market basis: useful for locating stations in suburban towns and outlying areas not identified by an FCC search.

Buy from Amazon.com:
Terk Antennas
Winegard Antennas
Zenith Silver Sensor
Channelmaster 4228 UHF Antenna
Channelmaster 9521a Rotor
Channelmaster 7777 preamp
Another internet source for OTA antennas is TV Antenna Source operated by Denny Duplessis. Check out this helpful site and especially the Ask Denny pages.

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