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HDTV Receiving Antennas

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Page bread crumbs: Welcome to ke3vin.org! - My Public Technical Notes - Hardware - Radio - Broadcast - HDTV - HDTV Receiving Antennas

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Some notes:

http://www.avsforum.com/avs-vb/showthread.php?t=381623

Still under construction - please check back

I am not an expert on antenna making but I am on many lists, read a lot on the subject, have many reference materials and most pertinent I have experimented with UHF quite a bit for my own radio systems and monitoring.

So with that in mind here is what I recommend.

Why bother with OTA signal reception at all?

Several reasons:

  • First of all expense. Many are simply tired of paying the cable company $40-100 a month for 170+ channels of unwanted programming. This is the main reason friends of mine express in wanting to do this.
  • Second of course you live where this is no cable service. Of course there nearly always is satellite service available to you in terrestrial United States and North America. But then again see the next bullet.
  • Third programming. Perhaps the channel you wish to watch is not carried by your cable or satellite provider as is often the case with religious and specialty programming.
  • Finally OTA reception is (currently) actually considered the highest quality high definition currently available to the consumer. Both Cable and satellite high definition transmissions are encoded (modulated) with MPEG-2. However worse in the case of cable as it stands now often is compressed in the 6 Mhz channel space at a 2-3 ratio. Many consider the quality of broadcast to be superior however frankly my research into the specifications I don't see the difference and doubt most could tell. Broadcast digital television is uncompressed but still MPEG-2 encoded and assuming a clean reception, no artifacts, etc. provides a technically superior image or so they say. Personally I think the real need for OTA is that today cable companies transmit to your box in analog QAM mode. Soon that will change to digital which will render older so-called "cable ready" (note: I am not talking about the newer DCR sets) sets useless. You will either need a (cable or broadcast) converter box.

Some background: Currently HDTV broadcast is modulated with 8VSB using MPEG-2 encoding via ATSC Standard whereas HDTV cable broadcasting is modulated with QAM using MPEG-2 or MPEG-4 encoding via DVB-C standard.

The usual difference however between cable and broadcast is not really the compression since in digital a signal is all intelligence but rather varying definitions, formats and resolutions. All of which is perfectly legal in the DVB-C standard.

Signal reception (in Central Florida).

Know that you WILL LIKELY HAVE TO INSTALL AN OUTSIDE ANTENNA. Get used to that fact. You may be fortunate enough to receive some of the HDTV signals indoors but I highly doubt you will receive them all. If inside reception is working like you want great but if not read on. Like the tire ad used to say "Antennas ain't pretty!". And as I like to say pretty antennas (usually) ain't good. Believe me I am married, have heard all the complaints and unfortunately live in a city that has rules about such things. By the way it wasn't a city when I moved here but I got voted down and yes I agree if your a ham or radio enthusiast stay away from such places although I admit it's getting harder to do that each day. Fortunately I don't live in a "CC&R". You should know that the FCC has your back (kind of) and that there are regulations ("OTARD") allowing your right to receive HDTV signals despite deed and covenant restrictions. Section 207 of 1996 Telecommunications Act says <i>"Any restriction, including but not limited to any state or local law or regulation, including zoning, land-use, or building regulation, or any private covenant, homeowners' association rule or similar restriction on property within the exclusive use or control of the antenna user where the user has a direct or indirect ownership interest in the property, that impairs the installation, maintenance, or use of:... (3) an antenna that is designed to receive television broadcast signals, ... is prohibited, to the extent it so impairs, subject to paragraph (b). For purposes of this rule, a law, regulation or restriction impairs installation, maintenance or use of an antenna if it: (1) unreasonably delays or prevents installation, maintenance or use, (2) unreasonably increases the cost of installation, maintenance or use, or (3) precludes reception of an acceptable quality signal. No civil, criminal, administrative, or other legal action of any kind shall be taken to enforce any restriction or regulation prohibited by this rule except pursuant to paragraph (c) or (d)."</i>. You should also know fighting for your rights can be exhausting and very expensive! And some times in the end you lose. Your mileage may vary but consider these things when you give up cable. Be prepared to install two antennas and two twin leads. In Central Florida almost all but three of the Digital television stations are transmitting from the Bithlo, FL tower complex at Richland Tower Complex. WESH-DT is the one lone hold out who is transmitting near me at Orange City, FL and is also on VHF (DTV Ch. 11 - PSIP Ch. 2.1 and (WESH-DT Weather Plus PSIP 2.2)). For this reason you will need a seperate VHF antenna pointed at Orange City. Refer to http://www.tvfool.com for signal locater.

The report will look something like this:

<img src="">

Since UHF signals are highly directional to begin with and the fact that digital requires a much higher capture than analog does this presents an even greater challenge than before to increase the signal to the set. This also means you may vary well have to have two or more antennas pointing at the different antennas or you may need a rotor. The problem with rotors other than the need to run more wire and the expense is that twin lead does not like to bent or pulled back and forth and will fail more rapidly that way. Already it only has a shelf life in heat soaked Florida of about five years as it is. So you will have to weigh this decision carefully.

Feed line.

Loss at UHF frequencies in feed line is considerable. So unless you are connecting to the back of the set and since we are making open air dipoles essentially I recommend using good quality 300 ohm twin lead like the good old days of aerial antennas. And not the cheap stuff at Radio Shack (particularly catalog #15-1175) but rather good quality foam filled low loss such as is available mail order at. 300 ohm is the proper match for a dipole not 75 ohms like cable companies use for coax. If you use coax from the dipole you will have to use a trans-match like similiar. The problem with twin lead is that it's influenced a lot by things touching it, or even very near to it. It can't be buried, and it can't be tied to a cable or anything metallic for long overhead runs. Keep it at least 4-6 inches away from any metal object, including gutters and pipes by using "stand-off" devices every three feet. Twin lead can be tied to a rope made of something that doesn't absorb water, like polypropylene. But when it rains or worse, when it snows or sleets it can become very lossy. For this reason I recommend running it through PVC pipe say 1/2 inch or so (the quality does not matter so much as it is fairly sturdy against winds and is supported to the structure it is running along). Make sure you TEST THE RUN FIRST BEFORE YOU MAKE IT PERMANENT! Flat-ribbon twin lead, shielded twin lead and solid-core coaxial cable don't work well for UHF. Lead-in lines deteriorate over time. Lead-in lines over five years old (or less depending on environmental conditions) should be replaced with new cables. However since the loss is so great in a transmatch device I still recommend twin lead over coax as a general rule for TV reception. Good condition 300 ohm twin lead actually has less UHF attenuation/ft than most coax. And match is very important! The problem becomes matching at the set or the converter box. Since 300 ohm has gone the way of the dinosaur I have not seen native connections for it in HDTV sets. On top of that it is likely you have more than one television set in your house so a distribution system may be in order. More on that later.

Impedance matching and the antenna.

Ok since we are talking match how long should the antenna be? My belief is the material is not as important on receive only antennas as it is on a transmitting antennas (velocity factor, etc..) however it is still important to match the antenna to the receiver. There is a popular video on Youtube.com that shows...

Distribution.

http://www.warrenelectronics.com/antennas/winegard_amps.htm

Signal, interference and noise

There is a reason I use cable. I can afford it and I live in a noise rich environment. On top of that I am sitting in the shadow for WESH.

Links for further research:

http://www.dtv.gov/

http://www.antennaweb.org

http://www.avsforum.com - particularly the HDTV Technical Forum

http://www.tvtower.com

http://en.wikipedia.org/wiki/ATSC_Standards

http://www.warrenelectronics.com - Makes good HDTV equipment like amps and antennas

http://forums.solidsignal.com/

http://www.keohi.com/keohihdtv/index.htm

http://www.fcc.gov/telecom.html - Telecommunications Act of 1996

http://www.hdtvantennalabs.com

http://www.engadgethd.com/

http://hdtvtalks.com/

http://forum.videohelp.com/

http://www.hdtvmagazine.com

http://www.tvtechnology.com/

http://www.avsforum.com/avs-vb/showthread.php?t=546066

http://www.tvtechnology.com/pages/s.0082/t.14400.html

http://www.hdtvsolutions.com/HDTV_antennas.htm

http://www.hdtvprimer.com/ANTENNAS/comparing.html

http://www.orlandodigital.tv/

http://www.transmitter.com/ - Doug Lung's RF Report

http://www.highdefforum.com

http://www.tvfool.com/


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Page last modified on September 30, 2009, at 08:36 AM EST