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Old 12-03-05, 07:20 AM   #1 (Print)
DrDon
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OVER-THE-AIR DIGITAL TELEVISION RECEPTION FAQ: New to OTA? Start here!


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Old 12-03-05, 07:24 AM   #2 (Print)
DrDon
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Do I Need a Special Antenna to receive HDTV?

No. Digital television signals occupy the same part of the television spectrum as analog television signals always have. Any antenna technology that worked for your trusty old television will work for digital. That said, digital is an all-or-nothing proposition. Where you may have been able to live with a fuzzy or ghosty signal on your analog TV, your HDTV may not be able to lock on. You may need more antenna. Depending on how far away from the towers you live, you may can get by with a pair of rabbit ears or you may need to invest in a rooftop antenna.

If you already have an old VHF/UHF rooftop antenna, it should work just fine. You may need to replace the coax running to it and/or add a pre-amp, depending on your specific situation. You can find out more by asking around in your local thread.

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Old 12-03-05, 07:27 AM   #3 (Print)
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How can I find out how much antenna I need?

Start by going to www.antennaweb.org and entering all of your information, or at least your zip code. You'll get a list of all of the available stations, analog and digital, the distance they are from you, the direction they are from you and - in the case of digital channels - the actual channel they broadcast on. The color code provided matches that on the boxes of various antennas. It is only a guide. You may need more or less antenna depending on a host of variables, including terrain, nearby structures and so forth.

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Old 12-03-05, 10:24 AM   #4 (Print)
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Do I need a rotator?

The antennaweb output will show if stations are widely separated in azimuth direction; if stations are more than 20 degrees compass direction apart and more than 30 miles away, in general, you will need to adjust your antenna. "High gain" antennas are very narrow in azimuth sensitivity. The half power points (3 db down) even down to 5 to 10 degrees in some cases for very high gain antennas.

If only two directions are of interest, it is possible to "gang" two antennas in different directions but with a 3 db loss and with the possibility of inteference.

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Old 12-03-05, 03:08 PM   #5 (Print)
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What about grounding an antenna?

Be sure to check your local building codes as these can vary from place to place. Generally though, good information is available at the following:

http://www.mikeholt.com/documents/g...d/satellite.doc

http://archive2.avsforum.com/avs-vb...667#post3618667

AVSforum member Signal posted the following helpful sites. Dish and antenna masts have the same grounding requirements.


National Electrical Code - Search for "dish" http://forums.nfpa.org:8081/necfaq/necsrch.htm

The information there also applies to antenna grounding. In the 2002 code update, if a water pipe is used, it must be all metal and connected to the electrical panel within 5ft of where the pipe enters the building. The connection to the pipe from the lightning arrestor/ground block and from the antenna/dish mast must also be within 5ft of the pipe's entry.


Preventing Damage Due to Ground Potential Difference
http://www.cinergy.com/surge/ttip08.htm

PSIHQ - Grounding Requirements
http://www.psihq.com/iread/strpgrnd.htm


Probably the most important parts of grounding are to ground the antenna mast and to bond any separate grounding rods to the main building ground. These are safety issues.

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Old 12-03-05, 05:17 PM   #6 (Print)
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Will OTA Broadcasts be UHF after analog shut off?

VHF and UHF Channels 2-51 are to be used for OTA DTV/HD broadcasting after analog shut off. Current UHF TV channels 52~69 are being reallocated for other uses.

However, the suitability of Lo-VHF channels 2-6 for DTV is currently in question and it may turn out to be the case that very few stations will end up on channel 2-6 after analog shut off.

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Old 12-03-05, 05:35 PM   #7 (Print)
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What are the VHF channels?

There are two bands for OTA VHF television channels :

VHF-LO = Channel 2-6 = 54-88MHZ

VHF-HI = Channel 7-13 = 174-216MHZ

Typical outdoor VHF/UHF combo antennas are designed for reception of all TV channels, including VHF Channel 2-13 and usually are also designed for FM broadcast band(88~108MHZ) reception. The longest elements(rods) on the antenna are for reception of VHF-LO TV channels+FM, as the lower the frequency, the longer the wavelength.

There are also VHF/FM "broadband" antennas available designed for reception of VHF TV channels 2-13 and FM, as well as antennas designed for VHF-LO band only, and for VHF-HI band only.

"Rabbit Ears" are currently the most effective VHF indoor settop antenna available.

Note that when seperate VHF/UHF antennas are used, a VHF/UHF joiner is required to combine the antennas if the use of a single feedline is desired.

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Old 12-03-05, 05:41 PM   #8 (Print)
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What are the UHF channels?

Current UHF TV band :

Channel 14-69 = 470-806 MHZ

Post-transistion UHF TV band(After analog shut off) :

Channel 14-51 = 470-698MHZ

Note that Channel 37(608~614MHZ) is not used for TV broadcasting, as it is allocated for Radio Astronomy.

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Old 12-03-05, 06:48 PM   #9 (Print)
richard korsgren
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What's better: more antenna or a pre-amp?

Thru years with FM and VHF, I have found that using a bigger antenna and getting more height on same is much better than a pre-amp. From my experience, a pre-amp helps to hold onto the signal you have at the antenna head but does not magically bring in a much stronger signal. In many cases, a rotator comes in very handy to direct the antenna right at the incoming signal. (more)

Pre-amps do more than overcome line loss, however:
Quote:
Originally Posted by NightHawk
STB's and receivers are not designed with maximum sensitivity in mind. Sensitivity is determined by system noise figure and the average STB is estimated to have a 7 dB noise figure. The better ones today may achieve 5 dB. Add to those numbers a 2 to 4 dB dB cable loss. A properly installed, mast-mounted pre-amp can set the system noise figure to equal the NF of the pre-amp and almost completely negate not only the cable loss but the relatively poor NF of the STB. Instead of of a system NF of 9 to 13 dB we can have with very little work a system NF 2.5 dB. This represents a very substantial advantage to the consumer living 50 miles from a half-power DTV transmitter. While I agree the best place to start for those folks is the highest gain antenna possible, a pre-amp is a legitimate next step for long-range reception regardless of cable loss.


Televes and Winegard and Channel Master all make very good antennas that last a long time. I have a Televes antenna and it looks very handsome as well and very well built. Always buy a little more antenna than you think you need. That extra will come in handy in bad weather. It can not hurt! Happy viewing and listening. By the way, a good place to find out about antennas and to buy them is at 'stark electronics'.

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Old 12-03-05, 06:58 PM   #10 (Print)
richard korsgren
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What is "multipath?"

Multipath is a signal taking different routes to arrive at your location. The main signal comes directly from the television station's transmitter to your antenna. But that signal may also bounce off of a nearby building or an airplane flying overhead. That bounced signal arrives at your antenna a split second later. With analog TV, this results in a "ghost;" a second, faint, image to the right of the main image. In digital television, receivers are designed to reject some multipath signals, but strong ones can wreck the signal enough that your tuner can't decode the digital signal. One sign of a digital multipath problem is a receiver that shows full signal strength, but acts as if it's barely getting any.

Directional antennas, like the ones common to rooftops, are designed to reject bounced signals. And some receivers are better at rejecting multipath than others.

A rooftop antenna should be grounded properly and the connections to be weatherproofed as well. (Attic antennas are not required to be grounded). The wire carrying the signal should be checked, maybe, yearly to see that all connections are sound and tight.

Attic antennas may work if the transmitters are no more than 15/20 miles away. But the attic, itself, may cause more multipath. (Your mileage may vary: some AVS Members have reported solid reception at farther distances using attic antennas) Trial and error is the best thing here. Each installation is different. A clean line of sight is important to the transmitters, of course. UHF antennas work for UHF stations and VHF antennas work for VHF stations. In some areas, you may need a combo antenna since some digital stations in those areas may be on VHF frequencies.

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Old 12-03-05, 11:32 PM   #11 (Print)
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Is a station's digital signal transmitted on the same channel as its analog signal?

No. Stations have been assigned a separate channel for their digital broadcasts. Each TV station has two transmitters and two antennas. One for analog and one for digital.

The actual channel number corresponds directly to a 6MHZ wide range of frequencies that is used by the signal. It is also the channel number referred to in the "Frequency Assignment" column in the results for your location from www.antennaweb.org.

It is sometimes important to know the actual channels for your local digital stations. Two of those reasons are :

#1). So you know whether to use a UHF, VHF or a combination of VHF/UHF antenna(s).

#2). In order to "scan in" an individual station so your receiver can use it, some receivers require you to input the actual channel number. Some receivers will also allow you to tune directly to the "actual" channel via direct access tuning to access the programming, either via a Major channel number, or a major/minor channel number combination, such as "28.3". Note that the minor channel x.3 in this case reffers to a MPEG2 program stream number.

With analog OTA reception, The "actual channel number" for any given analog station is what we are used to directly tuning to. For example, WNBC-TV analog in New York, NY transmits on VHF channel 4(66~72MHZ), and OTA viewers in NYC area tune their analog TV directly to channel 4 to receive them.

With digital OTA reception, WNBC-DT(digital) New York, NY currently actually transmits on UHF channel 28(554~560MHZ). Or, another way to say it would be WNBC-DT transmits on RF(Radio frequency) TV channel 28. But, with most receivers, viewers will need to tune to a virtual remapped channel 4.1, or 4.2 to watch programming from WNBC-DT. For more info, see "9. If I'm tuning to ch 45 to watch HDTV, why does the display say 7.1?. "

Note that after analog shut off, some digital stations will be moving to a different channel than they are currently transmitting on. For example, at the current time, KABC-DT, Los Angeles, CA is broadcasting digitally on UHF channel 53, but will switch their digital transmissions to VHF channel 7 after the DTV transistion is complete and analog shut off occurs.

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Old 12-03-05, 11:39 PM   #12 (Print)
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If I'm tuning to ch 45 to watch HDTV, why does the display say 7.1 ?

Within their signal, digital stations send channel remapping info via something called "PSIP". PSIP stands for "program and system information protocol" -- see here for more info : http://www.psip.org/ . Note that stations can, and do send quite a bit more info besides virtual channel remapping info via PSIP, such as Time/date info as well as Electronic programming guide.

In most cases, the virtual "remapped channel" number is the channel you will see displayed on your TV, when you tune to a local digital/HD station, and in most cases is the channel you'll tune to in order to watch that station.

In most cases, in discussions on AVSforum the virtual, "remapped channel" number is usually what we use when we list digital station channel numbers, and is also what is referred to in the "channel" column in your results for your location at www.antennaweb.org.

Virtual channel remapping via PSIP allows stations to keep the channel branding which exists for their current, analog station even though the actual channel* the digital station is broadcasting on is different currently, or may be a different actual channel number after analog shut off occurs. It also allows viewers to use the same channel number for the digital station they are used to using for the analog station.

* - For more info See 8. Is a station's digital signal transmitted on the same channel as its analog signal?

An important thing to remember is that the "remapped channel" is a "virtual channel" and has nothing to do with the actual channel/frequency the digital station is broadcasting on. Therefore even though it may appear when you tune to say, channel 4.1 that you are tuning to a VHF channel, the station may actually be broadcasting on a UHF channel/frequency and the tuner in your receiver/set is actually "tuning" not to channel 4, but to the actual channel the station is broadcasting on, even though it displays "4.1" on the screen.

For example, WNBC-DT(digital) New York, NY remapped channel is 4, although WNBC-DT actually transmits on UHF channel 28(554~560 MHZ).

Also, with Digital TV, "remapped" channels are displayed in the following format :

[ X.x ] X = Major remapped virtual channel number, and x= minor remapped virtual channel number .

A station will have one major remapped channel number, and, with multicasting can run several different program services on several different minor channel numbers. For example, WNBC-DT New York has the following remapped virtual channels :

4.1 for NBC/NBC HD/WNBC programming
4.2 for NBC "weather Plus"

In most cases the remapped major channel number will be the same as the analog station's channel number. For example, WNBC-TV(analog) transmits on VHF channel 4(66~72MHZ), WNBC-DT(digital) remapped major channel number is also 4, even though the digital station actually transmits on UHF channel 28(554~560MHZ).

One problem with virtual channel remapping is that an OTA only DTV receiver must be getting a "good enough" signal to acheive a signal lock from the station in order to receive the PSIP information from the station in order for the channel remapping to be accomplished. So, in some cases it can be difficult, and cumbersome, to adjust the antenna for reception of different stations while only using the "autoscan" feature of the receiver to "find" stations in your area. However, luckily, most, if not all receivers do have the capability to allow the user to either :

#1).Tune manually directly to the channel the station is actually broadcasting on via "direct acess tuning".

#2). Access a "channel edit" screen that will allow you to manually select actual channel numbers for broadcast stations in your area so that the PSIP info from the station will be "saved" when you achieve a signal lock on the station of interest.

#3) Via a menu option, to specify the Actual channel number the station is broadcasting on in order to "scan in" the station so you can view the signal meter on the receiver while adjusting antenna accordingly, or an option that will allow you to add/scan in a number of "new" channels without deleting previously "scanned in" channels.

It is often necessary to have these options not only for adjusting your "rabbit ear" antenna, but also so you will be able to "scan in" stations in different directions from your location given for example, the use of a directional antenna with rotor.

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Old 12-09-05, 09:48 PM   #13 (Print)
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Are there other sites I can go to to learn more?

Another tool for locating stations near you:
http://www.2150.com/broadcast/default.asp

Here's a page that discusses putting up antennas:
http://www.hdtvprimer.com/ISSUES/erecting_antenna.html

You can find general information on how antennas work and a glossary of terms here:
http://www.hdtvprimer.com/ANTENNAS/types.html

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Old 12-09-05, 10:37 PM   #14 (Print)
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Agree with Pat and of course it would have to be carefully worded. Don't want Doc to have to fly back from New Dehli to defend the Forum against a suit filed by high priced antenna lawyers.

And separately have to say it: Pat's 2nd cited link seriously undercuts mileage once in a while possible using attic antennas (with no qualifiers).
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Old 12-09-05, 11:47 PM   #15 (Print)
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How useful are antennas that clip on to a satellite dish and other antenna gizmos?

For analog reception, a lot of these antenna solutions work well, mostly because the signals they're designed to receive are largely VHF. Analog televisions are also very forgiving. A weak signal can look a little fuzzy. A slight ghost isn't that bothersome. But digital television is an all-or-nothing proposition. Instability in the signal can result in no picture at all. For this reason, dish clip-on antennas, "whole house wiring" antennas and other unconventional solutions may not work well with digital television. For more information, see section #2 here:

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

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Old 12-10-05, 11:13 AM   #16 (Print)
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The things that always bothered me about clip ons is they are relatively low gain folded dipoles which are size dependent for best frequency fit, and are bidirectional but cannot be aimed.

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Old 12-12-05, 10:38 AM   #17 (Print)
Wendell R. Breland
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For richard korsgren: In reference to your post #9. There can be situations where a antenna with a narrow beam patten will be desirable. This will usually entail a larger antenna with higher gain. If one has overload problems with a higher gain antenna the overload problem can be remedied by inserting a pad (6-12 dB) in the line.

PS - A compliment to the thread and all the post- Very Good Work

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Old 12-17-05, 07:32 AM   #18 (Print)
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It appears this FAQ is as complete as it's going to get, so I'm retitiling the thread.

Thanks, everyone, for your input!

Doc

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Old 12-18-05, 06:24 AM   #19 (Print)
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Is analog reception an indicator of how good digital reception will be?

It can be, but not always.

Some DTV stations are running at low, or reduced power, which makes it hard to tell since the analog station is running full blast. Some stations have their DTV antenna much lower on their tower or on a different tower altogether.

Still others have analog and digital channels at different ends of the band. An analog station at UHF22 may come in rock solid while its DTV signal at, say, UHF-62, won't.

Then there's the case of VHF analog stations with UHF digital counterparts. In those cases, analog reception is no guarantee of digital reception at all.

I'd go with a directional outdoor antenna, mounted as high as possible, and try a DTV tuner from a source that has a good return policy.

Bottom line is you have to try it to know.

(Originally posted by Ken H in another thread)

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Old 12-21-05, 09:18 AM   #20 (Print)
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My TV says it's HD Ready. Why can't I tune to any digital stations?

HD-Ready sets are just that - ready to receive HD programming from another source throught DVI, HDMI or component cables. They have no internal digital tuner needed to receive and decode OTA signals. An external Set-Top-Box is required.

If you're shopping for an HDTV that doesn't need a set-top box, look for "HD Built-in" or "built-in ATSC" tuner. ATSC is the digital standard used by over-the-air broadcasters. Don't trust the ads. Google the make and model number to see if the set you're interested has a built-in ATSC tuner. Better still, check the appropriate Displays forum right here on AVS.

Note that a "built-in NTSC" tuner only means that the set can receive standard analog television broadcasts.

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Old 12-21-05, 09:24 AM   #21 (Print)
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I was getting channel 'x' yesterday, but today, it's gone. What happened?

If you were receiving a station that you don't normally get, the atmospheric conditions that helped you get the signal yesterday have changed.

If the station is one you are supposed to get, there are a few possibilities.

1) The station is having a problem. Consult your local thread in the Local HDTV forum.

2) Your antenna is having a problem. This is unlikely if you're still getting other stations properly, but there are some failures that are frequency-dependent.

3) The station has changed their PSIP information. PSIP is a protocol that tells your receiver how the broadcaster is sending the data, as well as including program information. If this changes, some tuners won't rescan the PSIP information when you tune the channel, so they try to find data that isn't organized the same way. Sometimes tuning to the 'real' digital channel (the actual one they're broadcasting on digitally, not the virtual one idenified as x-1) corrects this. For other receivers, you need to do a complete channel rescan.
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Old 12-30-05, 11:22 AM   #22 (Print)
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I plugged my HDTV with built-in tuner into the cable and didn't get any HD. Why?

TVs and Set Top Boxes that exclusively tune over-the-air digital television won't receive HDTV over cable because cable systems use a different system. Broadcast stations transmit using ATSC protocols while cable systems transmit HDTV using QAM. Some tuners and televisions will get both ATSC and QAM. Check the specifications in your owner's manual to be sure. Satellite STBs will not receive QAM. Some cable systems encrypt some or all of their HDTV signals, so even QAM tuners won't display the channels. For that, you'd have to use the cable company's STB or a cablecard equipped STB or HDTV.

Conversely, you can't hook the cable company's STB up to an antenna to receive over-the-air HDTV for the same reason.

(clarifications welcome)

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Old 02-07-06, 09:43 PM   #23 (Print)
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Not sure if you want to add this but I wrote a short little article with pictures of an example.
http://www.hdbeat.com/2006/01/30/ota-hd-demystified/

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Old 03-08-06, 07:38 PM   #24 (Print)
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In addition to bdraw's excellent article, Here are a couple more links concerning #17 that some folks might want to look at(probably moreso the article in Sound+vision mag ) :

HDTV over the Air, from Sound and Vision Magazine(page 1 of 3)

I dunno about this one -- It keeps talking about "High definition" antennas<yikes!>, although otherwise it seems OK ...

An introduction to High Definition Off air antennas from about.com

4/3/06 Update :

Here is A blog of a TV antenna design engineer at Winegard. In addition to several other articles related to DTV transision, there are several excellent articles concerning OTA digital reception :

OTA HDTV Reception Q&A

Also, several excellent articles on OTA reception and antennas can be found in the "HDTV antennas and Reception" section in Right sidebar here :

http://www.hdtvexpert.com/

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Old 05-09-06, 09:24 AM   #25 (Print)
videobruce
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Better than AntennaWeb.............

Though the link was provided elsewhere, this is a complete 'HowTo':
I've done this many times for individuals that are having issues receiving stations or have no idea what/where they are or even if they are within range.

It's too bad AntennaWeb always gets referenced. It's no doubt for it's 'simplified' interface. I find it VERY lacking and with those 3rd grade color charts, I also feel that most that come to a forum as this are not your average 'joe sixpack' and can comprehend something better than AntennaWeb.

Just a few initial steps are all that is needed to have a far superior list for your local stations. It even includes Canada, where that 'other' site doesn't seem to know the country exists.

Step 1; Go here and enter your zip code;
http://www.census.gov/cgi-bin/gazetteer

Step 2; Click on the blue 'Map' link.

Step 3 (optional); This takes you to the 'Tiger Map Server' (it does go down once in a while). Click on the '+' magnifier and 'zoom' in on your location. You should get your latitude and longitude down to a couple of hundred feet (if you wish).

Step 4; Do a copy/paste of the latitude and longitude watching exactly what you copy. Include the '-' in the longitude with no spaces before either number and then go here;
http://www.2150.com/broadcast/default.asp

Step 5; Select how you want the search to configure by distance, by direction etc. Also choose the mileage you want to cover and if you want analog stations to be included.

step 6 (optional); To be really accrete you need to find the magnetic declination of you location here. A zip code should be sufficient;
http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp

Step 7; Click on "Compute Declination" and copy that number down in the space provided at the 2150 site (default is -13.25) and click on "Show Stations".

Step 8; If you are satisfied with the results you can 'save' this list as a bookmark by clicking on the "Bookmark this link to save this report" link which will bring up another window. This way all you have to do is refer back to the bookmark and all your data is there.

Special notes to interpert what you see;

Column 3; Channel, the first is the actual digital channel, the one in () is the orginal analog number.
Column 19; HAAT (Height Above Average Terrain) this is rarely the tower height since it takes into account the surronding terrain.
Column 11; The circle with the dot in the center is the transmitter location, NOT your location! Where that red line meets the outer circle is YOU!
Aim your antenna at the center.

The site will update on a regular basis. Hope this helps................

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Last edited by videobruce : 05-09-06 at 09:38 AM.
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