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Old 14-Dec-2009, 12:11 AM   #1
herplace
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digital transition puzzle

http://www.tvfool.com/?option=com_wr...7d52650483fa0f
I'm baffled by the apparent smothering of all the other stations by NBC yet all emmanating from the same place. I'm not savvy about the actual differences that would cause this. They all used to come in analog with snow more or less. now NBC has the as advertised digital perfection and all the others are gone. How do I get around the NM spread? CBS has 13. something and NBC is like 0.something.
Thanks,
HP

Last edited by andy.s.lee; 14-Dec-2009 at 9:45 AM.
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Old 14-Dec-2009, 10:09 AM   #2
andy.s.lee
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Originally Posted by herplace View Post
I'm baffled by the apparent smothering of all the other stations by NBC yet all emmanating from the same place.

They all used to come in analog with snow more or less. now NBC has the as advertised digital perfection and all the others are gone. How do I get around the NM spread? CBS has 13. something and NBC is like 0.something.
Hi, and welcome. Thanks for the tvfool link.

It looks like all the channels in your area are relatively weak, which is what you'd expect from being about 58 miles away from most of the transmitters. I don't think it's a matter of NBC "smothering" any other channels, but merely a case of the other channels not coming in strong enough.

Having a spread of NM values over 20-30 dB is also not a problem. Your tuner should be able to deal with that much variation without breaking a sweat.

If you would characterize your analog channels as "snowy" before, it probably means that you're not getting enough signal to lock onto the digital channels now. Digital TV signals need to be pretty clean to be locked on to. It's almost an all-or-nothing situation. If your tuner has enough signal to lock on to, you end up with the pristine DTV picture. If you're below the minimum threshold, even by a little bit, you will probably get no picture at all (and get the message "no signal" on your TV).

Having lots of excess signal does not make the picture any sharper either. However, sometimes having a bit of extra signal "buffer" is good for preventing the signal from fading into and out of signal lock (due to moving trees, cars passing by, weather variations, and other random fluctuations).

If you are indeed just a little short on the required signal, it would help to know a few more details about your current setup:
  1. What kind of antenna are you using?
  2. Where is the antenna installed (attic? roof?) and which direction is it pointing?
  3. Do you have a pre-amp?
  4. Approximately how long is the cable from the antenna to your TV?
  5. Do you split the signal among multiple TVs?

Your answers will determine whether or not the best solution involves getting a better antenna, adding a pre-amp, or something else.

Best regards,
Andy
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Old 14-Dec-2009, 2:41 PM   #3
herplace
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Hi Andy,
Thanks for your reply! I hope not to waste your time with my lack of understanding.
I measured the stretch from the back of the one T.V. to the attic location of the old style outdoor roof antenna which I'm still not clear what to call. The distance is about 30' using thin coax. Never have thought of getting a pre-amp. That's a new concept to me and I'd like to know more about that! The antenna is what I think covers both UHF and VHF ranges. It's not huge but it spreads out horizontally at one end with thin aluminum tubes and then on the southwest side of the mounting mast the main boom has a smaller spread of aluminum fluted extensions in a tighter configuration. It pretty much gets in the way up there. The boom has a southwest/northeast orientation if I understand the pointing question right. The roof is slate but there is a metal ridge cap and there is no house wiring at the level of the antenna although there is some running along the floor. There are no power lines around this location either. Can you tell from the information regarding the broadcasters signals why only NBC comes in so well? Would a Pre-amp really give my T.V. more to work with?
One more detail: Back in the analog days I had three channels with snow on some more than others. Its hard to recall if NBC was the best back then. The attic antenna had a really old style flat wire running to the T.V. location. At one point I had some insulation installed and something got bumped up there and Fox never came in again. Actually all the channels disappeared until the antenna got re-set. At that point it was just NBC and CBS that remained and I think one of them came in a little better than before the insulation project. I'd be interested to get advice on how to really point the antenna correctly.
Thanks very much for your questions and comments!
I really appreciate your insight!
HP
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Old 14-Dec-2009, 6:32 PM   #4
andy.s.lee
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Quote:
Originally Posted by herplace View Post
I hope not to waste your time with my lack of understanding.
No problem at all! We're just trying to help.

Quote:
I measured the stretch from the back of the one T.V. to the attic location of the old style outdoor roof antenna which I'm still not clear what to call. The distance is about 30' using thin coax. Never have thought of getting a pre-amp. That's a new concept to me and I'd like to know more about that! The antenna is what I think covers both UHF and VHF ranges. It's not huge but it spreads out horizontally at one end with thin aluminum tubes and then on the southwest side of the mounting mast the main boom has a smaller spread of aluminum fluted extensions in a tighter configuration. It pretty much gets in the way up there.
Sounds like a typical small combo antenna. The long elements at the back are part of a log-periodic antenna that handles VHF channels, and the short elements at the front are part of a yagi antenna that handles UHF channels.

NBC (WNYT) has their main transmitter on channel 12 (VHF), but they also have construction permits for two low power repeater stations on channels 18 and 45 (both UHF). All three of these probably map to the same virtual channel number 13.1.

I wonder which of these three signals you are receiving. One way to test may be to manually enter the real channel number into your receiver. If, for example, you type in channel 12 and your receiver automatically jumps to 13.1, then it probably means you're getting the real channel 12 off the air. Similarly for channel 18 and 45, if they automatically take you to 13.1, then it means that your tuner is able to lock on to each of those respective real channel numbers and map it to 13.1.

This will tell us whether or not the VHF or UHF portions of your antenna are responsible for getting NBC for you.

The "thin" coax you speak of might be RG-59. If there's any visible markings on the outer jacket of the coax, it may indicate the cable type. It is more common these days to use the slightly thicker RG-6 coax because it has less loss over distance and has better shielding.



Quote:
The boom has a southwest/northeast orientation if I understand the pointing question right. The roof is slate but there is a metal ridge cap and there is no house wiring at the level of the antenna although there is some running along the floor. There are no power lines around this location either. Can you tell from the information regarding the broadcasters signals why only NBC comes in so well? Would a Pre-amp really give my T.V. more to work with?

One more detail: Back in the analog days I had three channels with snow on some more than others. Its hard to recall if NBC was the best back then. The attic antenna had a really old style flat wire running to the T.V. location. At one point I had some insulation installed and something got bumped up there and Fox never came in again. Actually all the channels disappeared until the antenna got re-set. At that point it was just NBC and CBS that remained and I think one of them came in a little better than before the insulation project. I'd be interested to get advice on how to really point the antenna correctly.
Most of your channels come from a cluster 58 miles away at azimuth 221 (on a map), which is 235 on a compass. Ideally, you would want the sweet spot of your antenna to point in this direction.

CBS (WRGB) is on channel 6, another VHF channel. If channels 13 (analog NBC channel) and 6 (analog CBS channel) were the only working channels before, then is sounds like you were relying on the VHF capabilities of your antenna.



It sounds like there are multiple steps you can try to improve your signal. Just thinking aloud, I'd consider the following:
  • Install an antenna on the roof instead of the attic. Having the antenna outside gives it more signal to work with, but you'll need to consider the trade-off with protection from the elements (ie. snow) and having to go up on the roof.
  • Upgrade to a better antenna. Your choices may be limited if you're cramped for space in your attic.
  • Replace the RG-59 (if that is indeed what you have) with RG-6. This will reduce line loss and perhaps improve resistance to interference (eg., microwave ovens, electrical wiring, etc.) that might be present.
  • Install a pre-amp near the antenna. This boosts the signal right after the antenna and overcomes the effect of line loss and splitters (if you have any) that come after the pre-amp. This effectively lets you keep as much of the signal integrity as possible right after the antenna.
  • Re-check the aim of the antenna to make sure it is optimal.



If I were to re-order these from what I think is easiest and cheapest to try first, I'd probably approach this as follows:
  1. Check the antenna aim and connections first. This doesn't cost anything and gives you a chance to inspect the antenna, all the connectors, and wiring for any obvious problems (broken/bent/cut/shorted/etc.). You'll also want to make sure that there are no metal objects near or in front of the antenna. Did your new attic insulation include any metal foil backing that might block signals?
  2. Replace the coax with RG-6 if what you currently have is RG-59. RG-6 is generally easy to find and not that expensive, although you need to be comfortable with making your own cables (cut to proper length and add connectors to the ends). If this reduces your line-losses a bit, it might help you pull in a few more channels.
  3. Install a pre-amp. This will overcome most of your line-losses and give your receiver a better signal to work with. It doesn't improve the raw performance of your antenna, but eliminating the line-losses can result in higher quality signal (SNR) at the receiver. The choice of pre-amp to buy depends on what kind of antenna you may or may not buy (see next step). BTW, the first choice that comes to mind right now is a Channel Master 7777. If you end up choosing an amp, be sure to find one with a low Noise Figure (NF) specification (3 dB or less is considered good) because this determines the quality of the signal coming out of the amp.
  4. Get a better antenna. If your old antenna is broken (maybe when the insulation was installed) or deteriorating, then it may be time for replacement anyway. If the old antenna is still in good shape, then there probably isn't a good reason to switch just yet. If you do choose to try a new antenna, it would help to understand the space constraints in your attic to know what will fit.
  5. To get the best possible signal, moving the antenna to the roof would be the next step. The signal is going to be better up there and you probably have the option of using a larger antenna (better performing) to make sure you're getting the strongest signals possible. However, snow and ice concerns might make this a non-option.

Best regards,
Andy

Last edited by andy.s.lee; 14-Dec-2009 at 8:40 PM.
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Old 15-Dec-2009, 5:14 AM   #5
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Quote:
Originally Posted by andy.s.lee View Post
NBC (WNYT) has their main transmitter on channel 12 (VHF), but they also have construction permits for two low power repeater stations on channels 18 and 45 (both UHF).

I wonder which of these three signals you are receiving.
18 and 45 are not yet on the air.

I vote for a roof mounted antenna.
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Old 15-Dec-2009, 3:44 PM   #6
herplace
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Hello again Andy, and hello to you also Tower Guy!
Thank you very much for this exhaustive pursuit and solution path for what is my problem with my T.V. reception. Getting some RG-6 into the run was actually my first intention because I think there was some around here somewhere. It was left over from those expansive and often forgetful cable guys everywhere days. What I found was this thin stuff (about as thin as a typical chopstick) on a spool instead, but I still think there is some of the stuff that looks thicker also on a spool. Stupid questions: Could one use multiple runs of the thinner stuff and bring them together at each end and create a monster cable that way. And also is -incredibly more- better? Like that stuff that is as thick as a finger?
I was prepared to try a run from the roof as an experiment but that was before the ice season complicated the idea. Its funny now that this project has me thinking, I'm paying more attention to other antennas in locations I've noticed in my wanderings. Coming up to speed is kind of fun. I'll try to check on a few more details like what I'll call the "wingspread" of my attic antenna and explore just how much larger an antenna might be positioned there. I'm reluctant to really commit to the above roof solution because in addition to the weather issues mentioned I believe wind would be the most disrupting of factors here. Every once in a while there are these rogue wind bursts which can really cause havoc.
Reaching out into the farthest of possible dream set ups, if I may pose a hypothetical impractical solution question please: I have a high hill behind the house where line of sight might really be unobstructed. It is quite a hike but from the highest spot if an antenna station could be positioned perhaps in a storm proof non interfering shelter of some kind. Are there feasible options to get a signal down to the house. I know, I know. All that trouble for just a few commercial stations. But in fantasy mode I could see pulling in PBS from the north east and possibly more from there with the highest gain system assembled. Since Pre-amp seem to be required for extensive runs from any distant antenna, I would expect power might be an issue. I have some solar smarts so I think I could handle that. But I also recognize the obvious constraints of a wire run that far. The cost benefit definitely keeps this in a dream state but I was just wondering. Could there be a wireless solution from there to the house?
I also still don't quite get why NBC is dominating the spectrum. Why would the signal be any weaker from CBS assuming it's the same transmitter location. What am I missing here?
Thanks again for your attention to this situation!
HP
P.S. Is the horizontal boom the part of the antenna that should be pointed at the transmitter direction. Is there a tutorial on compass points for this effort. If NBC is so "there" why can't I assume the sweet spot is already right on?

Last edited by herplace; 15-Dec-2009 at 4:04 PM. Reason: more questions
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Old 15-Dec-2009, 7:27 PM   #7
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Quote:
Originally Posted by herplace View Post
Thank you very much for this exhaustive pursuit and solution path for what is my problem with my T.V. reception. Getting some RG-6 into the run was actually my first intention because I think there was some around here somewhere. It was left over from those expansive and often forgetful cable guys everywhere days. What I found was this thin stuff (about as thin as a typical chopstick) on a spool instead, but I still think there is some of the stuff that looks thicker also on a spool.
Try reading the print on the cable itself. You can usually find the cable type printed right on the outer jacket.



Quote:
Could one use multiple runs of the thinner stuff and bring them together at each end and create a monster cable that way. And also is -incredibly more- better? Like that stuff that is as thick as a finger?
You're best off having a single run of good quality cable. It is easier that way and the cable integrity is easier to maintain.

With cables, you want to pay attention to its characteristic impedance (for TV, you want that to be 75 ohms) and the amount of signal loss you get over distance. RG59, RG6, and RG11 are the most common cable types available for 75 ohm TV applications.

Line loss is frequency dependent. Higher frequency signals dissipate faster than lower frequency ones. If we look at the highest TV channel (used to be channel 69 at 803 MHz, but now is channel 51 at 695 MHz), we can see what the worst case loss would be. For example, a cable might lose 1 dB per every 100 feet at low frequencies (ch 2), yet lose about 4 dB per 100 feet at high frequencies (ch 51).

RG59 is the thinnest and also the most lossy. It will typically lose about 9-10 dB of signal per 100 feet at channel 51. RG59 is also unshielded, which make is a little more susceptible to noise ingress (eg. microwave ovens, vacuum cleaners, etc.) than the other options, if that's a problem you observe in your house.

RG6 is thicker, is less lossy, has a bit more shielding, and is probably the most readily available cable around. There are both "quad shield" (more expensive) and standard versions available. The standard versions also have shielding, but just not as much (about half as much as "quad shield"). RG6 will typically lose about 6-7 dB of signal per 100 feet at channel 51.

RG11 is even thicker, and has the lowest loss. It will typically lose about 4-5 dB of signal per 100 feet at channel 51. RG11 is getting thick to the point where it needs extra large fittings to get the F-type connectors on the ends.

The longer your cable run, the more significant the line loss will be. I generally use RG6 for everything (because its plentiful and easy enough to work with) unless I'm dealing with exceptionally long cable runs (~over 200 feet).



Quote:
Coming up to speed is kind of fun.
Yes, it is!



Quote:
I'll try to check on a few more details like what I'll call the "wingspread" of my attic antenna and explore just how much larger an antenna might be positioned there. I'm reluctant to really commit to the above roof solution because in addition to the weather issues mentioned I believe wind would be the most disrupting of factors here. Every once in a while there are these rogue wind bursts which can really cause havoc.
Signal-wise, a rooftop installation is always better.

In the attic, you may be limited by size, the ability to aim the antenna properly, and signal loss through some building material (foil, wire mesh, and other "hidden" conductive material can wreak havoc with your signals).

On the roof, there are far fewer size and mobility constraints, and best of all, you get a much cleaner (uncluttered) signal environment. Sometimes the added height also helps you get up to where the signals are stronger.

For average residential houses, I'd estimate that attic installations are at a 5-10 dB disadvantage compared to being on the roof (there are exceptions, of course).

If wind is your concern, then there steps you can take to make a rooftop installation more sturdy (mostly common sense, really):
  • Keep the mast short. You still want the antenna to be at least 4-5 feet off your roof, but don't go any higher than necessary. For taller installations (if that's what's required), use guy wires to stabilize the mast.
  • When choosing an antenna, look for antenna designs that have a low wind resistance. Snow and ice accumulation might also be a consideration.
  • Choose a mast with a larger outer diameter and thicker walls. Most antennas and mounts can handle mast sizes of about about 1.5" O.D. Thicker walls will, of course, add a lot of strength.
  • Be sure to use a sturdy, well built mount. There are several options depending on how you want to set up the mount (tripod? chimney? on a wall?)



Quote:
Reaching out into the farthest of possible dream set ups, if I may pose a hypothetical impractical solution question please: I have a high hill behind the house where line of sight might really be unobstructed. It is quite a hike but from the highest spot if an antenna station could be positioned perhaps in a storm proof non interfering shelter of some kind. Are there feasible options to get a signal down to the house.
Yes, there have been people who have done this before. It depends on how long the cable run needs to be. If it's too far, then cable loss will be difficult to overcome. How much distance do you think you're looking at?



Quote:
Since Pre-amp seem to be required for extensive runs from any distant antenna, I would expect power might be an issue. I have some solar smarts so I think I could handle that.
Many pre-amps can be powered through the coax itself. There is usually a power injection unit that is separate from the amp. The power injection unit can be installed at the other end of the coax (inside your house) while the amp sits outside close to the antenna. You could put the power injector closer to the amp if you want, but it's not required.

The power injectors work by putting a DC bias on the coax to drive the amp. As long as the voltage drop over the length of the coax is low enough, there should be enough for the amp to operate. By design, the power injector output is usually several volts higher than what's actually needed by the amp so that cable length is mostly a non-issue. If you know your cable length, you can usually look up the DC resistance of the cable to calculate the expected voltage drop for your setup.



Quote:
Could there be a wireless solution from there to the house?
No. Not really.

The only way to do that is to have a broadband repeater re-broadcast the signal to your house. I'm not aware of any product that is actually capable of doing this, and the FCC would probably need to get involved at some point.



Quote:
I also still don't quite get why NBC is dominating the spectrum. Why would the signal be any weaker from CBS assuming it's the same transmitter location.
Since your antenna is in the attic, it's not easy to tell how much signal is actually making it to your TV. The building materials might absorb or reflect the signal differently on different channels. Your antenna may also have different gain characteristics for each of the channels you are receiving.

According to your tvfool analysis, most of your signals are arriving (outside your house) at about the same power level +/- a few dB.

BTW, if you are using the signal meter built into your receiver, please note that they usually report a "signal quality" rather than actual "signal strength". It's possible for two channels to have very different "signal quality" measurements even if they are actually at the same power level. This can be affected by things like signal reflections (multi-path) and interference that corrupt the digital signal and make it harder to decode.



Quote:
Is the horizontal boom the part of the antenna that should be pointed at the transmitter direction. Is there a tutorial on compass points for this effort.
Yes, the boom should be pointed at the cluster of transmitters. The "narrow" end of the boom with the shorter antenna elements is the "front" of the antenna that points at the transmitters. For some information about azimuths and compass directions, you can read the section about aiming antennas here.



Quote:
If NBC is so "there" why can't I assume the sweet spot is already right on?
It's possible that your antenna is already optimally aimed. However, just receiving one channel does not mean you're really pointed at the best sweet spot. Maybe for one particular channel, you're getting more signal through the building, or perhaps you're getting a lucky reflection from somewhere that makes that channel work but not others.

Antenna aiming, especially indoors, sometimes requires a lot of trial and error because you just don't know what the environment is doing to the signals (reflection, absorption, interference, etc.). It's not an exact science, and that's why the rest of us are here trying to help.

Best regards,
Andy
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Old 16-Dec-2009, 6:15 PM   #8
herplace
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Thanks Andy,
I think I'm slowly getting the ideas here. This truly is a very helpful site!
I was able to check on the coax that was used for the attic run and it is indeed RG59 as you suspected. I am sure there is some of the thicker stuff around here because I found a piece of some that makes me certain I got it off a spool. I'll have to keep looking. The piece has some very tiny writing on it and I can make out "electronic type" 75 ohm, and series 6, unlike the thinner stuff this doesn't have RG particularly indicated but it is thicker and I assume the Series 6 would refer to what you're recommending. Hmm, just where did that spool get misplaced? If I give up perhaps I'll just spring for this RG6 or RG11 you mentioned. If I understand your guidance: Putting RG11 into the run will assure the best practical 30' loss protection? Today's other questions would be: When I get brave enough to explore the attic what kind of things ought I look for in the way of alignment of the various parts of the antenna? I wonder how perfect all those bristles at the back end of the boom have to be in terms of the horizontal plane and the distance apart from the boom to the tips. Should the antenna boom be absolutely "level" for starters? Would you happen to know if 100+ year old slate seriously deflects or impedes signals. I'm getting the notion that all the variable influences like the exact angle of a roof make compensation really tricky under a roof. I won't rule out a rooftop experiment some fine day. Your advice for mast integrity up there is very compelling. Quite a project, though not as daunting as the hilltop I guess. As I said that is quite a hike and the distance makes it sound like not many people would bother. I'll try to pace the distance out just to get a chuckle out of you. Maybe a solar powered T.V. "shack" there would be the best ultimate solution. Heh,heh.
Again I thank you for all this help. Your clear suggestions and instructions really build my confidence that OTA resolution is possible!
HP
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Old 16-Dec-2009, 9:47 PM   #9
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I'll just spring for this RG6 or RG11 you mentioned. If I understand your guidance: Putting RG11 into the run will assure the best practical 30' loss protection?
In most cases, it's not necessary to resort to RG11. If the length of cable from your attic to your TV is only say 40 feet, then the difference between RG6 and RG11 is only going to be about 1 dB. Hardly worth it considering that RG11 is more expensive and more difficult to work with (needs different F-type fittings, is stiffer, is heavier, has a larger bend radius, etc.).

Also, if you use a pre-amp, then the line loss after the amp doesn't really matter.

I think the ideal setup for your situation is a roof mounted antenna with a pre-amp and RG6 for all the connections in between.

Since WRGB is on channel 6, a full bandwidth combo antenna like the Winegard 7084P seems like a good fit. After the antenna, a few feet of RG6 would then connect into a pre-amp (like a Winegard AP 8275). More RG6 would connect from the pre-amp into your house and ultimately into the power injector. And finally, another short section of coax can connect between the power injector and your receiver.

If you have a chimney that rises above the roof by a couple of feet, chimney straps are a good way to mount the mast without having anything go into your roof (as opposed to something like a tripod mount). Eave mounts are another alternative.



Quote:
When I get brave enough to explore the attic what kind of things ought I look for in the way of alignment of the various parts of the antenna? I wonder how perfect all those bristles at the back end of the boom have to be in terms of the horizontal plane and the distance apart from the boom to the tips. Should the antenna boom be absolutely "level" for starters?
For combo antennas like yours, there are two sections.

The long elements in the back are a "log periodic" style of antenna designed to pick up VHF channels. This type of antenna is sensitive to the elements having the right length for optimum "resonance" on the desired channels. As long as the elements are not broken or have any shorts (electrical contact in places where there should not be any), then the antenna will probably work fine. It's not critical to have all of the elements perfectly flat within the same plane.

The short elements at the front of the antenna form a "Yagi" style antenna designed to pick up UHF channels. This type of antenna is sensitive to the length and spacing of the elements. These elements form a kind of "traveling wave conduit" that delivers the optimum signal to the sensing elements in the middle of the antenna. In order for this portion of the antenna to perform optimally, the elements should be aligned with each other and maintain their proper spacing intervals.

In most cases, an antenna that is slightly bent out of shape will still perform fine. It usually requires something significant (like a broken element or a short) to have a noticeable change in antenna performance.

Conductive objects in the space around an antenna (like plumbing, metal bracing, wire mesh, foil-backed insulation, ducts, appliances, etc.) can have just as much influence on reception as the antenna itself. In order for an antenna to perform up to its potential, it needs to be free of these other obstacles.



TV signals are horizontally polarized. This means receiving antennas will perform optimally when the elements are horizontal. However, it's sensitivity to this is pretty low. You can have a 10 or 20 tilt and barely notice any change.



Quote:
Would you happen to know if 100+ year old slate seriously deflects or impedes signals. I'm getting the notion that all the variable influences like the exact angle of a roof make compensation really tricky under a roof.
Sorry, I don't know. Also note that RF absorption rates can vary with frequency, so determining if it's transparent/translucent/opaque can get complicated. Trial and error is the best tool we have against so many unknown variables.



Quote:
I won't rule out a rooftop experiment some fine day.
It's good to stay open to ideas. A rooftop antenna does seem like the best solution in your case, so I do hope you'll give it a try someday (when the weather is nice).

Best regards,
Andy
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Old 16-Dec-2009, 10:26 PM   #10
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Originally Posted by andy.s.lee View Post
It's possible that your antenna is already optimally aimed. However, just receiving one channel does not mean you're really pointed at the best sweet spot. Maybe for one particular channel, you're getting more signal through the building, or perhaps you're getting a lucky reflection from somewhere that makes that channel work but not others.
I think that's a good guess.

I was in Eagle Bridge, NY yesterday helping a friend. A Winegard HD7082P at 15' properly aimed got WRGB only. When I added an HDP-269 preamp, all Albany stations were perfect.

The stations at your location are much weaker than Eagle Bridge.

For another story about DTV reception near you in Sandgate, VT, look here:
http://www.hdtvexpert.com/pages_c/OutToTheFringe.html
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Old 17-Dec-2009, 8:40 PM   #11
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Hey Guys,
This is all starting to look quite promising! All things not being equal RG6 will be somehow be obtained for the next um,TVeek. It would be nice to see this resolve without a pre amp but that too can be readily accepted if it will make that much difference. I'd still prefer stealth reception capability (under the roof in the attic) The aesthetics of that rooftop mount option and my resistance make the ultimate choice interesting to consider. I'd almost rather spend more to achieve attic reception if that is even possible than the inevitable added cost of getting things up on or above the roof. Working towards the next few steps: Would the purchase of a pre amp be specific to a particular antenna size? I'm presuming that what I have that is it's "type" is perfectly specific for this project for now. I'm wondering if with the existing antenna checking out in terms of its present condition being paired to a pre amp would then need to be different if I get a newer or possibly larger antenna? Is there a golden rule about antenna size? I guess I mean: Does the next size up of the required type end up taking up twice as much space? I realize it's all cut and dried from an objective point. "You want those channels? Just put it on the roof already!" I'm thinking if RG6 cable and the pre amp strike out under the roof with the existing antenna that the roof top mount experiment will deserve it's chance and rather than try and get the old antenna out and put a new one in it's place, I'll just try a new one on the roof, possibly a bigger one, if it'll fit in the attic or not. Hence the pre amp size question. Also, is there really much more to expect with a larger antenna anyway? Stupid question?
That Sandgate Vt. story was facinating! Thanks for the link Tower Guy! How much for a spectrum analysis? I'm not clear when that gets done though. Is it a way to check an antenna in a given location or does it just provide by itself the spectrum information at a specific location?
Talk about sweet spots:My old vs new antenna story I heard this past summer makes me wonder about all of the promotions I've seen elsewhere.Some folks I know had a new antenna installed with their new T.V. and were very disappointed. They hooked up the old antenna and just put up with the same results for a while. A roofer came and re did the roof and had to move the old antenna. He gently set it down in a bush next to the house. When I saw it it looked like it had been blown over. It was just lying there like on its side on top of the bush. They said to the roofer: "Whatever you do don't touch that antenna when you are done! We started getting all these channels perfectly ever since you put it down there!" Now that I'm studying this what was explained about tilt tolerance comes to mind.
Thanks again,
HP
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Old 17-Dec-2009, 9:35 PM   #12
andy.s.lee
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Originally Posted by herplace View Post
I'd still prefer stealth reception capability (under the roof in the attic) The aesthetics of that rooftop mount option and my resistance make the ultimate choice interesting to consider. I'd almost rather spend more to achieve attic reception if that is even possible than the inevitable added cost of getting things up on or above the roof.
The channels in your area are not very strong. Going to the roof is your best bet at getting reliable signals.

The attic has a chance of working, but since your attic is tight on space, you might not be able to go for the big high-gain antenna that you would need to make up for the building losses. It's more of a gamble if you want to give it a shot.



Quote:
Would the purchase of a pre amp be specific to a particular antenna size? I'm presuming that what I have that is it's "type" is perfectly specific for this project for now. I'm wondering if with the existing antenna checking out in terms of its present condition being paired to a pre amp would then need to be different if I get a newer or possibly larger antenna?
Not really. There are just a handful of pre-amps that get recommended a lot. It's very important to get a pre-amp with a low Noise Figure (NF), and these particular amps are known to have good NF specs (under 3.0 dB). For distant signals like yours (signal overload is not a concern for your location), then high gain amps like the Winegard 8275 or Channel Master 7777 are popular choices.

Even if you switched antennas, these amps would still work great.



Quote:
Is there a golden rule about antenna size? I guess I mean: Does the next size up of the required type end up taking up twice as much space?
There are no "standard" antenna sizes, so each manufacturer is free to come up with whatever sizes they think their customers want. In general, bigger does perform better. It's plain physics that you need more antenna to catch more signal.

Since you have a multiple VHF channels (6, 7, 9, 12, 13) to pick up, it means you'll need an antenna with very long antenna elements that take up a bunch of space. Low frequency means long wavelengths, and this requires long antenna elements.



Quote:
I'm thinking if RG6 cable and the pre amp strike out under the roof with the existing antenna that the roof top mount experiment will deserve it's chance and rather than try and get the old antenna out and put a new one in it's place, I'll just try a new one on the roof, possibly a bigger one, if it'll fit in the attic or not. Hence the pre amp size question.
That's perfectly sensible. Try what you prefer first, and if it doesn't work, then take the next step of making it better. As long as you don't mind a little bit of trial and error, then I'm sure you'll eventually settle on the solution that works best for you. If you plan it right, you can try each option and switch to the next "better" option as needed, and keep costs to a minimum.

One tip... If you are going to purchase things for "experimental" installations, be sure to check on the return policies of the stores you purchase from, and keep all receipts. Just in case something needs to go back, it's good to plan ahead.

Best regards,
Andy
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Old 18-Dec-2009, 4:30 PM   #13
herplace
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Greetings Andy!
I made a previous reply that I think got lost before I could send it. T.V. reception is not the only technical challenge around here.
That single line:
"Low frequency means long wavelengths and this requires long antenna elements."
Is highly instructive!
I think I'm getting this! I can't use my own words to describe how I know this yet. In my life I've heard some of the theory you seem to have such a formidable grasp of so something clicked when I read that from you! Thanks!
Step by step I'll tackle these options in some way and post some reports as results are realized. Depending on some of the available products (long range implementation here) I'm thinking of trying a bigger (longer antenna element option) in a placement closer to the floor of the attic to see if despite a few feet of elevation being sacrificed all things not being equal the stealth option could work there. How the existing envelope impacts this placement is not understood exactly of course. What I am now wondering about this is whether I could enclose the area above the antenna so there could be sort of a floor over it. Shelf like. I can only imagine that the transmitter direction end would have to be clear and open to what an antenna without a floor over it would present to the situation. Am I guessing wrong about this? Does the "signal" need more than this to be picked up by an antenna? If not, do I have any strong restraints to guide what this shelf could be made of ? I think it could protect a bigger antenna closer to the floor joists and that would give back some of the space up there for movement and access to storage areas the present set up just rules out. If the elevation loss is trivial then cable length loss would also benefit. I believe I'm clear about the pre amp being located pretty close to the antenna and also that all a pre amp can do is help over come signal loss in the cable from the antenna to the T.V. Would that pre amp use rule out 30' cable loss completely? I ask because in terms of elimination of issues if it does, it leaves the field cluttered with just: The building envelope can of worms, OTA signal strength, and Elevation right? In the big antenna realm an attic floor set up would potentially allow a huge antenna that would look ridiculous on top of this building. Perhaps a smaller rooftop set up would work better but I am just floating balloons here still trying to explore the stealth option as though price is no object.
Many thanks for having this forum to bounce ideas around on!
HP

Last edited by herplace; 18-Dec-2009 at 4:37 PM. Reason: spell check
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Old 18-Dec-2009, 7:16 PM   #14
andy.s.lee
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I think I'm getting this!
Great! We're here to share what we know, and it's good to hear that some of it is helping.



Quote:
I'm thinking of trying a bigger (longer antenna element option) in a placement closer to the floor of the attic to see if despite a few feet of elevation being sacrificed all things not being equal the stealth option could work there. How the existing envelope impacts this placement is not understood exactly of course.
The minor change in height from the floor to the ceiling of your attic is negligible. What matters more is the stuff right next to the antenna (which might alter the antenna's raw performance) and stuff that sits in the path between the transmitter and your antenna.

On the first floor of most buildings, you usually have a lot more "clutter" for the signal to pass through (walls, trees, fences, neighbors' houses, cars, etc.).

In the attic, you're above most of the dense "clutter" and mostly just need to worry about stuff in your own attic (and maybe a neighboring house or two).

On the roof, you're above almost everything, and the antenna can get close to its ideal behavior.



Quote:
What I am now wondering about this is whether I could enclose the area above the antenna so there could be sort of a floor over it. Shelf like. I can only imagine that the transmitter direction end would have to be clear and open to what an antenna without a floor over it would present to the situation. Am I guessing wrong about this? Does the "signal" need more than this to be picked up by an antenna?
If you install your antenna in your attic, it's a good idea to protect it from physical damage, which is what I think you're suggesting with a "shelf" or "floor". However, you do need to be aware of how you might be affecting the antenna's performance.

Most antennas are designed with the assumption that all the space around them is open (air). Surrounding the antenna with something else can impact its performance. Wood generally has a very mild effect on antenna behavior and is probably not a big deal, but I would be concerned about the nails or other metal objects used to hold the wood together. Metal has a big impact on performance and needs to be kept far away from the antenna elements when possible.

As a general rule of thumb, I'd suggest keeping the antenna out in the open as much as you can. It doesn't make that much difference whether the antenna is near the floor or near the top of the attic as long as the antenna is not being blocked by other things in the vicinity.



Quote:
I believe I'm clear about the pre amp being located pretty close to the antenna and also that all a pre amp can do is help over come signal loss in the cable from the antenna to the T.V. Would that pre amp use rule out 30' cable loss completely?
Essentially, yes.



Quote:
In the big antenna realm an attic floor set up would potentially allow a huge antenna that would look ridiculous on top of this building.
In my own experience, "large" antennas always seem huge at first because you're standing next to it while it's being assembled. Most of them are even bigger than I am. However, once you get these things up on a mast above the roof, it doesn't look that big any more.

As people get re-conditioned to the idea of seeing antennas on every-other rooftop, I think the "shock" of large antennas will go away. My wife didn't even notice that I changed antennas until I pointed it out to her.



Quote:
Many thanks for having this forum to bounce ideas around on!
Perfect! That's exactly why it's here.

Best regards,
Andy
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Old 21-Dec-2009, 3:49 PM   #15
herplace
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Andy,
I just wished to let you know that I saw the last message and will work towards the steps outlined in the suggestions generated here. Many thanks and I Wish you and all the Forum members Very Happy Holidays and better reception to all in a Happy New Year!
HP
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Old 15-Jan-2010, 3:39 PM   #16
herplace
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I'm coming up for air again, Over the air that is! And I am reporting back my attic adventures.I found the antenna to be in pretty good shape as far as nothing broken or even bent. I am still getting around to trying to aim it better. The one I have, have as the longest most rear elements a four foot tube off of each side of the boom. Then going forward the next elements are three feet and then two feet and then a foot. I think it may be pointed too much to the south. But I'll get back to that issue. I just wanted to check in with this info and see if this size description met with any comments. Even where it is there would seem to be more much more room to grow. I gues I should measure before I ask but have you all any suggestions for a good next size up? I'm still willing to ultimately end up above the roof of course but I just want to make this as hard as I can until then.
herplace
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Old 16-Jan-2010, 12:55 AM   #17
mtownsend
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Sounds like you're using a "small" full band combo antenna. Perhaps something like this:


Your tvfool report shows pretty weak signals (all in the "red" zone, with NM values in the 0-10 dB range). To get these channels reliably, you really do need to have the antenna on the roof, and the antenna probably needs to be about two sizes up from the one you've got.

I'm thinking something like the Winegard HD7084P or Antennacraft HD1200 would be about the right size. If you want to do this from inside the attic, you may need an even more powerful (meaning bigger) antenna.
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Old 16-Jan-2010, 1:24 AM   #18
andy.s.lee
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Even where it is there would seem to be more much more room to grow. I gues I should measure before I ask but have you all any suggestions for a good next size up?
Every attic is different. Some people have tons of room and others have hardly any room at all. The construction of the attic and roof can also make a big difference in how much signal can pass through the building material.

Do you think your attic has enough space to handle an antenna that is 10-14 feet long and about 9 feet wide? If you are fortunate enough to have a spacious attic, then maybe you'll be able to get a very large antenna in there and make it all work. If not, then a rooftop antenna might be the only way to go.

Best regards,
Andy

Last edited by andy.s.lee; 16-Jan-2010 at 1:50 AM.
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Old 17-Jan-2010, 3:24 PM   #19
herplace
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Hey folks,
Thanks for the encouragement and size specs. I actually think the floor area of the attic (with an eventual protective, open (to the antenna farm) ended shelf could handle the spread you describe. I almost sprang for 50' of RG6 coax during some errands but priced the stuff @ $45 and thought I'd check to see if that was a fair price. (I haven't found my missing spool yet) Just to satisfy my curiosity I had other expenses to cover and decided to hold off.
I finally got up there with the best compass I could find handy and drew the cardinal points and some degrees on the floor and found the boom pointing towards the 250* heading. I redirected the boom to 235* and checked the reception: No big change that I can tell. The new setting may improve the poor weather reception. I guess I'll find that out later today.
Would it be crazy to try to "build ones own " antenna? Considering as I understand it seems that the vhf is the only portion of signal that I could hope to gather from this location, I was wondering if the parts I do need could be assembled without the uhf end to get in the way. It looks much more simple. The picture submitted is similar to the antenna that is now in the attic except the vhf elements have a forward sweep from the boom so they are not perpendicular to the boom. At the present heading there is only another extended foot the longest elements could "grow" but this is quite close to the ridge of the roof. Once lowered either on a mast (upside down) or somehow set up in this yet to be designed shelf arrangement there is indeed much more room. As far as a "home brew" I only have vague notions of what exactly might be needed. Essentially copying something and trying to get it right. Ancient stories of making use of whatever there is around to achieve the desired result have me intrigued. What do you think?
Thanks, still looking for a misplaced spool of RG6,
herplace
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Old 17-Jan-2010, 6:33 PM   #20
mtownsend
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I almost sprang for 50' of RG6 coax during some errands but priced the stuff @ $45 and thought I'd check to see if that was a fair price.
Well, Radio Shack sells 100' of quad shield RG6 with connectors on the ends for $50. The same cable in 50' lengths is $40. They have regular RG6 (not quad shield) at $30 for 50'.

If you're planning on using raw cable and build your own, then the cable itself is usually pretty inexpensive. 1000' spools of bulk cable quad shield RG6 can usually be had for about $60 to $100. But then you need to invest in tools to attach the connectors (maybe another $50-$100 expense). If you go that route, compression fittings work better than crimp-on for making clean, weatherproof connections.



Quote:
Would it be crazy to try to "build ones own " antenna?
Not at all. If you're the hands on type and enjoy tinkering with these things, then it can fun and educational. I wouldn't necessarily do it to save money. For the cost of a commercial antenna, I can get very good performance in a well built antenna and save myself a whole lot of time. However, there's a great sense of accomplishment when you can make your own.

Note that most of the DIY antenna designs floating around the internet are primarily UHF antennas. You have three high VHF channels and one low VHF channel to get, so you'll want an antenna design that is strong at those frequencies.



Quote:
The picture submitted is similar to the antenna that is now in the attic except the vhf elements have a forward sweep from the boom so they are not perpendicular to the boom.
OK. More like this:




Quote:
As far as a "home brew" I only have vague notions of what exactly might be needed. Essentially copying something and trying to get it right. Ancient stories of making use of whatever there is around to achieve the desired result have me intrigued. What do you think?
I would not take antenna construction lightly. Your signals are not that strong, so you really do need an antenna with good sensitivity. You will not stumble upon a high sensitivity antenna design by accident. The few DIY antenna designs that actually work are based on some very real antenna engineering that has a long history behind it.

If you're just starting out, I recommend finding someone else's known working design and following their prescription as precisely as you can. Once you've had success building one antenna, you can then venture out with slight variations or other customizations.
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