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Old 15-Dec-2009, 6:27 PM   #7
andy.s.lee
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Join Date: Dec 2009
Posts: 54
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.



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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).



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



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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?)



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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?



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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.



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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.



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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.



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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.



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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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