TV Fool  

Go Back   TV Fool > Over The Air Services > Help With Reception

Notices

Reply
 
Thread Tools
Old 1-Sep-2010, 6:09 PM   #1
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Confused

My apologies if this is not being posted in the correct thread.

Due to finances I need to terminate my service with the cable companies ( can't say I am disappointed either). I have been researching what is needed for OTA reception and feel a little overwhelmed/confused. From this site I have determined that:
  • All but one station are 25 to 30 miles from my location
    All but one are within 5 degrees of one another
    According to atennaweb VHF except the one.
    The one is UHF\14 miles and in the opposite direction from the rest.
    According to this site, all fall in the color rating of Green. Antennaweb states yellow for most except a couple. i would rather over compensate my needs than the opposite
    All are LOS
    Not sure where I read it but the above staes were based on a 10 ft above ground attenna

Information Link here http://www.tvfool.com/?option=com_wr...a3626c94fc2747

Other considerations:
  • Cable run from antenna a good 30 plus ft
    Need to be split at some point to different rooms

my understanding from the above is that I need an outdoor directional VHF and a UHF omni direction antenna. My confusion comes from all the NM,Pwr and Gain info. Then there is the info on the gain from antenna vs from an amplifier, different companies etc. Without getting too technical can anyone put my needs in laymans terms?

thanks...just want to watch tv again.
acutshall is offline   Reply With Quote
Old 1-Sep-2010, 9:05 PM   #2
Dave Loudin
Senior Member
 
Join Date: Jan 2010
Location: King George, VA
Posts: 659
The forum where you typically ask for help is "Help with reception." Perhaps this will get moved there. In the meantime, some basic concepts:

1) Digital TV receivers need a minimum signal strength above background noise in order to decode a picture. The ratio of signal power to noise power is call signal-to-noise ratio (SNR or S/N). The standard for digital TV calls out the SNR that all receivers must be able to use.

2) TVFool predictions use this minimum SNR to establish a reference for the noise margin, or NM. If a signal is predicted to have an NM of 0 (zero), then, barring any other losses, a receiver will successfully decode it.

3) TVFool's prediction model doesn't take into account every possible way a signal can fade or be interfered with. Therefore, we like to add some additional margin by recommending designing to an NM of +10.

4) Antenna gain adds to NM and signal losses in the cable between antenna and receiver subtracts from NM.

5) A pre-amplifier will zero out cable losses, but will otherwise not add to NM. In fact, the internal noise of the pre-amp will subtract from NM.

6) The "Real Channel" is the actual channel stations are broadcasting on. The "Virtual Channel" is what your TV will map the broadcasts to.

7) Many stations broadcast "sub-channels" that offer different programming from the main program. To see a complete list for your market, go to this site, click on Tampa, then click on "expand all". It will take a moment for the screen to update.

I can't see your report right now, so additional advice will have to wait.

Last edited by Dave Loudin; 1-Sep-2010 at 9:22 PM.
Dave Loudin is offline   Reply With Quote
Old 1-Sep-2010, 9:14 PM   #3
Dave Loudin
Senior Member
 
Join Date: Jan 2010
Location: King George, VA
Posts: 659
Wow! You have very strong signals available to you. There are 19 digital stations with noise margins of +35 or more, so you don't really need an antenna with any gain in order to catch usable signals. Get a Terk HDTVi (NOT the HDTVa - you do NOT need an amplifier). The rabbit ears are needed for four VHF stations WTSP, WTVT, WFLA, and WEDU, and the space-agey part will pick up the rest.

Good luck!
Dave Loudin is offline   Reply With Quote
Old 1-Sep-2010, 9:15 PM   #4
mtownsend
Moderator
 
Join Date: Dec 2009
Posts: 632
Thread has been moved to correct area.
mtownsend is offline   Reply With Quote
Old 2-Sep-2010, 1:48 AM   #5
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Thanks for the info.

-So on the chart (signal power) is represented by NM and (noise power) is represented by Pwr, thus SNR?
-Do I subtract one from the other to get the net signal?
-The goal is to have a net of zero or above( plus number) or the other way around?
-Is the "some additional margin by recommending designing to an NM of +10already ." reflected on the charts

It might be more clear to me if you were able to provide a numerical example. i.e

Goal number = Current signal (NM), +- atenna gain, +-cable loss, +-spliter+-, amp or a link that already has this example.

The Terk would be nice but I have 4 tvs that i need to route the signal to.

Thanks again!
acutshall is offline   Reply With Quote
Old 2-Sep-2010, 6:08 AM   #6
mtownsend
Moderator
 
Join Date: Dec 2009
Posts: 632
Quote:
Originally Posted by acutshall View Post
-So on the chart (signal power) is represented by NM and (noise power) is represented by Pwr, thus SNR?
-Do I subtract one from the other to get the net signal?
The Noise Margin (NM) column is all that you really need. It already takes into account all the terrain, distance, Earth curvature, and SNR into account. This number needs to stay above zero in order for you to have a usable signal.

The Power (Pwr) column is just there for information purposes. When signals are too strong (at a level that might overload some electronics), it might be good to look at this number. However, in most cases, you don't really care what the actual power levels are.

The analysis will tell you Noise Margin "in the air" at your house, based on the address or coordinates you provide. The NM does not know what kind of antenna you have, the length of cable you have, the number of signal splits you have, etc. To calculate how much "net" NM you have, you need to add/subtract the gains/losses that are specific to your setup. Antenna gain gets added to the NM, everything else (cable losses, splitters, etc.) gets subtracted from the NM.

The channel list is color coded to give you a general idea of which channels are strong, medium, weak, or really hard to get. The color coding takes into account what you might find in "typicial" installations. An indoor (set-top) type antenna is probably good enough to pick up the "green" channels. An attic antenna is probably good enough to pick up the "yellow" and higher channels. A rooftop antenna is probably good enough to pick up the "red" and higher channels. Channels in the "gray" zone are very weak and will probably require extreme measures to get.



Quote:
-The goal is to have a net of zero or above( plus number) or the other way around?
After factoring in all of the specifics of your setup (antenna gain, cable loss, etc.), you want to end up with a positive NM.



Quote:
-Is the "some additional margin by recommending designing to an NM of +10already ." reflected on the charts
The NM values in the chart are "in the air" at your location. The tools do not account for anything that is specifically installed by you (antenna, cables, splitters, amps, etc.). You need to adjust the number to account for the details of your particular setup.

The "net" NM number you end up with tell you how much margin you have for natural signal fluctuations. Signals will naturally change throughout the day, under varying weather conditions, and from one season to the next. The more "excess" Noise Margin you have, the better off you will be. This allows your setup to tolerate more of these random fluctuations before having any channel drop-outs. Having an extra 10 dB of NM is generally considered good enough to have very reliable reception.



Quote:
It might be more clear to me if you were able to provide a numerical example.
Here's a post that works through some numerical examples: http://forum.tvfool.com/showpost.php?p=427&postcount=2

Last edited by mtownsend; 2-Sep-2010 at 8:45 PM. Reason: Fixed spelling error
mtownsend is offline   Reply With Quote
Old 2-Sep-2010, 5:50 PM   #7
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Becoming more clear, thanks
acutshall is offline   Reply With Quote
Old 2-Sep-2010, 5:56 PM   #8
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Very good examples on link. You listed loss for cable and splitters, is there somewhere to find out the loss specs for the cable and splitters? i.e cable x has a loss per foot of...

thx
acutshall is offline   Reply With Quote
Old 2-Sep-2010, 8:41 PM   #9
mtownsend
Moderator
 
Join Date: Dec 2009
Posts: 632
Quote:
Originally Posted by acutshall View Post
You listed loss for cable and splitters, is there somewhere to find out the loss specs for the cable and splitters? i.e cable x has a loss per foot of...
Cable loss varies somewhat, so each manufacturer may post slightly different loss numbers (construction material, conductor thickness, insulator density, and other variables can make some cables slightly better/worse than others). Also, loss per foot does depend on frequency. Higher frequencies lose signal faster than lower frequencies. Connectors, kinks in the cable, and other imperfections will account for small amounts of loss too.

You really need to check the specs from each cable manufacturer to know what you're getting, but in most cases, I just go by the ballpark numbers as follows. Note that upper UHF frequencies have the most loss per foot, so we can just use this number to represent the worst case loss estimation in most setups.

RG59 : VHF ~4.5 dB/100ft : UHF ~9 dB/100ft
RG6 : VHF ~3.5 dB/100ft : UHF ~7 dB/100ft
RG11 : VHF ~2.5 dB/100ft : UHF ~4.5 dB/100ft

Splitters drop the power depending on the number of ways the signal gets split. Note that most 3-way splitter are actually 4-way splitters inside with the extra port terminated internally. Splitters are almost always constructed in even powers of 2.

1:2 splitter ~4 dB loss
1:4 splitter ~7.5 dB loss
1:8 splitter ~11 dB loss

After you have calculated the total cable and splitter losses for your system, you might want to pad the number by an extra dB or two to account for miscellaneous other losses (e.g., imperfect connectors, slight impedance mismatches, etc.).



You might find some cable manufacturers that publish slightly better/worse specs than others. In most installations, the cable lengths are typically not more than about 50 feet or so. For most people, that means that the difference between cable manufacturers is in the noise of overall system performance (maybe only 1 dB or only fractions of a dB difference).



There are other important points to consider when choosing between the different classes of cable (RG59 vs. RG6 vs. RG11).

RG59 does not have as much shielding as the others. If the cable runs parallel to a lot of electrical wiring or is in close proximity to "noise generating" appliances (e.g., microwave ovens, vacuum cleaners, etc.), there's a greater chance of interference leaking into the cable.

RG6 is available in standard and "quad shield" (RG6Q) versions. Standard RG6 is good enough for most situations. The "quad shield" versions are only required if electrical interference is higher than normal. Signal-wise, it doesn't hurt to have extra shielding when you don't need it, but RG6Q does usually cost more and the cable does increase in thickness and stiffness.

RG11 is significantly more expensive than the others. Since it is also much thicker than RG6, you need special (more expensive) connectors and crimp tools if you want to make your own cables.
mtownsend is offline   Reply With Quote
Old 2-Sep-2010, 9:19 PM   #10
Dave Loudin
Senior Member
 
Join Date: Jan 2010
Location: King George, VA
Posts: 659
You're only a half-mile from one station (low-power, but still...) and pretty close to channel 10, so it is very likely any kind of amplifier will end up overloaded. A lower-gain antenna that covers high-VHF and UHF channels is the RCA ANT-751. You can mount this outside (avoiding up to 20 dB of loss through the walls) and run the cable to a 4-way splitter inside. You should have plenty of signal left for all the TVs, but now you know how to do the system design to be sure.
Dave Loudin is offline   Reply With Quote
Old 2-Sep-2010, 9:44 PM   #11
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Thx for the info on the cable specs, could explain some of the loss in quality that I experienced in the past with cable.

Based on your information, I have decided to:

-Replace my cable with the RG6
- centrally locate the antenna (20ft from splitter)to shorten the cable runs to each TV
- 4 room locations approx 25-30Ft from splitter
-purchase amp to boost signal



A couple more questions and I think I have enough info to start laying out what is needed and to start shopping around.

-The amp: is it better to have it outdoors on the antenna, prior to the splitter or both?
-All Channel antennas:

A sticky on the site talks about "all channel" antennas; my original plan was to have one directional for the VHF channels (since they are all within 4 degrees off one another) and a separate UHF antenna for the one station that is in the opposite direction mounted on the same pole . However after reading the post I am tempted to go that route. My only concern is that it looks very similar to a directional, so I'm not sure that it would pick up the UHF; also a little more expensive. Have you had any experience using all channels and is my concern justified?

thx again



http://forum.tvfool.com/showthread.php?t=231
acutshall is offline   Reply With Quote
Old 2-Sep-2010, 9:56 PM   #12
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Quote:
Originally Posted by Dave Loudin View Post
You're only a half-mile from one station (low-power, but still...) and pretty close to channel 10, so it is very likely any kind of amplifier will end up overloaded. A lower-gain antenna that covers high-VHF and UHF channels is the RCA ANT-751. You can mount this outside (avoiding up to 20 dB of loss through the walls) and run the cable to a 4-way splitter inside. You should have plenty of signal left for all the TVs, but now you know how to do the system design to be sure.
Thanks Dave. Cost is within reason too. So just point this towards the VHF (roof top level) and it should pick up channel 10 as well?
acutshall is offline   Reply With Quote
Old 2-Sep-2010, 10:48 PM   #13
andy.s.lee
Janitor
 
Join Date: Dec 2009
Posts: 54
Please DO NOT use an amp. The strong signals on your list are too much to handle for most amps so you really need to avoid them. The signals are already more than strong enough to drive all of your TVs.

Amps are normally used to hang on to really weak signals in the "red" or start of the "gray" zones on people's TV Fool reports. Amps don't have much tolerance for very strong signals because they overload easily. Overloaded amps create distortion across all of your signals and can make things worse rather than better.

You have LOTS of very strong signals, so any amp you use is surely going to have problems. You should avoid amps of any kind (standalone or built-in to the antenna).

Just follow Dave's suggestions and you'll do well.
andy.s.lee is offline   Reply With Quote
Old 2-Sep-2010, 11:17 PM   #14
Dave Loudin
Senior Member
 
Join Date: Jan 2010
Location: King George, VA
Posts: 659
^^^ Right! Please, no amplifier. Aim the antenna southeast, about 120 degrees. You'll get channel 10 off the back.
Dave Loudin is offline   Reply With Quote
Old 3-Sep-2010, 7:31 AM   #15
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Quote:
Originally Posted by andy.s.lee View Post
Please DO NOT use an amp. The strong signals on your list are too much to handle for most amps so you really need to avoid them. The signals are already more than strong enough to drive all of your TVs.

Amps are normally used to hang on to really weak signals in the "red" or start of the "gray" zones on people's TV Fool reports. Amps don't have much tolerance for very strong signals because they overload easily. Overloaded amps create distortion across all of your signals and can make things worse rather than better.

You have LOTS of very strong signals, so any amp you use is surely going to have problems. You should avoid amps of any kind (standalone or built-in to the antenna).

Just follow Dave's suggestions and you'll do well.
Thanks Andy; will do and purchase the antenna that he recommended.
acutshall is offline   Reply With Quote
Old 3-Sep-2010, 7:32 AM   #16
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
Thanks again dave; will be ordering tomorrow and aim it as you suggested.
acutshall is offline   Reply With Quote
Old 5-Sep-2010, 6:07 PM   #17
acutshall
Junior Member
 
Join Date: Sep 2010
Posts: 9
First thanks for this site and those who assist.

Dave ,
I ordered the RCA ANT-751, transformer and RG6 quad ( I would not know if I was receiving quad or not ) cable. I was a little unsure about the quality/vendor/type, F connectors and splitter.
For expediency I ordered the cable with compression type F connectors already attached however would like to customize the length later.

Cable
-Is there that much of a difference in quality of RG6 between vendors
-Do gold connectors provide a noticeable improvement in quality(cable/splitters) or is that just marketing
- For home use, do you recommend a particular F connector compression tool

Last, for those who have made the switch from cable to OTA, with ideal conditions can I truly expect to get HD quality ?

thx
acutshall is offline   Reply With Quote
Old 5-Sep-2010, 9:29 PM   #18
Dave Loudin
Senior Member
 
Join Date: Jan 2010
Location: King George, VA
Posts: 659
I'll answer what I know:

There is no real benefit to gold connectors (just marketing.)

Once a DTV receiver locks on a signal, the picture quality is fixed. You will get all the resolution a station provides. Most main channels will be in HD (there will still be 4:3 programs, though.) Most sub-channels will be standard definition. To see what your market offers, go to RabbitEars, click on the market, then explore the channels.
Dave Loudin is offline   Reply With Quote
Reply

Bookmarks

Go Back   TV Fool > Over The Air Services > Help With Reception


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off




All times are GMT. The time now is 8:33 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright © TV Fool, LLC