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Old 16-Oct-2011, 8:00 PM   #1
MayfairWantsPBS39
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How to select, or not, a distribution amplifier?

What is the formula that to calculate which, if any distribution amplifiers would fix pixelation?

Recently I bought a Tivo Premier XL. A channel scan shows it finds a signal for WPSJ in Winslow. The signal is sometimes OK, sometimes pixilated.

The run from the antenna to TV is 108. 2 pieces of cable. First piece is 56. Second 52.

TV Fool gives a WPSJ a NM (db) of 37.0. Power (dbM) of 53.8.

Location:

http://www.tvfool.com/?option=com_wr...60b5c13ca30309

Power is available at the end of the first piece of cable. Antenna and hardware are new this time last year. Local channels are perfect. Question came up because of the Tivo box. WPSJ hasnt shown up when I scanned the TV channels upstairs. Apparently that was because of the splitters.
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Old 17-Oct-2011, 12:35 AM   #2
GroundUrMast
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A DA is appropriate when splitting many ways. A preamp is appropriate when dealing with low NM at the antenna and/or splitting many ways.

A NM of 37 dB is not a low figure... Is your antenna aimed directly at that station? Are you using a single antenna? Your previous posts indicate a CM-3016.
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Last edited by GroundUrMast; 19-Oct-2011 at 6:44 PM. Reason: Clarity
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Old 18-Oct-2011, 1:18 AM   #3
MayfairWantsPBS39
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Antenna CM 3016, is aimed at 274. Where most of the channels are. WPSJ comes in the back to the antenna, at 154. The person who installed the antenna said my location had unusually strong signals. He was surprised that WPSJ came in. He was concerned that the signals might be too strong, but we attached a set and everything was Jake.

I read your other post. Unfortunately I cant quite figure out what numbers to put in where, to see if a DA would help. I bought one at a local retailer, and it made things worse.

If I remove the splitters going to the other sets, WPSJ comes in OK, with some pixelation. If I add even one splitter, it disappears. Id like to have the ability to use 4 or 6: basement, living room, Tivo, sewing room, master bedroom, spare bedroom.

Cable run, from the end of the 56 antenna lead to the other sets, is another 136.

To compensate for 6 splitters, and 136 of cable, what numbers on a DA should I look for, or what would a good DA be for this situation?
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Old 19-Oct-2011, 7:10 PM   #4
GroundUrMast
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Quote:
Originally Posted by MayfairWantsPBS39 View Post
Antenna CM 3016, is aimed at 274. Where most of the channels are. WPSJ comes in the back to the antenna, at 154. The person who installed the antenna said my location had unusually strong signals. He was surprised that WPSJ came in. He was concerned that the signals might be too strong, but we attached a set and everything was Jake.

I read your other post. Unfortunately I can’t quite figure out what numbers to put in where, to see if a DA would help. I bought one at a local retailer, and it made things worse.

If I remove the splitters going to the other sets, WPSJ comes in OK, with some pixelation. If I add even one splitter, it disappears. I’d like to have the ability to use 4 or 6: basement, living room, Tivo, sewing room, master bedroom, spare bedroom.

Cable run, from the end of the 56’ antenna lead to the other sets, is another 136’.

To compensate for 6 splitters, and 136’ of cable, what numbers on a DA should I look for, or what would a good DA be for this situation?
Given the large number of strong signals, many amplifiers will overload, which will make your situation worse. This seems to be verified by your experience with the DA from the local retailer.

I suspect that reception of WPSJ is poor because the antenna is aimed wrong (for that station). The existing antenna is no doubt receiving direct signal from the rear and reflected signal from the direction it's pointed. This is called multipath interference and no amplifier can correct that problem.

The solution for this depends on whether you want WPSJ on one, some or all TV's.

To address you question... If WPSJ were the only station you were interested in, I'd suggest a simple antenna such as a Antennas Direct DB-2 which has 8 dBd forward gain (conservatively speaking). The signal from WPSJ is predicted to arrive at your location at a Noise Margin of 37 dB. Add the antenna gain to that NM and subtract the cable and splitter losses.
If the antenna lead is 56' of RG-6 and there is an 8-way splitter (with all unused ports terminated) and there is 136' of RG-6 from the splitter to the tuner, the net NM at the tuner would be 37dB + 8dB - 12.5dB - 12dB = 20.5 dB NM.

{NM in the air + antenna gain in dBd - total cable loss (56'+136' @ 6.5 dB/100') - splitter loss (12 db for an 8-way is conservative)}
A noise margin above 15 dB at the set, is usually more than enough to provide nearly 100% reliable reception. You should not need a DA.

I'm not sure I understand how your distribution cable is arranged. Does the antenna lead go to a single splitter? Or does the antenna feed a splitter that then feeds other splitters? Ideally, you would want to use only one splitter and cable from there to each TV (home run from each TV to the one distribution point). Chaining from one splitter to another results in more loss than needed, especially at the tail end.

The attached PDF drawing does not account for cable losses but illustrates the difference between home-run vs. daisy chain layouts.
Attached Files
File Type: pdf Home Run versus Daisy Chain.pdf (32.1 KB, 244 views)
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Last edited by GroundUrMast; 23-Oct-2011 at 2:57 AM.
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Old 23-Oct-2011, 2:15 AM   #5
MayfairWantsPBS39
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Got several suggestions. Bought the least expensive (name brand, 1/2 price sale). Should know by next Saturday if it works.

Can't see using Slingbox or such for one channel.

Update. Saturday October 29.

The Channel Master 3418 or PCT-MA2-8P arrived today. Connected six leads and terminated the other 2, and the ones that don't have sets attached right now. Power. Scanned for channels. Channel 8.1 is strong. Also added 69.2-4 from Allentown. And 44 WMCN, Atlantic City. Cost $35. I'm happy.

The other amp that was highly regarded, an Electroline EDA-FT 08340 or 08341, was 3x as much.

Last edited by MayfairWantsPBS39; 30-Oct-2011 at 4:59 AM.
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