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Old 19-Oct-2011, 7:10 PM   #4
GroundUrMast
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Join Date: Oct 2010
Location: Greater Seattle Area
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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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