new set up-suggestions needed

[jf3233]

Just purchased a new 37" Sharp Aquos LCD for home. Pretty sweet picture quality but here is my question. Was running one HD TV prior. Had local HD with antenna no problem. I split that antenna feed and sent through diplexer so I could get locals on both. One TV gets all stations no problem. The other is missing 2. Prior all signal were strong with no problems as I am in Milwaukee about 5 miles from towers. Any sucggestions on how to boost signal? Am I losing that much by splitting?

[jfelbab]

Splitting cuts your signal strength in half. Not sure what a diplexor does to signal levels. Do you get any signal strength reading at all?  What channels don't you get?  Even cutting the signal in half should leave you with a pretty good signal if you are only 5 miles from the transmitters. You might get by with a simple rabbit ears or a set top antenna. What kind of antenna are you using?

[Mark Strube]

A splitter doesn't cut your signal strength in half. If that happened any digital signal would be completely unusable after a split. Most splitters will cut it by 3 to 6dB, but not in half. I'd guess the television having the problems is on a longer cable run. In either case, I'd get an amplifier and add it as soon after the antenna (and before the split) as possible. That would solve your problem.

A diplexor, assuming it's the right type, shouldn't be causing any issues... but I'd have it in the line before the amp, and before the split. Why are you using one in the first place? Were you having issues without one?

[jfelbab]

A splitter doesn't cut your signal strength in half. If that happened any digital signal would be completely unusable after a split. Most splitters will cut it by 3 to 6dB, but not in half. I'd guess the television having the problems is on a longer cable run. In either case, I'd get an amplifier and add it as soon after the antenna (and before the split) as possible. That would solve your problem.

A diplexor, assuming it's the right type, shouldn't be causing any issues... but I'd have it in the line before the amp, and before the split. Why are you using one in the first place? Were you having issues without one?

A -3dB loss is exactly a loss of half the signal power, Mark.

If you use a passive two-way splitter the original signal is cut by at least half usually by around 3.5 dB, and you have half the original signal power level out from the two ports.

If you use a 3-way splitter your losses are 3.5 dB and 7 dB and 7dB on the outputs.  That equates to 1/2 the original level at one output and 1/4 the original at the other two ports.  

A 4-way splitter would cut your power to less than a quarter of the original power level at each port. (7 dB at each output).

Diplexors and coaxial cable also have losses. 100' of RG6 typically introduces -5dB of loss. Diplexors, depending on the quality range from -1.5 to -3 dB of insertion loss.

Something to remember is that every time you split the signal in two with a passive splitter you cut the original single level at least in half (-3dB).

Here is a page to demonstrate.  If the formula is kind of nerdy go to the chart and look at the 3dB line.
http://www.pmel.org/HandBook/HBpage22.htm

[Audio Gnut]

Jf follow this link I found about hooking up a diplexor to your system.

http://www.satelliteguys.us/archive/index.php/t-30337.html

hope this helps

[Mark Strube]

I think that's a far too confusing and simplistic way of putting it, though. To someone like me, if you say you've only got HALF the signal left, then if you're starting with 100% signal strength on an OTA station, you'll end up with 50% signal strength on every split connection, which doesn't happen.

In any case, an amplifier should solve your problem, and remove the diplexor if it isn't needed. (And be sure that amplifier will boost the entire UHF band, many do not.) Oh, and your splitter may not be the best depending on how old it is... if it supports up to 1,000mhz or so, it should be fine.

[jfelbab]

I think that's a far too confusing and simplistic way of putting it, though. To someone like me, if you say you've only got HALF the signal left, then if you're starting with 100% signal strength on an OTA station, you'll end up with 50% signal strength on every split connection, which doesn't happen.

In any case, an amplifier should solve your problem, and remove the diplexor if it isn't needed. (And be sure that amplifier will boost the entire UHF band, many do not.) Oh, and your splitter may not be the best depending on how old it is... if it supports up to 1,000mhz or so, it should be fine.

Perhaps you can look at it this way, Mark

Your antenna can only pick up so much of a signal.  Call this 100%  if you need to spread this 100% over two sets each one can get half of it using a passive splitter.  100% in and two 50% outs.  It really is that simple when dealing with passive splitters.  There is usually a half a dB loss in the device itself but that is really inconsequential.

Anyone living 5 miles from the transmitting tower does not need an amplifier.  I'd lean towards a defective device in the signal path.  Either a bad connector or the diplexer itself.   That's why I asked which channels it is blocking.  Within 5 miles of the towers a piece of coathanger will pick up a strong signal.  Commonly problems that close are due to multipath reception. It is possible that multipath is canceling out the signal for the stations he is trying to receive.  If so realignment of the antenna may suffice or possibly a pad to "lower" the signal level. Lowering the signal level will lower the multipath signal which is weaker than the direct signal. if lowered enough through padding it is frequently possible to drop the multipath below the threshold of the receiver and leave the direct signal at a high enough level to work well.

[Mark Strube]

Perhaps you can look at it this way, Mark

Your antenna can only pick up so much of a signal.  Call this 100%  if you need to spread this 100% over two sets each one can get half of it using a passive splitter.  100% in and two 50% outs.  It really is that simple when dealing with passive splitters.  There is usually a half a dB loss in the device itself but that is really inconsequential.

That's still confusing, though. Without a split, my OTA receiver reports 18-1 at 99% signal strength. After the split, it's about 97%. That's not half the signal, as far as I'm concerned.

[jfelbab]

That's still confusing, though. Without a split, my OTA receiver reports 18-1 at 99% signal strength. After the split, it's about 97%. That's not half the signal, as far as I'm concerned.

Your receiver is reporting signal "QUALITY" not actual signal strength.  That's an entirely different measure.  If the signal quality is reasonable the measurement is pretty insensitive to the signal level, you can change the signal level by quite a bit with only a minimal change in the quality level measured.

[jf3233]

Thanks for the many responses. Here is the deal. I run DTV with four lines coming into my home and all four coming off the dish itself. Two lines go to my HD TIVo , 1 line to upstairs and one line to LR where the new TV is. The reason I am using the splitter and diplexers is so that I can get both the sat and ant signal into the house on one line. I have an older home as many do and do not have the luxury to set it up like I would want purely on a logistical basis. Before my addition I had a diplexer on the ant line going into the TIVO without any problem at all. All readings were very acceptable. I am now missing 58-1 amd 10-1 ( not really worried about 10-1 but 58-1 has many HD programs) on the new TV. I tried a crappy RS in line amp after the split on the affected line without any result! Yes the affected box is the longer of the two runs but only about 60 feet.

[mhz40]

Nearly impossible to advise without lots more info--and maybe a visit with a signal level meter. 58-1 is on UHF 46.  Do you get 18-1 off of UHF 61?  Did you ever get 18-1?  What are the frequency details on the diplex ports... unlike splitters, they are not all the same.

[jfelbab]

I believe the issue you have is caused by multipath reflection.  Can you try to reorient your antenna and see if you can find a sweet spot for those channels while still receiving the rest? Channel 10.1 is VHF and 58 is UHF as are all the other DTV channels.  What kind of antenna are you using?  Antennaweb.org will help with the orientation of the antenna but if multipath reflections are negating the signal of those two channels you may need to adjust from the suggested direction.

You didn't mention what kind of antenna you are using nor where it is mounted.  In locations close to the transmitters, an antenna with high directionality is often needed to minimize multipath.
 
Multipath is a reflected signal that is out of phase with the direct signal.  The out of phase aspect cancels out much of the original signal strength.  In an analog set this would cause ghosts with digital it reduces the signal level to below the cliff or threshold of reception and you get nothing.

The first thing I would try is to re-position your antenna to reduce the strength of the reflected signal.

You said you received these signals before on a digital tv correct?  What is different today?  A new splitter? A new diplexor? New connectors?  You could try replacing these one at a time to see if your issues are caused by a defective component.

[jf3233]

Well I have fixed the problem. I have absolutely no idea why 58-1 refuses to lock in on one box but comes in fine on another. All other channels on both TV's are fine. I replaced all connections, treid amp, changing antenna direction and checked all splitters and diplexers for problems and made sure they were correct frequency range. No luck at all. Ran digital scans about 30 times hoping to lock 58-1 no such luck. After all this------hooked up a very simple set of rabbit ears to the digital antenna feed on the new LCD and holy Sh--T, guess what every channel is picked up at well over 80%. Moto of this story, keep it simple I guess!

[Audio Gnut]

Here is another way of looking at multipath. When RF (Radio Frequency) energy is being transmitted to your antenna, the antenna is receiving several different signals. The most optimal signal is obviously the one that is coming in a straight line from the transmitter. The others are being received by the antenna after they bounce off objects such as a building or better yet your neighbors house. This is why some of you have to turn your attic mount antennas to pick up certain stations even though the towers might be on the same line of sight.

http://users.ece.gatech.edu/~mai/tutorial_multipath.htm - Multipath picture tutorial


Here is a guy that tested several antennas and how much multipath they receive.
http://hdtvexpert.com/pages/antin.htm - indoor antenna test
http://hdtvexpert.com/pages/antout.htm - outdoor antenna test


Mark did you go to the link that jfelbab provided regarding signal strenght in terms of DB? It clearly explains how a loss of gain of 3DB is either halving or doubling the power. Get out a calculator and work out a problem if you must.