Preamp lowers signal strength?

[Greglet]

Hi,

After installing a preamp on an HDTV antenna I'm finding that the signal at the Dish receiver drops significantly. Any ideas? Here's the setup...

We have a UHF antenna mounted in the attic. A single HDTV is connected through a Dish receiver to the antenna via a 70 foot coax run. When directly connected to the antenna, the dish receiver reports an 87-94% signal strength on most of the OTA channels. The picture is great.

However, we now need to split the signal from the antenna to several more rooms, some with long cable runs. For that reason, we decided to install a pre-amp to avoid signal loss problems after the new cables are run. Before running the additional cables, we installed the preamp first. Now, with the preamp installed, and the single TV connected trhoug the Dish receiver, our signal strength has dropped by over 20%. With the preamp in line we get signal strengths of 65-70%. with the antenna connected directly (no preamp), the signal jumps back up to 90%+. (We tested the power supply to the preamp and it is getting power).

Any ideas?

Thanks,

Greglet

 

[bhelms]

Did you check to see if the signal to all locations is adequate without the preamp? That's an obvious test you should do. Since you did test the set-up to just the TV with and without the preamp, that should rule-out any issues with the cables and connections in that part of your system, but you might need to double-check all the rest as well.

In reality, you don't need a preamp since the signal to one TV was adequate. If you find that the splitting causes unacceptable signal loss what you really need is a distribution amp, i.e., one that provides only a couple dB gain to each outlet. That would be a single piece unit that would be located in your centralized equipment place where the splits occur, not mounted at the antenna.

Welcome, BTW...

 

[navychop]

Yep. By and large, pre-amp for distant signals, distro amp for long/many feeds.

 

[Greglet]

My main concern was that the preamp was not working properly for some reason. There seems to be a concensus that the preamp is overloading the receiver, since there is only one TV connected. I think our next step will be to leave the preamp out of the system, connect all the additional drops, then bring the preamp back in if it is needed. Does anyone have experience with a Dish receiver lowering it's signal strength like this? It seems counter-intuitive to a lay person like me.

Anyway, one more question...

What is the conventional wizdom about using 75 ohm terminators on splitter outputs that are not being used? I've seen infomation saying they are important, and conflicting information saying they are unnecessary.

Thanks... and zip code is 20148.

Greg

 

[Tower Guy]

A preamp with too much gain can overload itself, or deliver too much signal to the the set top box. The more stations there are, the easier it is to get overload. There is an overload resistant amplifier, the Winegard HDP-269. It can handle stronger signals before it overloads and has less gain to minimize the overload of the TV set.

 

[Greglet]

You guys are great. Thanks very much for the help. Once we get all the runs complete, I'll forward the configuration.

In the meantime, can anyone explain WHY terminators are necessary? I've seen advice both ways, but I've yet to run across a good explanation of why.

Thanks again!

Greglet

 

[bhelms]

Also - you will have reflected signals back into the system from improperly terminated ports...

 

[Barry Erick]

The signal strenght is not a stest of rf level, it is also a test of quality in digital receivers. The preamp can be distorting the signal while providing more gain. Do check if your HD TV's have a LNA (Low Noise AMp) built in. With that, just use a splitter and toss the preamp. Even without, see how the other tvs work with just a splitter. I do that and the loss is minimal as it is an error rate measurement and not just how much rf I have.

 

[riffjim4069]

I agree with Barry...while a preamp will boost the signal, it will also add noise. A marginally strong signal may become much less stable after inserting a noisy preamp. Check the signal to noise ration (SNR) on your receiver, if available, and invest in a quality low-noise preamp like Channel Master and Winegard. The CM-7775 UHF preamp has +26db gain and only +2db noise. However, if you're looking for high quality ultra-low noise preamp with only 0.4db noise, then check out this post: http://www.satelliteguys.us/showpost.php?p=337640&postcount=3

Of couse, it will cost $$$. Offhand, placing your antenna on the roof (if possible) would be the best way to improve antenna performance.