If your antenna signal drops below satisfactory levels when you add a second or third TV, DVR, VCR, FM Tuner, etc. to the downlead, you can add a preamp
and/or a distribution amp
, depending on whether you have a preamp already installed, but you will have some tests to run because you need to see if there is now a risk of the newly amplified signal overloading one or all of the tuners that are downstream. Overload can cause damage. Please read the previous posts in this thread about Preamps and Distribution Amps before going further.
You'll need a pencil and paper to write down the name of each device we'll add and its signal strength results. Drawing a schematic of your antenna, gear, and cabling layout with the distances and signal strength results added can be helpful. For these tests lets assume that TV #1 is your main ATSC television and that we have installed a 2-way, 3-way, or 4-way splitter in the antenna lead just above that TV, depending on how many devices you want to run off that antenna.
1. disconnect all devices from the splitter except TV #1 and the antenna lead. If you have F-connector terminator caps for the empty splitter sockets put them on, but we'll be fine if you don't have them.
2. install the preamp directly to the antenna lead above the splitter as close as physically possible to the antenna itself on the mast, but make sure that the preamp's power source is not yet plugged in
3. on TV #1 tune to the strongest
DTV station you can find
If during step 3 the signal strength meter jumps to 100% you have a possible overpower situation. Imagine if the preamp had been powered up first: there is nowhere to go past 100% except overload, and it isn't pretty. If you have a possible overload situation don't worry yet, its not the end of the road. Its just a point to remember that your preamp could cause problems with your ATSC tuner(s) so you need to test further.
4. leave TV #1 on that same station, connect TV #2, and note the signal strength on TV #1
5. repeat step 4 one-by-one for each piece of equipment (TVs, DVRs, VCRs, FM Tuners, etc.) sharing the splitter, making sure to stop and note the signal strength after each addition.
If after all of them have been connected you still have very high signal strength on that station (like being a few blocks away from the CN Tower) you are very much in danger of the preamp overpowering the system if it is ever powered up. This poses a real problem if you need the preamp to receive some weak stations. Keep your signal strength notes and call a professional or come back here to DHC so we can discuss options such as attenuators, variable strength distribution amps, and other ideas.
If, on the other hand, you find that the signal strength drops accordingly with each device added to the splitter, its time for some further tests:
6. disconnect all TVs & equipment from the splitter except TV #1 and the antenna lead.
7. on TV #1 tune to one of the weakest
DTV stations (lots of pixellation or dropouts, or not able to lock on but showing some signal strength)
8. display the tuner's signal strength meter on the screen
9. power up the preamp and note any signal strength difference
During #9 if you notice a sharp jump upwards on the meter to 100% on such a weak station (highly unlikely!) you are possibly at risk of overpowering your receiver: imagine stations that were already at 100% now getting that power boost and you start to see the danger. Disconnect the preamp's power and either call a professional or come back here for advice.
If, on the other hand, it doesn't jump to 100% but the signal strength seems very high, don't worry too much yet. Lets add some more connections to see what happens.
10. connect TV #2's antenna feed and note any signal strength difference
If you have a nice balance of good signal strength by adding another TV but if TV #1 on its own would be in an overpowered situation, don't just accept things as they are. Install an in-line attenuator directly on the back of TV #1. This will lower the incoming signal just to TV #1, so that in the future if TV #2's lead is ever disconnected for more than a small amount of time you will avoid overdriving TV #1's ATSC tuner. Attenuator strength is usually shown as something like "-3db" so you can try a couple of different ones since they're relatively inexpensive.
11a. repeat step 10 as necessary for adding any other TVs, DVRs, VCRs, FM Tuners, etc. that will also be using the splitter located above TV #1, and observe the signal strength meter after each addition, checking to see if an attenuator is needed on any of them. Odds are you probably won't need attenuators for them. Odds are you might now need amplification
, but we'll get to that in a bit.
11b. there is a cheap and quick way to lower the strength of TV #1's input signal if you are going to add other devices. Splitters cause predictable signal loss (usually 2 or 3 db per splitter but at the risk
of adding signal interference) so we can sometimes use that predictable signal loss to our advantage. Splitters are relatively cheap and much easier to find than attenuators so they are a poor man's bandaid and not a proper solution.
Nevertheless: run a lead from the antenna to a splitter to TV #1 as usual with no attenuator, but then before it gets to TV #1 split it again into a 3 or 4-way splitter. Then add a DVR, a VCR, an FM Tuners, etc. and TV #1 to that new splitter and you will accomplish the same effect as an attenuator at that end, without lowering the signal as much on TV #2's branch (see why I draw schematics?
I do not recommend step 11b. without checking the signal strength on TV #1 one-by-one for each piece of equipment added because you could unwittingly lower the signal too far
! Maybe only 2 devices are needed to achieve the attenuation effect. Maybe 3 should go in alongside TV #1 and 2 should go above it... only testing will tell. Test until you see a suitable compromise solution in which all devices get relatively equal signal strength no matter which branch they are split from. As I say, by that point you are probably in need of amplification
If after adding TV #2 and especially after adding other devices your signal strength even on the strongest stations starts to drop unacceptably low, its time to add a Distribution Amplifier below the preamp. Think of it as a "powered splitter". Testing it is easy, just follow all the same steps as above. The goal is to get a good balance of signal strength across all your devices. You should be able to tell from your schematic drawing which branches of your system might need amplification or attenuation.
By the way, professionals use signal strength meters and spectrum analyzers so they don't have to do all this stuff unless abolutely necessary!