There is a 3.5 DBmv loss going through a two-way splitter. NOT 6. On a 3-way splitter, there is a loss of 3.5 dbmv on one port with a 7dbmv attenuation on the other two ports. The 3.5dbmv loss is across the spectrum. Cable companies are required to provide enough signal from the "tap" to feed two televisions. However, you should usually have enough signal to feed 3 or 4 tv's in your home. Given that you have the average cable drop from the tap to your ground block at the side of your home. The average drop runs anywhere from 75' to 150' to your home. Should your line be too long from the pedestal or telephone pole then a "mini amp" should be installed at the ground block to ampify your signal either 10 or 20 dbmv. If the splitters being swapped out by the CATV technicians are outside then you have to find the reason why they are constantly going bad. Maybe you have water hitting it too much and it may need better protection like under the deck or some silicone to protect it. If the splitter is inside then it should not be going bad. If so, it could be possible that you have a bad groun on the TV and it is sending voltage back through the coax (riding on the center conductor) and frying the splitters. This can be tested using a voltage meter and checking for AC current on the center conducter at the splitter (the cable going to the television). In rare instances, you may find 30 to 80 volts AC coming from the TV. To test the spare splitters that you have, you would use a RF meter to test the outputs. First, you have to measure the RF level going into the splitter then measure each output. This using the loss values I provided above. My suggestion, call for a service call and ask the technician to read the signal levels at your ground block and any splitters that you currently have in place. Log them for your records. Also, you will find the signal goes up during the cold times of the year and back down as the weather warms up again. The amplifiers on the trunk and feeder lines in the cable system have automatic gain controls however, it is not perfect. So you may add another 2 or 3 TVs in your home but to find the pix suffers as the weather gets warmer. Cable companies usually charge for mini amps to be installed at your home.
Cable TV Line Technician -- 10 Years