Combining in-house modulated signals with digital cable television signals is one of the most complex problems facing custom installers today. Digital cable signals are usually present above 550 MHz (CATV Channel 78) and often fill the entire band from 550 MHz up to 860 MHz (CATV Channel 135). These signals are used by most cable television companies, and are present on the line whether the customer subscribes to digital cable or not.
Most residential modulators have output ranges on the CATV band from Channels 65-135. Since the output of the modulator and the digital cable signals are on the same frequency, they cannot be combined onto the same coaxial cable without interfering with each other.
If the customer is not subscribing to the digital cable service, the solution is simple: (a) find out the frequency or channel number for the highest analog CATV signal offered by the local cable company, (b) insert a low pass filter that will block everything above that frequency, and (c) insert your modulator after the low pass filter.
If the customer is subscribing to digital cable service, don’t give up. In the drawing below, we have split the home into two zones. In your custom installation, you can split to as many zones as you need. The installation can even be designed with a separate zone for each television.
Starting at the beginning we have split the incoming cable television line three ways using a standard 5-1,000 MHz splitter. The first output will directly feed a cable modem. The second output will run into a low pass filter and eventually serve the entire house with analog cable television Channels 2-78. The third output is split with a standard 5-1,000 MHz two-way splitter to feed two individual digital cable converter boxes. The first converter box will be modulated on to Channel 85 and dedicated to Zone 1 having two televisions – the family room and bedroom two. The second converter box will be modulated on to Channel 90 and dedicated to Zone 2 also having two televisions – the main bedroom and the home office. We chose two different channels on the modulators for the digital converter boxes to avoid the possibility of interference from a back-fed signal on either box from one zone to the other.
We are also using a two-channel modulator to distribute a DVD player and a VCR on Channels 100 and 105. The output of this modulator is split two ways using a two-way splitter that passes infrared signals. One output will be used to feed Zone 1 and the second output will be used to feed Zone 2.
The output of the low pass filter is now split two ways. Using a three way infrared passing splitter in reverse, we will combine one output of the splitter from the line with the low pass filter (Channels 2-78), one output of the splitter from the DVD/VCR modulator (Channels 101 and 105) and the output of the modulator from the first digital converter box (Channel 85). The output of this three-way combiner will now feed a two-way infrared passing splitter that is used to feed the two televisions in Zone 1 via home run wiring.
Using another three way infrared passing splitter in reverse, we will combine the second output of the splitter from the line with the low pass filter (Channels 2-78), the second output of the splitter from the DVD/VCR modulator (Channels 101 and 105) and the output of the modulator from the second digital converter box (Channel 90). The output of this three- way combiner will now feed a two-way infrared passing splitter that is used to feed the two televisions in Zone 2 via home run wiring. Everything to this point is neatly mounted on a backboard in the basement or other central distribution point.
Each of the modulators in this system is equipped with infrared control capable of transmitting an infrared signal through an emitter that will control the modulated device. The infrared signal will originate from a remote control at the viewing site. An infrared target will be inserted in line at each television set. The infrared target will accept a signal from an infrared remote and transmit that signal through the coaxial cable in reverse. When the infrared signal reaches the modulator, it will be fed through the infrared emitter to the infrared eye on the device being modulated. This gives a viewer the ability to control the modulated device in the basement from the remote viewing location (bedroom 2, home office, etc.).
The user has the option to use the remote supplied with each modulated device or purchase universal remotes that can be programmed to control each device without interfering with another. Depending on distance and wire specifications, amplifiers may be needed to compensate for RF signal loss. We also recommend mounting all of the splitters on a backboard and racking all of the electronics in an equipment rack to add a professional look to the installation.