Channel Insertion!
Welcome to Tech Talk, Pico Macom's series of technical notes, featuring useful information and equipment tips. This installment of Tech Talk discusses Pico Macom’s line of channel elimination filters.
The crowded channel line-up
Inserting a security or DVD channel shouldn’t be difficult. To maximize the viewing experience, it’s easy to insert the desired channel into the existing line-up for whole-house distribution. This provides the flexibility of viewing the inserted channel from any room in the entire house. One note: The TV set and/or set-top box must be capable to tune to the selected channel.
In the past, when you wanted to add a surveillance channel to an existing cable television line-up, you might have heard the phrase, “Just put it above the highest channel,” and that worked. These days, most cable companies are using the channel spectrum below the lowest channel for signal return, the typically analog spectrum for channels 2~78 including the FM radio band, and the spectrum above it for digital signals.
This can be very misleading. Unless you are looking at the signal with a spectrum analyzer, it can be difficult to tell whether or not there is a signal. On a TV set it will just look like snow, and on a signal level meter it will look like an elevated level of noise. How can we be sure to have a clean location to insert our locally generated channel? If we insert a channel onto another channel, we will get distortion and snowy pictures.
The answer is to first filter out the channel spectrum where we want to insert. By doing this, even if there currently isn’t a channel that would interfere, our inserted channel is safe. If channel line-up changes or additions occur at the cable company, it will not affect our channel.
Simple Installation
Diagram A
Whole-house insertion (Diagram A) is easily accomplished. It isn’t so much the type of filter as much as the placement in the signal path. Place the filter and the inserted channel as close to the first point of contact to the house before any splitting. This ensures that the signal will go to all TV locations in the home.
Diagram B
In a “nanny-cam” surveillance application, the inserted signal may only be desired at specific locations and not every connected TV. This requires a slight variation of the whole-house insertion (Diagram B). The signal where it connects to the house is split using a TSB-2GFR two-way splitter. This creates two separate paths. Connect the filter and inserted channel only on one of the outputs. Then the uninserted line-up is distributed to all TV locations except in the locations where the inserted channel is desired.
There are two filter types used for channel insertion:
Low Pass Filters (LPF-Series)—These filters are designed to pass all channels below a designated frequency and filter out the channels above. These are ideal if you are only receiving the analog CATV channels and want to “just put it above the highest channel.”
Channel Elimination Filters (CEF-Series)—These filters are designed to remove a single channel without having a significant effect on the adjacent channels. An example of this would be if you wanted to filter out channel 3. These are ideal, since they are capable of passing the digital and return signals through and only affecting the specified channel.
The key to distortion-free channel insertion is to use a filter to clear out anything that can interfere with the inserted channel.
Use a quality Pico Macom modulator.
Match the signal level of the inserted channel to the level of the existing adjacent channels.
Our sales and engineering team at Pico Macom can assist you with selection of the best option of filter and modulator to ensure maximum compatibility. Please give us a call at 800-421-6511 and let us guide you through the selection purchase and connection process.
Click here to download the CEF Series Manual.