The internet has a lot of information but I was surprised that the answer to this isn’t already online. The best search result I found was a scanned PDF from about 25 years ago. So let’s dive in. First, the basics.
What is a headend?
“Headend” describes a television system that’s like a small cable TV system in a commercial building. There are a bunch of antenna tuners, cable boxes, or satellite receivers all in one place. Each one of them is tuned to a different channel. The signals from each box go into modulators, which are specialized pieces of equipment designed to put each signal on its own TV channel. (Maybe you had a modulator for your 90s-era video game system that put its output on channel 3. Does that sound familiar?
When a headend does its work right, you have one cable that can be distributed throughout a building, and people can tune to any one of those video sources just by changing the channel. You’ve seen these systems before in hotels and you probably just didn’t think about it.
Why would you use a headend?
The real allure of a headend system is its simplicity. If you were to put a satellite receiver in each room, you would probably end up running a wire from each receiver into a closet where you’d need a multiswitch for every 26 rooms. With a headend system the signal can be split and tapped off so that one cable run can serve all the TVs on a single floor. This means it’s easier to maintain and easier to upgrade. If you’re looking at a system with 100 or more televisions, this is going to be a lot easier to manage.
Another draw of a headend system is its low cost. You will basically pay a very small charge per channel and a very small charge per drop (A “drop” is industry talk for where the TV goes. It’s also called an “outlet.”) Headend systems with many drops are much cheaper than similar systems with many satellite or cable boxes.
How does the signal get from place to place?
Headend cabling is very simple as I’ve said before. You can have very long runs and lots of TVs on each run, and the key to that is having the right amplifiers in place. You load up the signal to be incredibly, incredibly strong when it starts out. Then, you split it or tap it as needed. (A tap limits the signal level on one output while a splitter doesn’t. Here’s a whole article on that.) You can make the outputs from the modulator incredibly strong — about 100,000 times stronger than the TV signal you need. Let’s dive into the real numbers.
At the headend
According to our friends at Televes who published these numbers in their software for cable TV meters, the signal level coming out of the headend should be between -15 and +55dBmV. (It’s not super important what a dBmV is right now, there are some good articles out there that explain it.) At the top end, we’re talking about 1,000 times more powerful than your average satellite signal traveling through the average home.
At the drop (at the TV)
Again relying on the experts at Televes, they say that when the signal gets to the TV it should ideally be between -15 and +5dBmV. Any less than that and you may find the signal gets grainy or blocky. Any more than that and you risk burning out the TV’s tuner which is generally the end of the TV.
How should you determine the right output levels?
You can use cable calculators to figure out overall loss, but there’s no subsititute for being onsite and testing everything with a meter. You can show up with the best possible plans but you’ll always end up tweaking things. Here’s a very general method for figuring out what you need to do.
First, start with the furthest TV. Measure the signal level there, on the highest possible channel. Higher channels have more loss than lower ones, in general. If the level isn’t good, you’ll need to turn up an amplifier somewhere or add another amplifier.
Then, work backwards making sure you get good signal levels on both the highest and the lowest channel on every TV.
Finally, check all the outputs at the headend to make sure none of the channels in the middle are too low or too high. You can generally adjust the outputs at the headend.
If you’re looking for help…
Give the folks at Signal Connect a call. They will help you find an installer in your area who can help you get your system working perfectly. The number you need is 866.726.4182.