SWM 101: Why does SWM need a return path?

DIRECTV SWM technology is a very different way of distributing signals than traditional satelllite TV. It was developed in order to help installers take advantage of existing cable television wiring. In the mid-2000s, as DIRECTV was exploding in popularity, the most common complaint in installations was that running two lines to every DVR and a single line to every receiver meant some very ugly looking installs. While many homes came pre-wired with RG6 cable in the walls, installers could not use that cable even if it met DIRECTV standards because of the need for a second cable to the DVR. Not only that, all lines for DIRECTV systems needed to be run to a central point, while cable installs did (and still do) use splitters to put signal in multiple rooms.

The SWM system allows for a single wire to go to each room regardless of how many receivers or DVRs are in use, up to a maximum of eight tuners. It also allows for splitters to be used so that it’s possible to run as few cables as possible. There’s a lot of benefit to SWM, but there are also some downsides. While a traditional satellite TV installation can be extended easily through the use of amplifiers, a SWM system has a hard distance limitation, and in most cases amplifiers cannot be used.

In most cases, the run from SWM to receiver should never be more than 250 feet, and where you are sharing programming between receivers, the total cable distance between receivers should never be more than 300 feet (in other words each run can be 150 feet.) If you’re interested in learning more, we have a whole white paper on that subject.

The real key to understanding the distance limitation inherent in the SWM system is understanding the concept of return path. With a traditional satellite system, a receiver is simply interpreting the signals that come to it. However, as soon as the receiver needs to send information back to the dish for any reason, things get more complicated. In a SWM system, the receivers and DVRs are in constant communication with the dish or multiswitch. The SWM system creates nine channels, each of which is on a different frequency, and each has only the signal that is requested by the receiver. If the receiver does not request a frequency, or if the SWM system can’t “hear” the request because it’s too far away, the whole thing begins to fall apart and you don’t get to watch what you want.

Amplifiers today are built to “protect” the return path but not to amplify it; even though the control signal is sent at a very low frequency (2.3MHz) it does eventually lose strength over enough distance. Some tests with a cable calculator will tell you that you should be able to go about 500′ with a SWM return path, but a number of other factors come into play and the generally accepted figure with RG6 cable is 250′. Beyond that you’re risking losing the return path and if you lose the return path, you lose the signal.