How do I Integrate an RF System using 8VSB?

How do I Integrate an RF System using 8VSB?

In a recent firmware update (v. 2.6.4), all QMOD encoders can now broadcast RF channels in 8VSB format. 

What is 8VSB?

Over-the-air TV channels are broadcast using 8VSB modulation, while cable channels use QAM to carry the video. QAM works well for cable, as the channels travel through nice, clean shielded coax cable or fiber, while 8VSB is designed to deal with all the interference, reflected signals, and other anomalies as the signal passes through the air. 

 Why Use 8VSB in an In-House RF System?

Most sites with in-house digital coax networks will use QAM-format channels. Designed for coax distribution, QAM can carry twice the payload of 8VSB, able to carry two HD programs in the same channel. QAM is the defacto standard for in-house and cable digital RF applications. 

However, there are cases where 8VSB is a great solution. Broadcast stations often monitor their and other local stations and don’t see the need to pay the cable companies for programming they can get for free with an antenna. They also know that the cable company compresses the heck out of the original video, so with 8VSB, they see the original quality. And the emphasis on this application, as for cable cutters, is that the programming is free. 

How Do I Create an In-House 8VSB System?

This is not a unique solution – way back in the day this was called an MATV (Master Antenna) TV system. It’s built with RG6 coax, amps and splitters just like a cable system. However it starts with an antenna, not a cable company.

The first step is to go to antennaweb.org and enter the ZIP code of the site. This will show you all the local channels, their actual channel frequencies, and what the channel lineup will be after the channel repack (stations will be shifting to operate between channels 2-36 over the next 2 years or so). The site will also provide information on the best antenna to use and where to aim it. An 2 to 8-bay bowtie antenna works well when the stations are within a 180 degree radius. 

Once the antenna feed is worked out, use a low-pass LTE Filter before combining the channels with the in-house QMOD feed. The filter passes through all channels from 2-50, but blocks out everything else above that. This gets rid of any stray noise above channel 50, as well as cell phone LTE traffic. This also gives you a clear space for the in-house channels, which would start at channel 56 and above. Channel Master Amplify series amplifiers are designed for antenna applications and the LTE filter is built in.

 Build the QMOD headend as normal for cable QAM operation. Starting with firmware version 2.6.4, you access the Common/Modulator menu and select 8VSB. After a minute or so, the encoder will now process the channel in 8VSB format and use off-air channel frequencies. That’s it. 

One note is that 8VSB can’t carry two full HD programs, so you have to tweak the settings so that the total bitrate of the two programs does not exceed 18 mbps. CR Tech Services found that setting Program A at 720p/1080i@12 mbps and Program B at 480p@6 mbps works pretty well.

    • Related Articles

    • Basic RF System Design

      RF distribution systems can be very complex or fairly simple, but they all follow the same rules.  The following basic system design won’t turn anyone in a master RF system designer, but it illustrates how signals are originated and attenuated. It’s ...

    • Basic Instructions for Integrating Display Express RF Control

      Display Express is a very easy system to install and integrate, compared to other video distribution and control systems. Though it’s really simple, it’s often a new way of doing things for integrators. in this blog, we’ll lay out the basic steps, ...

    • How to Integrate Captioning

      All new-gen QMODs have the ability to import captioning data for inclusion with each channel’s program.  SDI video has the ability to embed 708/608 digital captioning, while other inputs can provide captioning data on the unit’s composite video ...

    • Display Express TV Guide

      Here is a summary the “controllability” status of popular makes of TVs w/ Display Express Software. This summary will be updated as new facts and models are discovered. For example, a few sets need to be set in in a special mode, or an energy-saving ...

    • How Does MPEG Encoding Work?

      We refer to our QMOD solutions as HD Modulators – IPTV Encoders. That covers a lot of ground and requires a bit of explaining. A QMOD is an Encoder, as it accepts a video source and encodes it into an MPEG-2 stream. From there, it can package the ...