Monday, March 04, 2019

Optimizing a TV Antenna with an HDHomerun

I get asked by users of my Signal GH iOS app for the HDHomerun network TV tuner what measurement they are supposed to improve as they adjust their TV antenna systems.  

The HDHomerun provides 3 metrics describing the data stream coming from the over the air antenna: 
  1. Signal Strength
  2. Signal to Noise (or Signal Quality)
  3. Symbol Quality
I've been thinking about the analogy of someone with a noisy hearing aid trying to understand someone talking in a noisy room. From this way of thinking, Signal Strength is either turning up the volume or moving closer to the talker. It's how loud the voice is to the listener. The problem with this is, that the signal might be too noisy or maybe you are boosting as much noise as signal, or making it so loud that it's painful. Some gain might be useful, but just ramping up the Signal Strength has its limits. 

In this analogy, Signal Quality is how noisy the voice is when it gets to the listener, if the hearing aid is high quality, or the room is naturally quiet, even a fairly quiet talker can be understand. You might try buying a better aid which can add gain without adding additional noise, or move closer to the speaker. 

Finally, Symbol Quality is a measure of did you understand all the words the speaker said. If not, your understanding can be severely distorted. When it comes to digital TV, you either understand everything perfectly or the picture pixelates. So, when it comes to Symbol Quality you want 100% perfection, nothing else will do. This is why I show it as either a green filled circle ⬤ or a red ring  ⭕️ and don't bother to show the Symbol Quality number.

As you can see, I'm prodding you to understand that while some Signal Strength is necessary, and Symbol Quality perfection is mandatory, it is long term Signal Quality that you want to improve. This is why Signal GH graphs Signal Quality over time, and not the other two metrics. If you can get the Signal Quality consistently above, let's say, 80, this will lead to getting perfect Symbol Quality  so your job as an antenna system optimizer is to find out what steps it will take. 

In my case, several years ago, I went through the process of getting bigger and bigger quality UHF only antennas, on taller masts, using a quality UHF pre-amp, and using my Signal GH app to find just the right direction to point the antenna—actually I used more primitive tools in the beginning and it's what led me to develop Signal GH. With each step, signal quality for each of my local stations increased, and each would eventually have such consistently high signal quality that the Symbol Quality would pretty much never dip below 100% perfection. Initially, I pulled in 2-3 stations good enough to watch without pixelation, and now I have 8-9 with dozens of sub channels, including every major. It's a rare—and usually blustery day—when my picture breaks up. I have an advantage in that all the stations I'm interested in are in the same general direction, or are close by, so I didn't have to resort to exotic antenna configurations: just bigger and taller. 

One thing I like about networked TV tuners, like the HDHomerun, or the Tablo, is that since they are shared resources, I don't have to split my signal to every room in the house, instead, I split my antenna signal between an HDHomerun for live TV, and running my app; a Tablo for recording scheduled content; and my main TV for watching major sporting events, i.e. pro football. So, only split three ways. With a 3 way splitter, one of the splits gets twice the signal of the other two, and this output I connect to the Tablo, as it will be recording unattended. Minimizing splits is one way to get better signal quality. 

Another signal improving quality of networked tuners is shorter cable runs, as they can installed right next to the splitter. 

Here's a video I made to elaborate on signal metrics:

By the way, I occasionally hear from other Tablo users who own an HDHomerun solely to run Signal GH. Gratifying but I wish I could support the Tablo, but they don't appear interested in providing the data I would need.