Design Con 2015

Tuning in ATSC reception: Mohu's got a VHF fixation

-November 06, 2012

About a month back, I told you that I was in the midst of an arm-wrestling session with Comcast regarding my desire to obtain a CableCARD for use with a SiliconDust HDHomeRun Prime networked television receiver. First off, I've got some news to report. After connecting with SiliconDust technical support, I learned that the HDHomeRun Prime is CableLabs-certified, and therefore Comcast is required by FCC regulation to provide me with a CableCARD. If they don't, they're breaking the law. So I jumped on Comcast's technical support chat, threatened to file a formal complaint with the FCC, and within five minutes had an on-site visit scheduled for the very next morning ... on a Saturday, even.

Within five minutes of pulling into my driveway, the technician had the CableCARD activated. And although I'm having no shortage of struggles getting everything properly working with my Windows 7-based headless Media Center server, I'm making forward progress. In-between my two interactions with Comcast, however, I decided to see if I could get some sort of TV reception going using over-the-air ATSC. Therein the theme of this particular post.

First off, here's (again) what my reception is supposed to look like here, according to TVFool:


Click image to enlarge

As you can see, the bulk of the stations I supposedly can strongly receive are at a compass heading of ~30 degrees. Fortunately, as the magnetometer in my iPad indicates, one of the exterior walls in my residence faces that exact direction:



As a result, I decided to try using a comparatively innocuous antenna setup ... two of them, actually. Downstairs, connected to the PC via the SiliconDust intermediary, is a 10-15 dB amplified (USB-powered, to be precise) Mohu Leaf Plus antenna:



Mohu's gear is intended to stick to an interior wall and is white in color on one side (shown) and black on the other for maximum premises color coordination potential. Upstairs is an unamplified conventional Mohu Leaf, direct-connected to the TV for reception comparison purposes. Both antenna have dimensions of 9×11.5×0.04 in.

My first issue ended up being self-created. When I connected the Mohu Leaf Plus to the HDHomeRun Prime and did a channel scan, I kept getting the following error message:



Eventually I realized that the HDHomeRun Prime included QAM but not ATSC-compatible tuners. Fortunately, I also had a conventional (ATSC-compatible) two-tuner HDHomeRun unit handy, which I fired up. Next, I velcro-stuck the Leaf Plus to the wall downstairs, wherein I found that I was only able to tune in a handful of channels:



Next, on a hunch, I moved the antenna one foot to the right, where it was then velcro'd to a window instead of the wall. The results were dramatically improved:



Still, the unamplified antenna only ~10 feet upstairs pulls in more (and better quality, on average) signals than its amplified sibling below it. Part of the reason may be a robustness difference between the tuner built into the television and the one inside the SiliconDust device. And part of the reason may be that I'm in a fringe region where a few feet worth of elevation differential make a disproportionate difference. I haven't yet looked up the transmission patterns of the various area broadcasters' antennas, but since I'm southwest of them and the bulk of the area's population is to the east of them, any transmission asymmetry will be to my disadvantage.

But still, even though multiple stations' broadcast towers cluster on top of a hill approximately six miles away, my reception of them notably varies. To understand why, take a look at the following table of the transmitters on that hill:

StationVirtual ChannelPhysical Channel
KWGN234
KCNC435
KRMA618
KMGH77
KUSA99
KTVD2019
KDVR3132



The ones that come in the worst are KWGN (physical channel 34), KCNC (35) and KDVR (32). They're all solidly UHF channels. The best are VHF broadcasters KMGH and KUSA. And KRMA and KTVD are somewhere in-between those extremes. When I noticed this correlation, I read the fine print in the Mohu Quick Start Guide and realized that, as with Antennas Direct, I was dealing with a manufacturer who is taking some liberties with its "HDTV Antenna" claims:

The Leaf is optimized for UHF stations, which comprises about 95% of the HDTV stations today. The Leaf will receive VHF stations but it will not be able to receive them from as far away as the UHF band stations.

I'll close with one other gripe. Once again I found myself fighting with Microsoft's Media Center software. KMGH broadcasts on physical channel 7, for example, but Windows 7 still thinks it (to be precise, only two of the four sub-channels of it ... the other two are correct) are still transmitting on physical channel 27. It also assigned those two sub-channels to the program guide listings for low-power broadcaster KZCO. And there were other hiccups I had to un-do, too.

For most folks, technology is a means to a different end, not an end in and of itself. Most folks don't have time to wade through cryptic instructions. And they don't have time to tediously parse through "support" forums when they have problems. Wait ... didn't I just say that the other day? Alas, I did.


Read the whole series:


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