Sunday, August 5, 2012

RCA ATSC Converter Box Failure

Back when the great change from analog to digital TV broadcasting happened in 2009, I went out and bought an RCA ATSC Converter box.  There was a $40 coupon provided at the time, so it cost effectively nothing.

Over the last few months, we have been having an increasing problem with an intermittent signal failure.  The symptom at first is one that most of you already know: weird patches of color caused by the occasional loss of the delta frames.  What causes this?

Most digital video is done by sending a base frame (a full image) and then a series of delta frames, which are the differences between the base frame and the current image.  Theoretically, a video sequence where almost nothing changed from frame to frame could be sent as a single base frame and a bunch of delta frames.  A video sequence that changed rapidly might consist of almost nothing but base frames--but few video sequences look like that.

Now, this loss of frames could be caused by a bad antenna on our end, because have only amplified rabbit ears.  We are fairly remote from the television stations that are aimed at the Boise area, but it is line of sight to those antennae.  However, it appears that at least some antennae are directional--preference is understandably given to where the vast majority of their audience is located, and we are not it.

This problem has been getting worse, and now we are losing base frames as well, I think (my guess because we are occasionally getting an entire screen of a single solid color), and interestingly enough, it is not a consistent failure.  With the RCA box, you can put it in an antenna signal strength meter mode, and see the signal strength represented as a bar from zero to 100 on the screen.  When aimed as best we could, the signal strength varied from 68 to 73 -- and then, every once in a while, down to 0, and back.

We tried a different set of rabbit ears?  No difference.  We made sure all the cabling was tight.  No difference.  Because we are using the S-Video output of the box to talk to the S-Video input of the TV, we switched to RCA component output to RCA component input.  No difference (which tested both the S-Video cable, the RCA box S-Video output connector, and the TV S-Video input connector).

I replaced the box with a new RCA converter box, and the problem seems to have gone away.  We still get the occasionally dropped frame, but extremely rarely.  This is an adequate solution, and the box cost $49.

You are probably wondering: Why am I messing around with a stopgap technology like this?  If you buy a new HDTV, it has a built-in digital tuner, and there's no need for the box.  I'm really reluctant to spend that kind of money on a TV at the moment until the new semester starts, and our College of Western Idaho adjunct paychecks start to come in.  (For those who like to remind teachers that while they are badly paid, at least they have summers off--remember, their paychecks get the summer off, too.)

One of these days, this box will fail, or this ten year old TV will fail, and then I may feel courageous spending the money for HDTV--and by then, it will be a much bigger screen for the same money.


  1. Should you need another convertor again they periodically show up at the thrift stores in Boise for around half of the price you paid for the one you got---sometimes a little less.

  2. Have you thought about making a better roof-mounted antenna? Are you sure you've optimized the placement and positioning of your rabbit ears?

  3. I have thought about putting a proper roof-mounted antenna, but the winds we get recently picked up and turned over a barbecue that, with the concrete blocks as anchors, weighed about 50 pounds. I'm slightly concerned about getting an antenna to stay attached.

  4. The old box very likely was suffering from degradation of the type that hit the DSL modem: heat stress / junk capacitors.

    The "delta frames" are a bit stranger than you might think. Encoders locate square regions of very similar appearance that have moved between one frame and the next, and encode those by sending a motion vector.

    This is especially effective for pan shots (simple translational motion), but not very effective for zooms or rotations.

  5. I knew about the moving polygon feature (which comes out of computer graphics, back when the processing requirements for full motion video would have overwhelmed the CPU, but were easy to do on purpose-built graphics chips), but I didn't want to overwhelm the less technical readers.