Perhaps it's been a quiet week in Lake Wobegon... but it certainly hasn't been quiet here.  Frenetic would be a better description; broadcast engineering tends to be something of a roller coaster, with extended periods of intentionality rudely interrupted by episodes of sheer panic.  For the past week or so I've been in and out of town to deal with a whole range of unplanned and unrelated issues at our different stations... and as I wrote that, one of the stations just sent an email concerning yet another problem demanding time that simply doesn't exist right now.  This doesn't happen often, but once in a while we get so overloaded with niggling problems we can only react to, that I despair of actually accomplishing anything that would count as progress.  When I unlock my office door in the morning I have a mental list of things to accomplish; on a good day I can go home with most of the items crossed off.  We are overdue for some good days, but the prospects aren't terribly good for the next week or so.

Sigh.

Yesterday's newpaper included an interesting letter from a gentleman in Camillus who recently installed a DTV converter box and has discovered the "cliff effect".  We're accustomed to the way analog TV behaves as the signal degrades:  ghost images show up, the picture gets snowy.  If the signal gets really bad the picture will lose color and start to roll.  The thing is, the process is gradual, and you can still watch a really poor signal.

Digital TV is a whole different animal -- and this actually applies to digital satellite as well as over-the-air DTV.  As your signal goes downhill, the picture remains apparently perfect until it reaches a certain point where it becomes completely unviewable.  That mystical point is the "cliff", and you can't tell how close the edge is just by watching the picture.

In this gentleman's case, he has a fairly sizeable outdoor antenna on a rotor, and says that he receives 14 channels.  That's impressive: in Syracuse there are only 12 digital channels being transmitted now, so he must be receiving a station from some other market, most likely Utica or Rochester.  Interestingly, the stations he has trouble receiving consistently are 68 and 24... which actually transmit digitally on channels 19 and 25 with a substantial amount of power.

Which brings up another difference between analog and digital TV: we're used to the idea that a poor signal can be fixed by installing a bigger antenna or by sticking an amplifier in the line.  But for digital TV, less is often more.  In general, it takes far less transmitted power to cover an area with a digital signal than to reach the same area with an analog signal.  For instance, our Rochester station transmits 316,000 watts analog on channel 13; after next February they will run only 10,500 watts to cover the same area digitally on that channel.

So what's this viewer's solution?  It might very well be that on those two channels, he's hitting his receiver with too much signal.  I had exactly that problem last week in Elmira, where we installed an Insignia converter box to feed our local station to the cable system.  Hooked up the box and went through the setup steps... and was amazed to get only a mid-scale signal reading.  This wasn't a signal coming from some cheezy beat up set of rabbit ears... this was a direct sample feed coming straight from the transmitter.  We're talking an ideal case here, right?  Well, no.  An analog receiver would have loved it, but the digital box was overwhelmed.  Mae West once said, "too much of a good thing can be wonderful"... but converter boxes don't share her attributes.  I finally had to insert an attenuator pad before the converter's antenna input to reduce the signal level... but once I did, the signal meter jumped right up to the top of the scale.

Unfortunately, attenuator pads aren't all that easy to find outside of a specialty supplier.  Radio Shack used to sell a variable attenuator: a small box with a coaxial connector on each end and a knob in the middle to set the signal level... but when I tried to find one several weeks ago, it turns out that they have been discontinued.  Pity:  I expect that a number of people will find that they will need a solution like that.

In the meantime, if you suspect that you might be overloading your converter (this also applies to full-blown HDTV receivers), you can test that theory by getting a four-way passive splitter and three terminations.  Screw a termination on three of the splitter's outputs, and run the antenna feed through the splitter to the receiver.  (Oh, you'll also need an extra piece of coax cable, a foot or two long.)  A four-way splitter will drop the signal about 7 decibels, which should be enough to make a noticeable improvement if overload is the culprit... and you'll actually see the quality meter go up.

Someone's going to say, if the antenna is on a rotor, why not just steer it slightly away from the station?  Won't that lower the level and accomplish the same result?  Been there, tried that... doesn't generally work.  The problem is that while yes, it lowers the direct signal level, it also increases the amount of crud that's reflected from other surfaces... which makes the situation worse.

I'll do some research one of these days and give you a few places where you can get proper attenuator pads and other antenna supplies... assuming that the roller coaster ride slows down.  For right now I'll leave you with a charming sight:  a $60 converter box installed at a broadcast transmitter site doing the work of a $1,500 professional receiver that failed last week.  And it's delivering a better picture than the "professional" box.  So I suppose we made some progress, after all.

-- Jeff