White Spaces - RF beyond the Aesthetics

 

White Spaces,  Sounds like something your Art History professor would use to describe ‘the   power’ of an unpainted space on a Jackson Pollock.  

In fact White Spaces is the name for a contentiously battled over area of RF (Radio Frequency Spectrum) and yes it effects you and your AV business.

Until just a few years ago television stations broadcast their signals via three separate signals, one each for Picture, Color information and Sound. These three signals would be recombined inside the circuitry of your TV  to produce the complete picture.  These three RF spikes, creating mountains and valleys could be clearly seen on an off air oscilloscope.  The valleys and spaces between the channel signals is where many wireless devices would ‘sit’.  In large metropolitan areas where every possible channel was used, such spaces were invaluable.  When it came to wireless microphones, this was doubly so.  

Then came digital television.  This beast, not to be confused with HDTV -(the former can carry the latter but it may not always be the case), generates one signal with all the information.  Great! you might think - with two less signals to worry about there will be more room for other lower powered RF devices, right?

Um, No.  

While there is now only one signal it takes up a wide swath of space in a continuous signal. Bummer no? Yet there is a bright hope here.  The FCC mandated that all analog broadcasts (the three spikes) were to have ceased broadcast by June 26th, 2009. The plan is to sell off all the remaining ‘empty’ space to facilitate new communications technologies and less the RF congestion that now plagues wireless.  

Great, Right?!, Maybe.

Manufactures and audio industry folks have been raising a ruckus to insure that a defined space is available for the use of itinerant wireless devices such as microphones and intercom systems - such as those used at live events.  Sadly it took a small skirmish but it appears things have been finally worked out.

I learned about the true value of the analog television signals on  February 26, 1993, the day the World Trade Center was bombed.  One of my responsibilities as a rental tech was to test and calibrate wireless mic systems going out on jobs.  One of the tools we used ( and actually still have) was an off air oscilloscope or IFR, to insure that the IFR was itself calibrated we would tune it to a TV channel’s Picture RF spike.  Once we knew that the RF spike from. say channel four was reading accurate - we could then be confident that our mic signal was accurate and tune it accordingly.  On that February day I was still only just becoming comfortable with the operation of the IFR.  

As usual I brought up the Television channel to see that the unit was operating  as expected when it happened, the spikes - all three dipped then disappeared.  I checked a few more channels and they too were gone.  “Oh no”, I thought, “i have broken a $10k piece of test gear”.  With a mild sense of panic and depression I told the service manager of my actions.  He was a bit irked with me to say the least and stormed to my test bench.  He found the same thing I did until he brought up NY channel two, he then brought up the audio - which is where we heard the news that the WTC had experienced an explosion that had shut down the transmitter atop tower one. (Channel 2 still used the antenna atop the Empire State Building).  That is when we looked  out the office window which had a direct view of the WTC, to see smoke billowing up. I recall this event every time I look at a oscilloscope and it is the mental image I have of when I think of what the analog transmission shut down must have looked like.

Now that I am back in the event staging / live events world I have an renewed interest in just how the new landscape of RF should be handled and lucky for me the good people at AV Nation have a great podcast special on just this topic. The special broadcast includes Sennheiser's Eric Reese  and Kent Margraves with host Michael Drainer discussing  the FCC laws and tips to get your wireless to work flawlessly.  I highly recommend it to anyone who works with audio for live events, this is great stuff.