Study Hall

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The RF Spectrum Before & After The “Big Day”

A look at the spectrum between 500 MHz and 700 MHz.

So the big day (June 12, formerly February 17, 2009) came and went, and now we have the results of “the change”.

For those of you living under a rock for the past 10 years, what has happened is that full-power analog TV broadcasts have ceased in most US markets.

At the same time, most of the of spectrum between 698 and 806 MHz, formerly used by TV broadcasts and wireless microphones, now has new owners and is not populated by TV broadcasts any longer.

The legal status of wireless microphone systems in the 700 MHz band is not entirely clear, but the FCC’s intentions appear to be that wireless mics will not be allowed here.

So let’s look at the spectrum between 500 MHz and 700 MHz, covering most what is now available to DTV broadcasts and Part 74 users, including wireless microphone systems.

The first/top image (below) shows this range before the transition, and the second/bottom image (also below) shows the same spectrum after June 12. It is evident that almost all analog sources have disappeared, while only DTV sources remain.

What about using wireless microphone systems in the 700 MHz band?

First, you may still have systems in the 700 MHz band that will continue to operate, until such time as a new, strong signal comes along and interferes.

For many, this may be the right approach: use your equipment until it no longer works. However, keep your eyes open for any announcements about the likely FCC ruling rendering such systems actually illegal.

Currently, there are few signals in that range, but there are some, and soon there will be more.

For those of us using systems between 470 and 698 MHz, our lives should actually be a bit easier for a while. The spectrum is more open, and we should not see the kinds of rapid changes we have seen over the past couple of years.

DTV transmissions are still being optimized, and broadcasters are recommending that people “do a new scan for channels once a month”. I would suggest the same thing for your wireless microphone systems, to insure that you are steering clear of any potential interference. (But you were doing that already, right?)

As to what will become of the remaining usable spectrum, it’s too early to tell. But as TVBD (TV Band Devices) begin to appear, we’ll certainly learn more.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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