I don’t know what the National Association of Broadcasters is thinking with its latest campaign- urging anyone who visits its web site to contact the FCC and urge it to “tell them not to allow unlicensed personal and portable devices to operate in the television spectrum.” You know, wireless microphones, wireless video feeds, wireless intercoms, wireless IFB, wireless of all sorts! This is because “American consumers deserve and expect to have interference free digital television.”
Uh… how do we create television and films without wireless video and audio?
Does the NAB want to render every wireless mic from 54 – 800 Mhz illegal?
Broadcast Television in the US basically gets almost everything from 470 Mhz to 794 Mhz. You can see from the chart above (bigger one here from 9 Mhz to 300,000,000 Mhz) that a few broadcast stations share the same frequencies with mobile radios, or are adjacent to mobile radio transmissions. The handsets are usually 2 to 5 watts, the base stations 20 – 50 watts. These base stations are licensed and legal and transmit these high power signals right next to broadcast TV. This article is not about these mobile or fixed transmitters at 5 or 50 watts. No, it’s about the NAB and MSTV pressuring the FCC to outlaw devices that will transmit at 00.1 or 00.4 watts on unused TV channels in the broadcast TV spectrum because of widespread on-channel and adjacent channel interference.
There is confusion because there are already plenty of devices that legally operate this same very low power in the broadcast TV spectrum. You see, wireless mics, headsets and more all operate in the “white space” in between and even within normal TV channels. The reason they do this is because TV is (was) a constant. Every channel had the same broadcast spectrum output (DTV is different, but we’ll get to that later) and there are stations not being broadcast on every “channel.” This leaves big, empty gaps of wireless space where I can tune in my wireless mic and get the audio I need to get.
Here’s the NAB’s take:
Interference zones, sometimes referred to as “white spaces,” are areas where frequencies in the television spectrum are not currently occupied by television signals. When unlicensed mobile devices operate in these zones, they can cause interference to televisions in the area. And because the devices are not licensed, they are impossible to track down, so the interference can not be stopped. This interference has been confirmed by the Federal Communication Commission’s Office of Engineering and Technology in a report released in August 2007.
Those spaces have been referred to as white space for way longer than the 20 years I’ve been doing production. That first line ought to read: When a legal, unlicensed very low power device transmits in analogue broadcast transmission gaps or completely open frequencies adjacent to broadcast TV channels, places which have been called “white space” in the industry for decades, it may interfere with broadcast TV transmissions.
You can find out what channels are in use where you live by going to AntennaWeb.org and typing in your zip code. Note that when it say, for instance, WPVI is on channel 6 but WPVI-DT is on 64, that means the digital broadcast signal for my local ABC affiliate is actually on channel 64. You won’t be able to see DTV broadcasts with an analogue receiver, it will just look like noise. This is why it’s often difficult to know what’s flying through the air.
Frequency coordination is an important aspect of video production these days. You can’t get into the Superbowl, World Cup or Olympics without undergoing frequency coordination of anything wireless you may have. You can’t just show up, and turn your wireless anything on. Why is this an issue? Well, lets look at a very short and actually very small production I worked on recently…
When I was doing audio for the Speed TV channel show PINKS, I was setting up five wireless kits with four receivers, one IFB transmitter in each one. This was for a three solid hour shoot that produced one half-hour show.
This doesn’t take into account the FRS, GMRS and Business Band mobile radios which have their own dedicated frequencies (where our wireless mics are not allowed). If a receiver was close enough to one of the 5w walkie talkies when someone transmitted, the sensitivity of the receiver would drop to the floor and any distant mic transmitters would drop out completely.
You see, a 5000 mw (5w) transmitter right next to the receiver is a bazillion times stronger than the 50 milliwatt beltpack 100 yards away, through concrete, drywall, and who knows what metal.
Wireless mics can’t even be near land mobile and fixed, marine and amateur radio transmissions.
Even though a TV station may be 50,000w, 150,000w or more, it’s miles away, a constant transmission and it has holes. Okay… Analogue has holes, or gaps in the transmission signal where wireless mics can sneak in and operate. DTV is more like a big block of white noise. But even then, the use of pilot tones and the much closer proximity of the wireless mic enables it to continue to work. But I digress. The point is, frequency agile systems enable us to sneak around the spectrum and look for little mouse holes to scurry into.
Here’s a look at what is actually spit out of a TV antenna.
On the left, you can see the analogue signal for TV station KSNT. There is a spike for the audio carrier, a spike for the video carrier, a spike for the color subcarrier. But there are clearly troughs where a wireless signal can be tuned in and used. DTV makes it harder. You can see KSNT-DT (digital transmission) is a wall of noise, but actually it has no really strong carrier spikes to contend with. So as long as your wireless mic is closer and “louder” to the receiver than the DTV noise, then you are okay. Even better are the spaces in between stations, where the noise floor is low and wireless mics and other systems can frolic in the open (RF) fields.
A problem arises when you set your wireless mic for an open space in Chicago, and then turn it back on in Miami. You could very well be transmitting on a DTV frequency. Now, as long as you can hear the transmitter, you think you’re fine. But you might be causing interference to nearby DTV receivers.
I wont get into how the overwhelming majority of the USA is served by cable, satellites and other services— meaning they do not use broadcast TV at all. Let’s say the National Association of Broadcasters is right that those DTV transmissions need to be protected.
Is the solution to outlaw all unlicensed – but legal – transmitters?
Following the links on the NAB web site, you end up at The Association for Maximum Service Television.
As a side note, I had to laugh a few times at the MSTV.org video. It shows the digital cliff effect- when interference was bad enough, it completely froze. The audio vanished. The picture became completely filled with artifacts. That’s unwatchable. They really glossed over what happens with analogue TV, it gets snowy. The audio is still there, the picture is still there, you can still see and hear the program, yet MSTV calls the snowy analogue image “unwatchable.” Huh? Actually, if the program was one I was interested in, I’d take the fuzzies over the complete freeze, complete loss of audio, and complete image degradation of DTV any day. If it was the end of a close game featuring your team, that snowy image is quite watchable!
Anyway, back to the MSTV video…
They did not say what frequency the test “interference” was using.
They did not show the spurious emissions of the test transmitter compared to allowable.
They did not indicate its proximity in frequency to the test channels shown.
The did not describe the type of signal output from the test device.
How much like the antenna of the test device is the potential interferer’s?
Is it exactly the same as the devices MSTV fears?
Is transmission constant, or intermittent?
Is it set on one frequency or frequency hopping?
Is it narrowband, FM, AM or spread spectrum?
Does it detect existing broadcasts and change its own channel?
This report and this note seems to say so.
They used one of the cheapest DTV antennas available set up on the table right behind the TV viewed. The receiving antenna was in the house, pointing to towers tens of miles away.
What small percentage of Americans still receive over the air TV broadcasts? What vast percentage of those people are continuing to use the TV antennas on top of their house, or on a mast next to their house? What percentage is left that use only TV-top antennas? What percentage of viewers have so much extra kitchen countertop that they can reserve a big swath of it for their directional DTV antenna? And, lastly, what small percentage of them will be interfered with by these new devices? It’s nearly infinitesimal.
Moreover this entire campaign is so vague it can only do more harm than good.
What are the interfering frequencies in question?
The MSTV video shows a computer. It repeatedly shows the computer sliding into a “white space” in between what are seems to be labeled as active TV channels. (They didn’t provide a very big or clear video to make their case… wtf?)
So it would seem that something computer related is supposed to go into unoccupied TV channels.
Perhaps part of the FCC 700 Mhz spectrum auction?
We don’t know because they refuse to say!
It’s not WiFi, or Bluetooth, those are 2400 Mhz, well above the 800Mhz end of TV.
It’s not cellular broaband.
So what is it?
Even in PDFs published on the MSTV site are vague about the transmission:
Such interference will disable a consumer’s ability to receive the co-channel television station for up to tens of miles depending on the power and antenna height of the TV band device.
The severe effects of such co-channel interference are verified by an analysis of data submitted previously by Intel, despite its support of an aggressive “unlicensed devices” regime. Specifically, in its comments to the Commission, Intel suggested that the interference range of a 100 mW personal/portable unlicensed device is approximately 8 kilometers (or 5 miles) from a television contour, therefore acknowledging that in order not to cause interference to TV reception, any TV band device must operate at a sufficiently large distance away from the television contour. In fact, the actual zone of interference would be much larger, as Intel’s analysis incorrectly assumes a 14 dB antenna discrimination factor.
Here’s the PDF’s assessment of co-channel transmission:
As indicated by the above chart, DTV viewers, even hundreds of meters from a 100 mW TV band device operating on a first adjacent channel, will experience harmful interference. The interference concerns are even greater for the higher powered 400 mW devices which may cause interference to DTV services for over a kilometer.
Which I have to wonder, if a TV station can broadcast a full power analogue and a full power DTV signal on adjacent channels, (as demonstrated by the KSNT spectrum graph above) without interference to either the analogue or the DTV transmissions, what is it about these tiny devices, which operate at a tiny fraction of the power (00.1 w), that makes them so incredibly detrimental to the OTA signals?
By full power, I mean as much as 5000 kilowatts… or 5,000,000 watts.
In North America, full-power stations on band I (channels 2 to 6) are generally limited to 100 kW analog video (VSB) and 10 kW analog audio (FM), or 20 kW digital (8VSB) ERP. Stations on band III (channels 7 to 13) can go up by 5dB(W) to 316 kW video, 31.6 kW audio, or 63.2 kW digital. UHF, by comparison, has a much shorter wavelength, and thus requires a shorter antenna, but also higher power. North American stations can go up to 5000 kW ERP for video and 500 kW audio, or 1000 kW digital.
Harris has won a Technical Emmy Award for filters that enable a TV station to combine both broadcast signals into one cable and antenna, and still not interfere with each other.
How the heck does a 00.1 watt device kill a 1,000,000 watt TV station?
The PDFs are very expressive about what they want the FCC to do:
• Any new devices allowed to operate in the broadcast spectrum should be exclusively licensed; no unlicensed operation should be allowed. [emphasis mine]
• The Commission must enact a rigorous enforcement program. If the Commission allows TV band devices to operate in the spectrum, it must develop a reliable system to enforce the prohibition on these devices interfering with licensed services. Without such enforcement mechanisms, the rules prohibiting interference with incumbent services will be ineffective.
And what about the tens of thousands of wireless systems we use every day that transmit in the broadcast TV spectrum? Do we have to turn them all in at the local police station once they are ruled illegal? Will we get free tickets to the local SixFlags adventure park like those who turn in guns do?
It would be nice to see these campaigns be specific enough with the information they present as to not include any unlicensed but legal RF emitters like our wireless mics, wireless communications systems, and more. It would be nice if they provided us with balanced, detailed information as opposed to F.U.D.
As it is now, the NAB is asking everyone to ask the FCC and their member of congress to outlaw everything:
Call or write the Federal Communications Commission or your member of Congress, and tell them not to allow unlicensed personal and portable devices to operate in the television spectrum.
There’s a lot wrong with that.
If you belong to the NAB, I urge you to contact your organization NAB and tell them to explain themselves more clearly, and include language in their correspondence with the FCC that specifically targets these new devices and not be so vague as to outlaw everything that we already own and have unobtrusively used for decades.
Update (since originally writing this article)
The FCC has now confirmed that it is ready to re-evaluate a second round of devices from Redmond, Motorola, Philips, and startup Adaptrum Inc. Should these devices prove resistant to interference over the three month testing period, the coalition plans to release commercial products to coincide with the digital TV transition in 2009,
Still doesn’t give support to the “ban everything” mindset the NAB is promoting.