How a political convention looks to its radio-frequency coordinator (see the lexicon below for a guide to the acronyms):
In total, 718 frequencies were used or reserved for use during the convention, said Jim Schoedler, POLCOMM 2008 DNC RF coordinator. They broke down as follows:
- 207 wireless mic frequencies
- 144 frequencies used for two-way radio, including repeaters
- 111 frequencies for RF intercom
- 96 frequencies for IFB for talent
- 43 microwave channels
- 117 held in reserve or identified for other purposes
[…] Schoedler knew there wouldn’t be much frequency shuffling required as broadcasters moved from the Pepsi Center to INVESCO Field.
“When I compare[d] the two, we found they are not very different. Both facilities act as a shield to a certain amount of RF and are fairly similar,” he said. That knowledge gave Schoedler confidence that a frequency assigned for use at the Pepsi Center should be acceptable for use at INVESCO, he said.
However, there was one notable exception: use of 7GHz COFDM camera transmitters, he said. “There are STL and TSL signals basically shooting over the stadium,” he said. “Testing by Denver stations revealed that the use of the 7GHz channel for COFDM microwave camera transmission from inside the stadium would interfere with the STL and TSL transmissions passing overhead. To resolve the issue, no 7GHz COFDM camera transmission was allowed at INVESCO Field,” he said.
Making sure that devices don’t interfere with each other required “purity-testing”. Not this kind
. (The page I quote here describes the setup at the 2004 Democratic Convention. I assume that the 2008 Convention required similar testing.)
For four days, the Fleet Center presented the most hostile RF interference environment on the planet. Most local broadcasters had other obligations so the DNC enlisted the help of experienced local ham radio operators, many of whom were electrical engineers. Coordination was handled by Louis Libin of Broad-Comm.
Peter Simpson, KA1AXY (left) worked for the DNC RF frequency coordination and interference enforcement team. Three days prior to the start of the DNC, each piece of RF-generating equipment needed to pass RF-purity testing. Peter insured that each piece of RF equipment entering the area possessed an "RF tested-OK" sticker. No sticker, no entry.
Louis Libin is chairman of the Political Conventions Communications Committee, which handles frequency coordination at both conventions. He describes the challenge facing engineers at these events:
This year is the worst spectrum year ever for all different types of use. For instance, in St. Paul, we are able to use the lower UHF channels and divide them up for walkie-talkie use, IFBs and things like that. In Denver, we are stuck for spectrum because none of the channels in the lower UHF band are available. The FCC has granted us an STA to use business band, and as far as I know, this is the first time that we’ve ever used business band for broadcast-related uses.
We have made very strict, but necessary, guidelines for spectrum use that the networks and stations have all adopted. We also have other types of guidelines that have never been implemented before, such as the number of feet inside or outside that you need to separate the wireless mic from the receiver before you can use the mic. We’ve never had that before. Somebody is going to be only separated by10ft from his receiver; it’s great that they have a wireless mic, but the fact is that they are using that whole channel, and it’s actually putting a signal out that’s going far and has the potential to cause interference.
Between the mathematical and the natural, there’s a “technical sublime”, an awe at the scale of operations like these—a scale that defeats the imagination, even though the object of wonder was made by us.
Already in 1832, the spectacle of the railroad, conquering the vast American landscape, gave rise to feelings of a “technolgical sublime” (Leo Marx, The machine in the garden (Oxford, 2000; orig. publ. 1964), 195, quoting an article in Scientific American, 1832):
Alpine scenery and an embattled ocean deepen contemplation, and give their own sublimity to the conceptions of beholders. The same will be true of our system of Railroads. Its vastness and magnificence will prove communicable, and add to the standard of the intellect of our country.
That prediction has, sadly, not been confirmed. Not by the railroads nor by any of our more ethereal systems of communication.
: RF = radio frequency; IFB = interruptible feedback
(the transmission of instructions, etc. to on-air talent by way of wireless earphones); CODFM = coded orthogonal frequency-division multiplexing
(a way of improving the efficiency of RF communication by dividing a wide band of frequencies into many narrow bands); STA = special transmission authorization (granted by the FCC
); STL = studio-transmitter link; TSL = transmitter-studio link; UHF = ultrahigh-frequency (the soon-to-be-obsolete TV frequency band).