The great RF arena battle

The challenge: pulling in multiple channels of radio mics, seated in two separate sides of a 62,850 capacity sold out football stadium, to a bag-based setup with full mobility needed for documentary run-n-gun shooting, here we go.

I recently worked an NFL documentary shoot, with contributors attending an NFL game. The filming team had access to the pitch, so we could watch the contributors and accrue footage, with the goal to capture the contributors reactions to the action on the pitch. This was going to take some work to setup.

My choice of radio systems for this was the Audio Ltd A10, for 4 reasons; 1. They have onboard Timecode recording, vital to ensure that if the RF signal failed to reach me, we would have an onboard backup of the content. 2. They are digital radios, meaning the carrier wave of the signal has minimal harmonic frequencies, vital for me to squeeze upto 4 channels in an RF dense setting (a live high-level sports game, with ALL the production trimmings). 3. The A10 system has a “LR” (Long Range) transmission mode, which extends the effective transmission range over the Std (standard transmission mode) by about 250% (according to my tests of the feature during its beta period), at the cost of doubling the end-to-end latency from 2ms to 3.9ms. 4. Frequency range, I needed the widest possible tuning under and over the standard 606 coverage of my SRb, for flexibility in tuning.

At the receiver (bag) end, I decided to upgrade from the stock whips I usually use with this setup (this setup is mostly for corporate and small documentary jobs, where I’m in reasonable proximity to radio sources), as I knew the RF environment we were entering was going to be dense, with a full sports production worth of wireless equipment around me; other radios for players, refs, coaches, Docu teams capturing BTS of the game itself, coms systems for the different production units, multiple camera streams and wireless protocols, walkie talkies, not to mention the combined RF traffic of 62,850 phones from fans, plus the hundreds of production and site crew!

Beginning with the antenna themselves, I switched from the standard whips to a pair of Lectrosonic SNA600a passive dipole. I like these for three reasons, they’re incredibly light, with a form factor that allows them to be folded when not in use, and positioned in a non-obtrusive way, but also the design includes a small ground plane, which helps improve reception efficiency as it has a waveguide to the antenna. The dipole can also be “tuned” by changing the length of the antenna stems, which magnified the centre frequency of the range, which i optimized for the planned for radio frequencies.

With this floating mine field of RF in mind, filtering was going to be an essential tool to success, and so I migrated my trusty Audio Wireless DADM226 mk2 from my main narrative bag, into this setup. This allowed me to apply input filters to my antenna signal, (program 17 594-694MHz) as I knew the majority of audio RF was likely to be in the sub-600mhz range. These filters apply a -70dB of cut either side of the band, so already they’ll be chopping a lot of potential harmonics which could interfere with my reception. I also decided to boost the distro signal gain to the maximum 6dB, while this does bring up the noise floor (which was incredibly congested here), I knew it was a worthwhile risk, as while I was among high traffic, I wasn’t going to be stood directly next to the source of that traffic, so the harmonics would be somewhat blurred. Feeding this into the A10-Rx, allowed for the maximum use of the dual-diversity (full diversity) processing of the signal by the radio receivers, being of a modern design ethos, they work with emphasis on lower power carrier signals, & more efficient reception decoding.

And then onto frequency planning. Typically when I land on a location, my channel 38 license is sufficient for me to use (I rarely have to book additional channels), so I run a scan of the location and then plot a frequency plan around any possible issues at the location. On this occasion though, I knew full well I was going into an RF nightmare, and relying on channel 38 for 4 frequencies (even being narrow-band digital frequencies) was going to be overly optimistic. So after a lot of communication with the site, league production managers and OFCOM itself, I managed to secure 4 specific frequencies, plotted by OFCOM. I provided them with my radio system, tuning range and they did the frequency plotting and assigned me with the frequencies, and power level (maximum 10mw).

And so the morning of, with reception of these frequencies, I finished the details of the rig, battery’d up, and dove into the thick of it. The results were rather surprising, I fully expected a very tough day RF wise, especially when I was actually in the stadium, felt the amount of people, saw the amount of kit and really got a real world sense of the distance between the two sets of contributors. I did not expect to be able to pickup all frequencies from either side of the pitch (we were stationed on the sidelines of the game field), especially with the transmitters pushing out only 10mw of power, but to my surprise, it seemed all my optimizations worked! I was just about able to pickup RF from either side of the field, from the two different radio spots in the crowd (pictured). It was certainly an impressive example of what the kit is capable of. While we had the onboard recordings of the material, being able to pull in the signals live was a powerful tool, as it allowed for my director & camera operator (whom each an IEM receiving from a mono transmitter on my bag) to listen in to the contributors, & pick up on story points for the material.

Kit used;-

Audio Ltd A10 radios.

Audio Wireless DADM226 mk2 RF distro.

Lectrosonics SNA600a Dipole antenna.

Sound Devices MixPre 10ii mixer.

Sennheiser G2 EW100.

Sennheiser G2 IEM.

Sennheiser MKH8060.

DPA 4071.