Studio to Studio (STS) and Studio to Transmitter (STL) Links
We faced the challenge of tying program material for the new KBXE studio to the existing KAXE studio, separated by 73 miles of rural Minnesota not served by microwave links nor economical T1 service. An estimate from a local carrier of $550 per month for T1 at each end was out of budget for recurrent costs. At NAB, I spoke with Kevin Campbell of APT (WorldCast Systems) about their new codecs featuring SureStream technology that use diversity bit splitting of audio IP packets. We deployed a pair of APT WorldCast Oslo frames for the link between the KBXE studio in Bemidji and the KAXE studio in Grand Rapids over a pair of $40 per month consumer DSL lines. The system works well. We achieve CD-quality audio between the two stations with a 300 ms delay. This allows us to switch program origination between the two stations'' studios transparently and conduct interviews in realtime between them.
The STL brought its own challenges. Our transmitter is located 17 miles from the KBXE studio with no direct line of sight, so we constructed a two-hop microwave link using Ubiquity Nanobridge unlicensed radios on the first hop to a nearby tall building, and licensed 11 GHz Motorola Canopy radios from that building for the remainder of the distance to the tower. We used APT WorldCast NextGen IP audio codecs for this link. This allowed us to use the cascaded microwave links as one continuous audio path. A 1 Mbps DSL line installed at the transmitter site served as an alternate IP path. This combination gives a much-needed measure of redundancy. To finish the belt-and-suspenders approach, a backup to the IP STL is provided by a BW Broadcast RBRX1 receiver. This receiver takes an off-air signal from KAXE, 87 miles away, should the IP STL fail. In a roundabout way, we can originate program material at KBXE, send it to KAXE over the studio-to-studio link where it is transmitted at KAXE and received over the air at the KBXE transmitter site for broadcast! It works.
KBXE Engineering rack and audio codecs
Studio Console Selection
A major decision that I wrestled with was the studio console. I appreciated the solid reliability of a traditional analog console and was quite familiar with the TDM (Time Division Multiplexing)-based consoles at KAXE. I was torn between the technology that I was most experienced with, and realizing that the future is audio over IP. Questioning fellow broadcast engineer friends to the point of exasperation, I decided on AoIP as the basic architecture and decided to go with Axia for the availability of accessories, the large installed base, and several engineer friends that knew how to program the system. Along with the Axia Element and Radius control surfaces, I used StudioHub wiring. As has recently been discussed on PubTech, a public radio engineering e-mail list, the modular wiring is exceptionally easy to use but does not immediately lend itself to neat wiring, due the premade dongles and Cat-5E jumpers that never seem to end up exactly the right length.
While at NAB, I looked at several furniture manufactures and designs. Upon my return, and after discussing the furniture costs, a local cabinetmaker offered to make broadcast furniture for the studio and production rooms for the cost of materials as a contribution to KBXE. An exemplary craftsman, the cabinetmaker traveled to KAXE to see what staff liked, and did not like about the KAXE desk. He ultimately came up with an original design incorporating those ideas for KBXE. The studio broadcast desk was designed for ease of wiring access to the generous interior cavity with the decorative panels hinged on cabinet door swings. It has a wraparound top with large overhangs set above wheelchair height that allow guests to scoot up to the mic closely. Desktop mic stands were chosen to eliminate the “sea of spiders” effect and create clean sight lines. Keyboards for automation and studio computers reside underneath the console for the operator, as well as on top for guest host duties.
All clocks at the station are radio-controlled and synchronized to the NIST Radio Station WWVB time service broadcasting at 60 kHz out of Fort Collins, Colo. Clocks were chosen that have a second hand as well as 12- and 24-hour numerals. Retailing at less than $50, these clocks are spot on for network joins and adjust to Daylight Savings automatically. Since the cost is so reasonable, we mount clocks in as many locations as requested by staff including the restrooms!
- continued on page 3