Northern Community Radio Expands: An Engineer's Perspective

July 16, 2014

The main studio for Northern Community Radio's KBXE-FM in Bemidji, Minn.

When Northern Community Radio set out to build a new community radio station in rural northern Minnesota 38 years ago, naysayers said that it would be broadcasting “only to a bunch of gophers.” That station, KAXE, is still going strong and in 2012 put another rural northern Minnesota station on the air, KBXE, with full studios, transmission plant and antennas on a new 500-foot tower. Operating at 50 kW, KBXE was needed to give permanence to a signal previously served by a translator in the commercial band. Designed to operate as a network of two with transmitters 87 miles apart, both KAXE and KBXE contribute programming to the common air signal delivered across a large swath of northern Minnesota. Programming for the small network will originate live in either the KAXE studio in Grand Rapids, Minn. or at KBXE located in Bemidji, Minn. and switch locations several times throughout the day. With the studio-to-studio link, some programming is originated with hosts at both locations simultaneously.

Studio Construction

It has been said that an engineer should return to the first studio he or she has built and apologize for the mistakes made. Having been a new engineer when the KAXE studios were first being built, there are some issues I let slip by that I am now less than pleased with. The studios had been architecturally designed and are beautiful, but there are acoustic problems that I was determined not to repeat. Operating with a finite budget for KBXE that did not allow for hiring acousticians and state-of-the-art noise isolation construction, I was able to use simple noise isolation techniques and work with a receptive general contractor. Studio walls were double-frame stud walls; studs offset, plates resting on closed cell foam, and filled with fiberglass insulation. Internet research showed that people had been obtaining good isolation results with two layers of 5/8-inch sheetrock on the inside walls treated between the sheets with a product called Green Glue []. One half gallon of Green Glue was used between each 4'' x 8'' sheet layer, extruded out from quart sized caulk tubes with conventional sheet rock screws binding the layers together. Once cured, I was very pleased with the noise isolation of the studio and production room walls. Homemade absorptive sound panels using 2'' x 4'' Owens Corning 703 fiberglass drop ceiling panels mounted in a simple pine frame and covered with cotton cloth painted by a local artist finished the rooms and dampened acoustic reflections. Sound-isolating windows into the studio and a visual communication window between air studio and the production room were made by sandwiching two double-pane argon filled thermal windows together with a large air space between, for a total of four panes of glass in each window. Mounted in butyl to restrict vibration, these inexpensive windows work well.

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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.

Studio Furniture

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!

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Studio and Transmitter HVAC

Having learned a painful lesson at KAXE about poor HVAC control, we opted for a multi-faceted approach at KBXE. Combining a Fujitsu mini-split heating and A/C unit along with some low-velocity ducted HVAC from a central unit for the station, supplemented with electric baseboard heat, we ended up with very quiet heating and cooling in the closed studio. The Fujitsu indoor unit is exceptionally quiet in its “Quiet Mode” fan speed and can both heat and cool with good efficiency. Air source heat pumps such as these are being made with remarkable cold weather performance necessary for our northern Minnesota climate and can supply heat even with low outside temperatures.

The KBXE transmitter site has a wall-mount industrial A/C unit with outside air intake functioning as an economizer to save the A/C from running during cool weather or when the temperatures are below the minimum operating range of the compressor. Unfortunately, the logic on this particular economizer was poor, failing to return to A/C operation once daytime temperature rose above the enthalpy point. Several service calls to fix this issue did not have good results, so I built an economizer using the passive air ventilation I had specified to keep temperatures in check should the A/C unit fail, which it has done several times. Since the over temp ventilation fan and motorized intake louvers are on their own thermostat completely separate from the digital A/C thermostat, it was a simple matter to add an outside sensing open-on-rise thermostat in series with an interior sensing close-on-rise thermostat to have this backup system function as an economizer as well as functioning as an over temp failsafe.

Economizer system at TX site

Transmitter Building and Commissioning

Working with Master Electrician Brandon Chase from Hoffman Electric and the Nautel Recommendations for Transmitter Site Preparation, we laid out the ground buss bar, transmission line, service panels, LEA spike suppression and service entrance on the same side of the building to localize energy dissipation near the grounds in the event of a lightning strike. A halo ground surrounds the building. Each lobe of the triangular tower base, as well as each ice bridge post are separately grounded via a Cadwelded copper wire to a ground rod.

TX site electrical system

The assembly of the 3 1/8” rigid copper feed line from the transmitter to the transmission line gas block flange connector was a new experience for me. I was given a great suggestion by our project consultant, Gray Haertig, of Gray Frierson Haertig & Associates, to cut rigid line with a carpentry chop saw fitted with an 80-tooth carbide blade. A Commscope reverse osmosis line dehydrator pressurizes the transmission line after an initial nitrogen purge performed by the tower crew.

TX site transmission line routing

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KBXE TX and equipment rack

Commissioning of the Nautel NV15 was daunting as this was the first new transmitter and transmission plant I had built. After going through the startup procedures carefully, I hit the RF ON button on the GUI and was met with dismay as I saw my reflected power rise to a foreboding 666 watts. Fearing I''d assembled something wrong in the rigid copper line or in the Dielectric transfer switch, I turned off the transmitter and called Gray, panic-stricken. After telling me to take a deep breath, he suggested I go outside and look at the transmission line and antenna to see if anything was awry. As my eyes scanned upwards from the bright, new aviation orange and white tower paint, the tower was obscured with a layer of rime frost starting at 200 feet above ground level! As the sun came out that day, reflected power dropped to a satisfying 0 reflected watts.

Final Thoughts

To rephrase, “It takes a village to build a community radio station.” A radio station serving rural areas does not enjoy the economic base of metropolitan areas but has, perhaps, an even more important mission to serve its community. Supported by volunteers, staff, generous contractors and consultants, KBXE was a collaborative effort that brought many disciplines to the table and resulted in a very economically built studio and transmission plant using state-of-the-art equipment.

KBXE TX site building and tower

Houg is the Chief Engineer for Northern Community Radio, including KAXE-FM and KBXE-FM

KBXE Equipment List

  • Air Studio:
  • - Axia Element console with Powerstation and Aux
  • - ENCO DAD automation
  • - Telos Hx2 hybrid
  • - Electrovoice RE-20 mics
  • - 25-7 Profanity Delay
  • - Denon C635 CD players
  • - Custom locally constructed furniture
  • - Custom fabricated acoustic treatments
  • - Fujitsu mini-split HVAC
  • - Audio-Technica turntables and headphones
  • - StudioHub wiring
  • Production room:
  • - Axia Radius console
  • - ENCO DAD
  • - Telos Hx1 hybrid
  • - Denon CD players
  • - Tannoy Reveal monitors
  • Engineering:
  • - Sage ENDEC
  • - Dayton EAS receivers
  • - Best Ferrups UPS
  • - HP and Cisco switches
  • - Tieline Bridge-IT for remotes
  • - APT WorldCast Oslo IP audio codec for
  • Studio to Studio Link
  • STL:
  • - 2 hop IP microwave with redundant path
  • via DSL modem
  • - Motorola Canopy 11GHz radios plus
  • Ubiquiti 2.4 GHz NanoBridge radios
  • - WorldCast APT NextGen IP audio codecs
  • Transmitter plant:
  • - Nautel NV15
  • - Myat transmission line
  • - Commscope/Andrew dehydrator
  • - Tunwall transfer switch controller
  • - Altronic dummy load
  • - Orban 8500 processor
  • - LEA surge suppressor
  • - Thermobond building
  • - Dielectric 4 port 3 1/8” coaxial switch
  • - Inovonics 730 RDBS generator
  • - Unimar LED lighting and controller
  • - ERI tower and antenna
  • - Davicom remote control
  • - BW Broadcast RBRX1 receiver
  • - Custom HVAC economizer
  • - Middle Atlantic rack

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