by Steve Jensen
Director of Engineering
WFYI-FMINDIANAPOLIS We were moving the studios for WFYI-FM to a new
building. We needed audio and remote control telemetry to run between the old and
new buildings.
Cabling from the new location would
run under the parking lot, up the microwave tower, across the tower bridging and into the
microwave room of the old building. The total distance was about 600 feet.
Due to cost considerations, copper
cabling was contemplated. Video and audio copper tie lines between the buildings had
been used for other applications with mixed results. Special grounding techniques
and isolation transformers had to be used. Problems arose when lightning struck the
near tower. Fiber was an answer to many of these problems.
No signal loss
The Lightwave Systems
Fibox is a two-channel digital fiber optic transmission system for audio signals.
With a 20-bit linear A/D and D/A conversion, signal degradations caused by
distance, copper wire, ground loops and interference (EMI/RFI) are eliminated. |
Fibox
accepts line-level of microphone-level input signals, digitizes these inputs, multiplexes
the two channels and transmits all information down a single fiber optic cable.
Transmission distances of over two miles are possible with no signal loss. I found an ad for the Fibox system and gave
Lightwave Systems a call. The sales staff was helpful and sent me additional
information. They were able to configure a system I could use at an affordable
price.
I was impressed when the system
arrived. The boxes were attached by a tongue and grove method. They slide
together to form a 19-inch rack tray. Mounting ears are then attached to the box
ends.
Features include: phantom power,
mic/line input switch, overload indication at +20.0dBu (THD = +1 percent), gain
potentiometer for mic input, audio phase and ground lift switches, power connections,
audio XLR connectors, 48kHz sampling, as well as fiber connections. The Fibox
operates at 12V. Its constuction and capabilities make it possible to operate in the
field for remote production applications, as well as in studio STL applications.
The Fiboxes are connected together
with a pre-made wire harness. In our system we made use of eight boxes, four receive
and four transmit boxes at each end. A total of six transmit and six receive Fiboxes
can be connected at each end. |
Because all
the signals are multiplexed, only two fiber strands were used in this system. Each
Fibox comes with a complete data sheet plotting several operating parameters. The
system we are using has analog audio inputs and outputs with AES/EBU digital
inputs/outputs available. Larger fingers
A couple of problems occured installing
the system. We initially had a problem sliding the Fiboxes together. Some were
easier to slide together than others, but once we read the instructions, the installation
went a lot smoother. If the boxes are not slotted properly you can encounter some
sagging.
I also do not like handling the
circuit boards outside the box or attaching the wiring harness.
The wiring harness is pre-made for
the Fiboxes. Each cable is cut to length, which in tight quarters, or if you have
large fingers, make it difficult to connect to the boxes.
The total Fibox system went into
place very easily and has been working falwlessly for the last four months.
Lightwave Systems has checked with us to make sure the system is working properly.
For information from Lightwave
Systems, Inc., contact the company in Texas at (214) 741-5142; fax: (214) 749-1917. |
