When Clear Channel Minneapolis finished a consolidation in the summer of 2003, it was apparent to us that we could also consolidate a part of our transmission system to save a sizeable amount of money in telco costs. While it was once reasonable to have four T1 circuits from three studio locations prior to the move, I felt that this situation was somewhat ridiculous given the current cost of wireless alternatives.
I began to look at systems offered by two broadcast companies, comparing value and discussing reliability with other Clear Channel engineers who had systems currently in use. On the top of my criteria list was ease of installation. The tower didn't have room for waveguide, nor did I have the money for it.
With radios that are placed near the antenna, the Broadcast Electronics Big Pipe requires only four small cables between the radio and multiplexer shelf. There are two 75Ω coaxial cables that carry the DS3 information in and out of the radios, a 16-gauge twisted pair for radio power and a CAT-5 cable for Ethernet connection to the radio for monitoring and control.
The cabling was inexpensive compared to the other system I had considered, and I wasn't required to hide the radio in the studio building's penthouse away from the climate-controlled technical operations center. I'm a big fan of keeping equipment where I can see and monitor it easily. With Big Pipe, cable loss isn't as important.
The radios are about 12" square and 4" deep with TNC connections for DS3 data and circular connectors for power and Ethernet control. An N connector is used for a solid RF connection to the antenna. The radio mounts to any standard-size leg or member with round-member adapters, or as some like to call them: hose clamps. This provides a secure mount, and it makes it easy to get the radio right next to the antenna.
Performance at a glance
Cost-effective alternative to multiple telco circuits
Robust operation in a large metro area
Affordable cost for high bandwidth
Ideal for combined facilities
Radio installation was a breeze, with the exception of having to weatherproof power and data connectors that were placed in less than ideal locations for an easy tape and mastic application. A little extra time and creativity was required to make the job look neat, but this was only a minor inconvenience. The N connector is on the opposite side of the radio; it was rather easy to connect and weatherproof.
When it came time for a path study and antenna selection, Jim Moody from Broadcast Electronics was a big help. Information was provided in a timely manner with professional courtesy. Moody specified 6' solid antennas with radomes for our 12.1 mile path length. With an antenna of that diameter at 5.8GHz, the beam width is 2°, and the gain is a 38dB. The narrow beam width makes for excellent interference rejection given the fact that the path takes us over a mostly urban area.
I was concerned with interference. I worried about the possibility of having all the equipment installed and none of it working. We erected the studio antenna prior to having the tower work done so that we could have the tower crew align the antenna at the time of installation. When everything was connected at the transmitter site, I plugged my laptop into the CAT-5 cable attached to the radio on the tower to watch the signal level come up as the antennas were peaked. I was elated when the signal came up to -45dBm, which I am told is an excellent signal for these radios.
To peak the antennas, a voltmeter is plugged into a BNC connector on the radio. The highest dc reading is the peak. We aligned both antennas at the same time, alternating between tower and studio alignments until the highest signal level was achieved.
The transmitter is mounted outside next to the antenna.
I wanted to keep things similar to what we were using, so I elected to buy the 8xDS1 interface for a quick connection to our current Intraplex chassis. With this setup, I only needed to re-route data cables within our facilities. The studio site was simple, the Big Pipe indoor unit shares a rack with the DS1 multiplexers, and only a short CAT-5 jumper was required. The transmitter site required a little more effort, with cables run between three transmitter rooms and a separate building.
Once the system was operational, I decided to let it run by itself for a day or two before going full-time with our main program link. After the test period had satisfied me, I switched the stations onto the Big Pipe. I had one problem after the switch, but Richard Hinkle from Broadcast Electronics was there to help. It appeared the timing wasn't set quite right; both units were set to free running clocks. A simple configuration change to master-slave style timing was all that was required to get everything back to normal.
I have since moved our Burk full-time remote control equipment onto the DS1 multiplexer equipment using 3kHz voice and data cards to save even more money. With a dial-up backup, the $400-per-month cost of four non-equalized circuits is no longer required. I feel that our backups keep us from having all our eggs in one basket.
All in all, the system has been solid since the day it went in. With storms and heavy rain, the unit isn't fazed; it just keeps going. I keep 900MHz radios for backup — just in case — but the time we spend on them is much, much less than with the telco DS1 circuits I was used to. I think it's an excellent system for those looking to eliminate telco costs or consolidate multiple STL hops.
Meyer is chief engineer for Clear Channel in Minneapolis, MN.
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