Design a Backup STL
     

Fig. 1: Dave Radigan uses a switcher to select backup feeds to his transmitter.
The call came in at about 2 p.m. The station was off the air. A quick listen confirmed that the transmitter was on, yet the station was broadcasting no audio.

The STL to this transmitter site is via telco lines, so the staff placed a call to AT&T. The chief then headed to the transmitter while contract engineer Jim Schultz went to the studio, just to make sure it wasn’t a failed audio processor.

Over the years, “disaster recovery” is something to which Jim has accustomed himself. He says their first idea was to connect an MP3 player, pre-preprogrammed with some IDs, generic PSAs and music, at the transmitter site until AT&T could scrounge up someone who had a clue about program circuits.

Of course, that wouldn’t happen quickly. With afternoon drive only a couple of hours away, it was time to come up with a more immediate solution.

Turns out the station’s stream was up and running just fine, so why not use a 4G smartphone to feed audio to the transmitter?

One TRS (tip-ring-sleeve) mini plug and two XLR connectors later, the station was back on the air, with the smartphone’s output feeding the audio processing at the transmitter. And the station sounded pretty darn good.

Five hours later, AT&T replaced a power supply in one of its central offices, and the program lines were back in business.

A smartphone is certainly not the ideal STL; but the station didn’t miss a spot and the GM was quite happy. Isn’t that what every engineer wants: happy customers?

As for the commercials: It seems that you can legally air the stream but not stream the air. There were only two advertisers whose spots were missing from the stream blacked out, and the GM cleared any spots from those two advertisers during the time the station aired the stream.

Fig. 2: A streaming receiver provides backup audio should the main STL fail.
Jim is not the only engineer who has thought about using streaming as a backup STL.

Dave Radigan, president of WEBO(AM) in Owego, N.Y., took his backup system a step further. Using an audio switcher, pictured in Fig. 1, Dave can select from his stream, a utility feed or the phone. Fig. 2 shows Dave’s streaming radio, which feeds the switcher.

You can’t have too many backups!

* * *

Jim Schultz also stumbled across a handy item for his “bag of tricks.”

He had purchased a Tascam DR-40 recorder but was disappointed that its mic level input was fixed at –19 dB, which was sufficient for use with normally hotter condenser microphones, but way too low to give a decent signal-to-noise ratio with popular dynamics like the EV RE50, EV 635 or Shure SM58.

Two products that correct this problem are Cloudlifter and the Fethead. Each offers 20–25 dB of gain and run on phantom power. Originally designed to help low-output ribbon mics, these are a perfect solution to the gain issue.

Jim writes that he has no idea why a mic level input would be set at –19 dB; perhaps the designers felt the recorder would be used mostly for recording loud music. Jim has a Tascam recording codec that has the same issues on the Mic input.

Contribute to Workbench. You’ll help your fellow engineers and qualify for SBE recertification credit. Send Workbench tips to johnpbisset@gmail.com. Fax to (603) 472-4944.

Author John Bisset has spent 44 years in the broadcasting industry and is still learning. He handles West Coast sales for the Telos Alliance. He is SBE certified and is a past recipient of the SBE’s Educator of the Year Award.


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