More Choices Than Ever for Radio STL Unprecedented technology growth expands options for quality and price considerations By Kirk Harnack By the end of the 20th century, both wired and wireless STL systems began having some serious challenges. Telcos became less interested in supplying equalized program circuits — so much so that most stopped accepting orders for new circuits. And, in major markets — often with clustered tower sites — the 950 MHz RF band had no room for additional users. Today, it’s nearly impossible to even order new T1/E1 service, and observant engineers can easily see the deterioration of their telco’s outside wire plant. In some markets, ISDN usage became “unlimited,” so a few broadcasters employed either dial-up or “nailed-up” ISDN service with ISDN codecs at each end. These days, ISDN service is withering and new connections are generally not available. Despite the disappearance of old telco services and the congestion in some areas of the 950 MHz band, engineers actually have more STL choices than ever before. The key to new STL options is internet protocol — IP. And the best news about IP is that it can be transported in more ways than you might think. Let’s edit and append our list to strike through nonviable options and add new options:
The author is senior solutions consultant for the Telos Alliance in Cleveland. Radio World reports there are more than 22,000 licensed radio stations in the United States. Of these, more than 15,000 are tallied by the traditional accounting of fullpower AM and FM stations. Low-power FMs, translators and FM boosters add about 7,000 more. The vast majority of these stations employ some kind of audio link from the studio or other origination point to the transmitter site. That’s a lot of studio-transmitter links. CHANGING TECHNOLOGIES
What kind of STL was used by the first radio station where you worked? Forty years ago our main STL choices were these: • Equalized program lines from your local phone company; • Discrete (L/R) 950 MHz (band) TX/RX radios — one for mono, two for stereo; • Multiplex (MPX) 950 MHz (band) TX/RX radios. More choices arose during the 1980s — digital choices — such as the QEI CAT-LINK, which transported FM MPX over a T1 or E1 telco link, and Dolby’s 950 MHz STL transmitter/receiver pair. More audio data-reduction codecs allowed further choices in the 1990s, both in wired and wireless STL systems, including stereo and even multichannel digital STL systems. Most of these used either T1/E1 telco circuits or worked in the 950 MHz band in the United States, and other UHF bands for other countries. The 21st century brought upgraded digital RF STLs as well as a variety of budget-priced analog composite systems.
1. Equalized program lines from your local phone company; 2. Discrete (L/R) 950 MHz (band) TX/RX radios — one for mono, two for stereo; 3. Multiplex (MPX) 950 MHz (band) TX/RX radios; 4. ISDN codec (came and went over a 30 year period); 5. T1/E1 link (unavailable for new installation and dying quickly);
TRENDS IN CODECS & STLs Radio World | July 2020
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