Chapter 6 STUDIO TO TRANSMITTER LINKS (How To Get There From Here.) In Chapter 4, Studio Facilities, it was briefly mentioned that you should plan on including telephone lines into your Master Control Room studio. The telephone lines are not just so that you can make a call to home, or for your listeners to reach you with a call to "advise" you. These telephone lines needed are also so that you have a way to send your program signals across town to where the broadcasting station transmitter is located. Of course, some Radio Talking Book operations may be already located at the broadcast station site, but the majority of us are not and need an audio link to get us there. Telephone lines are the most commonly used method of accomplishing this. However, the telephone lines needed are not the same "voice grade" type that your telephones are connected up to! Whatever else you might do, don't ever let yourself be swayed into believing that since your broadcast programs are mostly of speech, a normal "voice-grade" telephone line is good enough. Nothing is farther from the truth. Voice grade, sometimes called "dial-up", telephone circuits have very poor audio ouality. They have neither acceptable low frequency or high frequency characteristics. Their frequency response is anything but "flat", and they are excessively lossy and noisy. And don't hope you can "fix them" with a bit of electronic equalization at the transmitter end, because there is nothing left to "fix" once your signals get there. What you require and must have are full time leased, private, equalized radio circuit lines. These line services are available with upper frequency response ratings of 3KHz, 5KHz, 8KHz, and l5KHz. Since you are, or should be, transmitting information whose frequencies extend to 5KHz, then that is the minimum equalized telephone line service you must use. I prefer to use the 8KHz lines because they usually are vastly superior to the 5KHz service and, generally, the cost difference is not very great. On the other hand, l5KHz lines are definitely "over-kill" for SCA program service and are considerably more expensive. I've been told several times, and I'm beginning to believe it, that we folks here in the Twin Cities area of Minnesota are blessed with the best "long lines" and "radio shop" services of all of this country's telephone companies. If this really is so then perhaps my view of how simple it is to call the local "Ma Bell" outlet and order a quality 5KHz or 8KHz equalized line to be installed within a week or two is highly distorted. At least that's how it works in my part of the world - the services are made available, it doesn't take very long, and the performance quality of the lines is nearly always quite excellent. The cost for this service keeps rising like everything else, but generally it is between $30.00 to $40.00 per month, unless your lines cross a telephone company's zone boundary line. (They almost always do, don't they?) In that case, the cost doubles because they then charge for a terminal connection at both the source and at the destination zones. In addition, they then also add on mileage charges for the distance the lines travel beyond the source zone. Incidently, the mileage is their wire route mileage, not the straight line point to point distance! This is just about all you need to know about equalized telephone lines procurement. I would advise you to ask the local telephone company business office or the local broadcast station's engineers, who to talk with in the "Radio Shop Services" of the phone company to get an understanding of what's available to you in your area. A very important consideration about equalized telephone lines is how to properly connect into and out of them. These lines cannot, and will not, provide the correct frequency response if connected up incorrectly. When the telephone company installs these lines for you they test and adjust them with a source and a termination which are both pure 600 ohm load resistors, and any connection other than this will skew the performance. Therefore, always drive into these lines through a source of true 600 ohms resistive, such as by using a loss pad network of 4Db or more. Another technique, which I by far prefer, is to drive into the equalized lines directly from the output terminals of a balanced pair driver amplifier constructed from two good IC operational amplifiers such as the 5534's. Include a series resistor of about 270 ohms from each amplifier output terminal to the telephone line connection. When driving your program signals into these equalized lines you should provide a signal level of +8Dbm on the lines. The telephone company expects this level as indicated by a standardized VU meter. Therefore, the telephone company expects to receive peak program levels which will be equivalent to +l4Dbm, the usual 6Db "error" lag of a VU meter. Their line equalizing amplifiers will begin to "clip" and distort on signals which exceed that amount. Of course, you could use lower levels than +8Dbm, but doing so will deprive you of full utilization of the available signal-to-noise performance obtainable. Note that if you are feeding these equalized lines through a loss pad, to assure a 600 ohm source resistance, the signal level from your studio into that !oss pad must be equal to +8Dbm plus the attenuation value (Db's) of the loss pad. Other than equalized telephone lines, the other usual method of delivering program signals from the studio to the transmitting site is by use of a radio channel. There is a special service assigned for this "STL" (Studio to Transmitter Link) by the FCC in the 950 MHz band. However, just as the current FCC rules prohibit broadcasting of an SCA when the FM stations main channel programming is not present, so also is it prohibited to use an STL channel to carry only an SCA program. (Several of us have petitioned the FCC to reconsider that rule for many years without success as of this time.) However, if the main channel is using an STL from their studios to a remote transmitting site then the SCA program can be also included once the SCA program signals reach the main channel studio location. It should be cautioned, however, that this is not necessarily a wise procedure even though it may reduce cost by allowing shorter equalized telephone lines to be used. Much of the STL channel equipment can produce "cross-talk" of the main channel programs into the SCA programs unless it is very carefully aligned and frequently adjusted and maintained, a condition which usually is not the case. So my opinion is that I would not include my SCA program signals on an STL unless it were the only method available to get there from here; that would be the case if the telephone company could not make any equalized lines available. This does often happen,especially when the transmitting site is located many miles from town in rural areas, or if it is on a mountain top. In that situation, I would then include the SCA on the STL as the 67KHz SCA channel, not as program signals to be delivered to the SCA generator at the transmitting site. Another way of stating this is that the stereo and SCA generators should be located at the studios and the STL used to convey the entire composite baseband modulation to the FM station's transmitting site. Once again, it has to be emphasized that the STL system must be very carefully aligned and tested as to proof-of-performance when used in this manner. If this is done the system can be made to work well. If not then the system can become your greatest source of crosstalk and/or low injection and cause your SCA program link to assume characteristics reminiscent of the "Missing Link".