Chapter 8 OFF-AIR RELAYS AND CABLES (How To Get On-the-Air Where You Aren't.) The Radio Talking Book SCA broadcast coverage predictions of Chapter 7 disclosed that we can't usually cover as much geography as we often would like to. To accomplish this task we must either increase the class of our transmitting system or build additional service facilities at the distant locations, perhaps both. A common method of extending an FM broadcast stations coverage to a distant community is to install a "translator" in that community. A translator is a low powered FM broadcast transmitter (10 watts) usually used with an antenna which is typically 100 to 200 feet above ground. The translator receives the original station's signal then converts it to a different frequency (place on the dial) and transmits it. The translator's receiver section which picks up the original station's signal must be quite good, and it must also use a receiving antenna which is very good and mounted quite high off the ground to assure getting acceptable reception of the original station's signals. The translation process must be very accurate and "broadband" if it is also to be expected to re-broadcast the FM station's SCA services. Some translators are not effective at this, so be cautious. The disadvantage of using a translator to extend your coverage is that they do not cover a very large area. They are intended to provide FM radio service to a small community, and generally have an effective range in the order of a two mile radius. Obviously, you would prefer to use a higher power transmitter to extend the coverage. So, if the distant community has an FM station whose SCA you could also be making use of, or if your station management decides to build additional stations throughout the area and create a network system, you will need to find a method to relay your Radio Talking Book SCA signals to it. The most conventional method of such a relay system is to select a location near to the new transmitting station and install a good antenna on a high site, and an SCA receiver. Upon successful reception of your Radio Talking Book programs, you feed them to the new transmitter via equalized telephone lines. A new SCA channel is generated by the new transmitting station, and you're all done. Be careful in selecting the location for the SCA relay receiver. It must be able to get a strong enough and a long term reliable enough signal from the originating station. Also, it must not be overloaded or otherwise interfered with by the new station's transmitted signals. For example, do not expect to be too easily successful if both the original and the new stations operate on the same frequency or within about one megahertz of each other. Expect to have reception problems if the receiver is located at the new transmitting location regardless of the frequency differences, because of high energy FM noise levels which are usually common at broadcast transmitting locations. Thus, the solution to the problems just mentioned are to avoid them initially, use innovative receiving antenna installation techniques, and/or employ carefully tuned cavity resonator filters in the receiving antenna feed line. Note that these cavity resonators cannot be simple, cheap devices! Also, if you live in a climate like Minnesota's, be wary of thermal drift! If the new station you are going to relay to is part of your originating station's network, then an alternative approach should be used. After you have obtained off-the-air reception of the original station do not demodulate the SCA channel to audio, nor the main channel to left and right audio. Instead, feed the entire composite baseband information, undeemphasized, directly to a 950MHz STL link which supplies the program modulation to the new transmitter. In this manner you will assure that all modulation conditions which exist at the originating station will (should) be exactly duplicated on the second station as well. If the distance between your originating station and the new station is too great for a dependable off-air relay receiver system, such as more than 60 miles, then a microwave system might be available for your use. If your originating station management is going to build such a microwave link to the new station, then all you have to do is wait for them to get it working. If not, then you could start looking for any such systems which might be in existence and going your way. Possibilities include "Ma Bell" (very expensive), Commercial microwave service carriers (not cheap either), CATV intersystem carriers (also expensive but maybe negotiable), Intracity TV microwave systems (might be able to make a good deal here, especially with Educational TV organizations). With any of the microwave systems, a modulator unit is needed at the originating end to accept your Radio Talking Book program audio. How you get the audio to there is, of course, by use of equalized telephone lines or an off-air receiver, or both. At the terminating end a demodulator is needed to convert the microwave information signals back into your Radio Talking Book audio program signals. You would use equalized telephone lines to carry your audio signals to the new transmitting location from the microwave system. The modulator and demodulator units required are usual and normal equipment for the microwave system and would normally be supplied by them. If the microwave system you plan to use is licensed as a TV intracity system, then you, and they, should be aware that there is an F.C.C. rule which prohibits the inclusion of your programs, since they are unrelated to the licensed purpose of the TV microwave system. However, the F.C.C. has readily and willingly waived this rule everytime we've asked them to. Just don't forget to remind the TV folks to request the waiver to keep it legal. Cable systems, often called CATV for "Community Antenna Television", offer an alternative method of expanding your Radio Talking Book service coverage. These community TV systems are usually affiliated with an intrasystem microwave linking service to bring them additional programs. As was previously mentioned, that microwave link might be an available vehicle to carry your Radio Talking Book programs across vast distances to a new transmitting location. Also, they could be carrying your programs to several communities CATV systems as well, or instead. But, just what is a CATV system? Simply expressed, it is a business which strives to sell TV (and other) services to homes in the community. CATV started in rural regions where the signals from distant TV stations, which were located primarily in larger urban sites, were too weak to be received by the local residents. To accomplish this TV service, the CATV company would construct a very tall antenna tower in order to pick up the distant TV stations. These TV signals are then delivered to the residents homes by means of a cable (wire) much like the telephone companies do to hook up a telephone in a persons home. And, like the 'phone company, the CATV company charges it's customers a fee each month for this service. Today CATV is becoming common and popular even in the large cities because they can bring in many more TV channels and other services than just the few local Tv stations. Among the "other services" CATV can readily supply is FM radio broadcast signals. In theory at least, a distant CATV company might be picking up the FM station whose SCA your Radio Talking Book service is on. If so, then the homes in that community should be able to get your service. If you supplied those residents with one of your Radio Talking Book receivers, and they connected their CATV cable onto the radio's antenna terminals, it should work. Why do I say "should" rather than "would"? Because they very often don't! There are a few reasons for this. First, many CATV systems translate your FM station's signals to a new frequency on their cable. If this is so, you would require a different Radio Talking Book receiver which was tuned to that frequency. Secondly, many CATV systems are of inadequate technical quality or maintenance to pass the FM broadcast signal including it's SCA subcarrier. Third, many CATV operators reduce the FM signal levels on their cables to a point where neither acceptable stereo nor SCA performance can be obtained. Finally, many CATV antenna systems are not adequate to deliver good reception of your specific station into their CATV system. However, if the CATV system is fairly modern and well maintained, and if the other mentioned problem areas are attended to, there is no technical reason that these CATV systems couldn't provide an inexpensive extention of your Radio Talking Book service. Understand that these CATV operations are individual private businesses for the most part. You must negotiate with their owners to achieve service to the community. Most CATV operators are willing to help carry your programs because it is a good public relations service to the community and they wish to be well thought of by the local town board, etc. Besides carrying your Radio Talking Book service as an SCA of the FM broadcast station on the CATV system, another method is possible, and far superior. Upon receiving your FM broadcast station, the CATV company could simply recover your Radio Talking Book programs from one of your supplied receivers, or one of their own. It is now possible for them to create an FM station on the CATV cable which is of your programs, rather than as an SCA. If that station was placed anywhere between 88MHz to lO8MHz, then anyone with cable service in the community could hear your Radio Talking Book service on their normal FM radios. This would be very, very, bad practice! If you were to do this you would lose all copyright release privileges for the materials you read, and in addition, you would be forced to edit out any "questionable"language from the books and magazines you read. If you neglected to do this you would be in legal jeopardy. If you did do it you would be misserving the people who need your services. Therefore, do NOT use the normal FM frequencies to which the general public has access. Use any frequency just above, or just below these. Incidentally, a frequency that is usually available is at 75.75MHz. The caution of using that frequency is that chroma (color) interference could result to TV signals on the CATV system located at either channels 3 or 6. This could occur if the local oscillator of the radio used to receive Radio Talking Book programs at 75.75MHz leaked out into the cable. Should that occur, this oscillator created interference frequency would be a either 65.05MHz or 86.45MHz depending upon if your radio used high or low side injection to obtain the conventional lO.7MHz I.F. frequency. This really shouldn't be a very serious concern, but is in- cluded here to make you aware of a possible pitfall before you stumble into it in the dark, and then realize you may need a different brand of radio. The CATV frequency that I prefer to use is llOMHz. This is just above the high end of the FM band available to the general public (lO8MHz). A "normal" but inexpensive FM radio can be very easily adjusted to reach this frequency so you do not require anything very special in selecting a radio to use. The disadvantage in using frequencies just above lO8MHz is that they lie in the band of frequencies normally assigned to aviation uses. Thus the CATV operator may have to get clearance to use these frequencies from the F.A.A. and/or the F.C.C., but that has not been a problem to date. Of course, you could also select to use a frequency just below 88MHz for the same reasons of staying near, but out of, the general public's FM band. However, this is where channel 6 TV resides normally, and may not be available. If it is available to you then using 86MHz would be a good choice too. Of course, as has been mentioned, you will have to supply your listeners on the CATV system with a radio which is tuned to the frequency you've decided to use. However, remember that these are not SCA receivers, but are simple monophonic FM radios which do not have to be of especially high quality. That is, they will, or can, be fairly inexpensive. By using this approach rather than the FM SCA method (which usually doesn't function on CATV very successfully) your Radio Talking Book services will carry over the entire CATV system with very good perfor- mance. Expanding your Radio Talking Book service to additional communities is, like so many other ventures, a matter of surveying the available resources and taking advantage of those which you can "horse trade" for. With the basic knowledge offered here and your creative efforts you soon could be on-the-air where you really aren't (yet!). A footnote to this chapter: The information that has been presented in this chapter is offered with the belief that you fully realize that the prime value of Radio Talking Book Services is the LOCAL informational value they provide. A superior system is one which can provide local input from it's cultural interest area rather than one which has a single voice speaking to many people in different unrelated communities. As you expand your service area, be cautious that you are really providing service. It may be wiser, and of greater public value, to assist another group in developing a local service, than to relay all of your (LOCAL) programming to there!