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A Bonus for CATV Subscribers: Cable FM
January 1971 Popular Electronics

January 1971 Popular Electronics

January 1971 Popular Electronics Cover - RF CafeTable of Contents

Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

According to a plethora of news reports in the last few years (I have posted links to many of them on RF Cafe), the "cord cutting" phenomenon is having a significant impact on cable media providers. Consumers long ago grew tired of the monopolistic practices of corporations forcing mostly unwanted programming onto everyone and then trying to convince them that they were getting a good deal if the cost per channel was considered. No one bought that argument, but it didn't matter because there was no competition for service. Public Utility Commission (PUC) efforts to force prime line owners to rent out "space" in an attempt to provide competitive products has never worked, but that doesn't keep PUCs from trying (job security). The advent of wideband wireless service has opened up a new realm of media delivery that is leaving wired service in the dust. Not only is cellphone (all the collective "#G"s) and WiFi providing people with effectively a la carte choices, but the old school over-the-air broadcast stations are seeing a resurgence in users. Both television and radio (AM and FM) report a steady increase in advertisers in response to new or returning patrons. Antenna sales are on an uptick, too, as a result. This all represents a 180° reversal to the topic of this Popular Electronics magazine article from 1971.

A Bonus for CATV Subscribers: Cable FM

A Bonus for CATV Subscribers: Cable FM, January 1971 Popular Electronics - RF CafeIf You Have It, It May Provide Better Stereo

By Edward A. Lacy

In hundreds of communities across the country, music lovers are discovering that cable TV has a surprise bonus for them: FM radio, which is piped into their homes on the TV cable but played through their FM sets, completely independent of their TV.

It's FM radio with a difference, however, for cable FM promises listeners the same benefits that cable TV gives its viewers: a choice of several stations, a minimum of multipath distortion, and a comfortable signal-to-noise level for each station.

"As a result of our strategic receiving locations and the use of highly directive and sensitive antennas," reports one leading CATV operator, "our FM signals are far superior to those received by the average FM listener. Even with all the signal processing that occurs on our cables, the FM bandwidth is not altered. The signals are inserted into the system with the same bandwidth, including guardbands, that the broadcaster transmits."

Be forewarned, however, that all CAFM (cable FM) systems are not working this perfectly - at least not right now. Some of them are carrying inferior signals, some do not have stereo signals (because of cross talk problems), and several systems actually cut down on the number of stations you can receive (as compared to a good outside antenna) .

The reason for this sad situation is simple: an unintentional neglect by the CATV operators who carry CAFM as a piggyback service. Reasonably enough, CATV system operators feel that they have a lot more important problems than CAFM. To name just a few: new FCC rulings that allow CATV systems to originate their own TV programs, possibilities of a synchronous communications satellite for national networking of cable TV, two-way transmission on the cable, etc.

Robert E. Cowley, manager of Flagstaff [Arizona] TV & Cable Company, expresses the industry's attitude: "We give FM as a bonus, when the TV cable is put in, as an added selling point. Our advertisements do not sell FM only cable TV."

Despite the lack of promotion, CATV customers do hear about CAFM, ask for it, and then like what they get. As a result, CAFM is one of the fastest growing businesses in commercial broadcasting, reports Harry E. Maynard, in Stereo Quarterly.

Most 12-channel CATV systems have the necessary band-width for carrying FM signals as well as TV signals. If they are not now carrying CAFM, it's probably because of disinterest, rather than some major technical problem.

A quick count of the 2400 or so CATV systems listed in "Television Factbook" shows 58% of them carrying FM. Of these 1413 systems, 236 did not state how many stations they were carrying, but 587 had between 1 and 10, 138 between 10 and 20, 59 more than 20, and 383 were carrying "all band."

Imported FM

For some systems, in areas where there are few if any local FM stations, it's necessary to "import" out-of-town stations. Flagstaff Television & Cable, for example, carries five stations, all of which are imported by microwave. Obviously, importing FM signals gives a listener several more choices than are possible through his own antenna, even if the antenna is highly directional and has a rotor.

On the other hand, most local FM broadcasters consider imported signals to be unfair competition. With half of the FM stations now losing money, it's no wonder they are touchy. What particularly worries them is that some CAFM stations carry imports but do not carry the locals. Nationwide, the FM industry has not yet agreed if importing is good or bad, and so the National Association of FM Broadcasters has not taken a position, one way or the other.

The National Association of Broadcasters, however, is quite concerned. In a filing with the FCC, they stated:

"Many CATV operators bypass local FM stations to bring in multiple FM signals from outside the area, usually from large metropolitan areas some distance from the CATV community.


Typical charges for cable FM are $7.50 to $10.00 for installation and a monthly charge ranging from free to $1.

"The deleterious effects of such leap-frogging have begun to be evidenced in communities where CATV has made significant penetration. In addition to badly fragmentizing local FM audiences, this practice actually denies local FM stations the opportunity to compete for cable listeners."

What does the FCC say about importing FM? Well, back in 1965 they asked for comments on the problem, but apparently never acted, probably because they have been so tied up with other problems concerned with CATV.

Other government agencies, it should be noted, have almost openly encouraged importing. For instance, the President's Task Force on Communications Policy, reported in 1968 that "The history of broadcasting indicates that complete reliance cannot be placed on a system of local over-the-air stations to achieve our goals. The regulation of radio on the basis of the local station concept limits the program choices available to the listener."

And, they noted, " ... national policy has carefully sought ... to develop a legal and economic framework for a communications policy which allows many voices to compete in the market place of ideas and of taste."

Whether they import or not, CAFM probably will eventually be forced to carryall local stations, just as CATV.

Taped FM

Rather than get involved with the trouble and expense of importing, some CAFM stations have taped their own music for use where there are few or no FM stations.

In Riverton, Wyoming, about 100 miles from the nearest FM station, a young college instructor, Richard L. Doering, has started what is probably the nation's first CAFM station, simply because he missed the good FM stereo music he enjoyed back east.

FM's Future

The Chase Manhattan Bank predicts that FM-equipped receivers will replace AM-only sets as the dominant type of radio sold by the early 1970's and that four out of every five sets sold in 1975 will be capable of FM reception.

Doering's station, "Radio 95," is carried to Riverton cable TV customers by Community Television of Wyoming, Inc., which houses the playback tape transport, stereo generator, and rf exciter. Doering tapes his programs and then sends the tapes to the cable company.

Since November 1968, Doering has been broadcasting in stereo 7 days a week, 8 a.m. to 11 p.m., with classical, popular, jazz, and country-and-western music rotating in half-hour segments. Fourteen minutes of uninterrupted music is provided for each 15 minutes of broadcast time, and advertising time is limited to 2 minutes per hour. Incidentally, advertising is the sole support of Radio 95.

Doering points out that cable FM is the perfect answer for communities too small to support an on-the-air station of their own.

Signal Processing

With the exception of locally generated signals such as Doering's, how many stations you will receive on CAFM depends not only on availability, but also on which signal processing technique the CAFM system uses: either all-band or discrete signals.

One metropolitan CATV system told us this about their experience with all-band processing: "Our original system for FM used an omni-directional antenna on top of a 350-ft building, All the signals received on this antenna were dumped into the FM band on the cable. But the results were unsatisfactory: too many channels with too great a variation in levels.

"We are now installing 20 discrete signal processors to include all of the city's FM broadcast transmitters and those closest to the city limits. Signals from directional antennas will be processed individually and controlled so that all channels are carried on the cable at the same level."

For discrete signal systems, FM stations are equally spaced across the dial with separations of 500 to 800 kHz. Each station is rebroadcast at a CAFM frequency different from that of the off-the-air frequency ; this creates a minor nuisance when tuning, but it's necessary to cut out interference between the cable signal and possible leakage from the off-the-air signal. How many signals are processed depends on availability as well as the CAFM operator's budget.

Theoretically, there should be no noticeable degradation of the signals.

The "delivered" signal strength can vary from 200 to 1800 microvolts across 300 ohms, depending on the system. Unfortunately, there is no industry or FCC standard for signal strength. The Canadians have specified a minimum signal level of 200 microvolts and a maximum of approximately 300 microvolts for carriers between 88 and 90 MHz and a maximum of 1000 microvolts for signals with carriers 90 MHz and higher.

The lower FM band signals are limited to prevent interference to channel 6 TV stations. The overall FM band signal limitation is designed to cut down on the background noise on the TV channels.

While CAFM signals are considerable better than those received with an indoor folded dipole at many urban locations, it must be admitted that such reception is not nearly as good as reception with say a 6-element FM antenna at a nearby suburban location.

CAFM - Where To From Here? With some prodding of the CAFM systems, CAFM manufacturers, and the FCC, audio enthusiasts may be able to get the minimum signal level set much higher. Since the FCC has not yet established technical standards for cable FM, now is the time for action by CAFM subscribers.

On July 1, 1970 the FCC issued a Notice of Proposed Rule Making on the establishment of technical standards for CATV. In the notice they said, "We are not at this time proposing standards applicable to the carriage of FM broadcast signals on CATV systems. "We may find it necessary to do so in the future ... We welcome comment on these points."

Considering the present and the expected improvements in FM reception brought about by CAFM, you might expect that an FM set could incorporate a few compromises in order to cut costs. Unfortunately, it can't be done.

Daniel R. von Recklinghausen, technical director for H. H. Scott, Inc., says : "For high-quality listening, a 60-dB signal-to-noise ratio is definitely desirable and this is the reason for using a high-quality tuner, even on a CAFM system. If you did not have a high-quality tuner, other performance characteristics most likely would be degraded and perhaps the expected signal-to-noise ratio would not be as great. For this reason I do not see any reason for connecting a 'cheap' FM tuner to a CATV or a CAFM system."

What type of tuner you do connect may be limited only by the imagination of the audio engineers. For example, with almost unlimited bandwidth available for CAFM, new techniques such as 4-channel stereo should be a breeze.

"Several organizations are working on special audio systems for cable FM," says one prominent CATV consultant. "Some will be in the FM band, but others are expected to use special tuners outside the present FM band to give additional channels and special features."

(Lead photo courtesy Jerrold Electronics Corp.)



Posted July 16, 2024
(updated from original post on 12/27/2018)

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