North Florida Amateur Radio Society
W4IZ Jacksonville FL
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Editor: Billy Williams, N4UF
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TELEVISION INTERFERENCE
Interference to television reception by Amateur Radio operators is relatively rare today. Broadcast signals are much stronger now and technology has improved.
But during the 1950s, 1960s and 1970s--hams in Jacksonville (and many other towns) received numerous interference complaints from neighbors.
Slanted newspaper articles and television news reports usually blamed the ham. Nationwide, some city and county governments threatened to ban Amateur Radio operation. Fortunately, FCC jurisdiction pre-empted these efforts.
Nevertheless, in some cases, hams became neighborhood "heavies."A major function of clubs, including NOFARS and the defunct Jacksonville Amateur Radio Society, was to help members minimize television interference (TVI) and to stand up for hams to counteract adverse publicity.
Signals from broadcasters were weak in those days. TV transmitter powers were a fraction of current levels. All TV reception was over-the-air.
Jacksonville did not get wide area cable service until the late 1970s. Area Cablevision, the first system in Jacksonville, used poorly-shielded coax and cheap connectors on overhead lines. Temperature swings worked shield connections loose allowing cable signal to leak out and interfere with two-meter operation.
Legal signals from Amateur Radio operators leaked into the cable causing gnashing of teeth and great consternation among the public. A decision to include ESPN programming on cable channel 18 (144-150 MHz) did not help.
After prodding by NOFARS and local hams, Jacksonville cable operators upgraded their system.
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The following article details television interference problems (and a creative solution) that beset hams in the Philadelphia area during the 1950s and 1960s.
THE TVI BATTLES--THEY WEREN'T PRETTY!
By Bob Thomas, W3NE
Mention of television interference (TVI) dredged up memories of the early history of Phil-Mont when the term "mobile radio" acquired new significance. It (TVI) began about a year after the war ended, as the first post war TV receivers began to appear. They were expensive and highly prized by adventurous first-adopters who had shelled out upwards of $400 for a 10" black and white set.
At that same time hams were beginning to get back on the air, many using the rigs they had left behind when they entered the service. It didn't take long for the two events to collide, as some owners of those expensive TV sets began to have their viewing pleasure ruined by black bars or herring-bone patterns floating across the screen and sometimes total loss of pictures for their favorite programs.
TVI was born!
Most transmitters at that time, if they were not old pre-war vintage, were new ones constructed the same way as they were before the war. They typically were built on an open chassis (or even on a wood board) or at best, as rack-and-panel modular units mounted in an open relay rack or ordinary metal cabinet.
Finally, the ARRL established local TVI Committees made up of amateurs and private citizens to diplomatically resolve stubborn cases of TVI. The procedure generally followed was for a member of the TVI Committee to first visit the amateur. If the ham was unable to transmit without causing TVI in own set, the case was put on hold until a subsequent visit from the committee showed the ham had eliminated his own TVI.
On the other hand, if the amateur was able operate his transmitter without interference to his own TV set the committee member went to the home where TVI had been reported. If a test transmission resulted in TVI, the committee representative had the difficult task of convincing the complainant that their receiver was at fault, and they were responsible for obtaining a service technician to cure it.
Similar problems also occurred with broadcast radios and telephones, for which the same procedure was followed.
Cost was modest for a mobile transmitter and a receiving converter feeding the car BC radio.
Best of all, when you were on the road there was no TVI. Well, not exactly ? there might be TVI, but it was fleeting as the mobile drove past. That phenomenon gave rise to a new sport among mischievous hams who delighted in driving along a suburban street so they could look into living rooms where images of TV programs flipped and rolled while they transmitted in motion.
Not nice, maybe, but amusing and completely immune from that dreaded phone call. The new freedom gave birth to the name of the clubnewsletter, TVI Retreat, edited by George King, W3PXY.
The name gradually morphed to the present title of our bulletin as it became commonly referred to as "the blurb."
Reputable TV receiver manufacturers finally acknowledged their error ignoring the importance of shielding and adequate front end filtering. They improved new models and offered upgrade kits for field installation by dealers.
The FCC entered the fray hinting that an amateur having a TV receiver in his house that was not affected by his own transmissions was absolved from responsibility for interference caused to neighbors' sets.
Nevertheless, in cases of acute interference the ham might be forced by the Commission to observe quiet hours, say from 4PM to midnight ? a draconian limitation that didn't go over very well. In any event, those actions put the ball squarely in the amateur's court.
The challenge to eliminate amateur radio's contribution to TVI was met on several fronts. Articles in QST and new designs published in the ARRL Handbook stressed the necessity for thoroughly shielding transmitters and bypassing all connections entering and leaving the Tx.
Articles showed liberal use of metal window screen coveringventilation openings, techniques for sealing physical gaps in the panels and doors of cabinets, and gave advice on design of power line and interface lead filtering. Traditional push-pull finals with link coupling were abandoned in favor of a single-ended configuration that lent itself to load matching with a pi-network, which also acted as a low pass filter to minimize harmonic output.
One of the most useful aids to amateurs for TVI reduction was a book published and distributed free by Phil Rand, W1DBM. It was a compilation of some QST articles and several chapters written by Phil describing all the techniques for elimination of TVI. Equipment manufacturers also responded with new products incorporating features that eliminated causes of TVI.
For example, the Johnson Viking II 100 watt AM transmitter was housed in a copper plated cabinet with a tight fitting lid bonded to the case with beryllium copper finger stock.
The back of the meter was shielded by a metal shield cup and every input and output lead was filtered with a series air-wound inductor and ceramic bypass capacitor. Complex coax low pass filters with very high attenuation above a 30 Mc. became available from several manufacturers at reasonable prices for harmonic suppression in the transmitter output.
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Editor: Billy Williams, N4UF
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