Re: What Happened To Channel 1

But by the 1950s, TV set manufacturers were installing "turret tuners"

> to simplify VHF tuning. A single knob rotated a cylindrical mechanism > fitted with twelve little hand-wired circuit boards, one for each > channel. Each circuit board had a bunch of capacitors, some > hand-wound coils, and a row of metal contacts that mated with metal > springs. As each circuit board was brought into position by the > rotating mechanism, the springs mated with the contacts on the board, > placing that board in the circuit. > After the introduction of UHF, turret tuners were manufactured with 13 > circuit boards, one for each VHF channel one that switched to a > separate UHF tuner. The UHF tuner was tuned in one continuous-tuning > dial.

As you linked to a picture of typical British VHF and UHF tuners, allow me to add a few more comments from this side of the pond.

In early times, many British sets had no outside channel selection, just a fine tuning adjustment. As we had only one TV service then, this wasn't much of a problem, unless somebody moved to a different area, in which case he would need to have the set retuned. Only channels 1 through 5 -- our low VHF band I -- were in use.

By 1955 Independent Television arrived and the turret tuner had became standard. All ITV transmissions were on high VHF band III, channels 6 through 12, later 13. External converter units were also sold to frequency convert band III signals down to band I for those using older sets.

There were also some sets in the later 1950s and 1960s which included an FM radio option (FM radio itself being a relatively new introduction, having started in Britain in 1955). There were only three BBC networks in those days, and some sets added three extra turret positions to tune the "band II" FM broadcast range (a separate cam and switch arrangement on the turret mechanism was generally employed to blank the screen during radio reception). These positions were sometimes labeled H, L, and T on the selector for the names of the BBC services (Home, Light, and Third).

The plan for UHF was ready by the early 1960s, so sets incorporating a UHF tuner started to appear. The complication was that existing VHF transmissions were still 405-line (system A) but the new UHF transmitters were to be 625-line (system I). The dual-standard sets had a *monster* changeover switch which had to not only switch from VHF to UHF but also reroute signals to different I.F. stages, switch the horizontal scan from 10.125 to 15.625kHz, change from AM to FM sound, invert video polarity, and so on. The switch was often a custom-made unit for the set which ran the full length of the chassis so that each pole was close to the required section of the circuitry.

Two switching approaches were used: One left the VHF turret positions as normal and used a completely separate rotary or push-button/rocker control to operate the changeover switch.

The other put a "U" position on the turret tuner to select UHF, with a cam and link rod on the mechanism to operate the changeover. The VHF tuner was then used as an "high I.F." for UHF reception. There were even some designs which used an auxiliary contact on the "U" position to apply power to a solenoid to operate the switch, presumably on the basis that a wire between tuner and main board was easier to maintain than a mechanical link which would need to be removed, reconnected, and adjusted if anything was taken out for servicing.

The UHF tuners came in two flavors: One was the continuously variable type as described, the other being a mechanical preset arrangement. The UHF band-plan was designed to allow an eventual four networks (BBC1, BBC2, ITV, plus a yet-to-be-determined fourth station), so many of these UHF tuners had four buttons.

These mechanical UHF tuners operated with permeability tuning (i.e. the slugs were moved in and out of the coils), with each button being turnable to set the preset to any channel across the UHF bands (bands IV and V, channels 21 through 69). This is similar to the arrangement which was employed on the mechanical presets of car radios at the time.

For several years, people needed both VHF and UHF in order to receive the full range of programs. The second BBC service, BBC2 went on air on 625/UHF in 1964. BBC1 and ITV started their 625/UHF broadcasts around 1968/69, but it would be several more years before UHF coverage was extended to most of the country. The fourth button on mechanical UHF tuners (sometimes marked "*" or "ITV2" in anticipation of a second independent network) was often used by those living on the boundaries of service areas to select an ITV broadcast from an adjacent region (BBC was networked most of the time, while in those days the ITV regions were far more autonomous and often had alternate programming).

Gradually, UHF covered most areas, and in the 1970s we started to see single-standard sets once again, only this time they were 625-line and came with only a UHF tuner. Small portables of the era tended to come with a continuously variable UHF tuner, while by the end of the 1970s varicap tuning and 6 or more preset positions was becoming the norm for larger sets.

Just to finish the story, that planned-for fourth network finally went on-air in 1982, and the 405/VHF transmitters -- still radiating just BBC1 and ITV in monochrome only -- were eventually closed down in


- Paul.


From: Joe Morris Subject: Re: What Happened To Channel 1? Date: Mon, 21 Mar 2005 13:57:19 UTC Organization: The MITRE Organization

Michael D. Sullivan writes:

Television, on tho other hand, started out in two discontiguous VHF > bands, with somewhat variable spacing between channels and a need for > precise tuning, and tuning in on a single band by twiddling an analog > variable tuning capacitor to the right frequency would have been > difficult. This tuning method was used on some early TVs; I don't know > whether they were tuned by numeric frequency or by channel number, but > it would not have been very convenient.

I'm not sure when the manufacturing of TV sets with a single analog tuner was finally discontinued in the US, but I recall my family having a very early duMont (?) receiver (maybe 5" diameter circular screen?) with an analog tuning knob which drove the tuning capacitor through a reducing gear. This would have been in the early 1950s when WDSU-TV [*] went on the air in New Orleans. And no, I can't recall the brand we got to replace this receiver, but my (non-parity-checked) memory says that it had a "revolutionary" drum tuner with detents and tuning settings for each of the channels.

[*] I get a number of questions at the office when my wallpaper changer pops up with the original WDSU-TV test pattern. It makes me feel old when I turn out to be the only person there who remembers when test patterns were routinely incorporated into the station ID slides ...

Joe Morris

[TELECOM Digest Editor's Note: I seem to recall when I was about five years old my parents had a television set with a tiny little screen which was maybe two or three inches round. And it had a _huge_ magnifying glass attached to the front of it. PAT]
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Paul Coxwell
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