As Hackaday writers we don’t always know what our colleagues are working on until publication time, so we all look forward to seeing what other writers come up with. This week it was [Al Williams] with “Things Your TV No Longer Needs“, a range of gadgets from the analogue TV era, now consigned to the history books. On the bench here is a device that might have joined them, so in taking a look at it now it’s by way of an addendum to Al’s piece.
When VHF Was Not Enough
In a Dutch second-had store while on my hacker camp travels this summer, I noticed a small grey box. It was mine for the princely sum of five euros, because while I’d never seen one before I was able to guess exactly what it was. The “Super 2” weighing down my backpack was a UHF converter, a set-top box from before set-top boxes, and dating from the moment around five or six decades ago when that country expanded its TV broadcast network to include the UHF bands. If your TV was VHF it couldn’t receive the new channels, and this box was the answer to connecting your UHF antenna to that old TV.
It’s a relatively small plastic case about the size of a chunky paperback book, on the front of which is a tuning knob and scale in channels and MHz, on the top of which are a couple of buttons for VHF and UHF, and on the back are a set of balanced connectors for antennas and TV set. It’s mains powered, so there’s a mains lead with an older version of the ubiquitous European mains plug. Surprisingly it comes open with a couple of large coin screws on the underside, so it’s time to take a look inside.
Inside: A Familiar Sight
![TV tuner front end block diagram. Chetvorno, [CC0].](https://i0.wp.com/hackaday.com/wp-content/uploads/2016/07/rf-front-end.jpg?w=466&h=262&ssl=1 "RF-front-end")
At first sight it’s fairly simple: a conventional mains DC power supply with no regulator and a metal tuner can. The scale mechanism is a string-and-gears affair, something quite common back in the day but a rare sight today. Unclipping the lid of the tuner can reveals its secret, this is the front end of a UHF TV tuner modified slightly to produce an output on a VHF broadcast channel. We’ve covered UHF TV tuners in the past, but if you’ve never encountered them here’s how they worked. Inside the can is a series of cavity tuned circuits containing two transistors. One of them is wired as an RF amplifier that works on the signal from the antenna, and the other is an oscillator. By mixing the amplified antenna signal with the oscillator output it’s possible to filter out an intermediate frequency, which is their difference. This was always 36 MHz, chosen because it lies just below the VHF broadcast band, and since this tuner needs to feed an unmodified VHF television, its output frequency will be a bit higher. We’re guessing that it’s been modified for a 41.25 MHz output, corresponding to the European VHF channel 1.
So in front of me I have a European thing that your TV no longer needs, and it’s one that probably didn’t have a very long market life. It’s a snapshot of a moment in consumer electronics history, when the number of channels could be counted on far less than the fingers of a hand. With analogue TV now long switched off it’s not even got a use any more except as a curio, so it joins the pile of museum-pieces alongside the 8-track player. Meanwhile if you’d like to see how an American city handled the UHF transition, we’ve been back to 1950s Portland, too.
Of course, UK TVs would not have benefited from that device as the UHF transmissions were in 625 lines, and had a totally different standard to the VHF 405 line pictures.
Incidentally, I used to have an earlier example of a similar convertor that enabled VHF Band 3 signals to be seen on a Band 1 only set (a Bush TV22) in the 1960s.
We had a service back in the early 80’s called “SuperTV” in my area. It was an over-the-air paid service. It broadcast on channel 54. The signal was scrambled and decoded with a simple one-button set-top box set to output on channel 3. The service included a cute little “cornered” log-periodic antenna for mounting and a monthly “TV guide” publication for the programming.
The service only broadcast in the evening, starting with kids movies, then mainstream and R movies, and several days a week finishing up the broadcast day deep into the night with adult programming. The first time I saw Star Wars and Time Bandits was on SuperTV. I’m not sure if there was normal daytime programming – I believe there was.
It eventually fell out of favor due to the market penetration of cable TV. Channel 54 became a normally-programmed TV station and eventually joined the UPN network.
I recall this experience right alongside the top-loading VCR with the WIRED remote.
Ah yes, blue boob TV – when viewed without the box.
Explains the popularity of Avatar years later.
Ours was a box brand named ” ON tv”. The box had one knob and it was marked off to the left an ON to the right. I also believe it was US channel 54.
Channel 52 in the Los Angeles area…and those boxes were easy to hack.
I’ve got (somewhere in the shed) yet another TV device that’s no longer used – it called itself a color corrector, and it output on channel 3 or 4, like a VCR, except it had a knob for some kind of color correction that I never used. What I did with it back in the day was to plug some composite security cameras into a switcher, and then the box, and then I could view them using the RF input of a TV instead of needing a composite input. I could even receive it wirelessly using a portable TV in the other room. Not bad, back before anyone was watching videos over wifi or on their phone, able to pause anytime they wanted. Plus, no real latency!