In the early 1980s, satellite television became a fairly large thing, especially for those who lived in rural areas and who couldn’t get cable. Indeed, even moderately wealthy city dwellers who had a large yard (or a large roof) would get satellite TV.
In order to watch multiple channels on multiple networks, you had to reposition your satellite dish to point at different satellites, then retune your receiver for the new satellite. Of course, people soon tired of moving the dish manually, so a market for satellite dish positioners arose.
A company in Winnipeg called ComSat commissioned Vansco to create satellite dish positioners for their customers. There were two or three models, with different sizes of memory storage, and sophistication of function. However, they were all front panel activated – one had a wired remote control.
On one of those existing dish positioner systems, I was asked to investigate recurring field failures, where the boards came back burnt up. The first thing we found out was that somehow the two opposite drive channels were coming on, shorting out the supply. As we were using thyristors (triacs), we suspected a thyristor commutation failure. The first thing I did was put a fuse in the circuit, to prevent board damage if and when such a failure to commutate should ever occur, although it really should never occur. Then we realized that the failure was occurring periodically as the dish positioner motor was crossing the end limit switch – apparently the inductive kick from the circuit opening was enough to engage both triacs! We replaced the fuse with a push-to-reset circuit breaker, and beefed up the copper weight on the output driver board (1/2 oz copper wasn’t enough, I had it increased to 1 oz on that board only), and we were able to start shipping again.
The market was calling for a high end dish positioner. I was to create a new product with wireless remote control, alpha display, high resolution high performance positioning, and full CSA approval.
The first thing, of course, was to address the problem we’d just been through. Rather than use triacs on full-wave-rectified DC, which would sometimes fail to commutate due to the induction of the motor under load, I created a full wave bridge using SCRs, which are guaranteed to commutate. And, of course, we used 1 oz copper on the output board 🙂
We got the high-end MC68705 MCU for the processing, with lots of program memory. We put an NM93C46 serial EEPROM for the many memories this unit would have.
I did a survey of the wireless remote control systems at the time. I tested RF and infrared remote controls… and briefly considered ultrasonic (my family had a very old Zenith television with Space Command, and as I recall, there was an electronic system that worked similarly). I didn’t seriously consider it.
In the end, we used a Philips infrared remote control system. The initial prototype used the Philips chips on both ends, but when we added up the cost of the bill of materials, the receiver chip was just too expensive! So on a lark, I wired the IR detector directly to the MCU and modified the code to try to decode it directly… and made it work! With only a minor bit of circuitry, we had full IR decode capability.
We built more prototypes. We contacted our local CSA office and proceeded to get the prototype CSA approved. It was all done, except for the issuance of the tags… when the project was cancelled.
It turned out that the satellite receiver manufacturers had figured out that they should incorporate the dish positioner into their receivers, so that customers could program one device with both the location of the satellite and the tuning. Can’t say I blame them. But, literally, the bottom fell out of the satellite dish positioner market, and we stopped making them. From something like 2,000 units a month to zero the next. Ugh, that hurt!
