SCS decoders  
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SCS decoders - 5/13/2008 7:38:38 PM   
jaymen


 

Posts: 204
Joined: 3/26/2003
From: Mission Viejo, CA, USA
Status: offline 		Anyone remember the SCS decoders used in early digital proportional radios for the receiver decoder circuit? They are Silicon Controlled Switches, and are basically two transistors hooked together. Initially thought to be superior to discrete transistorized decoders, they prooved unrelaible and prone to latching up. They were abandoned by the early 1970's as ICs became availlable.

Each SCS was in series with the next, so if one latched and quit, then all channels shifted over by one. This meant if normally you had Aileron, Elevator, Throttle, and Rudder as channels 1,2,3, and 4 respectively and the SCS for channel 2 latched up, then channel 3 became channel 2, and so on.....meaning you had control, but the servos were now on different sticks!!

Of course the system would resume nomal opperation when it was reset by turning the receiver off, then on again, making diagnosos all but impossible. The SCS would latch up due to being false tripped by noise spikes, or arbitrarily, as AM systems are suceptable to noise, especially when the signal levels change radically due to the planes attitude and orientation relative to the transmitter. This kind of problem rarely shows up on the test bench, or in the lab, making it particularly troublesome.

The availlability of high frequency and storage oscilloscopes, and spectrum analyzers was limited back then, they were prohibitively expensive, so alot of developement was done without them, basically it was empirical: you tried this and that, and went with whatever seemed to work best. If you had problems, then you tried to isolate the source by substitution or a process of elimination until the problem went away....and you hoped there were no more problems waiting to rear their ugly heads. Some guys got lucky, some didn't, there was alot of chance and black magic in the game. Not every aspect was fully understood, due to the inability to accurate measure and see what was going on.

This accounts for why so many prototypes and evaluation units that were reviewed by the magazines worked well, but had problems when released as production units, there were too many variables to control in a technology that was not fully understood. Any RF engineer will tell you experience, and a little luck never hurts!

I would say nerves, and perserverance played every bit as big a role as genius did in the developement of early R/C systems.

_____________________________

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RE: SCS decoders - 5/13/2008 8:06:14 PM   
iflyj3



Posts: 964
Joined: 5/18/2002
From: Paris, KY, USA
Status: offline
quote:

ORIGINAL: jaymen

Anyone remember the SCS decoders used in early digital proportional radios for the receiver decoder circuit?


I do. They were used in the Digitrio decoder for the 4 channel unit. I have two 5 channel units I built with new circuit boards that had the fifth channel added.

However, to my knowledge I never had the latch up problem. Hummmmmmmm, those unexplained crashes that I thought were dumb thumbs,,,,,,,,,Hummmmmmmm......

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Dan Thompson (Long live the ACE MicroPro 8000)
Visit www.groups.yahoo.com/group/mp8k for support

(in reply to jaymen)
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RE: SCS decoders - 5/13/2008 8:40:20 PM   
grotto2



Posts: 324
Joined: 2/3/2003
From: Palm Bay, FL, USA
Status: offline 		My comments are identical to Dan's.
The Heathkit GD-19 I built used SCSs in it's decoder and I don't remember it ever skipping channels. Then again.....
-Ron

_____________________________

I finally got a tattoo. It reads, "Born too loose."

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RE: SCS decoders - 5/14/2008 12:11:28 AM   
jaymen


 

Posts: 204
Joined: 3/26/2003
From: Mission Viejo, CA, USA
Status: offline 		Alot of it depended on how imune the receiver was to noise, and how well it was tuned, and a good clean installation didn't hurt either.
I guess that explains why some people had mixed results!

You guys must have done a good job of building and installing your radidios(sic)

I remember at the field that there was one guy they called "Pig Pen" because he always had shabby looking planes with a rat's nest inside...he made many take-off's, but always returned to the pits with the remains in a brown paper bag. We would run out into the field and pick the carcass dry of valued items like hinges, wheels and the fuel tank if it wasn't crushed. Back in those days us kids took advantage of anything we could get our hands on, we were like vultures at the R/C field(Mile Square Park) and went there purposely to get "booty". It was an adventure more exciting and rewarding than a trip to Frank's Hobbies in Orange. We would also dig into the 55 gallon trash cans at the field on Sunday afternoon, which was always crammed full with crashed airframes, to see what treasures we could recover for our projects. One of my buddies used a cut down wing from a wreck for a home brewed plane, that's how we afforded r/c.

We saw Phil Kraft, and Bob Dunham fly there back in those days, but didn't really appreciate it until many years later as we were always intimidated by the Big Shots and never dared to approach them. I'm sure they were cool, but we did not feel worthy. Only later did I realize who they were.

Later, when I worked in the hobby industry, at trade shows on set-up day, they would come by our booth and recognize me saying "hey, wern't you that kid that used to srounge planes out of the trash cans?" It was good for a laugh.

< Message edited by jaymen -- 5/14/2008 12:14:45 AM >

_____________________________

Did you charge the transitory remitter batteries ?

(in reply to grotto2)
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