Mode Zero

A couple of pics of the Digi 5 successor, The narrowband SSM from 1977.
This is a five channel set on 40 MHz. I have a couple of others on 35 MHz which have a different colour RF module (orange).
The RF module hopefully will facilitate a FrSky or similar module conversion to 2.4 in the near future.
Compared to the Digi 5, the gimbal stick units with a track and wiper linear pot now have separate electronic trim pots.
The Tx has a flashing green LED to show power on.
Compared to the Digi 5, it is much more "productionised" to de-skill the assembly procedure. Wiring on the Digi 5 is all hand laced into a loom for example.

Radio Modeller review here:
http://www.vrhc.co.uk/images/Heli%20Gea ... review.pdf

On the Encoder circuit diagram below. Looking at the back of Tx and from Left to Right, the Module pins are
4- Aerial
3- Ground (-ve)
2- Battery voltage (+ve)
1- PPM

Here's my SSM Contest 8 Special: Waiting for new wire wound stick resistor tracks.

Quick update and thanks to Peter Gruchot from Germany and our own Mike Kitchen, have now rigged up one of teh SSM Tx with a FrSKY DHT module.
I was struggling with the PPM out to the module transistor network connection on the back of the Tx, teh module would bind but wasnt getting the channel pot position signals.

Peter suggested using the PPM out signal on the Trainer port (5 pin Din plug), see the attached circuit diagram and k is the PPM signal......tried it this morning and great stuff, all 8 channels are now working perfectly on 2.4 GHz!

I just need to tidy up and make a more permanent connection to the FrSKY module.

Once again, thanks Peter for all your help!

Short video of my SSM Contest 8 working on 2.4GHz
https://www.youtube.com/watch?v=cBC275fHulE

Also, here is an analysis by Bruno (F2B) why the RF module bay PPM pin will not work with the FrSky PPM input

"Great for you that the SSM came to life in such a relatively easy way.
Looking at the circuit diagram (I should have one of my own, but I can’t find it any more) it all came back to me as why the FrSky module wouldn’t respond properly at the modulation on the SSM module bay.
Looking at the circuit, you’ll see, between collector of T7 and the base of T10, an inductor with a capacitor to ground.
This is a LC low pass filter, taking out all but the fundamental frequency in the pulse.
This way they obtained a very narrow bandwidth, as the side bands were only twice the pulse rate away. If modulation would have been a square wave, you’d seen way more bandwidth used.
Clever guys, there in Harsewinkel!

The reason the FrSky didn’t like this, is due to the fact that it’s waiting for a sharp rising or falling edge, so aptly removed by this LC combination. So nothing happened.
As soon as you picked up the signal from a point with the edge still present, the whole thing switched on immediately."

THANKS BRUNO!



Short video of my SSM Contest 8 working on 2.4GHz
https://www.youtube.com/watch?v=cBC275fHulE

Also, here is an analysis by Bruno (F2B) why the RF module bay PPM pin will not work with the FrSky PPM input

"Great for you that the SSM came to life in such a relatively easy way.
Looking at the circuit diagram (I should have one of my own, but I can’t find it any more) it all came back to me as why the FrSky module wouldn’t respond properly at the modulation on the SSM module bay.
Looking at the circuit, you’ll see, between collector of T7 and the base of T10, an inductor with a capacitor to ground.
This is a LC low pass filter, taking out all but the fundamental frequency in the pulse.
This way they obtained a very narrow bandwidth, as the side bands were only twice the pulse rate away. If modulation would have been a square wave, you’d seen way more bandwidth used.
Clever guys, there in Harsewinkel!

The reason the FrSky didn’t like this, is due to the fact that it’s waiting for a sharp rising or falling edge, so aptly removed by this LC combination. So nothing happened.
As soon as you picked up the signal from a point with the edge still present, the whole thing switched on immediately."

THANKS BRUNO!

All of a sudden, it occurred to me that both your examples (SSM 5 & 8) must have come from a Dutch source originally.
If you look at them and mine (a contest 8 special), you'll notice the identical, small pttRCD stickers.
These came with the licence, that belonged to each individual transmitter.
PTT stood for our Postal Authority and RCD for Radio Controle Dienst.

When all these govenmental bodies were privatized (read: stripped of their funding), it meant the end to a well regulated regime that was at least fair to all users of the airwaves.
Now it's just a matter of money. A tinkerer pays the same as a corporation with big money in the bank.

Here's my second DIY project (~1970) that I had to bring and collect at the test office in Den Haag for passing the test and aquiring the license + sticker:

No way I could have any DIY project tested here now for making it legal, like back in the days.
In that way, the present, bureaucratic state is the self proclaimed enemy of the tinkerer.

By the way, I still haven't found any replacement resistor strips for the Simprop sticks....

Indeed Bruno. they came from an acquaintance in the Netherlands who I believed owned a model shop at one time...Eric Goossens, do you know him?

Did you conatct that guy in Germany with the simprop radios for sale that I sent you the details about?

Indeed Bruno. they came from an acquaintance in the Netherlands who I believed owned a model shop at one time...Eric Goossens, do you know him?

Indeed Bruno. they came from an acquaintance in the Netherlands who I believed owned a model shop at one time...Eric Goossens, do you know him?

Indeed Bruno. they came from an acquaintance in the Netherlands who I believed owned a model shop at one time...Eric Goossens, do you know him?

Indeed Bruno. they came from an acquaintance in the Netherlands who I believed owned a model shop at one time...Eric Goossens, do you know him?