Radio, railways, stuff...

I’ve upgraded my Portsdown setup to Portsdown 4. Setup is used in as loose as possible a way here as it’s basically still a box of bits. This needs a Raspberry Pi 4 which arrived today, freeing up the current Pi 3B for use elsewhere. The docs suggest a 2Gb version but I got the 4Gb one. One slight hiccup is that the Pi 4 uses a USB-C for power so I borrowed a phone charger lead temporarily. I must say that the upgrade was very easy. Well, ok, the actual upgrade was attaching the Pi 4 to the back of the screen and downloading and installing the software on a freshly cut SD card, not upgrading the existing software. But, easy - ssh into the Pi and run 3 commands pasted in from the software page. Or simply buy a pre-cut SD card from the BATC shop. I also had a Pluto lying about (there, loose terms again in action, it was actually aimed to be the RF part of a Satsagen spectrum analyser setup, but hey). One thing I had not realised is you can run both the Pluto and the Lime Mini together, just not at the same time, so no wastage of the Lime. It also connects to the Minitiouner (V2 only which mine is). But the icing on this particular cake is that with the Pluto one can use the Langstone microwave transceiver  which is, in this case anyway basically an add-on package that is installed from an option in Portsdown via the touch screen. With the addition of a USB audio sound card dongle, which I had, plus my Heil headset it turns it into a transceiver able to work multimode across the amateur bands from 4m to 6cm with further plans in the pipeline. And, like the Portsdown installation itself, setting up the Langstone was equally easy. Hats off to all those who made this excellent product so easy to set up. More info at https://wiki.batc.org.uk/Portsdown_4 and https://wiki.microwavers.org.uk/Langstone_Project One thing to note is that the Pluto output is very rich in harmonics so filtering is a must. Not got that far yet! I need a box first.

Ok so I adjusted the teleprinter's transmitter to the correct tolerances and made matters worse! It was at least trying to send characters out in response to key presses even though they were all wrong. Now it sends fewer, i.e. some keys send nothing at all, but still equally wrong! I can't see how I made it worse by correcting it. But it's interesting delving into this beast. The transmitter itself is simply a series of contacts. The selector mechanism pushes on pins which push or leave the code bits, and these are then read by another set of contacts which fire in sequence to send the relevant word. But it would be nice if it worked... So I thought it might be an idea to get a meter on to each code contact to see if it was connected to mark or space when a key was pressed and the mechanism moved appropriately. Nothing. Ok... take the transmitter out again. It does not match the wiring in the book. The book / manual says that each code contact comes out on pins A1 to 5 but they aren't. There is no wire on A5 and in each case the code tongue is wired directly to the associated readout contact. There should be 18 wires on the plug - there are only 10. However, the change to the wiring should still work as the interconnections are essentially the same as would have occurred if wired according to the diagram. Update: after a lot more adjustment, taking it somewhat outside the design specification I can now semi-reliably generate the correct codes per key press. The machine skips sometimes, which needs sorting and it does not always generate a character, but when it does manage it is generally the correct one. So, some progress. Turning the machine by hand and checking each code contact does reliably get it right, just not at speed under motor control. Some further adjustment should cure this but I am concerned that the clearances are now a bit off from spec, as when in spec nothing worked at all. I am going to concentrate on why it will not receive properly when given a decent signal. At least that way if I can eliminate at least one of the two faults I'll be happier. Meanwhile the machine continues to migrate between the shack and the workshop, which is a trip of two flights of stairs and three doorways. But I am getting some exercise so no bad thing!

Having been unable to find any documentation at all for the CT100 TU I made a better effort at tracing the circuit out and I now think I know what connects to where. The magnet output is obvious, as is the audio input (TX output). I have now worked out the audio output (RX input) and traced enough of the circuit to figure out the keyboard input which has three connections for mark, space and tongue, the latter being connected to earth. The mark and space inputs pull down the inputs to matching nand gates and thence into the rest of the circuit. The keyboard connections were the last bit of information needed. Attaching headphones to the audio output I can trigger both tones by shorting each of the mark and space inputs. So far, so good. But... ...the keyboard outputs from the 75 are open circuit, yet at rest the 'stop' contact should be made and thus one of the keyboard connections should be connected to it. it isn't. A slight pressure on the contact makes it. Similarly, each of the 5 code contacts never 'makes' when operated (i.e. pressing a key and turning the motor by hand). But those code contacts are quite a long way off and I don't want to adjust them until I read up on that part of the mechanism. Amazon just delivered a set of feeler gauges (my set from motorsport days are very rusty!) and spring balances so I can begin to work through the adjustments. My general experience of teleprinters dates back to when I was still at school and all Creed 7E's... the 75 is quite different.