Amateur radio ⁽²⁵⁶⁾

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.

Getting serious now. I managed to sneak the 75 into the shack aka little bedroom. It is sitting on a bit of plywood to stop oil getting onto the desk. At least it is near the radios now. The device to the right is a Catronics CT103 RTTY terminal unit, but I currently have no information at all about it. It says CT100 on the front but the PCB is marked CT103 and the little information I found via old adverts suggests CT103 is a fuller version of the range. It does generate around 90V off load so is a step in the right direction. 4 DIN sockets on the rear have been marked by hand as Magnet, Keyboard, RX/TX and VDU. There are 5 switches inside, one row of 4 and one DPDT which appears to switch in a pair of NPN 300V transistors so I wonder if that converts between single- and double-current operation. I am trying to trace the circuit to make sense of the connections before I go further. Search engines have not been kind here, throwing up only advertisements for the TU and no actual information. Enquiries are ongoing! Update: Some progress made by trying to trace the circuit out by eye. There are two switches on the PCB, one 4-way and one DPDT. The DPDT brings in or isolates two power transistors and I figure this is to switch between single- and double-current operation. The 4 switches appear to switch in or isolate power resistors and I am assuming this is to set the loop current. As set, the CT100 produces 20mA when connected to the 75's magnet. This is with switch 1 and 4 on. Switching 2 on as well makes this 24mA. Audio in is via two pins on a 5-pin DIN, one having a ferrite bead and going via a resistor to antiparallel diodes, the other is earth. Feeding audio in from a known good RTTY signal in the 10MHz band does result in the signal and mark LEDs flashing and, when the station is sending RYRYs the 75's magnet makes that typical RYRYRY sound. So, so far, so good. All I need now is to figure out why the teleprinter does not respond properly to an input signal. I really need to tidy up as well... but to make things worse I really think I need to bring the TDMS in so I have a reliable code pattern to set the teleprinter up against. I may need to go weight training first!

After finding the dead LCD screen that was to be a 5.6GHz ATV receiver it also turned out that the 7" Pi screen on my Portsdown setup had similarly died - just white lines on the screen. No amount of stripping, reassembling and general fiddling fixed it. A new screen did. Anyway, I now have a Winterhill receiver. This came from a fellow ham and saved me building one. As is usual with any new box one absolutely must try it right away, which is how I discovered the bust screen on the Portsdown. After that was replaced I successfully sent a test card 40 inches across the desk! Small steps... and at least the Winterhill is in a nice box unlike my Portsdown which is still waiting for a suitably sized case - why is it all the nice metal boxes are a few mm lower than the 7" display needs. Huh.

I had a quick fiddle with the box of bits that should by now - in fact by a year ago - be a 5.6Ghz ATV transceiver. I now have a couple of Gibeon flat panel antennas which claim 24dBi as mentioned in the excellent resource on this topic at http://5-6ghz-atv.co.uk/ So, let’s have a play. I got a rather old fashioned Sandisk Photo Album, a slab of plastic that takes 5V and will present photos (and videos and sound files) to a TV via an AV output and the typical red, white and yellow RCA plugs. First off I  needed to make sure this worked. So, what has an AV input… er… Bedroom TV? Nope. An older Sony TV in another bedroom does and so it was plugged up. And nothing. Problem 1, it seems to take an age to turn on in response to its remote control. No switch of course. Problem 2, it would not read anything on the SD card I had with a test card image on. The only clue is it needs a ‘JPEG (Baseline, up to 16 Megapixel)’. No idea what I had produced via GIMP on the Linux box but it would not find anything at all. Maybe it’s the SD card. I found a very old 32Mb (!) SD card with some sundry photos on and those were fine. Ah, so maybe it cannot read big SD cards. Copied the test card file onto that and now it at least finds the card but says the format is unknown. After 3 iterations I fed the jpeg into Windows Paint, saved it (as jpeg) and it worked. And success, I can send the test card image to the TV via the TS832 transmitter and RC832 receiver. Next, I tried the flat panel antennas and they worked too, not that I would have expected any less as the little rubber duck antennas worked fine. However, offering the AV to my 12V monitor (ex eBay car reversing screen) just showed lines. No amount of shouting fixed this and it would appear that this monitor has simply died, perhaps having got fed up waiting in a box all this time. Anyway, now I need to actually construct the thing properly and work out a mount for the antennas.