Radio and rails...

Some aluminium arrived for a couple of antenna projects. This took a while as the first order got lost somehow and now they only sent part of what I ordered, but sufficient to make a start. The first ones are for 70MHz, a ground plane for 4m FM, so I can reinstall the AT588, and a halo. I can't fit a big wheel type in the loft but a halo will fit and replace the current dipole.

Not done very well at all with the current ISS SSTV event that runs from the 21st June, or with the previous event a few weeks before. So far, I have not one single decent image to show for it. Not sure why exactly, nothing has changed here. All I can think is the station transmits earlier, completing as it approaches the west coast of Ireland and so it does not start the next one until it is south-east from me. But I can't remember how it went last time so not sure if that is even a thing. Anyway, I submitted the 'best of the worst' image, which at least has a complete top and tail, but only a fuzz for the actual image of whatever it should have been. I could crack out the Arrow and go dancing in the garden. Maybe next time...

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…

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…

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…