Big wheeling

Seems the Big Wheel 2m antenna in the loft is working ok, at least according to 2m FT8 with a bit of lift. It manages a good spread… (there’s one 4m in there too)

ISS SSTV August 2021

Just managed to receive a fairly good image from the closest ISS pass. This started as it crossed the UK and continued as it passed onwards to Germany. There were a few dropouts (I run the FTM100DE with an open squelch for these) but all in all this pic is better than any that I managed from the last series. The transceiver is connected to a white stick 2m/70cm colinear in the loft and I really need to stop being lazy and set the Arrow up for these passes.

pi-star

No idea what my pi-star setup was doing the other day but this might amuse some:

With all that load it was still managing to do all the comms stuff! Rebooting it sorted it out and it has been back to it’s usual 0.1 load ever since.

Allstar Link project

One of my ongoing projects was to build an Allstar Link node. I had acquired a working Baofeng 888 from eBay some time ago and a few days ago duly programmed it (all the channels in case I ever accidentally turn that switch) to the 70cm frequency I want to use. Also in the box of waiting bits was a Pi 3B, ex my Portsdown project (that has a Pi 4 now), a CM108 USB dongle and a dummy load. Anyway, it came to the top of the project list (= I wanted something relatively simple to fiddle with.

The CM108 came from Amazon and only cost a couple of quid. They had four available, all of which are now here! Following the excellent guide (among other similarly excellent guides) at https://allstarsetup.com/modify-a-cm108-sound-fob/ this was abused into something ready for use. Next came the 888 modifications (all relevant information can be found via https://allstarsetup.com/allstar-mini-node-construction-details/) which went fine except the information I was reading did not make clear how one powers the radio. I figured that out. Note that the radio needs 3-and-a-bit volts so two diodes in series with the 5V line works ok here (I need to add another yet). Anyway, in the true spirit of let’s cobble stuff together and see if it works, here is the node in all it’s glory!

Powering it up resulted in the expected flashing of LEDs on the Pi and no release of magic smoke. But all was not well. The first issue I encountered was that it was not opening up the Ethernet port. Scrabbling about for an HDMI lead the Windows PC monitor was pressed into service and the Pi seemed to be endlessly rebooting. I caught sight of a message saying the voltage was low. Odd, as it was powered by a 5A bench supply. Anyway, plugging it into a Pi wall-wart cured that. But I did not get the expected voice announcement of the IP address. However, as I still had the monitor attached I plugged a UCB keyboard in to do the initial setup.

The setup failed at stage 1! The Allstar wiki gave a username and password that would not work. A bit of Googling threw up root / root (*) and that worked. After having gone through the setup all seemed ready to go. I am not yet sure of all the options so selected the default in a number of cases, but I did chose to invert the COS line. Google was not helpful here.

I could see it was transmitting as the red LED on the radio would light but nothing was being received. A check, again, on the saved CHIRP config showed that I had managed to set the channels up as duplex with a 5MHz offset. I don’t remember how but anyway… I changed those, uploaded it to the radio and power cycled the node and it duly announced my callsign and it’s IP address. Woo.

For now, it’s all back in the box waiting to be completed. I have a 5V PSU on order and will get a box and also connect up the two status LEDs. Now, what do you do with it? 🙂

Edit: (*) the user=repeater and password given on the Allstar Wiki works for that particular software, not the software I installed above linked from that website. I have also now downloaded that but am still fiddling while reading up on the whole thing and waiting for the PSU and box to arrive.

More projects

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.

ISS SSTV event

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…

Portsdown upgrade

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.

Creed transmitter

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!

Creed blues…

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.

Creed 75 getting serious…

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!

Categories

Tags

Recent Posts

Archives

Links