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!

More ATV fiddling

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.

5.6GHz experiments

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.

Spectrum analysers

I’ve been looking for some time for an affordable (i.e. used) and useful ranged (i.e. not cheap!) spectrum analyser. Obviously I want DC to light but don’t need it and don’t want to sell the house for a bit of test gear. I have a TinySA which is good to 960MHz but I will need a higher frequency range as I fiddle more with microwaves.

The ultimate, e.g. a Rigol or Siglent LCD type device is just far too expensive. Nice to have yes but something one would need to be using all the time in order to justify it. Then I came across Satsagen – http://www.albfer.com/en/2020/02/21/satsagen-2/

Satsagen runs under Windows and by default uses an Adalm Pluto as its interface to the real world. The software even does the necessary to upgrade the Pluto to the ‘full’ range of 70MHz to 6GHz (you can do this easily by hand but it’s nice of the software to do it anyway). The software has three basic function too – spectrum analyser, spectrum analyser with tracking, and generator. So, one PC, one Pluto, Satsagen and you get a pretty decent 70MHz to 6GHz spectrum analyser, tracking generator and signal generator.

I have not yet delved into all the functionality and only carried out a couple of quick tests on a handheld and on my 70MHz transverter, plus a very quick test of a FPV transmitter (TS832) up at 5.6GHz.

It will work with other devices such as the HackRF and the RTL dongle but it seems so useful I purchased a Pluto just for it (yeah, ok, I can use it for other stuff too but hey)

Antenna fiddling

I’ve been investigating putting some antennas outside and not getting very far. So I got a 2m ‘big wheel’ antenna off a trader on eBay. Plan A was to build my own but, being lazy I purchased a Wimo one. I’ve just installed this in the loft, directly above the shack so no issues of distancing (!) and it is a lot bigger than I had pictured. I now need to crawl under the thing to get to the fan dipole and other less important things such as the plumbing feeding the shower… hmmm.

Anyway, it all went together without much struggle and the NanoVNA shows a decent low SWR across the 2m band. I’ve had to rearrange stuff so the 4m dipole is now where the 2m one was and had to be rotated 90 degrees so is now roughly north-south.

Initial PSK Reporter results from the big wheel – note both the 2 and 4m antennas are fed from transverters from the transverter store in the Ukraine – showed 2m FT8 results of -14db into Cornwall and -10db into Cork plus a decent spread, and 4m picked up in south Wales so no worse than before. Of course, all these reports will probably be from stations with far better antennas than me, but hey.

The next task is to build a halo for 4m. I have some metal on order for that and other projects, like a 4m ground plane so I can do vertical as well as horizontal.

All still in the loft of course. One day these will be outside getting wet…

More on the ’75

Having now had a chance to take a closer look at the Creed to see why when Y is sent by the TDMS it prints as Z it is clear why! The following shows why… the TDMS is sending a continual stream of Y’s and then R’s:

This is the system between characters, all is well, but…

…this should be a Y, i.e. MSMSM (M = mark, S = space), but prints a Z, i.e. MSSSM.

And the R? This should be SMSMS, not SMSSS as shown. SMSSS is carriage return, no wonder then why the typehead remains firmly at the left of the platen.

But, checking the waveform output from the TDMS shows it is indeed sending a Y, and with a good square wave. This gets rather mangled when the teleprinter receive coil is connected but still has sufficient peaks to drive the thing. So the issue is between the input to the teleprinter and the selectors.

One item to note though is the three photos above are from a video recorded on my iPhone in ‘slo-mo’ – which proved to be really very useful here!

Time to read the manual more closely…

Categories

Tags

Recent Posts

Archives

Links