Amateur radio ⁽²⁵⁰⁾

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…

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…

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…

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…