Radio, railways, stuff...

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.