Wednesday, 15 July 2015

Old and New

Today has been a bit of old, and a bit of new, as far as radio work goes. I slept in very late, and eventually pottered into the workshop. First up, I decided to finally take a look inside this

 I salvaged a couple of these that were being junked, because the cases are nice aluminium extrusions, a new panel each end and they will make great project cases. Inside, theres a few nice bits, a bargraph LED block, some SIL resistor packs in sockets etc. Nice to see Zilog Z80 series chips again! The PCBs, once ive had any bits useful to me, will probably go in the 50p a go bucket at Finningley Rally.

Something else that ive been meaning to get around to doing is testing this MSF clock receiver

This was salvaged from the skip many months ago, probably years now, and its original case re-used as the housing of my Dekatron Spinner! I finally decided to actually power it up a few days ago and see if it worked, which it does! Next step then is to see if I can get it interfaced to something that can decode the time from it. It has only a +ve and -Ve connection - the signal pulses are output by pulling the supply line low. Im going to see about using a PIC to decode it, but Sam has also agreed that a Raspberry Pi might be the best way for him to learn programming, so ive given him a challenge to interface it to his Raspberry Pi (when I get him one)

 Also in the old list, Some time ago I got an old discone antenna from an ex-colleague. It had been up on a chimney for many years. The elements are bent, the feed open circuit, and very badly corroded and tarnished. Today I dismantled the feed section, and using a wire brush wheel on my drill press, removed the rust and corrosion.

 Now, with a new nut on the top, the feedpoint connections are all good again. I need to find a blind 'dome' nut and a suitable spring washer to suit, and I still have the 'cone' elements, which are aluminium tube, to straighten. My thought is to mount it on the workshop roof to give me a usable test antenna.

On the subject of antennas, I built the 4:1 balun today needed for the Cobweb antenna. This was a kit from Les at Amtools. I need to find a suitable box to mount it in now

The plastic case for the component tester also arrived today from China, so that is now built into its own box with three crocodile clip leads coming out of it. I managed somehow to mess up the measurements for the holes in the case for the LCD contrast adjust and the DC input, so these dont line up. I also couldnt find a button that would operate the power switch, so thats been removed and a SPST toggle switch mounted instead. At least now thats a nice convenient little test box, not an exposed PCB.

I also got around to testing my 80m ARDF beacon transmitter! The ATU is working correctly, but the NiCd battery pack went flat very quick, so I need to charge it up properly and redo the test.

The only other thing done today was to mock up on breadboard the 40kHz sawtooth generator circuit that will form part of the PWM modulator for the laser communications unit. This is only a simple 555 timer circuit and was very quick to get up and running, although my old oscilloscope took some time to become stable and not do silly things whilst displaying the waveform. I cant mock up any more of the circuit, as im still waiting on the comparitor ICs. 

My last chicken, Talullah, died a few days ago. She was very daft, more like a dog than a hen, and would follow me about. She was particularly fond of getting into the workshop and falling asleep on the bench

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