Monday, April 23, 2012

Sinclair Spectrum - 30 Years Old!

In 1982 after a lot of thought and constant mind changing I bought myself a Sinclair Spectrum 48k Computer. At the time I had looked at lots of other machines including the 'Oric', 'Dragon' and 'Lynx' computers, but was finally persuaded (rightly) by a friend to go for the Spectrum. The best thing I ever did! When I bought it Sinclair dropped the price of the 48k machine by £50 to £ off I went to W.H.Smiths to buy one. I even took some time off work expecting a huge queue, but no, only me. I asked the girl expecting that they had already sold out, but she smiled and went to get one. YES!!! I couldn't believe I went to take it to work to try it out!

Now instead of writing more, this guy says it all, so I am quoting this from his blog... Thank you Michael have said it all!

The Sinclair Spectrum - 30 today

"If there is something guaranteed to make a 47-year-old chap feel old, it is to be told that the first computer he ever got his hands on is 30 today. THIRTY! That’s how long ago Clive Sinclair released his groundbreaking ZX Spectrum home computer, a machine that was the future, once. And like millions I bought one, at the rather grand price of £125.

This was the bizarre false dawn of home computing, when a slew of standalone machines flooded the market, all mutually incompatible, incapable of being networked without some serious soldering and bought by people for the most part unaware of what to do with them. And nevertheless, we loved these strange gizmos which you plugged into the telly and required software to be downloaded via a cassette deck.
The Spectrum was far cleverer than most, and came in a natty black case that shrieked ‘Year 2000” and had a clever (and, crucially, cheap) rubberised one-piece keypad. It was the iPad of its day, well-made, hugely desirable and very stylish; I remember queues in the shops and fawning news items about this British marvel. This was a rare industrial success story at a time when unemployment was at a postwar high.
But what was it for? Playing games, that’s what. Yes you could buy a printer but I remember the results came on shiny four-inch-wide paper and no one pretended this was any kind of serious business machine. But at its heart lurked a fairly powerful processor (by the standards of the day) and a stripped-out operating system that allowed young and clever programmers too work wonders, creating innovative games with colour 3D graphics and wrestling every last pixel of resolution out of its primitive graphics hardware.

It is probably down to machines like the Spectrum, its predecessor the ZX81 and the Tangerine, an even more basic computer, that Britain led the world in the lucrative computer games industry (it is not widely appreciated that mega-successes such as ‘Grand Theft Auto’ are, despite their American ambience, as British as Wallace and Gromit. If you could program a machine like a Spectrum then you could program just about anything, and a whole generation of young programmers took full advantage.
Sadly I was not among their number. I had some friends who mastered the intricacies of machine code but my brain was just not up to it. I played other people’s games on my Spectrum for a year or so then the thing was packed away neatly in its box and forgotten. I have no idea what happened to it.
The early 1980s was an odd time in the computing age. The technology had advanced to the stage where machines that could fit on a table top were cheap enough to be sold to the public, yet there was no real computing architecture to support a true IT revolution. It was as though someone invented a car in a world where there there were no roads. You turn on an iPad and it’s all there – the all-powerful, all-singing Interweb, so intuitive now that five year olds have no problem. But turn on a Spectrum and you got a white screen – and a cursor. The fact that anyone managed to get the thing to play Space Invaders and the like was something of a miracle. I believe someone even managed to connect a Spectrum to the Internet once; the poor old thing must have had the shock of its life."

I can go one further than this...I did use my Spectrum on the primitive Internet and I also used machine code to programme it!

Saturday, April 21, 2012

Topband Transmitter F.G.Rayer

In 1970 just before I got my Amateur Radio licence I built my very first transmitter. The circuit came from Short Wave Magazine and was produced by F.G. Rayer G3OGR. My first attempt was built on an aluminium chassis and my Dad made me a front panel out of mild steel. At the time Neil, G3ZPL had built the same circuit and it worked great! The circuit consisted of an EF91 valve in the VFO and another in the buffer. The Power Amplifier (PA) was a 5763 valve which could run about 15 watt input.

The AM modulator consisted of a 12AX7 (ECC83) and 6BW6 amplifier.

After spending weeks of painstaking drilling, filing and soldering I finally got the transmitter to work, but it had a problem. The VFO seemed to react with the PA. When I tuned the transmitter to the antenna the VFO would pick up spurious signals and shift up the band! Although I had an OA2 stabiliser valve this did not solve the problem. Maybe this was caused by the power supply dropping in voltage when the PA was taking more power.
Later I borrowed my transmitter to George G3ZQS and his antenna got hit by lightning which welded together the vains on the tuning capacitor! Not to mention the Power Supply which 'blew-up' - one of the smoothing capacitors exploded leaving a permanent dint in the roof!
When I got my licence I rebuilt the transmitter with a screened VFO in a separate aluminium box, and an aluminium front panel, this worked really well and was completely stable. The modulator used an ECC83 which had a high gain, I seem to remember using an ECC82 which had a lower gain, but same valve pin configueration.
F.G. Rayer produced loads of circuits and designs for transmitters and receievers in the 1960's and 70's. Almost every month had a design from this guy in Practical Wireless, Short Wave Magazine or Radio Communication. Most were variations of a theme and at the time he was the Enid Blyton of radio. I have to admire Francis G. Rayer, his designs were always well written and easy to follow. I recently found out that he also wrote science fiction books!
Thank you G3OGR!

Wednesday, April 11, 2012

432Mhz HB9CV review

Having used an HB9CV antenna for 70Mhz for a while, I wondered how one of these for 432Mhz would perform while out portable up on the hills. Earlier this year I aquired a 4 element yagi for 144Mhz that is fine for portable use. This left me with a 144mhz HB9CV that I have had for years. I used it occasionally portable and before that used it vertically polarised on my mast at home.
So...what to do with my redundant 144Mhz HB9CV?
Out came my hacksaw along with some measurements and built my own little antenna for 70cms from an old 144Mhz HB9CV!
Looking at this little antenna made me think...will this really work? It tuned well on 432Mhz and during the last contest set it up on a small mast next to my car in the drive. I was quite surprised how I could hear stations that I could hear on my big yagi from the shack. I would have to wait a few weeks for the next contest to try it out proper.
Last night was the Tuesday night activity contest on 432Mhz, so I took my FT817 and HB9CV up to Winter Hill. Setting it up was easy with my window bracket and wooden base. I have to admit that I was amazed at the performance of this little antenna, I could hear stations as far away as the South Coast! I worked a few stations, but I wasn't really interested in the contest, just what I could hear and work long distance.
The HB9CV was remarkably sharp with a couple of side lobes on either side when listening to a distant station and the front to back seemed quite good. The VSWR reads about 1.5 to 1 which is good for a home built antenna!
The problem with 432Mhz antennas is that they are very sharp and we tend to have lots of elements. I used to have an 18 element parabeam, a fine antenna for fixed station and serious contest stuff, but you can miss an awful lot up there on the hills with a multi-element yagi!