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This page has had 238 views
Ever seen me at work??
On a good day...
A not-so-good day...
A really crap day...
Oops, forgot to disconnect the mains.
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Hi. I'm Alan Cordwell, humble peasant of this verdant country of England. I am 49 years young, and I live in Sheffield, UK. If you want to know where that is, starting from London you go north on the M1 for 160 miles and then turn left. You can tell when you get there because all the roads are full of potholes and you can't drive for more than 50 yards without getting stopped by a red traffic light. Or you could just stick a pin in the map somehere near the middle of the UK and you'd not be more than 20 or 30 miles out.
I'm married and have two teenage daughters. I work as a manager in the public safety sector, my field of expertise is IT and radio communications systems.
This is my chunk of web space, and is devoted to some of the things I do, find interesting, find funny, or just find.. Please feel free to look around, I hope you enjoy.
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If I said that a historic 35-year old recording of Rugby Radio GBR on 16kHz existed in just about every household, you'd think I was balmy, right? Well, it might be nearly true. When Mike Oldfield recorded Tubular Bells back in 1972, the Rugby signal was picked up in the studio somehow and recorded along with the music. Well, thanks to some interesting techniques we can see and hear parts of this recording. Now at this time, GBR still operated in CW (Morse) unlike in most of my living memory when it operated FSK.
 | In this spectrogram (left) you can clearly see the customary marine call up 'V V V GBR'. This is found right at the beginning of Tubular Bells Part 1. Can you hear it? You bet! Click here for audio clip. VVV GBR GBR! This was done using Spectrum Laboratory's powerful Digital Signal Processing capability to down-convert the 16kHz to 800 Hz, and then applying a narrow CW filter. I used RS Horne's Specrogram to produce the image. |
The rest of the recording contains fragments which include obvious test transmissions of blank carriers, alternating dit-dah sequences but also traffic containing some interesting procedural characters. But how did it get there? Tubular Bells was recorded in late 1972 and early 1973 at The Manor Studio, Shipton on Cherwell. This is about 35 miles from Rugby- not exactly on the back doorstep. There is no evidence of hum on the recordings so general poor shielding of a cable for example is unlikely. In my view, it could have been a playback head or dynamic mic whose coil just happened to be resonant at 16kHz. It would be interesting to find other recordings made at Manor and see if they also have this signal present on them.
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NEW LOOK WEB SITE!! If you've been here before you'll notice the somewhat different look- I needed to make my web site better to look at, as well as more efficient in server space. I took the opportunity to switch to using style sheets instead of thousands of font tags. It will take a few weeks to get all of the pages converted and the links working properly again, so please be patient.
WE'RE ON OUR WAY TO POLAND, WE ON OUR WAY TO POLAND! Yep, I'll be in Krakow next week so don't expect to see much work being done on this website. Or on anything else, as we will be on holiday with our friends Steve and Jane and, while we're there, watching my daughters Heather and Anna performing with the City of Sheffield Youth Orchestra.
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The raytracing software 'Povray' is capable of generating outstanding photo-realistic images, from a source code that you write using Pov's own Scene Description Language (SDL). I really enjoy using this and you can see some of my own original work here..
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Hi-Fix was a precision hyperbolic positioning system with a maximum accuracy of 1.5 metres at a range of 50 kilometres from the transmitters, introduced in 1963. It was originally intended as a portable system that could be deployed wherever survey operations were taking place but many fixed chains were in use as well. HyperFix was the successor system to Hi-Fix and remained in use until around 2000.
I have written a web site that documents these systems extremely thorougly, and includes hundreds of pictures in addition to the reminiscences of the people who built, deployed and operated them.
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I am currently working on constructing an HF receiver based around the Analogue Devices Direct Digital Sysnthesiser devices, with a Microship PIC doing the work of controlling it. The receiver uses a direct conversion architecture with excellent AGC and audio filtering. Tuning steps are variable from 1Hz to 10 kHz, via a free-spinning rotary encoder tuning control and there are 20 user memories for frequencies, plus one 'start with what we were doing last' memory. The audio filtering is selectable between 3kHz 'brick wall' or 1kHz +/- 100Hz CW filter. A wideband output is also available that should make DRM reception possible in conjunction with one of the free software decoders. The two-stage AGC operates on both the audio preamp and the RF stage and has a control range is in excess of 100db. Two selectable time constants are available and it can be extended to provide a squelch function. Primary reception modes are CW, SSB, AM (because you can zero-beat to well within 1Hz of the carrier) but trials have shown that the receiver gives excellent results in RTTY and FAX modes. Future work involves improving the spectral purity of the DDS local oscillator and making the currently manual preselector tunable by the PIC giving true 'single knob' tuning.
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If you have any comments about this web site, or would like to contribute pictures, stories or information, I would love to hear from you. Please contact me at the email address below. Best wishes; Alan Cordwell G0NFY.
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