Located on Hayling Island (south east Hampshire) since 1967.
This site is a work in progress - some of my calculation programs are ready to download but documentation is not currently provided. Watch this space!
The History of my Electronics years.
My amateur radio transmitting licence was achieved in August 1953 at age of 16 (my father had to hold it on my behalf!). I am from the era when a year of CW (morse) was mandatory and to qualify for phone (voice) operation your log had to be submitted to prove a sufficient proficiency had been achieved.
In practice I did not bother to apply for 3 years as CW was my prefered mode on 1.8MHz (Top Band where a limit of 10w DC power to the power amplifier of your TX (transmitter) and to some lesser degree on 3.5MHz (80m). At this time I was located at Hogarth Gardens, in Heston, Middlesex.
1.8MHz Voltage Fed 1/4 wave Antenna
This was my best performing antenna and ran between the house chimney 30ft agl and horizontally for around 100ft to two pine tree sections bolted together to form a 35ft mast. The vertical section was away from the buildings (in those times there was a small farm field beyond). The radio shack was located in the loft/attic so high impedance feeding was thought to be the way to go. The total length of wire was longer than 1/4 lambda. I drove in several deep earth rods and connected the wire via a ganged 500pF tuning capacitor (as commonly used to tune medium wave radio's.) In this way I found that I could resonate the system within Top Band (1.8MHz).
City Centre Folded Dipole made from 200 ohm Ribbon
In 1959 I married and moved to Windsor Road, Ealing in West London and lived in a 2nd floor flat which did not permit continuation of serious LF band operation. My attention was shifted to 14MHz (20m). The building was a very tall Victorian construction which had access to the roof via a window (2 storeys above us. I installed a centre fed Folded Dipole constructed entirely of plastic moulded 200 ohm ribbon transmission line, between the chimney and a tree. This was at around 50 feet above the ground and performed very well. The major problem in those days was interference with Television which was on channel 1 and around 42MHz so related to the Amateur (self training) Licenced allocation.
After a period of development of my transmitter I managed to reduce this interference to a minimum! The method I used was to generate the low power drive at 7MHz and designed and constructed a Push-Push Doubler. One of the available valves at that time was a Mullard QQV06-40. This all glass constucted valve was very suitable for my purpose.
The Grids were fed with a centre tapped tuned circuit at 7MHz (very small trim capacitors to achieve balancing were included) and the Anodes were joined in parallel and tuned to 14MHz. By careful attention to the layout the 2nd Harmonic (14MHz) was amplified and the 1st, 3rd, 5th, 7th etc was greatly reduced. The inclusion of a Filter as well turned out to be a workable solution in a city environment!
The Early Years Equipment.
With a TX using a stable valve Clapp Oscillator on 1.8MHz using a dual triode type 12AT7, a B7G base valve driving a 6V6, an IO based valve and having an Output power of a few watts with 10 watts of DC power. ie 250V @ 50mA. The middle stage being keyed with some shaping (slight rise time slowing to reduce clicks to locals.
There was also an Amplitude Modulator included around 1956. A war surplus US origin transformer was available very cheaply that suited this application, can't remember the model. I used a pair of KT66 audio valves in push pull which did the job very well.
The Receivers were various from the Type 18 manpack set, HRO, AR77, CR100 through to the well known R1155. But I think a good deal of my operating was using a Receiver type R103 which again was cheaply available in Tottenham Court Road, the centre of all things desirable at that time! Only a 2 band coverage but stable with a Muirhead slow motion drive with an engraved metal scale (Sun & Planet Type).
Attempts at building my own Receiver were not too successful initially but performance limitations were being noted and the desire to minimise these grew!
Soon after (about 1956/7) I became an apprentice at Ultra Electronics Limited on the Western Avenue, West London. This industrial education was to be greatly valued later!
The machine shop period was used to provide items for my two hobbies Amateur Radio and Cycling. Learning is much easier when the outcome is close to your heart. I started to build my ideal Receiver - mechanical construction was then the major part of a good design.
But it was many years later that a good design was realised. Many hours of operating and designing less than ideal equipment slowly crystallized in my mind and allowed for the construction of a top class receiver. This was during the mid 1960's. Since that time a multitude of very high performing and high priced equipments have been developed.
The heart of such equipments is down to the IF Filtering performance and the linearity of the early stages even on the HF bands.
After completing my apprenticeship I looked for another employer. As a consequence during early 1960 I moved from London to Havant, Southern Hampshire to begin a 25 year long stay at Plessey in Havant.
The first project I was working on as a Junior Development Engineer was an HF Manpack Transceiver for the Army, covering 2 to 8MHz.
The next 3 years were spent on developing and testing this unit. Test equipment results were good but "on air" with an antenna bigger than a 2m whip connected the RF Amplifier performance was poor. Amateur Radio experience showing that there was too much gain with too little linearity.
We had an Racal Receiver type RA17 in which there was an attenuator provided to help with this problem! The solution was a "power amplifier" design in the early stage and a balanced mixer! All semiconductors of course. The results were then good and even though a simple unit lead the way with the mentioned techniques.
At the beginning of 1963 I flew by Comet IV to Malaya with a Team to demonstrate the equipment in and around Kuala Lumpur and in the Rain Forrest, with the Malay Army along with their British Advisors or Instructors. The duration was about 2 weeks and very interesting not to say educational.
A brief comment on the immediate impression on arrival at Kuala Lumpur Airport. The landing was interesting as full reverse thrust appeared to be applied just before actual touch down. I realised why afterward - a railway embankment crossed the end of the runway! Walking off the plane was a strange sensation to one from coming 24 hours earlier from a British Winter. Wafting moist hot air greeted us and remained for the whole 2 week visit punctuated at 4 o'clock each afternoon by thunder storms and torrential rain without fail.
The view of the locals was that (like all their previous equipments) the weight carried into the Jungle was excessive for the expected results obtained ie none! Our experience was different. The equipment when backpack carried allowed communication at 100 yards but not 200 yards or just over 180m!! Note that it took 1 hour/100 yards to cut through the undergrowth.
However the conditions at the Base Camp in the Jungle, where I had a dipole erected for 7MHz or 40m Amateur Band. This was done by one of the burly Squaddies using a large Matchet to cut a pair of very big Bamboo poles to which we tied the dipole and put them back up to raise the antenna to a very respectable height with a vertical feed line to the Transceiver. With only 2 watts output not many two way contacts were made but stations in Europe including the UK were heard well.
So although Ground Waves did not travel the Sky Waves did. After the event the equipment was purchased and used in conjunction with a repeater station located on an Island some hundreds of miles away which allowed contact to be maintained between foot patrols anywhere in the Jungle by choosing the most suitable frequencies.
The More Equipment Development.
Following this project was period (perhaps 2 years?) spent building and perfecting the Flight Data Recorder Replay Unit for British European Airways or BEA.
The Avionics lab had designed and were flying the so called Black Box Data.
No sucessful replays of these flights were obtained for some time. The medium being used to save the data was very thin Stainless-Steel Wire (0.0015 inches dia) A very poor recording media ! So the task was to resolve this situation. Once a reliable replay was obtainable the real faults could be identified and removed. For example the uncertainty caused by multiple rotation of the encoder used for altitude encoding. Being a rotary device there was an uncertain position at the "0" or "360" which caused the altitude to appear to change from say 10000ft to 0ft and back very rapidly!
The variability of amplitude due to the poor magnetic properties. By peak detecting and narrowing the sampling periods the results eventually were excellent. The signal recovery was found to be very good even at the 5 times winding speed that was not intended to be used in this mode.
© Michael Walters 2010 Website by WaterPigs Web Design