Folder 0 MISCELLANEOUS TOPICS ( Microwave radiation,FOOD ......)
Quite a portion of my time has been spent on MICROWAVES --- yes, cookers included !!!!!!! as these domestic items have proved to be a Godsend to most families.
The vital piece of theory is given in the article LL where we see that IF THE LINE IS MATCHED then there is no reflected wave and all power is tranferred from one point to the next. A piece of apparatus, used by the author in the 1950's, is theNarda Impedance VSWR unit and an illustration can be downloaded from the link given below:- "Google or use link - Narda "
From voltage measurements and the positions of minima, impedance values could be calculated BUT IT MUST BE STRESSED THAT THE MEASUREMENTS WERE FOR A SINGLE FREQUENCY ONLY!!!! (Note - an AD 8318 logarithmic detector gives one a much better way of identifying "minima" -- with this detector these give high voltages of about 2 V.) The mounted detector is shown below and this can be powered from the USB port as only a small current is required.
As one moves up the RF frquency spectrum after about 10 MHz it is increasingly necessary to make sure the circuit is MATCHED. This means that a signal flows from a source -- through a component -- and into a detector will always proceed without reflections occuring otherwise the signal may not reach the detector. Lecher lines demonstrate this effect and the following video , MVI 0698.AVI , shows how a Standing Wave detector can be used to see where the microwave energy is going - a strong standing wave pattern indicates that all the energy is being reflected back to the source, a small pattern shows that the energy is being transmitted. ( I am grateful for my grandson's help in making this video). Getting the energy out of a line is quite a task. We see that an open line is a very good reflector. BUT by making a gradual change from a line to the outside world with, say a horn, one can see that most of the energy WILL radiate into space. This process of getting each load to look like the Characteristic Impedance of the line is called "MATCHING". In years gone by one was happy to get a microwave circuit matched at a single frequency; now we need "broadband" matching and something like a FIREFOX instrument from Keysight Technologies will help us in this task. Please see the TEN excellent videos from Jake Daly and David Von Workum on "Firefox Fundamentals" (www.keysight.com) .
A STANDING Wave demonstration in a coaxial line is carried out with a Narda apparatus click . The file can be copied if needed MVI 0698.AVI (this is not streamed so will take several minutes to load)
A further excellent demonstration of standing waves on a microstrip line is illustrated on the following video .
Fairly recently modern technology has made microwave experimentation that much easier. A single board analyser is available at a very modest cost. With a reflectometer attached any reflection can be measured over a whole frequency range of MHz to GHz.
A fuller description is given in the attached file MA .
Food is the primary source of our bodily energy - the sun heats planet earth up to a habitable temperature near to 293 degrees K ( Kelvin) or 20 degree C (Celsius) and then the "burning" / digestion of food lifts the body temperature to about 36 degree C; thus food is essential for mankind's survival and, indeed, for that of other members of the animal kingdom.
Although history tells us that humans together with the animal world were hunter/ gathers in the distant past, it was the development of agricultural methods that moved the human species to our modern world . In simple terms it was appeciating that by staying "put" at a specific location on the globe, one could practice land cultivation and animal husbandry from year to year giving a more predicable, stable and plentiful (?) supply of food.
A good account of "Food and agriculture" is given in Scientific American, SA, September 1976 in which the whole issue is devoted to the subject. A later article in SA , on the economics of food production , is given in September 1980, page 74 and this may be viewed here .
A type of farming that was practiced in North America and Europe for centuries is best described in the article " Farming in New England" and this was probably a sustainable way of life. I experienced this kind of farming in the WW II years on a small hill farm in North Yorkshire, UK, and it always felt that one was working with nature - rotation of crops reduced desease and pests naturally without the need of chemicals and soil fertility was maintained by the application of animal dung.
Further ideas are given on the web page of HOMESTEADER.
In LESS THAN A LIFE-TIME (my life!) farming in the UK has changed beyond recognition. Most arable crops require spraying three of four times with pesticides, herbicides and the like ... for efficient growth and machinery is involved at all stages of crop management.
Although many would say that this evolution of farming is a necessary fact of life https://www.tannertrading.co.uk/blog/farming-agriculture/the-benefits-of-modern-farming-practices/ it is difficult to envisage how modern farming practices, which involve so much investment in machinery and are so dependent on chemicals , can continue for many more decades ---- and what happens next will be a journey into the unknown.
As a little light relief one may wish to read a short introduction to farming written by my nephew
Forty Shades of Green David Welford (ISBN 978-0-9956121-3-6 ) published by Fryup Press, Whitby, North Yorkshire
(if you have difficulties obtaining this text please contact email@example.com ).
The story resumes in a later folder regarding sustainability
Some additional points
oddments in PHYSICS
The first experiment is about the Earth's Electric Field. We all know about the two other fields on the Earth; GRAVITY keeps our feet firmly on the ground and with the Earth's MAGNETIC field we make sure our feet are going in the right direction with the aid of a compass. Most people know little about electricity in the atmosphere until they are caught in a thunder storm and the sky is filled with bright flashes of light that stream across the sky. The following article gives a bit more information and, if you make a link to the Reading University site (a link is given in F_M) this shows how the electric field (normally about 100 V/m) varies with time... see F_M .
A little more detail about the apparatus is given in the video
This video presentation of a Field Mill is a large file --- takes SEVERAL mins to load
Another article of interest is the pathway from electronics to microwaves EM .
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