Recap on the ThyristorIn a previous article, I explained how a thyristor worked. This is a transistor-like device in which the current through it, (between anode and cathode), is controlled by the thyristor gate. However, unlike a transistor, the “through current” is not proportional to the gate current in a linear manner. Instead, the current … Read more
Electro-Magnetic radiation is not confined to broadcast, commercial and amateur bands, and figure 1 shows a significant portion of the electro-magnetic spectrum including the visible part. Particularly note the “fierce” logarithmic scales of frequency and wavelength. This is necessary to accommodate the huge range between “radio” waves and gamma rays in a single diagram. This … Read more
Some things can go faster than light, but not ‘material’ things. Three examples of these things are; the cutting point of scissors, the meeting point of lines as the lines go from crossing to parallel, and the phase of a wave. But these are imagined things, things in the mind. In the case of waves, … Read more
It would be no good removing the man-hole cover in the pavement and directly measuring the resistance between the metal pipes at either end of the plastic section, as these would be effectively shorted out by the surrounding earth, so I decided to simulate the real situation by measuring the resistance of a length of … Read more
Back In the hastily rearranged talk to the club on Tuesday, 21/11/06, Brian, G3YKB talked about many different methods of home construction of experimental or “one off” circuits. These included: conventional printed circuit board, strip board, “paddy board”, ugly bug, and others, and also how to make screened enclosures by soldering sheets of single sided … Read more
It has a similar layout to the alternators used for generating the country’s electricity supply, except that instead of having 6 poles for generating 3-phase 50Hz AC, it has 600 poles for generating single phase AC at 17,200Hz. It also rotates somewhat faster than the alternators supplying the national grid, and delivers 200 kW of … Read more
Back This is not really about amateur radio, but it is technical and it involves electricity. Have you ever got the Christmas Tree lights out from the box in which they had been carefully packed the previous year only to find that they no longer work? If so you will know that finding the offending … Read more
Back There has been some discussion on whether it is better to wind inductors as a torroid or as a solenoid on non magnetic material. Thoughts:-Magnetic lines of force add vectorially. They do not influence one another. Hence: The result of this is that the field near the centre of the solenoid is proportional to … Read more
AB INITIO PERFECTUS EST (or in plain English, this “From first principles” series is finished). This series of technical articles for the VARC Newsletter is now concluded. It has ranged over more than 3 decades and some 80 articles, although in the early days its publication in the VARC Newsletter was somewhat irregular. Its original … Read more
Back A dipole in free space, fed at its centre by a balanced feeder, can radiate all the RF power fed to it with no radiation from the feeder. Such a system is illustrated in figure 1. A dipole is a “resonant” aerial and its first “self resonance” is when its total length is approximately … Read more