If there is a sub-field of electronics which is never boring or totally foreign to the man in the street, it is radio. Radio will continue to be important because it is inevitably tied up with the basic human need to communicate. Radio amateurs, for instance, communicated by satellite long before you could even watch satellite TV programmes. Similarly, their packet radio networks were in existence ten years before the breakthrough of Internet, and they pioneered microwave communication decades before you could walk in the street talking into your mobile phone.

The great thing about being a licenced radio amateur (of any class) is that you are never stuck for ideas, helpful suggestions or even components when it comes to solving a problem related to electronics or microcontroller project construction. The radio amateur is never a lone battler because he can reach his allies via a variety of media, including telephony, television or even computer mail by air (free of charge, as opposed to any link by telephone). So, if you have ever had the desultory feeling of being the only electronics enthusiast for miles around, and have no one to assist you, consider seriously becoming a radio amateur. The hobby will put you in touch with hundreds of electronics enthusiasts of a wide diversity of educational levels. Many radio amateurs are friends for life although they live thousands of miles apart, and have never actually met each other in person. In the UK, the Radio Communications Agency (RCA) and the Radio Society of Great Britain (RSGB) will be pleased to show you the ropes to this highly interesting and educational pastime.

After a decline during the past five years or so, the number of licenced radio amateurs is on the rise again, witness the latest reports of the IARU (International Amateur Radio Union). The temporary drop in active amateurs is probably owing to the growing popularity, at the same time, of the personal computer. Now, the two hobbies are linked by the tremendous interest in packet radio, and even those who once gave up the tuning dial for the PC keyboard are now back on the air again as enthusiastic packeteers. Also, home construction is back on the rise again, with many amateurs becoming aware of the educational value of building a project, as compared to buying off the shelf and never knowing how it actually works. This goes for simple projects, like power supplies, to more complex stuff like a DTMF-over-air controlled digital heart for the local repeater station.

he alkaline-manganese battery is an example of the type of battery that until some years ago was available only in non-rechargeable (primary) form, but has since become available in rechargeable (secondary) form. It must be said, however, that this is primarily so in the USA and Canada; in Europe they are still very scarce, but demand (and supply) is growing. Manufacturers that supply rechargeable alkaline manganese cells and batteries include Union Carbide (Eveready), Ray-O-Vac (both USA) and Pure Energy Corporation (Canada). Today alkaline-manganese batteries are available also in many online stores.

These batteries use a unique electrochemical system, are maintenance free, hermetically sealed, and will operate in any position. Their discharge characteristics (voltage decrease, internal resistance and self-discharge) are very similar to those of a primary alkaline-manganese battery. Their capacity is comparable to that of a nickel- metal-hydride (NiMH) battery, that is, somewhat higher than that of a NiCd battery, but rather lower than that of a primary alkaline-manganese battery. Like NiMH batteries (but in contrast to NiCd batteries), rechargeable alkaline-manganese batteries do not contain heavy metals. They are somewhat dearer than NiCd batteries, but cheaper than NiMH batteries.

Charging (pulsed charging at a constant voltage of 1.8 V) is rather different from that of nickel-based batteries. The charging time for AA/R6/HP7 size batteries is 16 – 18 hours: fast charging is not (yet) possible. On the other hand, the battery can be charged at any time, irrespective of the state of residual charge: discharging it beforehand is not necessary.

The charge retention properties of secondary alkaline manganese batteries are as good as those of primary batteries.

The cell uses electrodes of powdered zinc and manganese dioxide with an electrolyte of potassium hydroxide. These are put together as shown and the cell is then hermetically sealed. The voltage per cell is 1.5 V. Batteries of higher voltage are made by connecting the requisite number of (similar) cells in series and sealing them in a metal case.

When the cell is being discharged, the manganese dioxide gives off hydrogen, which reduces its mass, while the zinc reacts with the hydrogen to form zinc oxide. When the cell is being charged, the zinc oxide is reduced to zinc again which is made possible, among others, by the separators (made of non-woven fabric) that are much stronger than those in a primary cell.

When energy is withdrawn from the cell, the terminal voltage drops slowly. The total voltage drop for a given energy withdrawal increases as the number of discharge/charge cycles rises. Furthermore, the available energy per cell diminishes with each discharge/charge cycle although the e.m.f. remains constant. If the power demands exceed the rated battery capacity, the cells cycle life will decrease more quickly. Nevertheless, when the cell is discharged at the maximum rate for a period of time and then recharged as recommended by the manufacturers, the discharge/charge cycle can be repeated many times before the cell e.m.f. will drop below 0.9 V.

Every electronics enthusiast needs test and measurement equipment. Even the most rudimentary electronics workshop should have at least a power supply, a multimeter and an oscilloscope. This sort of equipment is supplied by many specialized firms, in a wide variety of types and price bands. If you are on the lookout for a new test instrument, there’s really no need to go out of doors any more to collect catalogues etc. Today, all major suppliers of electronic test and measurement equipment run on-line product overviews on the web, allowing you to see what’s on offer, complete with prices and specifications.

Many of you will associate the name Fluke with the great multimeters produced by this company. Fluke’s product scope is much larger, however, ranging from calibrators to ‘ordinary’ oscilloscopes. Over the past few years, Fluke have also released a series of portable equipment sporting graphic displays: the so-called scope meters and graphic multimeters.

One of the worlds’s largest suppliers of test and measurement equipment is of course Agilent (some time ago it was Hewlett Packard, a.k.a. ‘HP’). Their offerings are overwhelming, and include something in every price band, whether an £195 power supply, or an analyser which sets you back some £40k.

This site allows you to request a catalogue on-line, and even place an order! Another well-known manufacturer of measurement equipment is Tektronix (a.k.a. ‘Tek’), whose multimeters, oscilloscopes, generators and other T&M jewels may be admired at http://www.tek.com/products.

Willtek (ex Wavetek), too, is a great alternative for various types of advanced measurement and test gear.

This site allows you to view an extensive overview of the various models. It is also possible to order a catalog, and request information on a certain piece of equipment. Although the Japanese manufacturer Yokogawa may not be very well known in Europe, its products are on a par with those of its American and European competitors. The site shows you the product range available for the European market, which includes recorders, digital memory oscilloscopes, function generators and power meters.

Iwatsu is a Far-Eastern manufacturer specialized in digital oscilloscopes featuring extensive operation options. The American branch of Iwatsu presents the technical specifications of some of these oscilloscopes.

Lecroy is an North American company which is also specialized in (digital) oscilloscopes. Lecroy have a branch in Switzerland. Their website  provides an overview of various LeCroy products, and also allows web surfers to request product information.

Finally, a German supplier of excellent test equipment: Rohde & Schwartz. This equipment is sure to be of interest to professional electronics engineers.

In case you are looking for other suppliers of T&M equipment, Internet search engines like Google and Bing are a great help in locating addresses and other useful information.

It is well known that the frequency of a crystal oscillator depends to some degree on the ambient temperature. Although this is often of no consequence, there are cases when the frequency is needed as a standard and any deviation from its true value is not acceptable. For instance, the crystal oscillator in most frequency meters and in many signal generators is fitted in an oven that keeps the crystal temperature at a stable value.

The temperature at which the crystal is held must at all times be higher than the sum of the ambient temperature and the self-temperature of the equipment in which the crystal is contained. Assuming a top ambient temperature of 30 °C, it is unlikely that the thermostat needs to be rated higher than 50 °C.

The idea of using a power transistor as the heating element is not new. This works in conjunction with a resistor with negative temperature coefficient (NTC) or a silicon sensor acting as the sense element. The output of this element drives the heating transistor via a control circuit and thus influences its dissipation. The difficulty of using this setup in a home-constructed equipment is obtaining good thermal coupling between the heating transistor and the sensor, which is, of course, essential for accurate and fast control of the temperature.

Many crystal ovens, however, use a different approach. In it, the base- emitter voltage of the heating transistor is used as the control voltage, so that a temperature sensing element is not required. It is known that this voltage in case of a p-n junction through which a constant current flows varies at a rate of – 2.2 mV/K. Such a voltage applied to an evaluation circuit is very suitable to assume control of the dissipation in the heating transistor. For this purpose, the heating is interrupted periodically for brief instants during which the base-emitter voltage of the heating transistor, through which a constant current flows, is measured. Its value is stored in a sample & hold circuit and used to control the collector current of the power transistor during the next heating phase.