Build Yourself a DIY AM Radio Transmitter

Introduction: Understanding the fundamental principles of radio waves, their generation, propagation and reception is essential not only for the electronic enthusiasts, but also in other disciplines of science which employ radio-frequency (RF) in scientific investigation and even in medical imaging and treatment. Here, the construction of a cheap and simple DIY (do-it-yourself) transmitter (Tx) circuit is described and its operations explained in simple terms.

Materials you'll need: A microphone, a transistor (ask your friends to help with the emitter, base and collector terminals. Alternatively, look up the web), a radio frequency coil (choke, RFC), a variable capacitor (365 or 500 pF; pF = pico farad), 2 resistors, 3 condensers , an aerial (antenna), a soldering iron, solder wire, a stripboard (also known as veroboard) and a power supply (9V).

Assembly: Clean the leads (wire terminals) free of oxides/ enamel coatings by rubbing with fine grained sandpaper. Next, in accordance with the accompanying diagram, wire the components together in one of the following ways:
1. Connect the components directly and cover these joints by insulating tapes such as black tapes, cello tapes or scotch tapes (it is said that the scotch tape emits X-rays when pulled off, well it's unimportant here) . This will prevent accidental shorting with similar joints.
2. Or use a breadboard and press-fit the leads in the slots. The breadboard has prewired connections within it, which will take care of the rest. Make sure that these prefixed connection layouts are followed. You may need to make some extra connections by using external hook-up wires/jumpers.
3. Or use a stripboard/veroboard: Put the components into the drilled holes according to the circuit layout. Now, solder the leads using a 20 watt soldering iron. It is the best option among the three mentioned.

When the iron is sufficiently hot, apply the hot tip to the component lead (not to the solder wire!) to be soldered, and bring the solder wire near it. Within a few seconds, solder will melt and flow evenly around the joint. Withdraw the iron (take as little time as possible).
Check with the circuit again. Cut any extra strip of copper track which might act as a potential short. You may need to make some extra connections by using external hook-up wires/jumpers.

Turn on your radio: Set your radio receiver to any empty slot on the medium wave frequency band. Switch on your newly assembled wireless Tx. Turn the spindle of the variable condenser of 'your set'. At some point you'll hear a 'smooth hissing carrier tone' on the receiver. Keep the variable capacitor there. You're almost done! Speak on the mike, you'll hear the same on the radio receiver. If you press the mike on your left chest, you will hear your heart sounds on the receiver set. You can make a 'phonocardiogram' too this way.

How it works: The Tank oscillator produces the carrier frequency (freq = 1/{2*pi*sqrt.[LC]}; L= inductance of the coil in Henry, C = capacitance in Farad, as dictated by the variable capacitor). To see an animation of how a 'tank circuit' works visit this page. The amplitude of the freq. of the carrier wave is modulated by the input from the microphone. As we speak on to the microphone, the diaphragm vibrates. This makes a coil of copper, wound around a powerful magnet, vibrate too, making induced current in the coil, the magnitude and frequency of which depends on the loudness and frequency of the speech/audio signal. The mike is connected to the base of the transistor via a capacitor. This capacitor allows AC (alternating currents) to pass, but blocks any DC component. The second feature thus, does not let the microphone change the bias voltage conditions of the transistor. The biasing of the NPN type transistor is done by one or two fixed resistor networks (one in this case).
When some audio signal is present, collector current will increase. Since it is the tank circuit at the collector load, the amplitude of the 'carrier frequency' will thus be modified. Amplitude Modulation has been achieved! You will notice that one end of the output capacitor has been connected to the antenna, while the other end is connected to the ground (earth, ground of your wall power outlet, or safer still the traditional lead water pipe). This arrangement makes the capacitor plates look like, as if, they are placed far apart; earth and sky! This causes dissipation of the energy in the form of electromagnetic waves.
Frequency Modulation (FM) transmission is better, since the static (electrical noise from man made appliances, lightnings etc) is almost absent and stereo signal can be transmitted, to name a few.

Experiments and lessons on it:
1. Move a magnet at the back of the radio receiver (where the RFC choke is located) with the receiver tuned to the short wave band. You'll notice that the frequency changes: many different stations come in (without even having to turn the tuner knob!). This happens as the magnet alters the local oscillator of the receiver.
2. Put the radio inside a metal container and try to catch a station. You won't succeed. This is 'shielding'; the metal does not allow electromagnetic wave to pass in. Co-axial cables exploit this phenomenon to avoid noisy interferences. Sensitive instruments used in medicine (e.g. EEG) or radioastronomy were often built underground. This phenomenon is exploited in a Faraday cage.
3. Just touch two different metals in front of the radio receiver: the radio will make noise. This is due to passage of free electrons between the metals.
4. Short two ends of a battery (cathode and anode), the radio hisses and makes noise. Obviously, electromagnetic fields are created.
5. The telltale undulations heard in shortwave, is due to the reflection (actually total internal reflection, a type of refraction) of radio waves from the Kennely-Heaviside layer of the ionosphere, a charged layer in the higher atmosphere, that frequently changes its altitude. If you put a laser beam or any light on the ground and put a mirror higher up, you would get a reflection. Moving the mirror up and down will put the reflected beam closer or further away (light is also an electromagnetic wave). This layer is absent in night time and Appleton layer still higher up reflects then. This is why SW broadcasting stations are best heard at different frequencies during different parts of the daytime.
6. You can listen to cosmic noise, falling meteors (by their 'heated' ionization trail) etc.
7. Take a radio and tune it to a station. Now take a second radio and turn the tuner knob till that same radio station is obtained. You'll notice a drop in volume of the former radio (and vice versa). This illustrates energy transfer by resonance.

Uses of Radio waves: Telecommunications, radar, radioastronomy, medical investigations such as MRI (NMR), medical therapies (radio frequency ablation in ectopic pacemakers of the heart (electrophysiology), short-wave diathermy, research procedures such as thought broadcasting etc.

N.B. : 1. This is a very simple, low cost transmitter, but many countries might have legal restrictions on it. A crystal controlled version of the set is more likely to be approved, as the bandwidth is less.
2. Other forms of electromagnetic waves may be broadcast in much the same way e.g. our good old TV remote uses infrared waves.

Last modified: Mar10, 2014
Reference: hyper-links, unless specifically mentioned

Master Of Puppets Im Pulling Your Strings

How big is the universe or what is a universe after all? Well, a web search on the definition did not say much about these. One site described it as all matter and energy in space. Then we must ask ourselves which method we should adopt to detect these ALL matter and energy/energies. For example, a bat can not see. To this creature, the universe would appear as its tactile senses and the ultrasound echoes (bats use echolocation) would allow it to perceive. It thus appears that our observation is not only limited to the gadgets we build, but also the degrees of freedom (dimensions) in which we are accustomed to. We can't visualize 7 or say 14 dimensions, can we? What if the universe consisted of many sub-universes containing as many or as few of these dimensions? We may try to conjecture the infiniteness of the universe in our own familiar dimensions in the form of the 'recursive' Klein bottle (picture on the left), or the Moebius strip.

Take the case of those working at the Chandra observatory. They can see through X-ray vision and see the universe at a completely different perspective. The picture of one x-ray galaxy is given here, for your reference. Thus you have infra-red, ultra-violet, radio-wave astronomy and many more. If you are bit observing, you'd note that all those modalities cited above used the electromagnetic spectrum; perhaps because light's (and all other electromagnetic waves) speed were the highest and possibly also because that we can not imagine any other type of constructs of the universe(s), since we are slave to our senses and the dimensions they restrict ourselves in. We have seen how quantum theory can wreck havoc with our classical thinking, by its killer 'superposition'; its time we greet the new kid on the block: String Theory. If you thought quantum theory was too much, then this one is for you. Watch this fabulous video. Do read the text and ponder over them. It suggests that we are floating in a three dimensional space, surrounded by membranes. Even if there is 'another universe' nearby, we could not reach out of our 'braneworld' and see or touch them. So check out this video. Enjoy the possible proximity with another universe (may be God's own) with in your own reach but don't try to reach out; for they can't see you!

By the way, I think, gravity waves are a good contender in this regard. They are supposed to travel at the speed of thought. Secondly, they pass through all matter unchanged, beating even light in this regard. When we develop better SQUID devices, we may be better able to explore the cosmos.

BTW, the title of this post has been taken from the Master of Puppets song by Metallica. Here 'Master of Puppets' refers to God, and Strings to String theory. Nothing serious!

Last modified: April 1, 2009
Reference: hyper-links, unless specifically mentioned

Cosmic Mirror

You are walking tired and thirsty on an unforgiving desert. Water is not to be found anywhere near. Broken hearted, you suddenly seem to spot an oasis. You rub your eyes, pinch your skin, but yes it is an oasis indeed. Oh NO, its only a mirage, an illusion that played tricks on you. You are crestfallen!

A situation like above occurs quite commonly. Here, for example, the air in the immediate vicinity of the hot sands are much lighter in comparison to that of the above. Just as light bends, due to refraction (changes at the interface, due to differing refractive indices of the medium), when a ray of light is made to pass through water from air, it bends (one can see it using lasers or using a straight rod which appears bent). A similar situation occur in deserts and in very cold climates.

Objects having mass, distort the space time curvature just in a similar way an iron ball would do to a piece of cloth, whose four corners are tied to four poles. There would be an indentation in the middle of the cloth. If one releases a small ball at one of its corners, the ball will proceed towards the dent, in a spiral way. Encircling, it will finally end up in the center. This is what we call gravity, and orbits (paths, the ball traces) have been proposed so that the ball doesn't end up with the ball at the center.

Now imagine a black hole, a very massive and dense object, with such a strong gravitational pull, that even light can not escape its fatal attraction. Thus it it is invisible. The gravitational pull near its surface will be maximum, while the pull will fade out away from it, inversely proportional to the square of the distance (of measurement). Hence we can visualize a situation akin to the mirage illusion already stated. Near the black hole the gravity (space time curvature) is densest, whereas gravity away from it is less so. This reminds us the analogy of refraction we saw with respect to light (electro-magnetic radiation). Thus, you certainly can expect to find gravitational mirrors (total internal reflection) in black holes.

The black hole won't belch out any of its secrets, as theory of quantum gravity prohibits it: it will only show the observer's curious face in its own mirror. Could there be a Grand Unified Theory now? Or, how about combing your hair using this MIRROR?

Maverick Moebius

In my article on 'the universe must expand' I mentioned a certain Mobius strip (also known as Moebius strip).

The Mobius strip, which is really interesting and thought provoking, can be prepared in a very simple way. What you have to do is, to take a rectangular piece of paper, say about 30 cm x 3 cm. Paint one surface green and the other surface red, for example. Now, obviously, the piece of paper has two surfaces and four sides. Hold the sheet longitudinally (lengthwise) and twist it a little and meet the ends together so that the red surface will meet the green one. Congratulation, you are done!

Now, how many surfaces/sides does it have? Run your finger along one surface and continue. You'll find that there's only one surface and not 2 as our intuition suggests. Now you may trace the line (margin/border) and similarly be prepared for another surprise. You'll end up in the same point you started with. It also has just one border. If that's not enough, cut the strip in half along its length. You wont get 2 strips, do it yourself!

Doesn't it give the feeling of infiniteness? The recursive pattern gives a pseudo-sense of infinity. A similar topological model called the Klein bottle illustrates this apparent fallacious of infinity. The universe which is infinite (is it?) could be thought of in this perspective.

P.S. The step marked in red may be omitted, it was invoked for sake of lucidity. Please wear your thinking cap for sometime and ask yourself if you could find any similarity of this with the 'infinity'.

Universe MUST Expand !

Lying idly under the starry night sky, atop the rooftop of my village home, is a rewarding experience for me. It seems to instill upon me it's vastness, the same awesome infinite which inspired many a philosophers' souls. I, like every little kids, was also spellbound at the beauty of the universe. Where did it end, I used to ask myself ( I still do now!). I reasoned that if it ended somewhere, then what/where is it's boundary and more importantly, what is that boundary wall? If it ends, then what lies beyond can NOT be a part of the universe. If there is one universe, which is more appealing (and less appalling than the multi-universe concept), then it automatically suggests that the universe is expanding, because a static universe would mean that it has an end.

Universe is thought to have been created 12-14 billion years ago from a cataclysmic event called the 'Big Bang'. NASA's Wilkinson Microwave Anisotropy Probe (WMAP) measures the heterogeneity (anisotropy) in the temperature of the Cosmic Microwave Background Radiation (CMBR). WMAP has determined how fast the universe is expanding. If you were curious about the oscillating 'cepheid variable stars' so far away from us, you may visit HubbleSite and may be see some videos there.

The occurrence of Big Bang may have been paraphrased by ancient religious scholars. Hindu sages' words ' tamaso ma jyotirgamaya' meaning from darkness (nothingness) to light (something); and 'let there be light' in Genesis, The Bible, are examples in point. What religion is doing on a science site can be understood when one considers what the great science fiction writer Isaac Assimov said: ""Properly read, the Bible is the most potent force for atheism ever conceived."" Now, lets navigate from spirituality to the realms of 'science' again.

Albert Einstein proposed the cosmological constant (to his repugnance) to fit into the theory of general relativity to achieve a stationary universe. He was fiercely against an expanding universe and the general theory of relativity needed a stationary universe to operate. But he knew that all the matter would attract each other and the universe would finally collapse. To remedy this he invented an anti-gravity force called the cosmological constant or the dark energy. It is not to be confused with dark matter which is attractive. Later, it was found out that the universe did expand, going by the observation of the Hubble redshift (due to moving of celestial objects away from the observer).

The expansion of the universe and its infiniteness is hard to comprehend. Einstein suggested that the space time was curved and if one started a journey he would come back to where he started from. One of the way it may be looked upon is in the form of the Moebius strip. This strip seems apparently unending.

Now if the universe is unending, then which/what is it expanding into? Then do we have to accept the existence of multiple universes? It's too mind boggling. We can not even employ something faster than light to investigate; for Einstein won't allow us to break the speed of light. So expecting that we will live that long to receive and (analyze) billions of miles (SORRY light years) away would be even beyond our wildest imaginations.

I sincerely think that this puzzle will remain unresolved. Immortality may be achieved by the help of stem cells, cloning of organ systems and (re) transplantation thereof and various other techniques, but the nebulous universe will probably continue to give us the slip!

Modified: April 1, 2009