It's November 6. How fast time flew by.

     Let's discuss a bit about mixing frequencies. Two frequencies can be mixed in a MIXER  stage. This is evident in the ordinary BC AM radio. The first tranny is the mixer stage.  The antenna tunes to the desired station with a frequency F1. A local frequency F2 is generated and these two frequencies are mixed. The result is the sum and difference of F1 and F2, and the two individual frequencies. Usually, the difference is chosen and is amplified. In the AM band, this difference is chosen to be 455khz. So, the local osc is always 455Khz below the incoming signal. It could well be above too and the 455khz will appear. This is called the intermediate frequency. Thus, a powerful RF amp is fixed tuned to 455khz. All stations are converted to this frequency. The local oscillator can be a single tranny and is usually done in the SW band. For the BC band, the mixer can also be tasked to handle the local oscillator, thus the stage is called the MIXER-OSCILLATOR stage.

     BUILD AN AM BC BAND RADIO AND LEARN ALL THESE PRINCIPLES.

     The tuning capacitor in an AM radio has tqo sections. One is for the antenna and the other one for the osc. They are ganged together. As you tune to a different station, you are also tuning the local osc so that the difference will always be 45khz.

Hi Friends. It is November. Over the long weekend, I completed my FM Receiver using a single FET transistor. MPF102, @N5457, etc...even the 2N5486. The Audio amp is the ordinary LM386 but with a transistor driver. It's load enough to drive a speaker. I even picked up the Control Tower with a change in capacitor. I built the tuning capacitor version and the slug tuned version. The later is compact and will be ideal for our FM Walkie Talkie!

     We can actually make any receiver(except for the very high frequencies) with just one FET transistor. Then we can use a common hi gain audio amp. We shall be moving towards building receivers using the intermediate frequencies, 455KHZ and the 10.7Mhz.

Hi, it's a new week, Oct 29. November is near.

     Anyone who would like to build this simple Walkie Talkie can contact me for advice.


Antenna: The longer the antenna the better but it may not fit your enclosure.  Also a pi network has to be included to match your antenna. It is a simple 2 capacitors before and after an inductor.

FREQUENCY:

     Let's talk about frequency.  The higher the frequency, the shorter the wavelength. Remember that. That is why making a WT in the AM broadcast band about 1 megahertz is not practical. 27 Megs happens to be just the allowed band by the U.S. FCC. Then they allowed at 49Megs. Newer WTs for the US market are on 49Mhz. They allowed for shorter antenna. Now, if we can go 100 Mhz, which is in the FM band, then antenna could be much smaller. A good example is the FM wireless microphones. Can we build a walkie talkie in the FM band?Well, just outside the commercial band  so where it is  unoccupied.  It is easy to make the wireless mic. Circuits are all over the WEB and Alexan Commercial carries a local kit. Now, if we can make a simple DIY FM receiver, that will be fun. An FM walkie talkie. It has clarity advantage but not so much on range. Perhaps we can increase the TX power so we can go 100 to 200 feet! Not bad if it just for camping and biking trips. Or Boy's Scout camps. Or sleeping in tents in the HS campus. Future projects!

                                                TRANSMITTER CIRCUIT ENLARGED


     Here is an enlarged circuit diagram of the transmitter. The Crystal is Base to ground, making this a Miller oscillator. The Pierce oscillator hjas the Crystal Base to Collector.

                                                          RECEIVER CIRCUIT




Great, we are able to move the schematic of the Receiver circuit for a Walkie Talkie Project. Take note, the power to the collector has been greatly reduced by the resistors in series, the 220 ohms and the 4.7k. The 33ufd is a stabilizer. In addition, the crystal was reboved and the 403 cap was directly connected to ground. The audio output is marked.

BK

Hi friends, it's Tuesday, 10/23.

     Well, for today I will continue on the transistor. Look at the transistor as a faucet. Water will flow but controllable by the handle. So with the tranny. The Base is the handle, the Emitter the input and the Collector the outflow. We like the faucet to be opened at a certain point. So with the tranny. We call it biasing. A bit of pus to turn it on. We can uise a single resistor from the plus line to the base , such as 180k. But it is more stable to put a voltage divider. In fact if you are designing, use a variable resistor across the power lines. The wiper moves across choosing the right bias to the Base. Or fixed one and make the other one variable.
     

    In the diagram shown, the biases are the 33k to plus and the 15k to minus. Here it is shown on the TX mode. Note the Crystal to ground via a 403 to Base.

Hi Good Friday Morning!  I have not scanned my diagram but we can spend sometime discussing ceertain basics. Let us start with the transistor.

     Transistors can be used for our projects would be the following:

BC547       CBE
C945          ECB


     Be careful of the pin configuration especially that of the BC547. If you are looking at the flat side, left pin is C. Most transistors have E on that side. A transistor can be configured as a common Emitter amplifier, Common Base and Common Collector. The most popular is the common Emitter. But for our oscillators, the common Base is used. This means that the base is held fixed, rigid and the signal is fed into the C and E. You will note that the coil will be on the C and sometimes they say it a load on the C. While that is correct, I like to see the coil as inputting its signal into the C of the transistor. You will note there is a capacitor between C and E. THE PURPOSE OF THIS CAP IS TO TRANSFER THE SIGNAL FROM THE COIL AT C TO THE E OF THE TRANSISTOR. E is also an input, remember. B is not an input pin in a common Base configuration.

THE DC SET UP OF A TRANSISTOR

     The DC set up or DC circuit of a transistor is the biasing. The transistor should be brought to a desirable condition so it becomes sensitive. Look at the OSCILLATOR, we have the critical forward and reverse biases to the Base. If we view the two resistors across the power supply, they form a voltage divider. IN OTHER WORDS, THERE IS AN IDEAL VOLTAGE TO THE BASE OF THE TRANSISTOR. The series resistors on the Emitter leg also contributes to the bias and it also limits the current flow across the C E junctions.

Hi friends, am back, the last update was Oct. 7. It's the 18th. We will have to squeeze in a side topic for some students in Zambales  It's on MODULATED IR.


MODULATED IR

     Usually, when working with IR, ambient light is a problem. At the other end, usually a photo transistor is used. One solution is to house the photo transistor in a straight tube, say 6 inches. Only a straight beam can enter when it is aligned with the tube. The other way is to modulate the IR at about 1 khz using a 555 timer IC. Then the photo transistor is fed into an LM567 frequency decoder. The tube may still be used in addition. I will post the schematic later.

BK


Back to our main topic, OSCILLATOR.

     Hmmmmm, let's see. What can we build to learn about oscillators?. Answer: A Walike-Talkie! A WT is just a pair of units which has a TX and an RX in each unit. In short, the TX and RX are just duplicated. WE DONT HAVE TO BUILD BOTH for learning. We build one each, ok?

     Which one first? If we build the RX, we have no TX to test it with. If we build the TX, we have no RX to test it with. It's the Chicken and Egg Paradox! But wait a minute, we can build a very simple RF detector which will tell us if the TX is putting out signals.


     THE RF PROBE:

             JUST GET TWO IN4148 DIODES. JOIN THE PLUS END TO THE MINUS END OF THE OTHER DIODE. CONNECT THE OPEN ENDS TO YOU VOLTMETER SET TO THE LOWEST VOLTAGE RANGE. OR IF YOU HAVE VU METER, CONNECT TO THE VU METER. THE PLUS OF THE DIODE SHOULD GO TO THE RED PROBE OF YOUR METER. THE VU HAS A PLUS AND MINUS MARKING TOO. SOLDER A PIECE OF WIRE SAY 6 INCHES LONG to the joint ends of the diodes AND PUT A TINY ALLIGATOR CLIP. DONE. YOU NOW HAVE AN RF DETECTOR .

     If you have a toy transmitter, touch the clip to the antenna and press transmit. See the needle jump?

THE TRANSMITTER IS AN OSCILLATOR


     (to follow since I will have to scan a schematic diagram) 

The OHMS LAW is E=IR. Please comment here if there is something wrong.

E= Electromotive Force
I=Current
R=Resistance


     The units used are: Volts for EMF, Amp for I and Ohm for R.


So much for that.

Let's move on into OSCILLATION, our last topic.


         In the case of using a battery to energize a tank circuit, we cannot catch up with the speed at which to recharge the circuit. A Q (transistor) can do the job. It will keep on feeding the TANK circuit and will it it oscillating.

         The poroblem was to keep the frequency stable and the answer was QUARTZ! Quartz Crystal we call it. It can be ground to vibrate at a certain frequency and the beauty of the crystal is that it remains stable in its oscillation even at a wide arange range of temperature. But crystals do not vibrate by itself. Electric current has to be fed into it. PERFECT, it is widely used to keep the frequency of our oscillator steady.

CAN WE TRANSMIT USING A SINGLE Q?   YES!


BK

If there was a way to increase/decrease the strength of the osacillations(not affecting its freqwuency), we could have modulated our voice into the tuning fork! AM!


ELECTRICAL RESONANCE

     Now, let's see, we had the tuning fork, we can vibrate or oscillate something in the higher frequencies, at frequencies we ourselves can no longer hear. YES, in an electrical circuit, a coil is like a generator and a capacitor is like a rechargeable battery. What if we connect them together, will they short out each other? Well, eventually but they will first feed into each other. The cap as a battery will energize the coil and the coil will swing it back to the capacitor. This is called a TANK circuit. it will oscillate when initially energized with a battery for example. When the battery is removed, it will whine down and stop. The interesting part: The cap and the coil sets the frequency! Increase the cap, the frequency goes down. Increase the turns on the coil, it does the same thing. So, we can tune the tank by either using a varicap or by putting a slug inside the coil which can vary its inductance. TUNABLE!



to be continued......BK

Before tubes came around, there was a man who was fascinated with the buzzer. MORSE. He asked his assistant to make combinations of the short and long buzz to be called dot and dash. The Morse Code! he probably didn't realized that he had stumbled on BINARY since he also used two symbols only, dot and dash, 0,1, not there and there. So, all over America there was a pair of wires along the railroad tracks carrying the Morse Code! Another man , BELL, wanted to send his own voice over a pair of wire. He made a speaker, moving coil with a cone. Then he sent electric current to it via a carbon tip touching a paper diaphram. When he spoke on it, it vibrated and the current running through the wires vibrated correspondingly. The TELEPHONE!


CONTROLLING ELECTRICITY

     It was all because of Edison's light bulb! After Edison invented the light bulb, other experimenters like Lee de Forest played around with the bulb. The DIODE was discovered via an vacuum tube. Electrons flowed from the heated element called the Cathode to a Plate but not the other way around. Then when a thord element was put between the Cathode and Plate, to be called the Grid, electron flow from the Cathode to the Plate can be controlled by a tiny current on the grid. The TRIODE, an amplifier!

     MAN went to WAR in 1917 with internal combustion engines on biplanes, with machine guns in front of the pilot.. In 1938 when Germany invaded Poland, WW2 began and MAN had vacuum tubes! The famous walkie talkie of the US army, backpacks with long antennas. Vacuum tubes.  The Germans used them in their V-1 rockets send to England. There were Pentagrid tubes.

     Then Peace in 1945. The Americans at the Bell Labs in California discovered SEMICONDUCTORS. The original material was the GERMANIUM. And they were PNPs! It was developed in 1949 and by the early fifties, a Japanese company called SONY corporation made the pocket radio, an AM BC radio working on batteries!

     Communications technologies were developed during the tube era. Superhet for tube receivers, vacuum tube analog computers. These technologies simply were applied using semiconductors called transistors.


WHY WERE THEY CALLED VALVES?

      It was because they were valves controlling the flow of electrons! The transistors are still valves not requiring heaters. The Emitter-Collection junction is controlled by teh Base Emitter junction. Tickle the Base and electrons flow in the E-C junction!


Now, what is WIRELESS?

      In Europe before tubes and transistors were around, they experimented with SPARK GAPS. It was like lighting matches. The electric spark spewed waves of many frequencies. It was NOISE! Electrical noise. The receiver was a simple glass tube filled with iron filings. The filings aligned themselves when a spark occurred. Contact was made and it was a simple switch! Aha, WIRELESS. In the meantime, the mathematicians like MAXWELL in England theorized that signals can travel in space and information can be imbedded in it by changing the signal strength. Aha, AM!


RESONANCE

     Get a pair of tuning forks of the same note, bang one and the other one RESONATES! PHYSICAL RESONANCE! The frequency was within the human hearing range.

Hi readers.....many students had asked me to create my own blog on WIRELESS DEVICES and here it is. This is dedicated to wireless things, controlling devices and communications projects.

THIS IS ESPECIALLY DEDICATED TO ECE STUDENTS who after all should master ELECTRONIC COMMUNICATIONS.

I will do my best to start you off with a bit of history and human experience in this field. May the Holy Spirit inspire and guide me.


BK


INTRO AND HISTORY

     It is said that the planet earth is 20 billion years old. Jesus was here 2012 years ago and Abraham, 2000 before Him. Then Adam and Eve 3000 years before Abe. Gee, we are recent visitors! Only 7000 years in this planet of millions of planets.

     Let's go. When the caveman saw the lightning, it was his first experience of electricity. It was huge and lethal and can fry a man. He couldn't do anything with it. Let's jump to the 19th century in Europe.  The Europeans loved frog's legs.  They hang in markets like the meat they sell today. To bring it down, metal rods were used. It was always a wonder why the leg would move when the rod gets near it. Nobody knew and many perhaps thought it was the spirit of the dead frog! STATIC ELECTRICITY!

     Then the alchemists came around. Scientists they call themselves and were experimenting with chemicals. Names like Faraday and Volta appeared in the scientists' circle. They discovered that there is electricity in chemicals. Two unlike metals in a solution called ELECTROLYTE produced electricity. Perhaps they used their tongues to feel it. You can do this today. Pierce a iron paper clip and copper wire into a calamansi and taste the ends. You will feel electricity!

     Then they discovered wires ( they already knew about magnets they called loadstones). Wires wrapped around a nail and fed electricity became magnetized and they called it ELECTROMAGNET. Volta theorized  the electric pressure present and later on in his honor, it is called a VOLT. GALVANI invented the GALVANOMETER. It was actually a voltmeter. He made a rocker with a needle then placed a coil in front of it. The strength of the magnet rotated the rocker and the needle. Then AMPERE came into the picture. He said that while there is an electrical pressure, there must be an electrical volume. Actually we later found out it is the amount of electrons moving. In his honor, it is today called an AMPERE.  Ha, there is a third guy called OHM. He says that if V moved the I (for current in ampere), the medium offered a RESISTANCE to the flow. It was later called OHM in his honor. It was OHM who defined the relationship of Electrical Pressure, Volume of electrons, and Resistance. The units were defined as a VOLT, an AMPERE, and an OHM! He says that ONE VOLT pushes ONE AMPERE around a RESISTANCE of ONE OHM. The OHM'S LAW!  E for Electromotive Force in Volts, I for current in Amps, and R for resistance. The relationship:


                                           E=IR


     So, get  a 6V battery, put a light bulb. Measure the current in the line, the resistance is defined to be 6V/ by the current and if it is 1 amp, the R would be 6 Ohms! If the V is 1 Volt, the current is 1 Amp, the Resistance is 1 Ohm!


     THERE WAS AN EXPLOSION OF EXPERIMENTS INVOLVING BATTERIES, WIRES, ELECTROMAGNETS TO MAKE THE BUZZER, MAGNETS ETC.  With the GALVANOMETER AS THE FIRST TOOL, MAN was able to detect electricity. It was also discovered that magnets moved in front of a coil produced electricity! So, magnets can produce electricity to charge the batteries! WHAT A DISCOVERY. Electricity can be STORED!

But there was no light bulb. To produce light from electricity, the arc lamp was used, two pointed carbon touching and creating light. What a waste. In the early 20th century, arc lamps were all over Europe and America. It took EDISON from Ohio to invent the light bulb. There was already the steam engine and the internal combustion engined invented by a German, OTTO. Electric generators were running all  over the planet producing DC electricity! Why DC? Because MAN started off with batteries. A Russian convinced the world that AC is the way to go. TESLA. Today, all over the world, AC is used. It is easier to produce requiring NO commutation in the genset, can be converted into different voltages (transformer) which  can be  transmitted cheaply at high voltages using thinner wires, and can be transformed easily in homes to different voltages.

NEXT......THE VALVES AS THE EUROPEAN CALLED THEM OR TUBES AS THE AMERICANS CALLED THEM. THE BEGINNING OF MAN CONTROLLING ELECTRICITY .