A Simple Science Fair AM Transmitter [BETTER]
A Simple Science Fair AM Transmitter https://shurll.com/2tgpFz
AM radios are relatively simple devices, and building one is a good way to start exploring the world of radio communications. [GreatScott] does exactly this in the video after the break, building both a transmitter and receiver.
Using one transistor, one resistor and one capacitor, he describes the circuit and how the components affect the frequency of the sawtooth wave the oscillator creates. [Eric] uses the oscillator to build a simple LED blinker and shows what happens when he changes the transistor and adjusts the voltage or resistance. He also shows the circuit as a tone generator and adjusts the tone by replacing the resistor with a potentiometer. And then, for fun, he modifies the circuit to show the oscillator as an AM transmitter. Check out his video after the break.
Check out and try the simple spark gap transmitter. This is what radio was in the earliest days. The only thing a Morse code radio operator would hear through his headphones is those scratchy clicks. You might want to demonstrate this before starting this project.
AM is also inefficient in power usage; at least two-thirds of the power is concentrated in the carrier signal. The carrier signal contains none of the original information being transmitted (voice, video, data, etc.). However its presence provides a simple means of demodulation using envelope detection, providing a frequency and phase reference to extract the modulation from the sidebands. In some modulation systems based on AM, a lower transmitter power is required through partial or total elimination of the carrier component, however receivers for these signals are more complex because they must provide a precise carrier frequency reference signal (usually as shifted to the intermediate frequency) from a greatly reduced \"pilot\" carrier (in reduced-carrier transmission or DSB-RC) to use in the demodulation process. Even with the carrier totally eliminated in double-sideband suppressed-carrier transmission, carrier regeneration is possible using a Costas phase-locked loop. This does not work for single-sideband suppressed-carrier transmission (SSB-SC), leading to the characteristic \"Donald Duck\" sound from such receivers when slightly detuned. Single-sideband AM is nevertheless used widely in amateur radio and other voice communications because it has power and bandwidth efficiency (cutting the RF bandwidth in half compared to standard AM). On the other hand, in medium wave and short wave broadcasting, standard AM with the full carrier allows for reception using inexpensive receivers. The broadcaster absorbs the extra power cost to greatly increase potential audience.
A simple form of amplitude modulation is the transmission of speech signals from a traditional analog telephone set using a common battery local loop.[3] The direct current provided by the central office battery is a carrier with a frequency of 0 Hz. It is modulated by a microphone (transmitter) in the telephone set according to the acoustic signal from the speaker. The result is a varying amplitude direct current, whose AC-component is the speech signal extracted at the central office for transmission to another subscriber.
While this is a simple AM radio transmitter, it is also a bad one inthe sense that it not only transmits at the frequency of the oscillatorbut also at a range of frequencies above and below it. It alsobroadcasts on harmonic and subharmonic frequencies which are multiplesand submultiples. For example a harmonic of 1.8MHz is 2x1.8, or 3.2MHz.A subharmonic of 1.8MHz is 1.8/2, or 0.9MHz (900kHz). Use it only forfun, demonstrations or science fair projects.
To limit it's range, don't use a powerful sound source or keep thevolume of the sound source low. Also, keep the output antenna wire short.Video - How to Make AM Radio TransmitterHere's a video I made showing step-by-step how to make thissimple AM radio transmitter on the breadboard as shown in photosabove, along with demonstrations of me using it.
From 1921, at first as an experiment, a civilian transmitter broadcast music programmes, columns, and lastly the \"Journal Parlé\" (spoken news) from 1925, picked up by amateurs on simple crystal radio sets. Radio Tour-Eiffel was well-known to Parisians at the time.
One of the challenging aspects of the coronavirus COVID-19 crisis is the time spent at home in quarantine. For those with a Do-It-Yourself (DIY) bend, this might be the perfect time to build a fairly inexpensive crystal radio. Complementing that build is the construction of a simple AM broadcast station to allow you and your family to both listen and transmit to the radio.
On the other hand, astrocytes may expand the possible consequences of a single neurotransmitter on network function. Indeed, in the CA1 area of the hippocampus, glutamate released from Schaffer collaterals excites postsynaptic pyramidal neurons as well as inhibitory interneurons, which in turn activate astrocytes elevating their intracellular Ca2+. This astrocyte Ca2+ signal stimulates the release of ATP, which after being extracellularly degraded to adenosine leads to synaptic depression of adjacent excitatory synapses (Zhang et al. 2003; Serrano et al. 2006). Therefore, this heterosynaptic depression of synaptic transmission is mediated by the coordinated activation of successive intercellular signalling events (i.e. excitatory axons stimulate interneuron activity that triggers a GABA-mediated astrocyte Ca2+ signal that, in turn, stimulates release of ATP that is converted to adenosine to depress synaptic transmission) and represents a simple but elegant example of the emergent consequences provided by astrocyte activity on neuronal network signalling.
The picture to the left is a high quality radio transmitter for the A.M. broadcast band. The transmitter legally operates with \"micro-power\" and will not set any distance records but, unlike simpler designs, the frequency stays put and the fidelity is excellent. Although the schematic looks somewhat complex, the circuitry is easy to build and adjust for experimenters with a little \"tweaking\" experience. A simple output meter confirms proper signal level and checks antenna tuning while \"on the air\". Add an audio mixer, tape recorder, and perhaps a CD player and have a near-professional micro-power station.
Is your science fair student old enough to shovel the walk this winter They could use this experiment to go the extra mile in de-icing the walk to the mailbox. Place the same number of ice cubes into separate bowls. Apply each melting material to the ice. Observe the melting ice. Which bowl melts first Record your results in your lab notebook. Repeat the experiment several times for accurate results.
We have gotten many requests for projects involving fiber optic communications for science fairs and K-12 science class projects. We thought we'd share with you the projects we developed for our own kids in the scouts and has been used in classrooms and science fairs. We've added a few more advanced exercises to enhance it for older students.
You can duplicate this experiment for your class or science project. You need an acrylic plastic rod about 25mm (1 inch) diameter (available online) and a green laser pointer. The green pointer is more visible than the regular red laser pointer. To get light into the plastic rod, you need to polish the end of the rod which is usually just sawed off. Start with fine sandpaper from a hardware store - 1200 to 3000 grit - to remove the saw marks, then polish the end with polishing compound - the same stuff used to remove scratches and polish cars. It should have a mirror-like finish for best results. Once the rod is polished, you can see the laser pointer beam in the plastic rod like the demonstration above. Lower room lights to see it better. At a science fair you can paint the inside of a box black and cut holes in each end for the plastic rod to fit through it to block outside light and improve visibility.
Orthogonal frequency division multiplexing (OFDM) is a technique used to combat multipath interference [3] . In OFDM the channel frequency is divided into subcarriers of smaller bandwidth than the channel. This reduces the bandwidth of transmitted samples to only a fraction of the whole channel. The higher data rates make it diffi- cult to solve the problem with simple channel equalization, but OFDM solves the problem by sending the data in parallel on orthogonal frequencies. As long as the delay spread of the signal is less than the symbol period on the subcarrier, then the multipath problem is solved fairly well. However, as we are moving to higher data rates, the subcarriers can only allocate so much bandwidth and thus the spread of the signal will again induce ISI. Coexistence studies of other in-band signals with OFDM-based communications were conducted [4] -[6] . 153554b96e
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