Transmitters that transmit AM signals are known as AM transmitters. The two types of AM transmitters that are used based on their transmitting powers are:. High level transmitters use high level modulation, and low level transmitters use low level modulation. The choice between the two modulation schemes depends on the transmitting power of the AM transmitter. In broadcast transmitters, where the transmitting power may be of the order of kilowatts, high level modulation is employed.
In low power transmitters, where only a few watts of transmitting power are requiredlow level modulation is used. Below figure's show the block diagram of high-level and low-level transmitters. The basic difference between the two transmitters is the power amplification of the carrier and modulating signals. Figure a is drawn for audio transmission. The required transmitting power is obtained from the last stage of the transmitter, the class C power amplifier.
The carrier oscillator generates the carrier signal, which lies in the RF range. The frequency of the carrier is always very high.
Because it is very difficult to generate high frequencies with good frequency stability, the carrier oscillator generates a sub multiple with the required carrier frequency. This sub multiple frequency is multiplied by the frequency multiplier stage to get the required carrier frequency.
Further, a crystal oscillator can be used in this stage to generate a low frequency carrier with the best frequency stability. The frequency multiplier stage then increases the frequency of the carrier to its required value. The purpose of the buffer amplifier is two fold. It first matches the output impedance of the carrier oscillator with the input impedance of the frequency multiplier, the next stage of the carrier oscillator.
It then isolates the carrier oscillator and frequency multiplier. This is required so that the multiplier does not draw a large current from the carrier oscillator.
Simple Low Power AM Radio Transmitter
If this occurs, the frequency of the carrier oscillator will not remain stable. The sub-multiple frequency of the carrier signal, generated by the carrier oscillatoris now applied to the frequency multiplier through the buffer amplifier. This stage is also known as harmonic generator. The frequency multiplier generates higher harmonics of carrier oscillator frequency. The frequency multiplier is a tuned circuit that can be tuned to the requisite carrier frequency that is to be transmitted.Jacks fiji vacancies
The power of the carrier signal is then amplified in the power amplifier stage. A class C power amplifier gives high power current pulses of the carrier signal at its output.
Make Your Own Low-Power AM Radio Transmitter
The audio signal to be transmitted is obtained from the microphone, as shown in figure a. The audio driver amplifier amplifies the voltage of this signal. This amplification is necessary to drive the audio power amplifier.What is attractive in this circuit is its simplicity.
It won't cost more than USD, the components are everywhere readily available or, they can be cannibalized from any old AM portable radio. It can be constructed and tested in less than 2 hours. Construction It can be constructed with only 7 components. The transistor can be of any type.High Power AM Broadcast Station Diplexer.
In the above diagram Diag. The transistor T can be of any type. US Silicon models with similar characteristics would probably be the 2N, 2N, 2N and their derivatives. It might be necessary to adjust the values of R2, depending on the transistor used. Sometimes instead of the variable capacitor of pF as C1 I use a fixed pF ceramic capacitor. With that the transmitting frequency is around kHz but the stability suffers a bit. The ferrite rod I currently use is just 8cm long because the, very fragile, original 14X0.
I believe that a longer ferrite rod can increase the range somewhat. I initially used as T an AF transistor with a power voltage of I fed it with more voltage to increase the range, but it finally blew after working sometime at 9V. I later used the AF 2G type instead.
With more than 6V this transistor is overheated, so a heatsink can save it, for sometime, with 7. In fact with less than 9V the range is very limited just a few metresbut with 12V or more I use an 18V power supply at the moment, for best results.
My next project will be to increase the voltage to 24V and even 35V if the transistor survives! I believe that with a decent antenna 24V will give me an effective range of 1 Km and even more with 35V. I also plan to use a 2N tranzistor and see what happens! The use of a power transistor with a heatsink as transistor T will definitely improve the range, as it will allow higher voltages. I think that a lengthier ferrite rod one about 19cm long will also improve the radiating power and, hence, the range.
Adjustments When your construction is finished earth ground the unit, connect the antenna, switch on your audio source, tune an AM radio on a clear channel between kHz, make sure that the polarity of the power supply to the transmitter is the right one and then switch on the transmitter.Simple cfd code matlab
Adjust the C1 var. A 75cm telescopic antenna is better if someone want to use them as AM walkie talkies along with small portable AM radios. The construction can be put inside an emptied plastic 4. The range will be somewhere between m. If used for low power broadcasts instead of a microphone, connect the unit to the phone jack of a stereo unit, an audio mixer or a PC sound card!
Use a longer antenna if you want to be heard in some distance. Antennas and Grounding AM transmitters require long antennas and good grounding to perform at their best.
AM Radio Transmitter
In that unlikely case, just hang down the wire out of your window, to have a true 60m vertical antenna! Grounding must also be good for best results. One way is to connect it with a lead to a metallic water pipe or a tap.
Mains voltage can kill. For those perfectionists out there, there are more elaborate much more effective ways to earth their TX units. Grounding frames, grounding radials etc. Range That's the most important aspect in transmitters, is it not?Shown below is my 1 st prototype of an A. Don't laugh!!! It's resonant, has a 1. The goal was to keep it under 9.
Tuning is very touchy and bandwidth is always narrow for such short antennas for. The capacitive "hat" a pie plate was my lazy way of lowering. To be strictly FCC legal you should. Shown Below is my 2 nd prototype with tune-able loading coil. Below is a close up of the tapped loading coil and tuning capacitor arrangement.
After getting it all working I weatherproofed the air variable. Low Power Radio Repository. Search this site. Building Bus'tr By Mike Sokol. Construction Plans, Medium Frequency Antennas.
To be strictly FCC legal you should resonate your antenna without the capacitive "hat".Just got the mosquito as a gift. I am very much a. Did you ever get a reply to this question? Did you fashion an antenna for your rig?Root asus a007
How did you get on? Thank you very much for your comments. The challenge with a simple short wire antenna is that this kind of antenna can damage the transmitter. This is because the transmitter works best with a 50 Ohm load on the antenna terminal. A simple wire antenna would need to be about feet long to provide a 50 Ohm load at Khz. That's why we use loading coils or dummy loads. A dummy load is just a 50 ohm load with an antenna connector. You be able to pick up our transmitter if you are near by but there won't be any significant range.
Connect one end of the coil to the transmitter and the other to a 10 to 20 foot wire antenna. It's not that hard and if your transmitter has a good ground connection you'll get great range. That link to dummy loads shows dummy loads with non - BNC connectors. How does one connect such a dummy load to the Mosquito when the mosquito has a BNC female connector for the antenna? Post a Comment. Please visit our Amazon Search Page to find low power radio gear! Email This BlogThis! Newer Post Older Post Home.
Subscribe to: Post Comments Atom. Search for AM transmitters on Ebay. Shop Amazon.On my webpages there are several construction projects for low power medium wave broadcast band AM transmitters.
The Canadian and US regulations are essentially the same, limiting output stage power to mW and antenna length to no more than 3 metres 10 feet. These constraints ensure that these transmitters will have an effective range of no more than about 30 metres feetwhich is perfectly fine for experimentation, and broadcasting music to your antique radio collection. However, this is where some problems arise.
But, getting that signal to radiate out of a 3 metre or shorter antenna is another matter entirely. So, they assume that they need more power.
Matching a transmitter to an antenna is more involved than simply connecting a piece of wire to the transmitter output. This is not going to be a rigorous treatment by any means. There are a few different definitions of an electrically small antenna.Ld player lag fix
Electrically small antennas present a few difficulties which will be discussed here. On the other hand, the fact that they are physically much smaller than the wavelengths at which they operate, means that they can be analyzed using basic circuit theory, rather than having to resort to specialized antenna software.
For the purpose of this discussion, we will assume that our antenna is a simple 3 metre tall vertical monopole with a ground plane, which is the closest approximation to what is likely to be the real life antenna, and for which there is well developed theory. Following is a schematic that shows the equivalent circuit of our 3 metre vertical antenna.
The antenna conductor inductance is the inherent inductance of a straight conductor. For an electrically small antenna, it will be a very small value, compared to the antenna reactance X aand can usually be neglected.
This inductance in henries is given by:. The antenna reactance X a for an arbitrary antenna may be either capacitive or inductive and varies with frequency, and will in fact change from inductive to capacitive and vice versa over a range of frequencies. However, in the case of our electrically small antenna, it will be strictly capacitive.
The reactance of a vertical monopole in ohms is given by:. The loss resistance r a is simply the loss due to the resistance of the antenna conductor including skin effect. The loss resistance in ohms is given by:.
The ground system resistance r G accounts for the fact that the ground return is never a perfect ground and will always exhibit some resistance, and hence a loss. There is no simple formula for determining ground loss resistance, but it can be estimated. A good ground will have a resistance of a few milliohms, while a poor one could be tens of ohms.
The radiation resistance r R represents the radio frequency energy radiated by the antenna. Normally, a resistance represents the electrical energy which escapes from a circuit by being converted to heat.
In this case however, the electrical energy is converted to radiated electromagnetic waves. So this is the important factor that determines how much RF power the antenna will radiate.Forums New posts Search forums.
Articles Top Articles Search resources. Members Current visitors. Log in Register. Search titles only. Search Advanced search…. New posts. Search forums. Log in. Welcome to our site! Electro Tech is an online community with overmembers who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register.
It's to help out a few young fellows with their interest in radio. I would really like to better understand how the one achieves AM and the other FM, as the oscillator circuits are so similar.
If anyone can shed some light on this, it would be appreciated. Any additional info on the theory of operation or calculations involved would also be most welcome. There are so many novel designs posted, but the authors almost never provide a comprehensive explanation of how the component values are derived or their function in the circuit. With it being more and more necessary to use substitute parts, this aspect has become essential.
This is especially true in some of the more novel designs. The transistor has a collector to base capacitance of about 9pF when it is turned on hard and about 4pF when it is almost turned off. Such a small capacitance does not affect the frequency of a 1MHz AM transmitter where the tuned circuit has a pf tuning capacitor but causes FM in a MHz FM transmitter where the tuning capacitor is only 25pF.
Transistor datasheets show the base-emitter voltage and the range of current gain for you to calculate biasing resistors. Thanks Audioguru. I really appreciate the quick reply. I'll have a close look at the transistor datasheets and work through the equations based on the values on the original schematic. Then I'll do it again with the "equivalent" parts I've been able to purchase.
Doing this, I hope to end up with some backup for choosing particular component values and a bit of a writeup of how the whole thing works. With your numbers and explanation, I should now be able to do this. By the way; as the general circuit is so similar although of lower frequencyI assume this mean that some of the optimizations made in the recent plans for the FM Transmitters might be applicable to the AM one?Many of us love building crystal radio.
But you need to live close to the radio station and you need a very good antenna and ground. City Dwellers like me do not have the luxury of pulling long antennas and a decent earth. How about building this low power AM Transmitter, solely for the educational purpose to test your crystal radios?Convolution example problems
Using or Owning a radio transmitter without a license is illegal in some countries. Please check and decide whether to use one at your own risk.
Depending on the length of the antennait can cover within 3 meters by a crystal radio. If you lay wires around the room, you can listen to crystal radio around the room. For conventional off the shelf radio10 meters with reasonably good audio quality. Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson. How to build this low power AM Transmitter, solely for the educational purpose to test your crystal radios.
The whole transmitter can be fit into this small box. The screws are for connection to Antenna or telescopic antenna and ground. Current consumption is 3mA using CR 3V button cell.
Connect ground of the circuit to your earth connection for crystal radio testing or your water pipe. To avoid disturbing your neighbours and breaking laws in your country, your transmission should not leave the room. Output is lower and distorted when connecting the crystal oscillator output directly to the antenna as the antenna cannot resonant with the transmitter.
I initially used 6V, but after changing from 6V to 3V power supply, the transmitter becomes more stable. By cheungbx billdiy. More by the author:. Follow this video for the instructions:. Add Teacher Note. Components: 1. The lower left pin is Nc the pin with a Dot. Connect the left pin of the coil with the output of the crystal oscillator ST32 8 ohm : 1. The side with two wires is for 8 ohm.
The side with three wire is for 1. Connect the Ground of cryatal oscillator to -3V. Connect one of the pin of the 1. Connect the other pin from the 1. Connect audio input to the two pins on the 8 ohm side of the transformer. Plug the audio cable into the phone's headphone jack. A regular Mic will not work. Connect a 3 meter Antenna to the middle pin of the coil. Tune the khz IF transformer until you hear the loudest audio from the crystal radio.Seven deadly sins grand cross global pre registration
Move your crystal radio further away to test the range of the transmitter. The audio impedance matching transformer plays a big part in the transmission. Suitable audio transformers in decending order of fitness.
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