DIY electronic devices, data on electronic components, homemade antennas, radio transmitters and receivers, microcontrollers and their programming. Electronics for beginners
Today I decided to test a radio transmitter for a frequency of 3.57 MHz, which I made on the SN74HC14N microcircuit. This microcircuit contains six inverting Schmitt triggers. I assembled it according to the scheme shown in the photo. The master oscillator is made on one trigger and a quartz resonator for a frequency of 3.57 MHz. Next comes the buffer cascade and a power amplifier on four triggers. Instead of an antenna, I connected a 50 Ohm resistor to the load. With a power supply of 5 volts and a current consumption of 20 mA, the output power was 67 mW. And everything would be fine if I did not switch the oscilloscope probe divider to ten.
Now the oscilloscope shows a triple transmitter frequency of about 10.7 MHz. This bothered me a bit and I spent the whole evening trying to figure it out, but in the end I realized that it is better not to make a transmitter on this microcircuit, after all it is a logical microcircuit.
But I have another similar microcircuit, only MM74C14N, it is also a Schmitt trigger, but with a power supply from 3 to 15 Volts. In this radio transmitter circuit, this microcircuit starts working from about 9 Volts, it will not work below. But if you switch the divider to 10 on the oscilloscope probe, the frequency will remain stable at 3.57 MHz, and not multiply by three.
On the left in the photo, the microcircuits operate at 9 volts, and on the right at 5 volts of power supply.
The operation of the microcircuits was tested only in this circuit, in other devices that are not for high frequencies, these microcircuits will work according to the datasheet
Today I will disassemble the board from the NOKIA 3210 cell phone. On the board there is an inscription: GF7_20B 9854307 and also S0101a. On the board of this phone there are interesting electronic components on which you can assemble radio transmitting devices. I will tell you about this
PMB2353 is the processor for this phone
4370351-unknown
EPCOS B7103 is a SAW filter 71MHz, as well as EPCOS 4693 RX filter 1800MHz, EPCOS 4109 is a SAW filter for a frequency of 1747.5 MHz, EPCOS 7604.
232-2 this 1800MHz TX IF filter
670L 6pin TX amplifier?
PF01420B -900MHz power amplifier GSM
PF04110B -1800MHz power amplifier DCS
White ceramic parts are possible ceramic directional couplers
K1747 in metal case, possibly RF combiner
Two light metal cases are voltage-controlled oscillators. FDK IM013B and FDK IN068. On the first one you can assemble a radio transmitter for frequencies of 1860-2140 MHz and on the other one 438-485 MHz. The frequencies are reconfigured by applying different voltage to the control input. I provide the connection diagram for IN068 in the figure. Apply an audio signal to output 6 and the radio transmitter is ready.
In TVs or cell phones, where there is a radio receiving or transmitting board, you can see a part in a metal or other case on the board. This part is called a SAW filter or a filter on surface acoustic waves. I will briefly tell you how it works in this article.
To make it clearer, I disassembled one SAW filter, on the body of which there is an inscription KYOSERA 38.0. This is a bandpass SAW filter from a TV to an intermediate frequency.
Inside the filter you can see a transmitter and receiver, which are located on a substrate. By sending an electrical signal to the transmitter, it is converted into mechanical or acoustic energy, which spreads along the surface of the piezoelectric material (substrate). This energy is sent to the receiver and converted back into an electrical signal. What is this for? It is necessary to filter out unnecessary frequencies and pass the necessary ones. For example, a SAW filter from a TV (CRT TV) will pass frequencies from 34 to 39 MHz, and suppress the rest of the frequencies. Filters in a cell phone work in much the same way. The EPCOS 4109 filter at 1747 MHz from the NOKIA 3210 phone will pass the necessary frequencies and suppress the unnecessary ones.SAW filters can operate at very high frequencies, unlike quartz and other filters.In a quartz filter there are vibrations of a quartz plate, but in a SAW filter there will be a surface wave.
I fed a signal from a generator, the frequency of which I will change, to the input of the SAW filter from the TV. I connected an oscilloscope to the output of the filter to observe the signal.
At the filter input the frequency is 32 MHz, at the output the signal is suppressed
At the input of the filter there is a signal with a frequency of 35 MHz and the filter passes this signal and it is visible on the oscilloscope
Now the filter input is 41 MHz and the signal at the output is suppressed. The filter passed the necessary frequencies and suppressed the unnecessary ones.
Let's look at a SAW filter from a cell phone under a microscope
The size of SAW filters in phones is small compared to filters in TVs, since such filters operate at even higher frequencies.
When setting up homemade radio transmitters, you need to know their output power. There are special devices on sale that will measure the RF output power, but I also use a method to measure the output power using an oscilloscope. Here's how I do it. This method can measure the output power of radio transmitters.
You will need a good 45 cm long coaxial cable with a 50 Ohm characteristic impedance. For the load, you will need a non-inductive 50 Ohm resistor, I made it from two 100 Ohm resistors connected in parallel. I got a resistor with a dissipated power of 4 W. This resistor simulates an antenna that should be connected to the output stage of the radio transmitter. Of course, you will also need an oscilloscope that should measure well and work at the frequency of the radio transmitter.
My homemade radio transmitter operates at a frequency of approximately 7 MHz with a power amplifier on a BS170 transistor. The output power of such a transmitter will not exceed 2 W, this is a low-power radio transmitter. Connect the cable to the output of the radio transmitter where the antenna or cable should be connected.
Connect a 50 ohm resistor to the other end of the cable.
This is what it looks like
There is a divider on the oscilloscope probe. Set the divider to 10, this is what you need to do when you measure frequencies above 5 MHz, this way the readings will be better.
We supply power to the radio transmitter. My transmitter, when powered by 9 volts, consumes a current of 60 mA. This means that the power consumption of the radio transmitter from the power source is 540 mW. Here is the formula: W = V * I or 9 * 0.06 = 0.54. Why do you need to know this? This is necessary in order to exclude gross errors in measurement. If after calculations it becomes known that the output power will be 700 mW with a power consumption from the power source of 540 mW, then there is clearly an error here.
So, the oscilloscope shows the range of the double amplitude of the Peak-Peak signal 1.28V. This is the range of two amplitudes of the positive and negative half-waves, we only need to know the amplitude of one half-wave. To do this, divide 1.28 by 2 and get 0.64 and multiply by 10. Ten is the division of the divider that I installed on the probe. It turned out to be 6.4 Volts. This is the amplitude of one half-wave or Peak.
So, the oscilloscope shows the range of the double amplitude of the Peak-Peak signal 1.28V. This is the range of two amplitudes of the positive and negative half-waves, we only need to know the amplitude of one half-wave. To do this, divide 1.28 by 2 and get 0.64 and multiply by 10. Ten is the division of the divider that I installed on the probe. It turned out to be 6.4 Volts. This is the amplitude of one half-wave or Peak.
The first formula for calculating the output power of a radio transmitter is quite simple. We take 6.4, multiply it by 6.4 and divide the product by 100. We get 0.4096 or round it up to 410. 410 mW is the output power of the transmitter.
The second formula. 6.4 Volts (Peak) divided by the square root of two .The result is 4.52548339959. This is RMS. Then we square it and divide by 50, which results in 0.4096. The output power, if rounded, is 410 mW.
On one transistor RD15HVF1 you can make a high-frequency generator, from the antenna of which you can illuminate lamps holding them in your hands and conduct other experiments. Here I will tell you how to make it and set it up and what nuances need to be taken into account
Coil L1 and L2 are wound with a wire with a diameter of approximately 0.7 mm. L1 has an internal diameter of 3 mm and contains 8 turns of wire, and coil L2 has an internal diameter of 7 mm and contains 10 turns of wire. The transistor is mounted on a small heat sink. The antenna is 3.5 cm long, the operating frequency of the generator will depend on the length of the antenna. First, install an antenna 5 cm long and reduce the length of the antenna to achieve the best performance of the generator. I used a trimmer capacitor with a capacity of 6-25 pF, but you can also try to install it on a different capacity.
A few words about the RD15HVF1 transistor. Today there are many counterfeit transistors of this type on sale, I bought used transistors and they may be original from MITSUBISHI. The transistor flange is not a drain but a source and the pinout is different, unlike most MOSFET transistors. One such transistor has an output power of 15W at a frequency of 520 MHz, this is very cool.
The generator is assembled and now it is time to set it up, without setting up high-frequency devices may work poorly or not work at all and the transistor may fail when first turned on
What should be done first? First, limit the current that you will power the device with. Set the maximum output current of the power supply at 1.5 A. If you do not do this and if you do not configure the device, the current consumed when turning on may be very large and cause a sharp heating of the transistor.
Set the trimmer resistor to the middle position.
Now apply 7 Volt power. If the current consumption is more than 600 mA and the fluorescent lamps near the antenna do not light, then the generator is not adjusted. Turn off the power and adjust the trimmer capacitor and apply power again. The generator should start working and by changing the capacity of the capacitor, achieve the highest radiated power from the antenna.
Make a HF probe on two diodes and a LED. The LED will shine brightly near the antenna. The greater the radiated power of the generator, the brighter the LED shines.
Adjust the current consumption with a trimmer resistor. Normally, with a 7 Volt supply, the current consumption should be around 350 mA and the transistor should be warm
Using the GY561 device, I measured the frequency of the radiation, and it was about 170 MHz, although the device may show a harmonic and the real frequency is completely different
Now the generator is working and you can conduct various experiments.
What else should be taken into account. The power supply may not correctly display the consumed current. This happens due to the influence of high-frequency radiation on the electronics of the power supply. I have ferrites installed on the power supply wires so that interference does not penetrate the power supply. If these ferrites are installed on the wires closer to the generator, then its operation will deteriorate slightly, since high-frequency current is present on the power supply wires.
Do not touch the antenna wire, high-frequency current is present on the antenna.
The generator emits a radio signal and it is possible that in your area it will interfere with radio communications. Well, that's all.
