This circuit is an amplifier for small transmitters operating in the UHF band, specifically in the 450-800MHz range. The amplifier works in class A and we used the well-known Philips BLW33 transistor for its manufacture. The construction, although simple, can be said to be quite critical due to the high frequency singularity. To achieve this, a double-sided printed circuit is required, where the lower face is used for grounding with conventional materials. Is preferred not to use many surface support materials so you can make the amplifier as easily as possible. The amplification of the BLW33 transistor is 8.5dB at 860 MHz and 11.5dB at 470MHz.
Click here to download the full size of the above Circuit.
So if we give it as a driving power of -60dB, then its output will deliver a power of 120mW at 470MHz and 900mW at 860MHz.
Increasing the output power as a function of the input power does not mean that it will deliver at the same time a clear signal. The output signal from one point on will be distorted. This problem arises because of intermodulation derivatives.
The theoretical circuit
The transistor to work needs, like any construction, a stabilized power supply with very good stabilization, output voltage 25V and current capacity of at least 0.5A.
The most efficient point of class A transistors is the 24V power supply and the 33 Ohm collector current. Under these operating conditions it can pull out at least 1.2W. The transistor is available in ceramic shell SO122. If for any reason the transistor suffers some damage, you do not have to mistreat it, as Of course any other. Its base is made up of beryllium oxide (BeO), a substance that is extremely toxic and carcinogenic. The theoretical circuit is shown in the figure.
As we can see, there are three fixed surface mount capacitors C1, C4 and C8. C1 is to isolate the constant voltage that can be displayed by the drive circuit while the others are used for decoupling.
The adjustment of the transistor to the 50Ω output line is done with the help of the C10 and C11 variable capacitors, and the power lines at the output circuit respectively. Similarly, the input of the amplifier is adapted via the variable capacitor C2.
In the circuit is preferred the transfer lines instead of coils to make construction easier. The transmission lines have a more stable behavior than the coils. The transistor, in order to work in class A, needs an additional polarization circuit for its base.
This circuit consists of a transistor, T2 (BD136) and a voltage divider with the resistors R1, R7 and R8 polarizing the base of T2 and the triplet R6, which regulates the base current of the BLW33. The polarization circuit is shown in the figure above.
R1,R3,R5 = 10Ω
R2 = 33Ω
R4 = 220Ω
R6 = 220Ω trimmer
R7 = 150Ω
R8 = 1,8ΚΩ
C1,C4,C8 = 100pF
C2,C10,C11 = 1-4pF
C3 = 100nF
C5 = 470nF
C6,C7 = 6,8pF/63V
T1 = BLW33
T2 = BD136
D1 = BAW62
L1 = 1μH
The first image shows the theoretical circuit of the circuit and the printed double-sided PCB, in which you will place the components. The BLW33 transistor needs a small heatsink to cool. Coil H has a value of 1μH. For the polarization circuit, there is not PCB, since it is customary to be placed outside the amplifier circuit for protection purposes and to avoid any interference it may cause to the circuit.
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
The best human ear can capture sounds from 20Hz to 20KHz. These limits are known to be the broadest that can exist. Normally the normal limits range from 100Hz to about 13KHz and depend on the age and health of the individual. We for our measurements and to....