Simple Diode Radio For Low Impedance Headphones

Diode Radio For Low Impedance Headphones - using small amount of component , germanium diode semiconductor you can build small radio equipment that can pick up lot of AM/LW/SW frequency . This project will talk about this purpose. if you ever look at construction notes for building old detector type radios the type of headphones specified always have an impedance of 2 X 2000 Q. Nowadays the most commonly available headphones have an impedance of 2 x 32 Q, this rel- atively low value makes them unsuitable for such a design. However, with a bit of crafty  transformation these headphones can be used in just such a design. To adapt them, you will need a transformer taken from a mains adapter unit, the type that has  a switchable output voltage (3/4.5/6/9/12 V) without the rectifying diodes and capacitor. Using the different taps of this type of transformer it is possible to  optimise the imped- ance match.

For the diode radio (any germanium diode is suitable in this design) the key to success is correct impedance matching so that none of the received signal energy is  lost. The antenna coil on the 10 mm diameter by 100 mm long ferrite rod is made up of 60 turns with a tap point at every 10 turns; this is suit- able for medium wavereception. If a long external aerial is used it should be connected to a lower tap point to reduce its damping effect on the circuit. 
You can experiment with all the available tapping points to find the best reception. With such a simple radio design, the external aerial will have a big influence.

After construction done, connect ground to water pipe/make the grounding your own. The Key is the good grounding, so there is voltage between the air radio signal from the grounding, and this radio signal picked up by this circuit. This is such building a Crystal Radio

Component Lists :

Small PCB

Mini Box

Antenna Telescopic/Wire Cable AM/MW/LW/SW

Germanium Diode

VC1 500 pF

C2 10 nF

Headphone 2 X32 Ohm

Headphone Jack

Best One Transistor Radio

 

One Transistor Radio - Here is a simple circuit for a one transistor Audion type radio powered by a 1.5 V battery and Transistor BC548 It employs a set of standard low- impedance headphones with the headphone  socket wired so that the two sides are connected in series thus giving an impedance of 64 Q. The supply to the circuit also passes through the headphones so that  unplugging the headphones turns off the supply Using an Audion configuration means that the single transistor performs both demodulation and ampli- fication of the  signal. The sensitivity of this receiver is such that a 2 m length of wire is all that is needed as an antenna. The tap on the antenna coil is at l/5th of the total  winding on the ferrite rod.The antenna coil on the 10 mm diameter by 100 mm long ferrite rod is made up of 60 turns with a tap point at every 10 turns; this is suit- able for medium wave reception. If a long external aerial is used it should be connected to a lower tap point to reduce its damping effect on the circuit.  This circuit is suitable for reception of all  AM transmissions from longwave through to shortwave.

Parts List :

Transistor BC548

R1    100K

VC1     500pF

C2     10uF

C3     100nF

L1 10mm diameter Coil, 100 mm long Ferrite rod

60 turns with a tap point 10 turns

Headphone 2 X 32 Ohm

Battery 1.5 V

Mini Box

PCB 

Antenna Telescopic

Reference : Elektor Electronics - B.Kainka

DIY miniature antenna booster

When using a good antenna amplifier for the UHF range, programs can be received from television stations which, without a preamplifier, only deliver a very noisy "snow field". The antenna amplifier described here is very simple. It can because of its small dimensions directly in the junction box of Antenna to be accommodated. The small coupling capacitance in the input protects the transistor from overvoltages that may occur during a thunderstorm. The built-in resonant circuit in the collector branch can be tuned to any frequency between 470 and 790 MHz.

Because of the extremely low retroactive effect  of this transistor is the amplifier stronger very stable, even with poor matching of the input and output. The bandwidth of the circuit is about 15 to 40 MHz.

reference : Elektor Electronics

How to create a simple circuit that makes an LED blinking continuously ?

How to create a simple circuit that makes an LED blinking continuously ?  - The special thing about this circuit is that both transistors are either conducting or both are blocking. As long as the lamps are not lit, only small currents flow, that benefits the battery. A further advantage of this circuit is that only a single capacitor determines the flashing frequency.the benefits of this circuit can be used for tower lights or tower antennas.

Reference : Elektor Electronics

How do I make a mini walkie-talkie?

How do I make a mini walkie-talkie? - The walkie-talkie, a portable two-way radio, consists of three blocks, namely receiver, transmitter and modulator (amplifier). The former is a super regenerative  receiver (Figure 1). Using this circuit, gains of more than 10000 times can be achieved. The output voltage is over 20 mV. In the receiving state, the signal from  the receiver is fed to the AF amplifier.
The DC-coupled amplifier (Figure 2) has an amplification factor of 500 . When using a 150 L> speaker in the final stage, you get about 70 mW output power, which is also suitable for playing a walkie-talkie enough. During transmission, the loudspeaker is at the input of the amplifier, so it works as a microphone. Because of the high amplification of the circuit, which 
now works as a modulator, a sufficient degree of modulation is obtained when speaking from a normal distance to the microphone (loudspeaker). The output signal is  now sent to the transmitter.
The transmitter (Figure 3) is a quartz-controlled oscillator with an oscillating frequency of 27.125 MHz. The quartz ensures an extremely constant frequency. 
The LF signal is superimposed on the HF carrier frequency via the collector.
If there are no obstacles to the If the carrier frequency is between the interlocutors, you get a range of about 1 kilometre. In residential areas, this is a few hundred meters.
During assembly, the receiver and amplifier can be placed in one housing. It is important to ensure that there is a short distance between the two; shielding 
by means of a copper plate is to be provided.
An antenna with a length of 70 cm should be used for a compact design and good matching. We expressly point out that for the operation of the transmitter, 
no matter how small, a permit must be obtained from the Government Authority.

Reference : https://archive.org/details/elektor197101v005/mode/2up?view=theater