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70 - 120MHz FM Receiver
This simple one chip FM receiver / TV tuner will allow you to receive frequencies from 70 up to 120MHz. With this small receiver it is possible to pickup TV stations, entire 88 - 108MHz FM band, aircraft conversation and many other private transmissions. It is a perfect companion to any FM Transmitter especially if FM band in your area is very crowded. TDA7000 receiver offers very good sensitivity therefore it will even allow you to pickup weaker signals that cannot be heard on conventional FM receivers.
Simple FM Receiver
With the TDA 7000 you can build an FM radio with a minimum of components; most of them so easy to manage...like the ceramic capacitors that do not require polarization...and only two resistors. The components you will employ will be of small dimensions and low cost. Even the integrated circuit itself, the TDA 7000, is not of great cost.
27 MHz Receiver
This is a simple RF receiver mainly for low-distance digital radio receiver application. The analog output of this circuit should be connected to a schmitt-trigger signal conditioning circuit with a proper value capacitor (from collector of T3). L1 for 27Mhz is about 10 turns, 6 mm diameter coil body.
27MHz / 49 MHz Walkie Talkie
Lots of people are requesting walkie-talkie and RF remote control schematics, so here is some. Building these circuits needs special equipment and expertise in RF circuits. If you are going to experiment with these circuits, please note that I did not build them, and I am not able to help you with any details. If you have no experience in RF, I suggest that you choose the easy way and buy a ready-made RF module. Otherwise you can realize you have an exact copy of a circuit in your hand, still it doesn't work the way it should.
4 Transistor FM Receiver
This is a pocket sized receiver I built in 1994. The idea was to make a simple but useable receiver running off 3V. My previous 6 transistor receiver was more bulky, requiring 12V. This meant 10 x AA cells. I designed and made a PCB, and constructed a small aluminium case to keep the receiver as comact as possible. There is nothing unusual with this design. The detector uses a simple Colpitts oscillator and is of a type commonly used in other super regen receivers. Of course it is self quenched. Sensitivity with this type of detector is relatively low, but it's simple and easy to get working. As always, I provided a regeneration control to set the optimum operating point; ie. max sensitivity and minimum SCA/stereo subcarrier beat.
Aircraft / Airplane Radio Receiver
The communications between commercial aircraft and the ground can be interesting, amusing and sometimes even disturbing. However radios that receive the approximately 220MHz to 400MHz band commonly used for aircraft (both military and commercial) are not easily found. And scanners can be complicated, large and expensive. With an easy to build circuit such as this one, everyone can enjoy listening in on these conversations.
AM Radio built around LM555
AM radio built around 555 timer chip. The only active device (silicon, germanium, or otherwise) is the LM555. The tuning is accomplished with an inductor and a capacitor, and the LM555 acts as an AM demodulator and class-D power amplifier to drive the speaker. You may be wondering how all this is accomplished with a 555. Here’s how the circuit works: The AM radio signal is tuned by inductor L, which is 300 turns of wire on a 1/2 inch diameter cardboard tube made out of a paper roll, along with the 100pF variable capacitor. One end of the parallel configuration of L and C connects to an antenna (surprisingly long!) and the other end connects to a ground wire which is tied to the AC outlet ground (old books tell you to ground it to a water pipe). So far this is exactly like an AM crystal radio.
The 555 timer is configured as a pulse width modulator in a non-traditional configuration. If I used the standard approach and connected the input to the CV pin, the low impedance of the pin would prevent the circuit from receiving any radio signals. I had to invert the circuit and tie both high impedance analog pins, Threshold and Trigger to the radio signal input. This is the reason why the CMOS version of the 555 timer performs much better than the standard bipolar, which has higher input bias current.
Crystal Detector Radio Receiver Set Varactor Varicap Capacitor Diode Tuned
Traditionally, in a crystal detector radio tuned circuits, a mechanical type variable capacitor is used. For those of you who would like to eliminate this mechanical component, here is a modern version of the classic detector set. This radio, as shown on Figure 1, uses a varactor diode instead of the usual mechanical rotary device. The varactor is also known as a variable capacitance or a varicap diode. It provides an electrically controllable capacitance, which can be used in many different circuits. Varactors are small and inexpensive, which makes their use advantageous in many applications. Its disadvantages are a lower Q (quality), nonlinearity, lower voltage rating and a more limited capacitance range. A tuned circuit with a higher Q has a narrow pass-band that makes it better able to pick out a station of many equally strong. A lower Q tuned circuit has a wider pass band. It allows more neighbor stations through and makes listening to either radio stations frustrating. Frequency change with a varactor diode equipped tuned circuit is as simple as a voltage change.
Direct SW Receiver for AM, AM-SSB & CW Signals
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Direct SW Receiver for AM, AM-SSB & CW Signals
SSB stands for Single Side Band, which signifies the amplitude - modulated signal which gets its signal carrier and one sideband suppressed in the transmitter. Carrier suppressing gives huge savings in transmission power (the power necessary to accomplish the desired reach of the signal is significantly smaller than in the conventional - type transmitters), and cancellation of one sideband makes the signal have its spectrum two times narrower, allowing twice as many transmitters as usual to be placed into the same bandwidth.
FM / AM Regenerative Receiver
The following is a design for a separately quench super regen receiver I first tried in early 1992. It worked far better than any other solid state design, so I built a portable version for use during my commuting from the Blue Mountains to Sydney on the train. Running off 10x AA nicads, this gave me a weeks listening before recharging. Only recently, I submitted the basic circuit to Silicon Chip, whereupon it was published in the April 2003 issue (and I won a nice true RMS meter as a result). My portable version differs in that I use varicap tuning, the output transformer has a 1K primary, and the output transistor is a BC108, with bias components to suit. It also uses the headphone lead for the aerial.