Shortwave SW Transmitter Based IC BEL1895

Here the SW transmitter circuit based on IC BEL1895. This particular transmitter circuit works in shortwave HF band (6 MHz to 15 MHz), and can be applied for shortrange communication and for educational purposes.

Shortwave (SW) Transmitter Circuit diagram :

The circuit is composed of a mic amplifier circuit, a variable frequency oscillator, and modulation amplifier stages. Transistor T1 (BF195) is put to use as a simple RF oscillator. Resistors R6 and R7 determine base bias, while resistor R9 is utilized for stability. Feedback is provided by 150pF capacitor C11 to maintain oscillations. The primary of shortwave oscillator coil and variable condenser VC1 (365pF, 1/2J gang) form the frequency determining network.

By altering the coil inductance or the capacitance of gang condenser, the frequency of oscillation can be modified. The carrier RF signal from the oscillator is inductively coupled through the secondary of transformer X1 to the next RF amplifier-cum-modulation stage assembled around transistor T2 that is run in class ‘A’ mode. Audio signal from the audio amplifier assembled around IC BEL1895 is coupled to the emitter of transistor 2N2222 (T2) for RF modulation.

IC BEL1895 is a monolithic audio power amplifier intendeded for sensitive AM radio applications. It can deliver 1W power to 4 ohms at 9V power supply, with low distortion and noise characteristics. Since the amplifier’s voltage gain is of the order of 600, the signal from condenser mic can be straightly linked to its input without any amplification.

The transmitter’s stability is managed by the quality of the tuned circuit parts as well as the degree of regulation of the supply voltage. A 9V regulated power source is required. RF output to the aerial consists of harmonics, because transistor T2 doesn’t have tuned coil in its collector circuit. However, for short-range communication, it does not create any trouble. The harmonic content of the output may be lowered by means of a high-Q L-C filter or resonant L-C traps tuned to each of the prominent harmonics. The power output of this transmitter is about 100 milliwatts.

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SW Converter for Digital AM Car Radio

This circuit is purposely offered with many bathroomse ends (not actually, of course) to stimulate experimenting with RF circuitry at a small outlay. Looking at the circuit diagram you could additionally recognize a modified model of the SW Converter for AM Radios described in different situations in that issue. The changes had been necessary to make the circuit compatible with a digital quite than analogue AM car radio. The main distinction between digital AM radios and their all-analogue predecessors is that tuning is in 9 kHz (some-times 4.5 kHz steps) in compliance with the international frequency allocation for the band. Obviously, that exact step dimension, fascinating as it can be on MW, is a stumbling block if you want to use a digital AM receiver together with a frequency step-up converter for SW, where chaos reigns and there isn't any fastened step dimension. The first try was once to make the crystal oscillator variable through about 5 kHz each and every approach.

 

Circuit diagram :

SW Converter for Digital AM Car Radio Circuit Diagram

 

Unfortunately, regardless of serious efforts, the crystal could not be pulled more than 1 or 2 kHz so some different resolution had to be found. After finding out the NE/SA602/612 informationsheet, it was once found that a variable LC based totally oscillator was once one of the best different. The circuit labored after winding a resonant LC circuit and including a zero.1 µF sequence capacitor to dam the DC element on pin 6 of the NE602 (612). When the tuning used to be found to be a bit sharp with the original capacitor, a simple bandspread (or advantageous tuning) characteristic used to be added via shunting the LC resonant circuit with a lightly loaded 365 pF tuning capacitor (C10) which, like the principle tuning counterpart, C8, was once ratted from an outdated transistor radio. The tuning coil, L1, consists of 8 to 10 turns of 0.6-0.8mm dia. enamelled copper wire (ECW) on a 6-8 mm dia. former with out a core. With this coil, frequency protection shall be from about 4 MHz to 12 MHz or so. Details on Tr1 may be discovered in the referring article.

 

Note that no tuning capacitor is used on the secondary — the input stray capacitance of the NE602 (612) does the trick. A BFO (beat frequency oscillator) was once delivered to let SSB (single sideband) signals to be received. The BFO built round T1 is inconspicuous, has a heap of output and that is steady enough to automobilery an SSB signal for a few minutes with out adjustment. The BFO frequency is tuned with C3. Tr2 is a ready-made four55 kHz IF transformer whose inner capacitor was once first crushed after which eliminated with pliers. When S2 is closed the BFO output sign is solely superimposed on the NE602 (612) IF output to the MW radio. The converter will have to be built into a steel box for shielding. If you in finding that the BFO provides too much output, disconnect it as steered in the circuit diagram and let stray coupling do the work. Sensitivity, even on a 1-metre size of automotive radio aerial, is quite superb. Bearing in mind that many of the main international SW broadcasting stations like Radio NHK Japan, Moscow, BBC and many others.) generate enough power to ensure that you are going to hear them, it's nonetheless kind of thrilling to pay attention to such signals for the first time in your automobile radio. 

http://www.ecircuitslab.com/2012/02/sw-converter-for-digital-am-car-radio.html

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Shortwave SW Transmitter Based IC BEL1895

Here the SW transmitter circuit based on IC BEL1895. This particular transmitter circuit works in shortwave HF band (6 MHz to 15 MHz), and can be applied for shortrange communication and for educational purposes.

Shortwave (SW) Transmitter Circuit diagram :

The circuit is composed of a mic amplifier circuit, a variable frequency oscillator, and modulation amplifier stages. Transistor T1 (BF195) is put to use as a simple RF oscillator. Resistors R6 and R7 determine base bias, while resistor R9 is utilized for stability. Feedback is provided by 150pF capacitor C11 to maintain oscillations. The primary of shortwave oscillator coil and variable condenser VC1 (365pF, 1/2J gang) form the frequency determining network.

By altering the coil inductance or the capacitance of gang condenser, the frequency of oscillation can be modified. The carrier RF signal from the oscillator is inductively coupled through the secondary of transformer X1 to the next RF amplifier-cum-modulation stage assembled around transistor T2 that is run in class ‘A’ mode. Audio signal from the audio amplifier assembled around IC BEL1895 is coupled to the emitter of transistor 2N2222 (T2) for RF modulation.

IC BEL1895 is a monolithic audio power amplifier intendeded for sensitive AM radio applications. It can deliver 1W power to 4 ohms at 9V power supply, with low distortion and noise characteristics. Since the amplifier’s voltage gain is of the order of 600, the signal from condenser mic can be straightly linked to its input without any amplification.

The transmitter’s stability is managed by the quality of the tuned circuit parts as well as the degree of regulation of the supply voltage. A 9V regulated power source is required. RF output to the aerial consists of harmonics, because transistor T2 doesn’t have tuned coil in its collector circuit. However, for short-range communication, it does not create any trouble. The harmonic content of the output may be lowered by means of a high-Q L-C filter or resonant L-C traps tuned to each of the prominent harmonics. The power output of this transmitter is about 100 milliwatts.

Read More..