Broadcast Hardware

The simple switch shown so far can be used in simple audio applications. Here is a simple “all-master” intercom circuit that steers an audio amplifier towards one of several distant receivers. All units shown are identical and are connected to the same multipair cable. One battery powers all units. You press the button corresponding to the station to whom you want to talk. When any “TALK” switch is pressed, the horisontal diodes feed 12v DC power from the cable to the MIC amplifier 741. Here you can see how diodes are used to combine the DC to a common source. This prevents power being ... Read Full Story

Now this is an interesting amplifier and can be built for almost any AF power level you want from or more. I will give you suitable examples for the 30 – 100watts version. RV must be set to minimum resistance before application of power. To set up the amplifier, advance RV SLOWLY whilst monitoring the DC current through R7. Set RV for about 40mA. If you have a digital voltmeter then you can adjust for 8mV accross R7 and R8. If this standing current becomes too high (more than 80mA without a signal) when the transistors become warm then add a 1K0 thermistor accross ... Read Full Story

Here's a broadband FM RF amplifier using 2SC1971 VHF power transistor. The RF Amplifier PCB layout designed for FM broadband 88-108 MHz using microstripline technique. This 8W RF amplifier circuit provides an appropriate power boost with an input of 500 mW. RF Amplifier PCB The PCB outline is 77 x 56 mm use FR-4 double sided photoresist epoxy pcb material for best results. RF Amplifier Construction All SMD components are 1206 types. Connect the bottom layer (groundplane) on several points (through via's) with the top layer of the PCB. Note : CuL = magnetwire, enameled copper wire - 1 mm equals approx. to #18 ... Read Full Story

This is a RF power amplifier design using 2SC2782 bipolar transistors in a tuned class C circuit. The amplifier can be driven to full power with less than 1 watt driving power, so that a large gain margin results in this FM transmitter . To obtain stability in this rf amplifier , I employed several techniques, such as placing the resonances of base and collector chokes far apart, damping the chokes with resistors, using RC combinations for absorption of unwanted frequencies, using feedtrough capacitors for bypassing on the board, etc. It took some tweaking, but the amplifier ended up unconditionally stable. RF Amplifier Low-pass ... Read Full Story

Here's an interesting S-AV10H TOSHIBA RF Power Amplifier Module circuit. It can deliver over 14W with as low as 100-200mW input power. The system is tuned for 50 ohm input and output. The frequency can be 150-175MHz. This is how the Module looks like. To the left is the power input pin. Then comes power control, main power line and to the right is the output power. As you see there are quit many components inside and both input and output are matched to 50 ohm. RF Power Amplifier Module S-AV10H TOSHIBA Schematic The main part of this project is an oscillator which you ... Read Full Story