Maximizing RF Power Output

KB4ZGC on how to make a highly accurate yet inexpensive dummy load and wattmeter capable of showing 1/10-watt differences in RF power. If you use a wattmeter characterized for the HF frequency region, it will not give accurate results at the much higher two meter frequencies, although it will be quite adequate for go/no-go testing.

The simplest way to ensure maximum reasonable power output without component damage is to run the DC voltage in the 13 to 14 volt range, observing a maximum limit of +15VDC. Typically, an automobile power source is 13.6 volts when the engine is running, and most mobile rigs are specified at this voltage level.

IMPORTANT NOTE: If you are experimenting with this transmitter and see a sudden and massive increase in power output and DC current, you have not reached the promised land or created a 100 watt amplifier! Sudden surges like that are a sure sign of amplifier self-oscillation. Kill the DC power supply immediately because your RF power transistors are heading to self-destruction while probably interfering with every TV set in the neighborhood! A poorly matched antenna along with higher supply voltages is usually responsible for this occurring. Any prolonged "parasitic" emissions may also overheat and destroy other components in the amplifier.

TROUBLESHOOTING HINTS

The QRP power amplifier is very straight forward and simple to troubleshoot. When beginning to track down a problem, use some common sense to narrow down your search area.

If the amplifier is not keying upon application of RF power, check to see if the T- R relay circuitry is operating. A quick read-over of the theory of operation tells us the diode detector senses the RF and a pair of transistors amplifies the signal to activate the T-R relay. Proper logic tells us to: 1) First check and see if RF is getting to the diodes; 2) see if they are detecting RF; 3) see if the transistors are driving the relay. Proper procedure is to take just one part of the circuit at a time and follow the signal through.

If the amplifier does not amplify, check to see if RF is flowing through to transformer T2 and across to the RF power transistors. Amplified output should appear at output transformer T1 and then on to the low pass filter. Remember that RF enters and exits through relay contacts on K1.

Do the transistors get too hot? Do they get hot without amplifying? Things to

QAMP-40 • 15

QAMP40 specifications

The Ramsey Electronics QAMP40 represents a notable advancement in the world of audio amplification, catering to both DIY enthusiasts and professional users alike. This compact, yet powerful audio amplifier is designed for high performance while maintaining ease of use and versatility, making it an excellent choice for various applications, from home audio systems to automotive setups.

One of the main features of the QAMP40 is its robust power output, delivering 40 watts per channel into an 8-ohm load. This capability allows it to drive a wide range of speakers effectively, producing clear and dynamic sound. Users can enjoy enhanced audio quality whether for casual listening, home theater setups, or more demanding audio applications.

The QAMP40 utilizes a Class D amplifier topology, known for its efficiency and minimized heat generation compared to traditional analog amplifiers. This technology not only ensures that the amplifier can operate quietly without the need for extensive heat dissipation measures but also allows longer play times on battery-operated systems. The compact form factor makes it easy to integrate into smaller spaces where traditional amplifiers might struggle.

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In summary, the Ramsey Electronics QAMP40 is an excellent audio amplification solution that combines compact design, powerful output, and advanced technology. Its Class D architecture, versatile inputs, and user-friendly interface make it suitable for a wide range of applications. Whether you are an audio professional seeking a powerful amplifier or a hobbyist looking to enhance your sound system, the QAMP40 offers a compelling blend of performance and convenience that can meet diverse audio needs. Invest in the QAMP40 to elevate your listening experience today.