Ramsey Electronics QAMP20 Your Power Supply And Rf Output Power, Verifying Transmitter Rf Output

4.Temporarily install a jumper from the collector of Q3 to ground.

5.Apply power to the amplifier but do not turn on the transmitter. Measure the current drawn by the amplifier and slowly rotate the bias pot, R4, clockwise until you reach a reading of ¼ amp. Do not allow the current to rise above ½ amp. If you cannot adjust or reduce the current, disconnect the power supply and consult the troubleshooting hints section. The voltage at TP1 should be about 3.2 to 3.5 volts.

6.Turn off power. Disconnect jumper from Q3 to ground.

7.Connect the QRP transmitter to the input of the amplifier. Key the transmitter. You should hear the T-R relay click and see amplified power output. Measure the DC current draw; it should be in the 1 to 3 amp range depending upon power output. Unkey the transmitter. The relay should drop out and the current should drop back down to ¼ amp.

This completes the testing of your QRP power amplifier. The PC board should be mounted into a protective enclosure to guard against accidental contact. The Ramsey CQAMP case set provides an ideal perfectly sized cabinet that matches all other Ramsey kits.

Study the following sections on DC power supply and RF power considerations. Operate your transmitter with good amateur practice.

YOUR POWER SUPPLY AND RF OUTPUT POWER

For optimum performance, one or two volts of extra DC supply power can make quite a difference in any RF power amplifier. For example, two lantern batteries in series, or 8 D cells, will obviously provide about 12 volts with sufficient current capability for casual operating. For maximum RF output power, use a supply of 13 to 14 volts DC. The easiest method is to place two fresh D cells in series with your power source if a full 13.6 - 15 volts DC is not available. Be aware that batteries are not the optimum power source, especially if you are prone to long QSOs! A word of caution concerning wall plug style AC adapter power supplies: They are not suitable for operation of your amplifier due to their poor regulation, AC ripple content, and RFI susceptibility.

With 1 watt of drive and a supply voltage in the 11-12 volt range, you can expect a 1 to 2 amp current draw and about 10 watts of RF output power. With a solid 13 to 14 volt supply, you can expect about 2 to 3 amps current draw and up to 10 or 12 watts of RF output power. With 2 watts of RF drive, expect up to 20 watts RF output!

VERIFYING TRANSMITTER RF OUTPUT

The most important thing to know is whether your transmitter is delivering some measurable and reassuring level of RF power. Then you can continue on to adding the QRP amplifier and checking out the whole set-up.

QAMP20 • 13