QAMP20 • 13
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.
Summary of Contents for QAMP20
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