Receiver & Transmitter RF Filter:
The easiest way to tune the RF
input filter is to peak C-14 and
C-18 in receive mode for loudest
signal while listening to a
relatively constant carrier from
your antenna. This provides both
receive and transmit mode
alignment of this filter.
Transmitter Driver
There is no tuning involved in adjusting the transmitter drivers section, but you do have to set
the bias adjustment. Drive level adjustment will be done in the RF PA alignment section.
1. Connect a 2 to 3 ampere DC ammeter in series with the +12 volt line to your
transceiver.
2. Disconnect the microphone or short it's output so there will be no audio entering
the microphone amplifier.
3. Key the transmitter and note the idling current. Unkey the transmitter.
4. Key the transmitter and slowly adjust R-8 for an increase of 20 ma. Unkey the
transmitter.
NOTE: You can alternatively monitor the voltage drop across R7 to
measure idling current in the PA driver amplifier. This is a 2.2
ohm resistor so 20 ma of current would equal a voltage drop
of (0.02 X 2.2 =) 0.044 volts.
RF PA
There are no tuning adjustments in the RF PA section, but you do have to adjust the idling
current on the two IRF510 MOSFET devices and then set the drive level for best output
linearity. To do this you will need an ammeter with a capability of reading 2.5 or 3 amperes.
PA Idling Current Adjustment:
1. Connect an ammeter in series with the power lead that supplies 12 volts to your
transceiver.
2. Disconnect the microphone, or short it's audio output so that no audio is going to
the microphone amplifier.
3. Key the transmitter (use a dummy load please) and note the idling current.
Unkey the transmitter.
4. Key the transmitter and slowly adjust R-91 until this current increases by 50 ma.
Unkey your transmitter. Note the new idling current.
5. Key the transmitter and slowly adjust R-2 until the idling current increases by
another 50 ma. Unkey the transmitter.
Drive Level Adjustment:
RF output level can be adjusted for up to 20 watts in most transceivers, but
compression of the RF envelope usually starts at about 10 watts. To preserve
output linearity you should set the RF output level no higher than the point where
