Ramsey Electronics FX-440 Manual page 134

,Stage
TX:
Transmitter Buffer, Driver and Final
The transmitter section, Q10, Q9 and QB, is conventional UHF RF
circuitry that has proven quite reliable in Ramsey transceivers. Just a few
circuit notes are in order.
Transistor Q10, the transmit Buffer, amplifies the VCO output from C56
to about 10 milliwatts, quite sufficient for checking modulation and PLL
alignment in transmit mode as soon as this stage is built. Operating bias
is supplied by the PLL lock detect voltage from USB through R110. If the
PLL unlocks, Q10 does not operate, preventing the radiation of
out-of-band signals.
The MRF559 Driver, Q9, amplifies the output of Q10 to drive QB to its full
rated output. QB, the popular MRF630 or its equivalent, has physical
characteristics that the builder should understand. Many RF transistors of
this style have the Collector lead common to the case. Through
sophisticated insulating technology, the Emitter lead is common to the
case. There is significantly better gain because there is no emitter lead
length to speak of. This relatively small transistor package can handle
large power dissipation IF the case is properly soldered to the
groundplane of the PC board as detailed in
the
assembly instructions.
The transistor is fully intended by the manufacturer to be heat-sunk in
this manner: don't worry about soldering heat damaging the device.
An unusual set of parts are the C73,75A,75B, SMT "chip capacitors".
They are installed on the solder side of the board, and their leadless
design is what allows Q9 to deliver such exceptional gain.
DO NOT install any transmitter parts without at least reading over the
assembly details first and the reasons for the sequence that we have
recommended. The PIN T-R diodes D7, D6 and D2 are discussed in
section DR. In brief review, D7 passes RF to J3 during transmit while D2
and D6 protect the receiver RF input. The antenna input is designed for a
50 ohm resonant antenna C84 and C7 4 are tuned for maximum RF
output (2 to 4 watts). These adjustments are part of final transmitter
alignment.
Maximum RF output depends critically on following the coil winding
instructions EXACTLY in Stage "TC".
Stage TX:
TRANSMITTER SECTION ASSEMBLY:
Install the components in the order recommended and DO NOT under
any circumstances connect DC power to the unit unless instructed to do
so at a particular point. The following assembly
ste~
presume that Stage
"TC" (RF coil preparation) was done. Refer to "TC if you have any
Assm. 72 FX-440