Ramsey Electronics FZ-146 Specifications download pdf (Page 129)

FX-146 • 129

Stage TX: Transmitter Buffer, Driver and Final

The transmitter section, Q10, Q9 and Q8, is conventional VHF 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 U5B through R110. If the PLL

unlocks, Q10 does not operate, preventing the radiation of out-of-band

signals.

The 2N3866 Driver, Q9, amplifies the output of Q10 to drive Q8 to its full

rated output. Q8, the popular MRF237 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 part is C75, a SMT "chip capacitor". It is installed on the solder

side of the board, and its 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 C74 are tuned for maximum RF output (3 to 5

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 steps presume that Stage "TC" (RF

coil and choke preparation) was done. Refer to "TC" if you have any

question on these parts, which also may be built up as you proceed.

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Ramsey Electronics FZ-146 Specifications Page 129