The basic idea for making this RF Booster amplifier is to boost the performance of my TJ-4A You-Kits 10W low power transceiver with components and circuit boards available in my shack.
RF Booster is ideal for enhancing the performance of low power transceivers (5 to 10 watts) commonly available in the market. It increases the O/P power of the rig to about 100W and increases the receiver sensitivity significantly, thus making the transceiver super hot!
Two essential building block of the booster are:
a) 100W Linear Power Amplifier for transmitter and
b) Tunable RF Pre-amplifier for receiver.
Rest of the circuit includes switching of input / output relays, selection of frequency bands, RF gain control, sensing of forward / reflected power, interfacing with low power rig, etc.
Tunable RF Pre-amplifier covering 40, 20, 15 & 10M bands with gain control has already been covered earlier on this site.
100W linear power amplifier has been taken from an old non-functional FT 757 transceiver. The chassis modified suitably with new front and back panels. The block diagram of Tunable RF pre-amp for 4-bands, relays for switching and interface circuits is as shown in the figure 1.
RLY1 has been provided for additional safety of tunable pre-amp. Its function is as follows:
In the absence of RLY1, the RF pre-amp is connected to the input through N.C. connection of RLY3. In the event when Booster power supply is not yet switched on and the driver transceiver goes into transmission mode, the output power of low power transceiver gets dissipated on the output side of RF Pre-amp, thus distroying it immediately. Through addition of RLY1, until the booster power supply is switched on, the pre-amp is protected because of N.O. connection of RLY1.
Fig. 1