Bi-Directional Amplifier Stage
This stage is one of my designs that came into being about 7 or 8 years ago and has been used in the KWM-4 as well as about a half dozen of the current rigs. The deisgn has been ported over to software that can be cut on my CNC mill. So whenever I need another board I just fire the CNC, load the G Code and boom in a few minutes I have a new board. I have also built this circuit using the MeSquares from W1REX (Rex) which also works very nicely.
The feature of this design is that it uses basic readily available parts. There are three communications type relays used for the swithcing. In the normally closed position of the relays the signal from the antenna is routed through the receive side of the bi-directional amplifier on to the band pass filter. On transmit the relays are shifted from the NC to the NO position and the signal passes through the half of the circuit used on transmit and the 3rd relay now connects to the additional stages of the transmit chain. Both circuits are iodentical and are good for about 10 dB of gain, whihc is adjustable. Noteworthy is that both amps see a constant 50 Ohm load on the output which helps with the stability. In practice itis best to have the gains at about 2/3 of max. You will find that there is a real boost of the receive signal --but you are also boosting the noise! On the transmit side you will find that about 2/3 gain is about the max you need to drive the follow on amp. The 2N3904 in the TO-92 version has a device dissipation of aout 625 Milli-watts. So it is easy to get 200-300 MW out of a 2N3904. The relays used are the Omron G5V-1 series.
A bit of tribal knowledge about wiring standards. In the 2nd photo you will see mnostly yellow wires and but one orange wire. The Orange is used for receive cicruits and the yellow for transmit. On this board the only thin powered on receive is the 2N3904 amp that is used as the receiver RF amp. The yellow wiring powers the three relays and the 2N3904 used on the transmit side. The squares are 1/4 inch on a side and you need a 3X4 pad for each amp.