The Freedom7 HF Transceiver has yet to receive or transmit however, I’m making progress and I’m designing components in a modular fashion. The image here below in this post shows my solution to Receive and Transmit switching. The screw terminal block on the side of the PCB has 4 connections for 5v, ground, receive digital, and transmit digital. The two RX/TX connections will be HIGH/LOW or LOW/HIGH respectively at any time.
This is but one module called RX/TX Switching and it’s made to perform one task. This module will act as a stand-alone design that could be improved and replaced with a better module at a later time. I will share that I’ve done one PCB earlier e.g. with no screw terminals but later realized that solder pads were not supportive of a true modular concept. This is a work in progress. Future PCBs will be easy to implement and change out. Also note that a production-ready version of Freedom7 will probably be much different in high-level design. These modules will support my Freedom7 working prototype.
I’ll share an early schematic but talk to the upper part of this. There are two MOSFETs that act as a 28v switch. Where did we get 28 volts you may ask? Well, I used a boost regulator MT3608 that converts 5v to 28v, with the help of a variable potentiometer. Either side will be biased at any time, i.e. the 1N5711 Schottky diode will be reverse-biased with 28v at the cathode side of the diode, thereby greatly blocking the flow of RF. This is not perfect but the small leakage that can occur is also choked with a 10 microhenry inductor and 3.3k resistor. I have calculations on these values. P.S. I also should call the digital control inputs just RX_BIAS and TX_BIAS.
My About page provides the background of my project, the Freedom7 HF Transceiver.
If this story resonates, comments are welcome. You can also reach me at david [at] kr4bad-dot-communications. no com
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73 KR4BAD David
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