//Continued from: [[5V (USB) DSB DC RX (Pt1)]]//
Over the past few days I have had to come to terms with a simple fact, it is very hard to make a transistor HF Power Amplifier work at 5V efficiently. I can make it work, but then there are issues of matching the high current output, and it goes on… If I do want this to run of 5V in the final design, I will need a voltage up converter; this may give me more flexibility as I can then run a PA more efficiently at 24 or even 28v.
[img[http://img.mabsoft.org/m/IMG_20160122_092305575.jpg]] //Add a DDS and Arduino 2016-01-21//
Here I am testing it beside the FT817 to see if I can hear the DDS carrier, and the receiver can hear a signal. I did a lot of playing with the gain of the LM386 here, but it seems the high gain mode just won’t work consistently, with the audio amp constantly oscillating, overdriving and clipping audio. I’m assuming the issue here is some sort of mismatch between the SA612 and the LM386, or the SA612 is doing a good enough job amplifying the incoming signal.
[img[http://img.mabsoft.org/m/IMG_20160122_220255.jpg]] //Now with Arduino Nano clone, hooked up to an antenna, I can hear stuff!//
Yup, it works. Initially I heard a VK5 station who was only a few km away, so my first thought was about gain and the problems with the LM386. About an hour later I caught the end of the DX net, and a VK7 & VK4 taking to each other. I was so excited I forgot to write down the callsigns and look up locations. But even from this location with this antenna, this is rare, not even the FT-857D has done this well, maybe I just got a good time where neighbours had turned off their noisy appliances!
This version also has up and down tuning, two buttons that runs up and down in 1kHz increments from 7150kHz.
Another note is on input filtering, I can hear at least 3 local broadcast stations wherever I tune the radio. Time for a high pass filter.
//Continued: [[5V/12V DSB DDS DC RX (Pt3)]]//