Once we’re through with this section, we should have a working receiver. We talked in the last section about how the received signals get from the antenna, through the receive mixer, and then through the crystal filter. What should be left is a very narrow range of frequencies containing our desired signal at 9 MHz. The product detector, U1, mixes that input with the signal from the BFO (just a bit higher than 9 MHz) to convert them to audio frequencies. After that, it’s simply a matter of amplifying the audio so we can actually hear it.
There’s a lot of parts to install in this section:
C34, C40, C44, C51, C57, C65, C68
Q14, Q16, Q18
R27, R30, R31, R32, R34, R38, R41, R43, R44, R45
The Survivor instructions “Theory of operation” section describes the operation of this part of the circuit quite well, and I’m not going to try to repeat it here, other than to say that much of this circuit is devoted to the operation of automatic gain control (AGC). AGC, of course, is what prevents really loud signals from blasting our ears unexpectedly, and we appreciate that, right?
At this point we should have a working receiver. This is the point where you really need to be able to connect the tuning caps, the volume control, headphones, and the antenna to the board so you can test. The digital dial is very handy at this step, too. So, get everything connected up as described in the Survivor instructions, and connect the digital dial to the BFO test point on the board (right next to R37). Power up the board, set the tuning cap to about the middle of its tuning range, and adjust T3 for maximum audio. This effectively sets it to be most sensitive in the middle of the tuning range. Next, the BFO trimmer cap CT1 needs to be adjusted. Start by adjusting it so that the digital dial reads about 9.001 MHz. Then find a signal on the air and tune it in. See if it sounds like what you’d expect from a SSB signal. If not, adjust CT1 a little bit and retune the signal. Keep at it until the signals sound best. Keep in mind, though, that you won’t want to stray more than a couple hundred Hz from 9.001 MHz. You’ll see why when we finish up with the transmitter PA and get everything adjusted right.