Added up-to-date PCB photos Changed default volume setting.

QCX-SSB.ino

@@ -1259,7 +1259,7 @@ inline int16_t ssb(int16_t in)
 
 #define MIC_ATTEN  0  // 0*6dB attenuation (note that the LSB bits are quite noisy)
 volatile int8_t mox = 0;
-volatile int8_t volume = 8;
+volatile int8_t volume = 12;
 
 // This is the ADC ISR, issued with sample-rate via timer1 compb interrupt.
 // It performs in real-time the ADC sampling, calculation of SSB phase-differences, calculation of SI5351 frequency registers and send the registers to SI5351 over I2C.

README.md

@@ -3,7 +3,7 @@ This is a simple and experimental modification that transforms a [QCX] into a (C
 
 The SSB transmit-stage is implemented entirely in digital and software-based manner: at the heart the ATMEGA328P is sampling the input-audio and reconstructing a SSB-signal by controlling the SI5351 PLL phase (through tiny frequency changes over 800kbit/s I2C) and controlling the PA Power (through PWM on the key-shaping circuit). In this way a highly power-efficient class-E driven SSB-signal can be realized; a PWM driven class-E design keeps the SSB transceiver simple, tiny, cool, power-efficient and low-cost (ie. no need for power-inefficient and complex linear amplifier with bulky heat-sink as often is seen in SSB transceivers).
 
-For the receiver, a large portion of the original QCX circuit has been removed and implemented in digital manner (software): the ATMEGA328P is now implementing the 90 degree phase shift circuit, the (CW/SSB) filter circuit and the audio amplifier circuit (now a class-D amplifier). This has simplified the QCX circuit a lot (50% less components needed), and there are a number of advantages and features: there is no longer a need for an alignment procedure due to the very accurate 90 degree Hilbert phase shifter; and there are now adjustable IF DSP filters for CW and SSB; and there is an AGC and there is a noise-reducing DSP signal conditioning function and there are three indepent built-in attenuators in the analog front-end which helps utilizing the full dynamic range. The speaker is directly connected and driven by the ATMEGA. A digital mixer with narrow low-pass window (2 kHz), steep roll-off (-45dB/decade) combined with an oversampling and decimating ADC are responsible for a processing gain, dynamic range and alias rejection sufficient to handle weak and strong signal conditions (e.g. contests or listening on 40m just next to broadcasting band).  
+For the receiver, a large portion of the original QCX circuit has been removed and implemented in digital manner (software): the ATMEGA328P is now implementing the 90 degree phase shift circuit, the (CW/SSB) filter circuit and the audio amplifier circuit (now a class-D amplifier). This has simplified the QCX circuit a lot (50% less components needed), and there are a number of advantages and features: there is no longer a need for an alignment procedure due to the very accurate 90 degree Hilbert phase shifter; and there are now adjustable IF DSP filters for CW and SSB; and there is an AGC and there is a noise-reducing DSP signal conditioning function and there are three indepent built-in attenuators in the analog front-end which helps utilizing the full dynamic range. The speaker is directly connected and driven by the ATMEGA. A digital mixer with narrow low-pass window (2 kHz), steep roll-off (-45dB/decade) combined with an oversampling and decimating ADC are responsible for a processing gain, dynamic range and alias rejection sufficient to handle weak and strong signal conditions (e.g. contests or listening on 40m just next to broadcasting band).
 
 This experiment is created to try out what is can be achieved with minimal hardware while moving complexity towards software; here the approach followed is to simplify the design where possible while keep a reasonable performance. The result is a cheap, easy to build, versatile QRP SSB transceiver that actually is quite suitable for making QSOs (even in contest situations), however due to the experimental nature some parts are still in progress and hence limited. Feel free to try it out or to experiment with this sketch, let me know your thoughts or contribute here: https://github.com/threeme3/QCX-SSB  There is a forum discussion on the topic here: [QRPLabs Forum]
 
@@ -53,7 +53,7 @@ This modification consists of a few component changes and wires:
 - **To simplify things, 78 components are no longer needed** (and you could omit them on an unbuilt QCX): IC6-10,R11-40,43,55,R59-64,C1,5,8,C9-28,C31,52,53,L1-3,D5,Q7,T1,JP1/DVM/FREQ.
 - **SDR receiver**: change R7,10(82k); C4,C7(1nF), remove R11,12,14,15,17,27,29,59,IC10; wire IC2(pin15) to IC10(pin1); C39(R27/R29 side) to IC5(pin1); C40(IC10 side) to IC5(pin7), and disconnect R50(5V side) and R52(5V side) and wire both to IC2(pin21). Note on a QCX Rev5 you need to restore/insert manually the missing R49,50,53,C39 (see schematic). If you want to build-up the original (analog) QCX receiver, you can skip this step and insert a SPDT switch between C21(+ side) and IC9(pin1) for CW and R27(pin2) for SSB (as was done in [original QCX-SSB modification]).
 - **SSB transmitter**: change D4,R56 (10k); R58 (.22uF); C32 (10uF), remove C31; wire IC2(pin21) to pin R57(side DVM-pin3); wire IC2(pin20) to DVM(pin2); wire IC2(pin18) to junction D4-C42-R58; install a microphone to tip (+ of electret) and sleeve GND of paddle-jack; PTT-switch to ring and sleeve ([X1M-mic]).
-- **Multiband support**: remove C1,5,8,R64,T1; at T1 landing pattern (see [QCX Assembly instruction] T1) install R (1k) over 6-8; R (1k) over 3-4; C (10nF) over 4-8; C30 (30pF); L4 (1uH/16t); replace C25-28,L1-L3 with LPFs for different bands (e.g. [QRPLabs Low Pass Filter kit]).
+- **Multiband support**: remove C1,5,8,R64,T1; at T1 landing pattern (see [QCX Assembly instruction] T1) install R (1k) over 6-8; R (1k) over 3-4; C (10nF) over 4-8; change C30 (30pF); L4 (1uH/16t); replace C25-28,L1-L3 with LPFs for different bands (e.g. [QRPLabs Low Pass Filter kit]).
 
 **Firmware**: download [latest released hex file] and install with [standard QCX firmware upload procedure] (see also <sup>[note 1](#note1)</sup>).
 
@@ -63,6 +63,9 @@ Below the layout with components marked in red that needs to be changed; gray co
 Below the wires that needs to be installed on the bottom PCB. Note that a circle represents resistor R50/R52 that is in series with the wire and the pad at which the circle is drawn (the resistor is no longer connected to its original neighbour pad and its probably the best to place this wiring and resistor at the components side):
 ![pcb](pcb.png)
 
+See here the resulting modification (includes PA bias mod <sup>[note 3](#note3)</sup>, does not include LPFs):
+![](pcb-top.png)
+![](pcb-bottom.png)
 
 ## Operation:
 Currently, the following functions have been assigned to shortcut buttons (L=left, E=encoder, R=right) and menu-items: