diff --git a/QCX-SSB.ino b/QCX-SSB.ino
index 2944f42..3bd2ed2 100644
--- a/QCX-SSB.ino
+++ b/QCX-SSB.ino
@@ -2,7 +2,7 @@
 //
 // https://github.com/threeme3/QCX-SSB
 
-#define VERSION   "1.01j"
+#define VERSION   "1.01k"
 
 // QCX pin defintion
 #define LCD_D4  0
@@ -181,6 +181,7 @@ public:
   #define SI_CLK_SRC_MS 0b00001100
   #define SI_CLK_IDRV_8MA 0b00000011
   #define SI_CLK_INV 0b00010000
+  #define SI_PLL_FREQ 400000000  //900000000
   #define SI_XTAL_FREQ 27004900  //myqcx1:27003847 myqcx2:27004900  Measured crystal frequency of XTAL2 for CL = 10pF (default), calibrate your QCX 27MHz crystal frequency here
 
   volatile uint8_t prev_divider;
@@ -292,11 +293,11 @@ public:
   }
   void freq(uint32_t freq, uint8_t i, uint8_t q)
   { // Fout = Fvco / (R * [MSx_a + MSx_b/MSx_c]),  Fvco = Fxtal * [MSPLLx_a + MSPLLx_b/MSPLLx_c]; MSx as integer reduce spur
-    uint8_t r_div = (freq > 4000000) ? 1 : (freq > 400000) ? 32 : 128; // helps divider to be in range
+    uint8_t r_div = (freq > (SI_PLL_FREQ/1800/1)) ? 1 : (freq > (SI_PLL_FREQ/1800/32)) ? 32 : 128; // helps divider to be in range
     freq *= r_div;  // take r_div into account, now freq is in the range 1MHz to 150MHz
     raw_freq = freq;   // cache frequency generated by PLL and MS stages (excluding R divider stage); used by freq_calc_fast()
   
-    divider = 900000000 / freq;  // Calculate the division ratio. 900,000,000 is the maximum internal PLL freq (official range 600..900MHz but can be pushed to 300MHz..~1200Mhz)
+    divider = SI_PLL_FREQ / freq;  // Calculate the division ratio. 900,000,000 is the maximum internal PLL freq (official range 600..900MHz but can be pushed to 300MHz..~1200Mhz)
     if(divider % 2) divider--;  // divider in range 8.. 900 (including 4,6 for integer mode), even numbers preferred. Note that uint8 datatype is used, so 254 is upper limit
     if( (divider * (freq - 5000) / SI_XTAL_FREQ) != (divider * (freq + 5000) / SI_XTAL_FREQ) ) divider -= 2; // Test if multiplier remains same for freq deviation +/- 5kHz, if not use different divider to make same
     /*int32_t*/ pll_freq = divider * freq; // Calculate the pll_freq: the divider * desired output freq
@@ -376,7 +377,8 @@ volatile bool vox_enable = false;
 enum dsp_cap_t { ANALOG, DSP, SDR };
 static uint8_t dsp_cap = 0;
 static uint8_t ssb_cap = 0;
-volatile bool att_enable = false;
+volatile uint8_t att = 0;
+const char* att_label[] = { "0dB", "-6dB", "-20dB", "-26dB" };
 //#define PROFILING  1
 #ifdef PROFILING
 volatile uint32_t numSamples = 0;
@@ -391,7 +393,7 @@ inline void txen(bool en)
       si5351.SendRegister(SI_CLK_OE, 0b11111011); // CLK2_EN=1, CLK1_EN,CLK0_EN=0
       digitalWrite(RX, LOW);  // TX
   } else {
-      digitalWrite(RX, !(att_enable)); // RX (enable RX when attenuator not on)
+      digitalWrite(RX, !(att == 2)); // RX (enable RX when attenuator not on)
       si5351.SendRegister(SI_CLK_OE, 0b11111100); // CLK2_EN=0, CLK1_EN,CLK0_EN=1
       lcd.setCursor(15, 1); lcd.print((vox_enable) ? "V" : "R");
   }
@@ -1363,8 +1365,8 @@ public:
     numSamples = 0;
     func_ptr = sdr_rx;  //enable RX DSP/SDR
     if(dsp_cap == SDR){
-      adc_start(0, true, F_ADC_CONV); admux[0] = ADMUX;
-      adc_start(1, true, F_ADC_CONV); admux[1] = ADMUX;
+      adc_start(0, !(att == 1)/*true*/, F_ADC_CONV); admux[0] = ADMUX;
+      adc_start(1, !(att == 1)/*true*/, F_ADC_CONV); admux[1] = ADMUX;
     } else { // ANALOG, DSP
       adc_start(0, false, F_ADC_CONV); admux[0] = ADMUX; admux[1] = ADMUX;
     }
@@ -1523,7 +1525,7 @@ volatile uint8_t menumode = 0;  // 0=not in menu, 1=selects menu item, 2=selects
 volatile int8_t menu = 0;  // current parameter id selected in menu
 const char* offon_label[] = {"OFF", "ON"};
 
-enum params_t {ALL, VOLUME, MODE, FILTER, BAND, STEP, AGC, NR, SMETER, CWDEC, VOX, DRIVE, PARAM_A, PARAM_B, PARAM_C, FREQ, VERS};
+enum params_t {ALL, VOLUME, MODE, FILTER, BAND, STEP, AGC, NR, ATT, SMETER, CWDEC, VOX, DRIVE, PARAM_A, PARAM_B, PARAM_C, FREQ, VERS};
 #define N_PARAMS 14   // number of (visible) parameters
 #define N_ALL_PARAMS 16  // number of parameters
 uint8_t eeprom_version;
@@ -1546,7 +1548,8 @@ void paramAction(uint8_t action, uint8_t id = ALL)  // list of parameters
     case STEP:   paramAction(action, qcx.stepsize, F("A5"), F("Tuning step"), /*qcx.*/stepsize_label, 0, sizeof(/*qcx.*/stepsize_label)/sizeof(char*) - 1, false, qcx.STEP_1k); break;
     case AGC:    paramAction(action, agc, F("A6"), F("AGC"), offon_label, 0, 1, false, true); break;
     case NR:     paramAction(action, nr, F("A7"), F("NR"), offon_label, 0, 1, false, false); break;
-    case SMETER: paramAction(action, qcx.smode, F("A8"), F("S-meter"), qcx.smode_label, 0, sizeof(qcx.smode_label)/sizeof(char*) - 1, false, 1); break;
+    case ATT:    paramAction(action, att, F("A8"), F("ATT"), att_label, 0, 3, false, 0); break;
+    case SMETER: paramAction(action, qcx.smode, F("A9"), F("S-meter"), qcx.smode_label, 0, sizeof(qcx.smode_label)/sizeof(char*) - 1, false, 1); break;
     case CWDEC:  paramAction(action, cwdec, F("B1"), F("CW Decoder"), offon_label, 0, 1, false, false); break;
     case VOX:    paramAction(action, vox_enable, F("C1"), F("VOX"), offon_label, 0, 1, false, false); break;
     case DRIVE:  paramAction(action, drive, F("C2"), F("TX Drive"), NULL, 0, 8, false, 4); break;
@@ -1827,12 +1830,6 @@ void loop()
         break;
       case BL|SC:
         //calibrate_iq();
-        /*
-        if(dsp_cap){
-          encoder_val = 1; paramAction(UPDATE, att_enable, NULL, F("Attenuate"), offon_label, 0, sizeof(offon_label)/sizeof(char *), true);
-          txen(false); // submit attenuator setting
-          wdt_reset(); delay(1500); wdt_reset(); change = true; // wait & refresh display
-        }*/
         int8_t _menumode;
         if(menumode == 0){ _menumode = 1; if(menu == 0) menu = 1; }  // short left-click while in default screen: enter menu mode
         if(menumode == 1){ _menumode = 2; }                          // short left-click while in menu: enter value selection screen
@@ -1921,13 +1918,20 @@ void loop()
     }
     if(menumode == 2){
       lcd.setCursor(0, 1); lcd.cursor(); delay(10); // edits menu item value; make cursor visible
-      if(menu == 2){ // post-handling Mode parameter
+      if(menu == MODE){ // post-handling Mode parameter
         change = true;
         si5351.prev_pll_freq = 0;  // enforce PLL reset
         // make more generic: 
         if(mode != CW) qcx.stepsize = qcx.STEP_1k; else qcx.stepsize = qcx.STEP_100;
         if(mode == CW) filt = 4; else filt = 0;
       }
+      if(menu == ATT){ // post-handling ATT parameter
+        if(dsp_cap == SDR){
+          adc_start(0, !(att & 0x01), F_ADC_CONV); admux[0] = ADMUX;
+          adc_start(1, !(att & 0x01), F_ADC_CONV); admux[1] = ADMUX;
+        }
+        digitalWrite(RX, !(att & 0x02)); // RX (enable RX when attenuator not on), otherwise keep Q5 off (attenuate)
+      }
     }
   }
 
diff --git a/README.md b/README.md
index c14e6fe..bf05208 100644
--- a/README.md
+++ b/README.md
@@ -33,6 +33,7 @@ pe1nnz@amsat.org
 - Possibility to extend the QCX analog phasing stage with a **DSP stage**
 - Could replace the QCX analog phasing stage completely with a **digital SDR receiver stage**, taking away the need for the manual side-band rejection adjustment procedure and delivering DSP features such as the joy of having a **AGC, adjustable CW/SSB filters**.
 - A theoretical **digital receiver dynamic range of 83dB** at 2.4kHz BW.  (1 dB) Compression point (at -126dBm sensitivity): -44dBm/1mV (for in-band signal); -4dBm/160mV (for signal at 15kHz offset); 19dBm/2V (for signal at 100kHz offset or more).
+- Switchable attenuator steps: 0dB, -13dB, -20dB, -33dB
 - SDR implementation **simplifies** the receiver heaviliy and **shaves off roughly 30% of the components** from the original QCX design while adding new and improving existing features. On a new QCX build: 46 components less to be installed, 8 component design changes, 9 additional wires.
 - Can be used as alternate firmware on an unmodified QCX.
 
@@ -134,6 +135,7 @@ The following performance measurements were made with QCX-SSB R1.01, a modified
 1. <a name="note1"/>To support multi-band operation, the RX BPF can be omitted (C1,C5,C8, secondary 3 of T1). To improve RX sensitivity on higher bands, T1 and R64 should be removed and on the original wire-endings of T1 (see [original Assembly instruction] chapter 3.56 for PC Board pattern) the following components should be installed: resistor 1K over 6-8 and 3-4; capacitor 10nF over 4-8. A switchable LPF-bank could replace the existing LPF C25-28,L1-L3, or a wire may bypass if external LPFs are present; the matching network C30,L4 should be set to 30pF and 1uH (16 turns). A switchable filter-bank could potentialy be controlled via I2C I/O port.
 2. <a name="note2"/>The QCX-SSB firmware can be uploaded to ATMEGA328P chip placed in the QCX via ISP programming on an Arduino Uno board. To do so, istall an [Arduino] environment, connect an Arduino Uno board to PC, upload this [ArduinoISP] sketch to Uno, install a new ATMEGA328P chip in QCX, connect Arduino Uno to QCX via [ISP jumper] wiring, power on QCX, in Arduino select "Tools > Programmer > Arduino as ISP", select "Tools > Board > Arduino/Genuino Uno", select "Tools > Port > /dev/ttyUSB0 or ttyACM0", select "Tools > Burn Bootloader", upload [QCX-SSB Sketch] by opening and selecting "Sketch > Upload Using Programmer". Once upload succeeds the LCD should display "QCX-SSB". Make sure that the Microphone is not connected during programming.
 Alternatively a firmware hex file can be uploaded with avrdude: avrdude -c avrisp -b 19200 -P /dev/ttyUSB0 -p m328p -F -U flash:w:QCX-SSB.ino.with_bootloader.standard.hex
+Suitable fuse settings are: avrdude -c avrisp -b 19200 -P /dev/ttyUSB0 -p m328p -U efuse:w:0xfd:m -U hfuse:w:0xd1:m -U lfuse:w:0xF7:m
 3. <a name="note3"/>The occupied SSB bandwidth can be further reduced by restricting the maximum phase change (set MAX_DP to half a unit-circle _UA/2 (equivalent to 180 degrees)). The sensitivity of the VOX switching can be set with parameter VOX_THRESHOLD. Audio-input can be attenuated by increasing parameter MIC_ATTEN (6dB per step).
 4. <a name="note4"/>To implement the SDR stage, the 17 component changes of installation step 1 are easiest to be implemented on a newly to be build QCX. Alternatively, on an already built QCX it is easier to bypass the CW filter (see <sup>[note 4](#note4)</sup>), this maintains the hardware compatibility with the original QCX firmware. Optionally this can be extended with a Arduino based DSP filter stage (see <sup>[note 5](#note5)</sup>).
 5. <a name="note5"/>To implement SSB receiver via CW filter bypass: disconnect C21(+) and wire to common of a SPDT switch; wire R27(pin2) and IC9(pin1) both to each throw of SPDT switch. (see here the corresponding [schematic](https://raw.githubusercontent.com/threeme3/QCX-SSB/26c4e97a034d367e1325c5587a56a7c2a43c69f3/schematic.png) and [layout](https://raw.githubusercontent.com/threeme3/QCX-SSB/26c4e97a034d367e1325c5587a56a7c2a43c69f3/layout.png)).