--- /dev/null
+/*
+ * Contribution of DL1YCF Christoph van W"ullen:
+ *
+ * This is the "ramp" with length 200 which is
+ * the step response derived from a digital filter
+ * with a Blackman-Harris window.
+ * It is used to shape the rising and falling
+ * edge of a CW pulse. The goal is to have
+ * a pulse whose off-center frequency components
+ * quickly fall off.
+ *
+ * The Blackman-Harris window function is
+ *
+ * B(x) = a0 - a1 Cos(2 Pi x) + a2 Cos(4 Pi x) - a3 Cos(6 Pi x)
+ *
+ * with coefficients
+ * a0 = 0.35875
+ * a1 = 0.48829
+ * a2 = 0.14128
+ * a3 = 0.01168
+ *
+ * And the ramp of length 200 is
+ *
+ * cwramp[i] = (Integral of B(x) from zero to i/200) / a0
+ *
+ * where a0 is (Integral of (Bx) from zero to one)
+ *
+ * such that cwramp[0] = cwramp[200] = 0, and the values rise
+ * with the shape of a sigmoid.
+ *
+ * The values here are calculated using MATHEMATICA with 32-digit accuracy
+ * (more than we need for double) and copy/pasted into this file.
+ *
+ *
+ * MEASURING SPECTRAL POLLUTION
+ * ============================
+ *
+ * Using an SDR, a DummyLoad/Attenuator and my Kenwood TRX for receiving
+ * the signal, I started a 20 wpm CQ call on the SDR at 7010 kHz and
+ * monitored the S-meter of my Kenwood rig for different frequencies.
+ * I used a 60dB attenuator which made a S9+50dB signal in my Kenwood
+ * out of the 10 Watts output of my SDR.
+ * Three cases were measured:
+ * a) "hard" CW signal, rectangular CW pulses
+ * b) CW signal with linear ramps, width 4 msec
+ * c) CW signal with Blackman-Harris ramp (as defined here), width 4 msec
+ *
+ * These are the results:
+ *
+ * Freq / kHz S-Meter S-Meter S-Meter
+ * "hard" "linear" "Blackman-Harris"
+ * ------------------------------------------------------
+ * 7010.0 S9+50 S9+50 S9+50
+ * 7009.5 S9+25 S9 S9+10
+ * 7009.0 S9+20 S6 S0
+ * 7008.5 S9+15 S4 S0
+ * 7008.0 S9+10 S3 S0
+ * 7005.0 S9+5 S0 S0
+ * 7000.0 S8 S0 S0
+ * -----------------------------------------------------
+ *
+ * (for frequencies above 7010 kHz, one gets mirror-image results).
+ *
+ * The linear ramp is a big improvement, but the Blackman-Harris
+ * ramp does far better if more than 500 Hz off.
+ */
+
+double cwramp[201] = {
+0.0,
+9.01187795859706156177643839E-7,
+2.194323834526231706516646770E-6,
+4.282571576728779171701009811E-6,
+7.59152417258436512341254065E-6,
+0.00001258041690211947993636267109,
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+0.00004295902553278649886291894300,
+0.00006032493666320024489466741405,
+0.00008256344218126450788500686944,
+0.00011057044070320856501019611699,
+0.00014535344574159831560164368292,
+0.00018804250547447493441427381117,
+0.00023990100480207670388152058280,
+0.00030233631828325189492558643061,
+0.00037691027797158203918335035555,
+0.00046534941554435985240942810166,
+0.00056955493350364783431057938016,
+0.00069161235569682109078184134293,
+0.00083380080302407864906440039504,
+0.00099860183604212891204121277035,
+0.00118870780230554127073025982217,
+0.00140702962277747793984056753115,
+0.00165670394855476385194253550184,
+0.00194109961655060504615626150874,
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+0.9999978056761654737682934833532,
+0.9999990988122041402938438223562,
+1.0000000000000000000000000000000};
+
int cw_not_ready=1;
// cw_shape_buffer will eventually be integrated into TRANSMITTER
-static int *cw_shape_buffer = NULL;
+static double *cw_shape_buffer = NULL;
static int cw_shape = 0;
+// cwramp is the function defining the "ramp" of the CW pulse.
+// is *must be* an array with 201 entries. The ramp width (200 samples)
+// is hard-coded.
+extern double cwramp[]; // see cwramp.c
extern void cw_audio_write(double sample);
tx->samples=0;
tx->pixel_samples=malloc(sizeof(float)*tx->pixels);
if (cw_shape_buffer) free(cw_shape_buffer);
- cw_shape_buffer=malloc(sizeof(int)*tx->buffer_size);
+ cw_shape_buffer=malloc(sizeof(double)*tx->buffer_size);
fprintf(stderr,"transmitter: allocate buffers: mic_input_buffer=%p iq_output_buffer=%p pixels=%p\n",tx->mic_input_buffer,tx->iq_output_buffer,tx->pixel_samples);
fprintf(stderr,"create_transmitter: OpenChannel id=%d buffer_size=%d fft_size=%d sample_rate=%d dspRate=%d outputRate=%d\n",
static void full_tx_buffer(TRANSMITTER *tx) {
long isample;
long qsample;
- double gain,fgain,sidevol;
+ double gain, sidevol, ramp, fgain;
int j;
int error;
int mode;
if ((mode == modeCWL || mode == modeCWU) && !tune) {
//
// "pulse shape case":
- // shape the I/Q samples with the envelope function stored in cw_shape_buffer
- // and produce side tone (again with shaped pulses)
+ // shape the I/Q samples with the envelope stored in cw_shape_buffer.
+ // We also produce a side tone with same shape.
//
- fgain=gain*0.005; // will be multiplied with cw_shape
- sidevol= 1.29 * cw_keyer_sidetone_volume; // will be multiplied with cw_shape
+ fgain=gain; // will be multiplied with ramp function
+ sidevol= 258.0 * cw_keyer_sidetone_volume; // will be multiplied with ramp function
for(j=0;j<tx->output_samples;j++) {
- gain=fgain*cw_shape_buffer[j];
+ ramp=cw_shape_buffer[j]; // between 0 and 1
+ gain=fgain*ramp;
double is=tx->iq_output_buffer[j*2];
double qs=tx->iq_output_buffer[(j*2)+1];
isample=is>=0.0?(long)floor(is*gain+0.5):(long)ceil(is*gain-0.5);
// since we may use getNextSidetoneSample for local audio, we need
// an independent instance thereof here. To be nice to the CW
// operator, the audio is shaped the same way as the RF
- sidetone=sidevol * cw_shape_buffer[j] * getNextInternalSideToneSample();
+ sidetone=sidevol * ramp * getNextInternalSideToneSample();
old_protocol_iq_samples_with_sidetone(isample,qsample,sidetone);
break;
case NEW_PROTOCOL:
void add_mic_sample(TRANSMITTER *tx,short mic_sample) {
int mode;
double sample;
- double mic_sample_double;
+ double mic_sample_double, ramp;
int i,s;
if(split) {
// cw_key_down can be zero, for inserting some space
//
// We HAVE TO shape the signal to avoid hard clicks to be
-// heard way beside our frequency. The envelope goes up
-// and down linearly within 200 samples (4.16 msec)
+// heard way beside our frequency. The envelope (ramp function)
+// is stored in cwramp[0::200], so we "move" cw_shape between these
+// values. The ramp width is 200 samples (4.16 msec)
+//
+// Note that usually, the pulse is much broader than the ramp,
+// that is, cw_key_down and cw_key_up are much larger than 200.
//
cw_not_ready=0;
if (cw_key_down > 0 ) {
- if (cw_shape < 200) cw_shape++;
- cw_key_down--;
+ if (cw_shape < 200) cw_shape++; // walk up the ramp
+ cw_key_down--; // decrement key-up counter
} else {
if (cw_key_up >= 0) {
// dig into this even if cw_key_up is already zero, to ensure
- // that cw_shape eventually reaches zero
- if (cw_shape > 0) cw_shape--;
- if (cw_key_up > 0) cw_key_up--;
+ // that we reach the bottom of the ramp for very small pauses
+ if (cw_shape > 0) cw_shape--; // walk down the ramp
+ if (cw_key_up > 0) cw_key_up--; // decrement key-down counter
}
}
- cw_audio_write(0.00003937 * getNextSideToneSample() * cw_keyer_sidetone_volume * cw_shape);
- cw_shape_buffer[tx->samples]=cw_shape;
+ // store the ramp value in cw_shape_buffer, but also use it for shaping the "local"
+ // side tone
+ ramp=cwramp[cw_shape];
+ cw_audio_write(0.00003937 * getNextSideToneSample() * cw_keyer_sidetone_volume * ramp);
+ cw_shape_buffer[tx->samples]=ramp;
} else {
//
// If no longer transmitting, or no longer doing CW: reset pulse shaper.
-// This will also swallow any pending CW in rigtl CAT CW and wipe out the
-// cw_shape buffer very quickly. In order to tell rigctl etc. that CW should be
+// This will also swallow any pending CW in rigtl CAT CW and wipe out
+// cw_shape_buffer very quickly. In order to tell rigctl etc. that CW should be
// aborted, we also use the cw_not_ready flag.
//
cw_not_ready=1;
cw_key_up=0;
cw_key_down=0;
cw_shape=0;
- cw_shape_buffer[tx->samples]=0;
+ cw_shape_buffer[tx->samples]=0.0;
}
tx->mic_input_buffer[tx->samples*2]=mic_sample_double;
tx->mic_input_buffer[(tx->samples*2)+1]=0.0; //mic_sample_double;
projects / pihpsdr.git / commitdiff