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authorKyle Keen <keenerd@gmail.com>2013-11-04 19:07:10 -0500
committerSteve Markgraf <steve@steve-m.de>2013-11-05 20:58:17 +0100
commitc5b8a213000751d5ab6c42f73aca89cb4d2fc6e3 (patch)
tree66f4fcd5340ece5cd13c334fce49ee150fec9abd /src
parent8f1d1081225bb30280c00717573445dc1f3a1633 (diff)
rtl_power: more lowpass options
Signed-off-by: Steve Markgraf <steve@steve-m.de>
Diffstat (limited to 'src')
-rw-r--r--src/rtl_power.c123
1 files changed, 100 insertions, 23 deletions
diff --git a/src/rtl_power.c b/src/rtl_power.c
index 64fe71b..b63fd71 100644
--- a/src/rtl_power.c
+++ b/src/rtl_power.c
@@ -34,7 +34,6 @@
* general astronomy usefulness
* multiple dongles
* multiple FFT workers
- * bandwidths smaller than 1MHz (with optional xlate?)
* check edge cropping for off-by-one and rounding errors
* 1.8MS/s for hiding xtal harmonics
*/
@@ -88,6 +87,7 @@ struct tuning_state
long *avg; /* length == 2^bin_e */
int samples;
int downsample;
+ int downsample_passes; /* for the recursive filter */
double crop;
//pthread_rwlock_t avg_lock;
//pthread_mutex_t avg_mutex;
@@ -103,6 +103,8 @@ struct tuning_state
struct tuning_state tunes[MAX_TUNES];
int tune_count = 0;
+int boxcar = 1;
+
void usage(void)
{
fprintf(stderr,
@@ -127,9 +129,11 @@ void usage(void)
"\t[-w window (default: rectangle)]\n"
"\t (hamming, blackman, blackman-harris, hann-poisson, bartlett, youssef)\n"
// kaiser
- "\t[-c crop_percent (default: 0%, recommended: 20%%-50%%)]\n"
+ "\t[-c crop_percent (default: 0%%, recommended: 20%%-50%%)]\n"
"\t (discards data at the edges, 100%% discards everything)\n"
- "\t (has no effect for bins > 1MHz or bandwidth < 1MHz)\n"
+ "\t (has no effect for bins larger than 1MHz)\n"
+ "\t[-F enables low-leakage downsample filter (default: off)]\n"
+ "\t (has bad roll off, try with '-c 50%%')\n"
"\n"
"CSV FFT output columns:\n"
"\tdate, time, Hz low, Hz high, Hz step, samples, dbm, dbm, ...\n\n"
@@ -144,7 +148,7 @@ void usage(void)
"\trtl_power -f ... -e 1h | gzip > log.csv.gz\n"
"\t (collect data for one hour and compress it on the fly)\n\n"
"Convert CSV to a waterfall graphic with:\n"
- "\thttp://kmkeen.com/tmp/heatmap.py.txt\n");
+ "\t http://kmkeen.com/tmp/heatmap.py.txt \n");
exit(1);
}
@@ -477,7 +481,8 @@ void frequency_range(char *arg, double crop)
// do we want the fewest ranges (easy) or the fewest bins (harder)?
{
char *start, *stop, *step;
- int i, j, upper, lower, max_size, bw_seen, bw_used, bin_e, buf_len, downsample;
+ int i, j, upper, lower, max_size, bw_seen, bw_used, bin_e, buf_len;
+ int downsample, downsample_passes;
double bin_size;
struct tuning_state *ts;
/* hacky string parsing */
@@ -492,21 +497,28 @@ void frequency_range(char *arg, double crop)
stop[-1] = ':';
step[-1] = ':';
downsample = 1;
- if ((upper - lower) < 1000000) {
- crop = 0.0;}
+ downsample_passes = 0;
/* evenly sized ranges, as close to 2MHz as possible */
for (i=1; i<1500; i++) {
bw_seen = (upper - lower) / i;
bw_used = (int)((double)(bw_seen) / (1.0 - crop));
if (bw_used > 2000000) {
continue;}
- if (bw_used < 1000000) {
- downsample = 2000000 / bw_seen;
- bw_used = bw_seen * downsample;
- }
tune_count = i;
break;
}
+ /* unless small bandwidth */
+ if (bw_used < 1000000) {
+ tune_count = 1;}
+ if (boxcar && bw_used < 1000000) {
+ downsample = 2000000 / bw_used;
+ bw_used = bw_used * downsample;
+ }
+ while (bw_used < 1000000) { /* not boxcar */
+ downsample_passes++;
+ downsample = 1 << downsample_passes;
+ bw_used = (int)((double)(bw_seen * downsample) / (1.0 - crop));
+ }
/* number of bins is power-of-two, bin size is under limit */
for (i=1; i<=21; i++) {
bin_e = i;
@@ -526,7 +538,7 @@ void frequency_range(char *arg, double crop)
fprintf(stderr, "Error: bandwidth too wide.\n");
exit(1);
}
- buf_len = (1<<bin_e) * 2 * downsample;
+ buf_len = 2 * (1<<bin_e) * downsample;
if (buf_len < DEFAULT_BUF_LENGTH) {
buf_len = DEFAULT_BUF_LENGTH;
}
@@ -539,6 +551,7 @@ void frequency_range(char *arg, double crop)
ts->samples = 0;
ts->crop = crop;
ts->downsample = downsample;
+ ts->downsample_passes = downsample_passes;
ts->avg = (long*)malloc((1<<bin_e) * sizeof(long));
if (!ts->avg) {
fprintf(stderr, "Error: malloc.\n");
@@ -578,6 +591,58 @@ void retune(rtlsdr_dev_t *d, int freq)
fprintf(stderr, "Error: bad retune.\n");}
}
+void fifth_order(int16_t *data, int length)
+/* for half of interleaved data */
+{
+ int i;
+ int a, b, c, d, e, f;
+ a = data[0];
+ b = data[2];
+ c = data[4];
+ d = data[6];
+ e = data[8];
+ f = data[10];
+ /* a downsample should improve resolution, so don't fully shift */
+ /* ease in instead of being stateful */
+ data[0] = ((a+b)*10 + (c+d)*5 + d + f) >> 4;
+ data[2] = ((b+c)*10 + (a+d)*5 + e + f) >> 4;
+ data[4] = (a + (b+e)*5 + (c+d)*10 + f) >> 4;
+ for (i=12; i<length; i+=4) {
+ a = c;
+ b = d;
+ c = e;
+ d = f;
+ e = data[i-2];
+ f = data[i];
+ data[i/2] = (a + (b+e)*5 + (c+d)*10 + f) >> 4;
+ }
+}
+
+void remove_dc(int16_t *data, int length)
+/* works on interleaved data */
+{
+ int i;
+ int16_t ave;
+ long sum = 0L;
+ for (i=0; i < length; i+=2) {
+ sum += data[i];
+ }
+ ave = (int16_t)(sum / (long)(length));
+ if (ave == 0) {
+ return;}
+ for (i=0; i < length; i+=2) {
+ data[i] -= ave;
+ }
+}
+
+void downsample_iq(int16_t *data, int length)
+{
+ fifth_order(data, length);
+ //remove_dc(data, length);
+ fifth_order(data+1, length-1);
+ //remove_dc(data+1, length-1);
+}
+
void scanner(void)
{
int i, j, j2, f, n_read, offset, bin_e, bin_len, buf_len, ds;
@@ -601,20 +666,28 @@ void scanner(void)
rms_power(ts);
continue;
}
- /* sign and downsample */
+ /* prep for fft */
for (j=0; j<buf_len; j++) {
- fft_buf[j] = 0;
+ fft_buf[j] = (int16_t)ts->buf8[j] - 127;
}
ds = ts->downsample;
- j=0, j2=0;
- while (j < buf_len) {
- fft_buf[j2] += (int16_t)ts->buf8[j] - 127;
- fft_buf[j2+1] += (int16_t)ts->buf8[j+1] - 127;
- j += 2;
- if (j % (ds*2) == 0) {
- j2 += 2;}
+ if (boxcar) {
+ j=2, j2=0;
+ while (j < buf_len) {
+ fft_buf[j2] += fft_buf[j];
+ fft_buf[j2+1] += fft_buf[j+1];
+ j += 2;
+ if (j % (ds*2) == 0) {
+ j2 += 2;}
+ }
+ } else { /* recursive */
+ for (j=0; j < ts->downsample_passes; j++) {
+ downsample_iq(fft_buf, buf_len >> j);
+ }
}
- /* fft */
+ remove_dc(fft_buf, buf_len >> j);
+ remove_dc(fft_buf+1, (buf_len >> j) - 1);
+ /* window function and fft */
for (offset=0; offset<(buf_len/ds); offset+=(2*bin_len)) {
// todo, let rect skip this
for (j=0; j<bin_len; j++) {
@@ -707,8 +780,9 @@ int main(int argc, char **argv)
char t_str[50];
struct tm *cal_time;
double (*window_fn)(int, int) = rectangle;
+ freq_optarg = "";
- while ((opt = getopt(argc, argv, "f:i:s:t:d:g:p:e:w:c:1h")) != -1) {
+ while ((opt = getopt(argc, argv, "f:i:s:t:d:g:p:e:w:c:1Fh")) != -1) {
switch (opt) {
case 'f': // lower:upper:bin_size
freq_optarg = strdup(optarg);
@@ -762,6 +836,9 @@ int main(int argc, char **argv)
case '1':
single = 1;
break;
+ case 'F':
+ boxcar = 0;
+ break;
case 'h':
default:
usage();