From c5b8a213000751d5ab6c42f73aca89cb4d2fc6e3 Mon Sep 17 00:00:00 2001 From: Kyle Keen Date: Mon, 4 Nov 2013 19:07:10 -0500 Subject: [PATCH] rtl_power: more lowpass options Signed-off-by: Steve Markgraf --- src/rtl_power.c | 123 +++++++++++++++++++++++++++++++++++++++--------- 1 file 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<samples = 0; ts->crop = crop; ts->downsample = downsample; + ts->downsample_passes = downsample_passes; ts->avg = (long*)malloc((1<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> 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; jbuf8[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