diff --git a/fft-beacon-finder/finder.c b/fft-beacon-finder/finder.c
index 1c4490a..8bf4ff3 100644
--- a/fft-beacon-finder/finder.c
+++ b/fft-beacon-finder/finder.c
@@ -5,61 +5,114 @@
 #include <stdio.h>
 
 const float SAMPLINGRATE = 1000000.0;
-const float FFT_LEN = 256;
+const float FFT_LEN = 512;
+
+int spectral_bin_to_fft_idx(int bin) {
+    if(bin == 0) {
+        return FFT_LEN/2;
+    } else if(bin > 0) {
+        return bin - 1;
+    } else {
+        return bin + FFT_LEN;
+    }
+}
+
 
 int main() {
-    FILE* output = fopen("output.csv", "w");
+    FILE* output_csv = fopen("output.csv", "w");
+    FILE* output = fopen("output.raw", "w");
     FILE* input = fopen("input.raw", "r");
 
+    nco_crcf correction = nco_crcf_create(LIQUID_NCO);
+    nco_crcf_set_phase(correction, 0.0f);
+
     float complex * fft_in = (float complex*) malloc(FFT_LEN * sizeof(float complex));
     float complex * fft_out = (float complex*) malloc(FFT_LEN * sizeof(float complex));
 
     // create FFT plan
     fftplan fft = fft_create_plan(FFT_LEN, fft_in, fft_out, LIQUID_FFT_FORWARD, 0);
 
+    int next_fft_in = 0;
     int pos = 0;
     float in[2];
+
     while(fread(in, sizeof(float), 2, input) == 2) {
-        fft_in[pos] = (in[1] + I * in[0]);
-        pos += 1;
-        if(pos == FFT_LEN) {
-            pos = 0;
-            fft_execute(fft);
+        complex float cplx_in = (in[1] + I * in[0]);
 
-            float fft_min = cabsf(fft_out[0]);
-            float fft_max = cabsf(fft_out[0]);
-            for(int i = 0; i < FFT_LEN; i++) {
-                float mag = cabsf(fft_out[i]);
-                if(mag < fft_min) {
-                    fft_min = mag;
+        if(next_fft_in <= 0) {
+            fft_in[pos] = cplx_in;
+            pos += 1;
+            if(pos == FFT_LEN) {
+                pos = 0;
+                fft_execute(fft);
+
+                float fft_max = cabsf(fft_out[0]);
+                for(int i = 0; i < FFT_LEN; i++) {
+                    float mag = cabsf(fft_out[i]);
+                    if(mag > fft_max) {
+                        fft_max = mag;
+                    }
                 }
-                if(mag > fft_max) {
-                    fft_max = mag;
+                //printf("Min: %f Max: %f\n", fft_min, fft_max);
+
+                for(int bin = -FFT_LEN/2; bin < FFT_LEN/2; bin++) {
+                    int idx = spectral_bin_to_fft_idx(bin);
+                    float mag = cabsf(fft_out[idx]);
+                    mag = mag / fft_max;
+                    fprintf(output_csv, "%f;", mag);
                 }
+
+                printf("===========\n");
+                float max_levels = 0;
+                int max_center = 0;
+                for(int bin = -50; bin <= 50; bin++) {
+                    int center_idx = spectral_bin_to_fft_idx(bin);
+                    float center_val = cabsf(fft_out[center_idx]) / fft_max;
+                    if(center_val > 0.25) {
+                        printf("Found peak candidate at %d\n", bin);
+                        int left_idx = spectral_bin_to_fft_idx(bin - 127);
+                        int right_idx = spectral_bin_to_fft_idx(bin + 127);
+                        float left_val = cabsf(fft_out[left_idx]) / fft_max;
+                        float right_val = cabsf(fft_out[right_idx]) / fft_max;
+
+                        if(center_val + left_val + right_val > max_levels) {
+                            max_levels = center_val + left_val + right_val;
+                            max_center = bin;
+                        }
+                    }
+                }
+
+                if(max_levels > 0.0) {
+                    float center_freq = max_center * SAMPLINGRATE / FFT_LEN;
+                    printf("Found center at %f\n", center_freq);
+                    nco_crcf_set_frequency(correction, -(2 * M_PI * center_freq) / SAMPLINGRATE);
+                }
+
+                fprintf(output_csv, "\n");
+
+                next_fft_in = SAMPLINGRATE / 10;
             }
-            //printf("Min: %f Max: %f\n", fft_min, fft_max);
-
-            for(int i = FFT_LEN / 2; i < FFT_LEN; i++) {
-                float mag = cabsf(fft_out[i]);
-                mag = (mag - fft_min) / (fft_max - fft_min);
-                fprintf(output, "%f;", mag);
-            }
-
-            for(int i = 0; i < FFT_LEN / 2; i++) {
-                float mag = cabsf(fft_out[i]);
-                mag = (mag - fft_min) / (fft_max - fft_min);
-                fprintf(output, "%f;", mag);
-            }
-
-
-            fprintf(output, "\n");
+        } else {
+            next_fft_in--;
         }
+
+        float complex x;
+        // increment internal phase
+        nco_crcf_step(correction);
+        // compute complex exponential
+        nco_crcf_cexpf(correction, &x);
+
+        float complex cplx_out = cplx_in * x;
+
+        float buffer[] = {creal(cplx_out), cimag(cplx_out)};
+        fwrite(buffer, sizeof(float), 2, output);
     }
 
     fft_destroy_plan(fft);
     free(fft_in);
     free(fft_out);
 
+    fclose(output_csv);
     fclose(output);
     fclose(input);
 
diff --git a/fft-beacon-finder/generate-testdata.grc b/fft-beacon-finder/generate-testdata.grc
index 563bbd9..9bcddbb 100644
--- a/fft-beacon-finder/generate-testdata.grc
+++ b/fft-beacon-finder/generate-testdata.grc
@@ -32,6 +32,27 @@ options:
     state: enabled
 
 blocks:
+- name: offset
+  id: variable_qtgui_range
+  parameters:
+    comment: ''
+    gui_hint: ''
+    label: ''
+    min_len: '200'
+    orient: QtCore.Qt.Horizontal
+    rangeType: float
+    start: '-35000'
+    step: '1000'
+    stop: '35000'
+    value: '0'
+    widget: counter_slider
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [448, 12.0]
+    rotation: 0
+    state: true
 - name: samp_rate
   id: variable
   parameters:
@@ -60,7 +81,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [984, 148.0]
+    coordinate: [1152, 148.0]
     rotation: 0
     state: true
 - name: analog_sig_source_x_0
@@ -151,6 +172,28 @@ blocks:
     coordinate: [208, 404.0]
     rotation: 0
     state: true
+- name: analog_sig_source_x_1_0_0_0
+  id: analog_sig_source_x
+  parameters:
+    affinity: ''
+    alias: ''
+    amp: '1'
+    comment: ''
+    freq: offset
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    offset: '0'
+    phase: '0'
+    samp_rate: samp_rate
+    type: complex
+    waveform: analog.GR_COS_WAVE
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [952, 476.0]
+    rotation: 0
+    state: true
 - name: blocks_add_xx_0
   id: blocks_add_xx
   parameters:
@@ -166,7 +209,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1192, 240.0]
+    coordinate: [1360, 240.0]
     rotation: 0
     state: true
 - name: blocks_add_xx_1
@@ -202,7 +245,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1320, 236.0]
+    coordinate: [1488, 236.0]
     rotation: 0
     state: true
 - name: blocks_multiply_xx_0
@@ -223,6 +266,24 @@ blocks:
     coordinate: [1048, 256.0]
     rotation: 0
     state: true
+- name: blocks_multiply_xx_0_0
+  id: blocks_multiply_xx
+  parameters:
+    affinity: ''
+    alias: ''
+    comment: ''
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    num_inputs: '2'
+    type: complex
+    vlen: '1'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [1192, 272.0]
+    rotation: 0
+    state: true
 - name: blocks_multiply_xx_1
   id: blocks_multiply_xx
   parameters:
@@ -251,7 +312,7 @@ blocks:
     maxoutbuf: '0'
     minoutbuf: '0'
     samp_rate: samp_rate
-    sensitivity: '10000'
+    sensitivity: '40000'
   states:
     bus_sink: false
     bus_source: false
@@ -337,7 +398,7 @@ blocks:
     bus_sink: false
     bus_source: false
     bus_structure: null
-    coordinate: [1320, 124.0]
+    coordinate: [1488, 124.0]
     rotation: 0
     state: true
 - name: rational_resampler_xxx_0
@@ -367,10 +428,12 @@ connections:
 - [analog_sig_source_x_1, '0', blocks_add_xx_1, '0']
 - [analog_sig_source_x_1_0, '0', blocks_add_xx_1, '1']
 - [analog_sig_source_x_1_0_0, '0', blocks_multiply_xx_1, '0']
+- [analog_sig_source_x_1_0_0_0, '0', blocks_multiply_xx_0_0, '1']
 - [blocks_add_xx_0, '0', blocks_file_sink_0, '0']
 - [blocks_add_xx_0, '0', qtgui_waterfall_sink_x_0, '0']
 - [blocks_add_xx_1, '0', blocks_multiply_xx_0, '0']
-- [blocks_multiply_xx_0, '0', blocks_add_xx_0, '1']
+- [blocks_multiply_xx_0, '0', blocks_multiply_xx_0_0, '0']
+- [blocks_multiply_xx_0_0, '0', blocks_add_xx_0, '1']
 - [blocks_multiply_xx_1, '0', blocks_add_xx_1, '2']
 - [blocks_vco_c_0, '0', blocks_multiply_xx_0, '1']
 - [blocks_vector_source_x_0, '0', rational_resampler_xxx_0, '0']
diff --git a/fft-beacon-finder/view_waterfall.grc b/fft-beacon-finder/view_waterfall.grc
new file mode 100644
index 0000000..93e68b8
--- /dev/null
+++ b/fft-beacon-finder/view_waterfall.grc
@@ -0,0 +1,341 @@
+options:
+  parameters:
+    author: ''
+    catch_exceptions: 'True'
+    category: '[GRC Hier Blocks]'
+    cmake_opt: ''
+    comment: ''
+    copyright: ''
+    description: ''
+    gen_cmake: 'On'
+    gen_linking: dynamic
+    generate_options: qt_gui
+    hier_block_src_path: '.:'
+    id: view_waterfall
+    max_nouts: '0'
+    output_language: python
+    placement: (0,0)
+    qt_qss_theme: ''
+    realtime_scheduling: ''
+    run: 'True'
+    run_command: '{python} -u {filename}'
+    run_options: prompt
+    sizing_mode: fixed
+    thread_safe_setters: ''
+    title: Not titled yet
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [8, 8]
+    rotation: 0
+    state: enabled
+
+blocks:
+- name: samp_rate
+  id: variable
+  parameters:
+    comment: ''
+    value: '1000000'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [184, 12]
+    rotation: 0
+    state: enabled
+- name: blocks_file_source_0
+  id: blocks_file_source
+  parameters:
+    affinity: ''
+    alias: ''
+    begin_tag: pmt.PMT_NIL
+    comment: ''
+    file: /home/sebastian/projects/QO100-trx/prototypes/fft-beacon-finder/output.raw
+    length: '0'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    offset: '0'
+    repeat: 'False'
+    type: complex
+    vlen: '1'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [184, 212.0]
+    rotation: 0
+    state: true
+- name: blocks_file_source_0_0
+  id: blocks_file_source
+  parameters:
+    affinity: ''
+    alias: ''
+    begin_tag: pmt.PMT_NIL
+    comment: ''
+    file: /home/sebastian/projects/QO100-trx/prototypes/fft-beacon-finder/input.raw
+    length: '0'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    offset: '0'
+    repeat: 'False'
+    type: complex
+    vlen: '1'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [176, 92.0]
+    rotation: 0
+    state: true
+- name: blocks_throttle_0
+  id: blocks_throttle
+  parameters:
+    affinity: ''
+    alias: ''
+    comment: ''
+    ignoretag: 'True'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    samples_per_second: samp_rate
+    type: complex
+    vlen: '1'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [496, 244.0]
+    rotation: 0
+    state: true
+- name: blocks_throttle_1
+  id: blocks_throttle
+  parameters:
+    affinity: ''
+    alias: ''
+    comment: ''
+    ignoretag: 'True'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    samples_per_second: samp_rate
+    type: complex
+    vlen: '1'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [400, 124.0]
+    rotation: 0
+    state: true
+- name: qtgui_freq_sink_x_0
+  id: qtgui_freq_sink_x
+  parameters:
+    affinity: ''
+    alias: ''
+    alpha1: '1.0'
+    alpha10: '1.0'
+    alpha2: '1.0'
+    alpha3: '1.0'
+    alpha4: '1.0'
+    alpha5: '1.0'
+    alpha6: '1.0'
+    alpha7: '1.0'
+    alpha8: '1.0'
+    alpha9: '1.0'
+    autoscale: 'False'
+    average: '1.0'
+    axislabels: 'True'
+    bw: samp_rate
+    color1: '"blue"'
+    color10: '"dark blue"'
+    color2: '"red"'
+    color3: '"green"'
+    color4: '"black"'
+    color5: '"cyan"'
+    color6: '"magenta"'
+    color7: '"yellow"'
+    color8: '"dark red"'
+    color9: '"dark green"'
+    comment: ''
+    ctrlpanel: 'False'
+    fc: '0'
+    fftsize: '4096'
+    freqhalf: 'True'
+    grid: 'True'
+    gui_hint: ''
+    label: Relative Gain
+    label1: ''
+    label10: ''''''
+    label2: ''''''
+    label3: ''''''
+    label4: ''''''
+    label5: ''''''
+    label6: ''''''
+    label7: ''''''
+    label8: ''''''
+    label9: ''''''
+    legend: 'True'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    name: '""'
+    nconnections: '1'
+    norm_window: 'False'
+    showports: 'False'
+    tr_chan: '0'
+    tr_level: '0.0'
+    tr_mode: qtgui.TRIG_MODE_FREE
+    tr_tag: '""'
+    type: complex
+    units: dB
+    update_time: '0.10'
+    width1: '1'
+    width10: '1'
+    width2: '1'
+    width3: '1'
+    width4: '1'
+    width5: '1'
+    width6: '1'
+    width7: '1'
+    width8: '1'
+    width9: '1'
+    wintype: window.WIN_BLACKMAN_hARRIS
+    ymax: '10'
+    ymin: '-140'
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [712, 156.0]
+    rotation: 0
+    state: true
+- name: qtgui_waterfall_sink_x_0
+  id: qtgui_waterfall_sink_x
+  parameters:
+    affinity: ''
+    alias: ''
+    alpha1: '1.0'
+    alpha10: '1.0'
+    alpha2: '1.0'
+    alpha3: '1.0'
+    alpha4: '1.0'
+    alpha5: '1.0'
+    alpha6: '1.0'
+    alpha7: '1.0'
+    alpha8: '1.0'
+    alpha9: '1.0'
+    axislabels: 'True'
+    bw: samp_rate
+    color1: '0'
+    color10: '0'
+    color2: '0'
+    color3: '0'
+    color4: '0'
+    color5: '0'
+    color6: '0'
+    color7: '0'
+    color8: '0'
+    color9: '0'
+    comment: ''
+    fc: '0'
+    fftsize: '4096'
+    freqhalf: 'True'
+    grid: 'True'
+    gui_hint: ''
+    int_max: '10'
+    int_min: '-140'
+    label1: ''
+    label10: ''
+    label2: ''
+    label3: ''
+    label4: ''
+    label5: ''
+    label6: ''
+    label7: ''
+    label8: ''
+    label9: ''
+    legend: 'True'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    name: '""'
+    nconnections: '1'
+    showports: 'False'
+    type: complex
+    update_time: '0.10'
+    wintype: window.WIN_BLACKMAN_hARRIS
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [704, 348.0]
+    rotation: 0
+    state: true
+- name: qtgui_waterfall_sink_x_0_0
+  id: qtgui_waterfall_sink_x
+  parameters:
+    affinity: ''
+    alias: ''
+    alpha1: '1.0'
+    alpha10: '1.0'
+    alpha2: '1.0'
+    alpha3: '1.0'
+    alpha4: '1.0'
+    alpha5: '1.0'
+    alpha6: '1.0'
+    alpha7: '1.0'
+    alpha8: '1.0'
+    alpha9: '1.0'
+    axislabels: 'True'
+    bw: samp_rate
+    color1: '0'
+    color10: '0'
+    color2: '0'
+    color3: '0'
+    color4: '0'
+    color5: '0'
+    color6: '0'
+    color7: '0'
+    color8: '0'
+    color9: '0'
+    comment: ''
+    fc: '0'
+    fftsize: '4096'
+    freqhalf: 'True'
+    grid: 'True'
+    gui_hint: ''
+    int_max: '10'
+    int_min: '-140'
+    label1: ''
+    label10: ''
+    label2: ''
+    label3: ''
+    label4: ''
+    label5: ''
+    label6: ''
+    label7: ''
+    label8: ''
+    label9: ''
+    legend: 'True'
+    maxoutbuf: '0'
+    minoutbuf: '0'
+    name: '""'
+    nconnections: '1'
+    showports: 'False'
+    type: complex
+    update_time: '0.10'
+    wintype: window.WIN_BLACKMAN_hARRIS
+  states:
+    bus_sink: false
+    bus_source: false
+    bus_structure: null
+    coordinate: [696, 60.0]
+    rotation: 0
+    state: true
+
+connections:
+- [blocks_file_source_0, '0', blocks_throttle_0, '0']
+- [blocks_file_source_0_0, '0', blocks_throttle_1, '0']
+- [blocks_throttle_0, '0', qtgui_freq_sink_x_0, '0']
+- [blocks_throttle_0, '0', qtgui_waterfall_sink_x_0, '0']
+- [blocks_throttle_1, '0', qtgui_waterfall_sink_x_0_0, '0']
+
+metadata:
+  file_format: 1