diff --git a/soapypower/power.py b/soapypower/power.py
index 811b942..6e40e72 100644
--- a/soapypower/power.py
+++ b/soapypower/power.py
@@ -252,7 +252,8 @@ def psd(self, freq):
             logger.debug('    Repeat: {}'.format(repeat + 1))
             # Read samples from SDR in main thread
             t_acq = time.time()
-            acq_time_start = datetime.datetime.utcnow()
+            if repeat == 0:
+                acq_time_start = datetime.datetime.utcnow()
             self.device.read_stream_into_buffer(self._buffer)
             acq_time_stop = datetime.datetime.utcnow()
             t_acq_end = time.time()