From dfb2022f37b20823e093daa62b08afb0052a46a4 Mon Sep 17 00:00:00 2001
From: Eric Kooistra <kooistra@astron.nl>
Date: Thu, 6 Jun 2024 08:29:26 +0200
Subject: [PATCH] Add functions to find specific frequency or gain value in
transfer function.
---
applications/lofar2/model/rtdsp/fourier.py | 39 ++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/applications/lofar2/model/rtdsp/fourier.py b/applications/lofar2/model/rtdsp/fourier.py
index b49c8e79bc..1b319fa972 100644
--- a/applications/lofar2/model/rtdsp/fourier.py
+++ b/applications/lofar2/model/rtdsp/fourier.py
@@ -133,6 +133,45 @@ def dtft(coefs, Ndtft=None, zeroCenter=True, fftShift=True):
return h, f, HF
+def estimate_gain_at_frequency(f, HF, freq):
+ """Find gain = abs(HF) at frequency in f that is closest to freq.
+
+ Input:
+ . f, HF: frequency axis and spectrum as from dtft() with fftShift=True
+ . freq : frequency to look for in f
+ Return:
+ . fIndex: index of frequency in f that is closest to freq
+ . fValue: frequency at fIndex
+ . fGain : gain = abs(HF) at fIndex
+ """
+ fDiff = np.abs(f - freq)
+ fIndex = fDiff.argmin()
+ fValue = f[fIndex]
+ fGain = np.abs(HF[fIndex])
+ return fIndex, fValue, fGain
+
+
+def estimate_frequency_at_gain(f, HF, gain):
+ """Find positive frequency in f that has gain = abs(HF) closest to gain.
+
+ Input:
+ . f, HF: frequency axis and spectrum as from dtft() with fftShift=True
+ . gain : gain to look for in HF
+ Return:
+ . fIndex: index of frequency in f that has abs(HF) closest to gain
+ . fValue: frequency at fIndex
+ . fGain : gain = abs(HF) at fIndex
+ """
+ pos = len(f[f <= 0])
+ HFpos = HF[pos:]
+ HFgain = np.abs(HFpos)
+ HFdiff = np.abs(HFgain - gain)
+ fIndex = pos + HFdiff.argmin()
+ fValue = f[fIndex]
+ fGain = np.abs(HF[fIndex])
+ return fIndex, fValue, fGain
+
+
###############################################################################
# Radix FFT
###############################################################################
--
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