From deeab3233ee5c9249601c5e678bd84ecb64255f5 Mon Sep 17 00:00:00 2001
From: Eric Kooistra <kooistra@astron.nl>
Date: Thu, 23 Nov 2023 18:06:00 +0100
Subject: [PATCH] Clarify fftshift for N is even and odd.
---
.../lofar2/model/pfb_os/dsp_study_erko.txt | 24 +++++++++++--------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/applications/lofar2/model/pfb_os/dsp_study_erko.txt b/applications/lofar2/model/pfb_os/dsp_study_erko.txt
index 382ab3c98e..8964b652a7 100644
--- a/applications/lofar2/model/pfb_os/dsp_study_erko.txt
+++ b/applications/lofar2/model/pfb_os/dsp_study_erko.txt
@@ -212,20 +212,24 @@
-0.5, 0, 0.5 [fs]
. N even, e.g. N = 4:
- <---- N = 4 ----->
- 0 fs/2 fs
- | | |
- n = 0 1 2 3
- 0/4 1/4 2/4 3/4 4/4
- DC positive negative
+ <------ N = 4 ------->
+ 0 fs/2 ( fs )
+ | | ( | )
+ n = 0 1 2 3 ( | )
+ 0/4 1/4 2/4 3/4 ( 4/4 )
+ DC positive | negative
+ |
+ \--> fftshift([0, 1, 2, 3]) = [2, 3, 0, 1]
. N odd, e.g. N = 5:
<------- N = 5 -------->
- 0 fs/2 fs
- | | |
- n = 0 1 2 | 3 4 |
- 0/5 1/5 2/5 | 3/5 4/5 5/5
+ 0 fs/2 ( fs )
+ | | ( | )
+ n = 0 1 2 | 3 4 ( | )
+ 0/5 1/5 2/5 | 3/5 4/5 ( 5/5 )
DC positive | negative
+ |
+ \-->fftshift([0, 1, 2, 3, 5]) = [3, 4, 0, 1, 2]
. With K = N // 2:
. N even : DC, K - 1 positive, fs/2, K - 1 negative frequencies
--
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