From 7ed5bf4e2b881fce87a255377e5e62e005cc0d73 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20=C3=96stling?= <robert@ling.su.se>
Date: Tue, 29 Aug 2017 13:35:24 +0200
Subject: [PATCH] Imported WSPR encoder script

---
 encode.py | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 encode.py

diff --git a/encode.py b/encode.py
new file mode 100644
index 0000000..6618d66
--- /dev/null
+++ b/encode.py
@@ -0,0 +1,130 @@
+# WSPR protocol encoding script
+#
+# Input: callsign/locator/power
+# Output: raw symbol sequence (4-symbol alphabet for FSK)
+#
+# Robert Östling SM0YSR
+# 2017-08-29
+
+ALPHABET = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ '
+ALPHABET_IDX = {c:i for i,c in enumerate(ALPHABET)}
+
+LOC_ALPHABET = 'ABCDEFGHIJKLMNOPQR'
+LOC_ALPHABET_IDX = {c:i for i,c in enumerate(LOC_ALPHABET)}
+
+SYNC = [1,1,0,0,0,0,0,0,1,0,0,0,1,1,1,0,0,0,1,0,0,1,0,1,1,1,
+        1,0,0,0,0,0,0,0,1,0,0,1,0,1,0,0,
+        0,0,0,0,1,0,1,1,0,0,1,1,0,1,0,0,0,1,1,0,1,0,0,0,0,1,
+        1,0,1,0,1,0,1,0,1,0,0,1,0,0,1,0,
+        1,1,0,0,0,1,1,0,1,0,1,0,0,0,1,0,0,0,0,0,1,0,0,1,0,0,
+        1,1,1,0,1,1,0,0,1,1,0,1,0,0,0,1,
+        1,1,0,0,0,0,0,1,0,1,0,0,1,1,0,0,0,0,0,0,0,1,1,0,1,0,
+        1,1,0,0,0,1,1,0,0,0]
+
+def encode_word(callsign, locator, dbm):
+    if not callsign[2].isnumeric():
+        assert callsign[1].isnumeric()
+        callsign = ' ' + callsign
+    if len(callsign) < 6:
+        callsign = callsign + (' ' * (6-len(callsign)))
+    assert len(callsign) == 6
+
+    callsign = [ALPHABET_IDX[c] for c in callsign]
+    assert callsign[1] < 36
+    assert callsign[2] < 10
+    assert callsign[3] >= 10
+    assert callsign[4] >= 10
+    assert callsign[5] >= 10
+
+    n_callsign = callsign[0]
+    n_callsign = 36*n_callsign + callsign[1]
+    n_callsign = 10*n_callsign + callsign[2]
+    n_callsign = 27*n_callsign + (callsign[3]-10)
+    n_callsign = 27*n_callsign + (callsign[4]-10)
+    n_callsign = 27*n_callsign + (callsign[5]-10)
+    assert n_callsign < 37*36*10*27*27*27
+
+    assert len(locator) == 4
+    assert locator[2:].isnumeric()
+
+    locator = [LOC_ALPHABET_IDX[c] for c in locator[:2]] + \
+              [ALPHABET_IDX[c] for c in locator[2:]]
+
+    n_locator = (179 - 10*locator[0] - locator[2])*180 + \
+                10*locator[1] + locator[3]
+    assert n_locator >= 179
+    assert n_locator <= 32220
+
+    assert dbm > -64
+    assert dbm < 64
+    n_dbm = 64 + dbm
+
+    n = (n_callsign << (15+7)) | (n_locator << 7) | n_dbm
+
+    # MSB -> LSB order
+    return n
+
+
+def convolute(n):
+    def parity(x):
+        assert x >= 0
+        p = 0
+        while x:
+            p ^= (x & 1)
+            x = x >> 1
+        return p
+
+    # Add zero bits at the end for padding
+    # Total number of bits at this stage: 81
+    n = n << 31
+
+    r0 = 0
+    r1 = 0
+    for i in range(81):
+        b = (n >> 80) & 1
+        n = n << 1
+        r0 = (r0 << 1) | b
+        r1 = (r1 << 1) | b
+        b0 = parity(r0 & 0xF2D05351)
+        b1 = parity(r1 & 0xE4613C47)
+        yield b0
+        yield b1
+
+
+def interleave(s):
+    def byte_bit_reverse(x):
+        assert x >= 0 and x <= 255
+        return int("{0:08b}".format(x)[::-1], 2)
+
+    d = [None]*162
+    s_i = 0
+    for i in range(256):
+        d_i = byte_bit_reverse(i)
+        if d_i < 162:
+            d[d_i] = s[s_i]
+            s_i += 1
+    assert s_i == 162, s_i
+    assert not (None in d), d
+    return d
+
+
+def wspr_encode(callsign, locator, dbm):
+    n = encode_word(callsign.upper(), locator.upper(), dbm)
+    convoluted = list(convolute(n))
+    interleaved = interleave(convoluted)
+    assert len(SYNC) == len(interleaved), (len(SYNC), len(interleaved))
+    symbols = [s + 2*x for s, x in zip(SYNC, interleaved)]
+    return symbols
+
+
+if __name__ == '__main__':
+    import sys
+    if len(sys.argv) != 4:
+        print('Usage: %s callsign locator dbm' % sys.argv[0])
+        sys.exit(1)
+    callsign = sys.argv[1]
+    locator = sys.argv[2]
+    dbm = int(sys.argv[3])
+    print('{%s}' % ','.join(
+        str(x) for x in wspr_encode(callsign, locator, dbm)))
+