Differences

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--- info:40m [2024/09/07 15:58] – [7050-7053 sub-band plan] m5mpc
+++ info:40m [2025/11/12 21:24] (current) – m0lte
@@ Line 1: / Line 1: @@
 ====== 40m Packet ======
-.45 (centre) has been used for FSK300 IL2P packet for some time now, but suffers from bad general QRM / other digital mode traffic.
+.45 (centre) was used for FSK300 packet for some time, but suffers from bad general QRM / other digital mode traffic.
-There is a carve-out in the UK 40m band plan for unattended digital modes at 7050 to 7053. [[https://ukrepeater.net/|ETCC]] have been perfectly willing to grant FACs within that carve-out for UK packet radio stations.
+There is a carve-out in the UK 40m band plan for unattended digital modes at 7050 to 7053. [[https://ukrepeater.net/|ETCC]] have already granted several FACs within that carve-out for UK packet radio stations.
 There is a known long-standing source of QRM at 7055 LSB (3kHz), rendering the top 1kHz of the carve-out compromised.
-Known UK users have now migrated to that carve-out, as follows:
+UK users have now migrated to the sub-band between 7050 and 7053, as follows:
 ===== 7050-7053 sub-band plan =====
-^  Slot^ Usage                              ^ Centre freq ^ USB dial freq   ^
+^  Slot^ Usage               ^ Centre freq ^ USB dial freq   ^ NinoTNC MODE DIP switch ^
-^  1| FSK300 IL2P                           | 7050.30     | 7048.60 (FSK) 7048.8 (BPSK)        |
+^  1| AX.25 FSK300 IL2P+CRC  | 7050.30     | 7048.60 (FSK) (7048.8 if channel is migrated to BPSK in future)  | 1110 / 14 |
-^  2| ARDOP 500Hz                           | 7050.95     | 7049.45         |
+^  2| ARDOP 500Hz            | 7050.95     | 7049.45         | |
-^  3| BPSK300 IL2P+CRC                      | 7051.60     | 7050.10         |
+^  3| AX.25 BPSK300 IL2P+CRC | 7051.60     | 7050.10         | 1000 / 8 |
 Note - For Slot 1, NinoTNC tone frequency centre is 1500Hz for BPSK, 1700Hz for FSK.  Hence different dial freq.
-Note - QT Soundmodem users, for slot 1, can use dial 7048.8 with a CT (Centre Tone) of 1500Hz for both FSK and BPSK - Just change the mode setting.
+Note - QT Soundmodem users only, for slot 1, can use dial 7048.8 with a CT (Centre Tone) of 1500Hz for both FSK and BPSK - Just change the mode setting.
 "Centre" means the spot frequency on which the mode's RF energy, whatever the mode, should be centred. As a convenience, I have included the dial frequency (the frequency you set your radio's VFO to) required for the NinoTNC (different per mode).
@@ Line 32: / Line 32: @@
 The end result should be three separate data channels, co-existing harmoniously within a single ~1.8kHz audio passband, with less QRM from other band users / intruders.
-==== Notes ====
+===== Modes =====
+Slot 1 is currently FSK300 IL2P+CRC AX.25 (packet). Slot 2 is reserved for ARDOP (not AX.25) in coordination with existing users. Slot 3 is currently BPSK300 IL2P+CRC AX.25 (packet).
+IL2P is Improved Layer 2 Protocol. +CRC is a recent enhancement over IL2P to bring the chance of corrupt frames being returned to the host to effectively zero.
+**All HF stations in this sub-band use and require IL2P+CRC.**
+FSK300 IL2P+CRC //sounds like// "classic" 300 baud AX.25 packet, but is not decodeable by legacy TNCs.
+BPSK is binary phase-shift keying, an alternative to frequency-shift keying, which achieves around 7dB more sensitivity, all else being equal.
+IL2P+CRC and BPSK are decodable by [[https://www.cantab.net/users/john.wiseman/Documents/QtSoundModem.html|G8BPQ's QtSoundModem]] and the hardware KISS [[https://wiki.oarc.uk/packet:ninotnc|NinoTNC]].
+===== Notes =====
 With 500Hz occupied bandwidth, there is 150Hz guard between slots.
@@ Line 38: / Line 52: @@
 With 600Hz occupied bandwidth, there is 50Hz guard between slots.
-We will be close together, but not overlapping. It is important to be accurate with frequency selection.
+We are close together, but not overlapping. Just because you hear tones other than your own mode, doesn't mean your modem can't hear the expected mode - the audio tones don't overlap.
-Precise occupied bandwidth is dependent on both the mode and the particular modem implementation.
+It is important to be accurate with frequency selection, and to ensure the cleanliness of your transmissions (use a websdr to monitor, you should be ~500Hz wide with clean edges. If you aren't, you are likely overdriving your radio with too much audio, or have a ground loop [[https://wiki.oarc.uk/radios:ft-450d#usage_with_ninotnc|info on resolving that]]).
+Precise occupied bandwidth is dependent on both the mode and the particular modem implementation - and this is different from determining interoperability.
 QPSK2400 (~2.4kHz occupied bandwidth for 2400bps) has proven too difficult for the SNRs we can practically achieve on 40m HF NVIS.
-BPSK300 should provide around 7dB more sensitivity than FSK300, all else being equal.
+===== QtSoundModem recipe for monitoring traffic =====
+Set the radio dial to 7049.45 USB
+Set modem 1 (slot 1) to:
+  * FX25 mode: none
+  * IL2P mode: IL2P only
+  * Send CRC: checked
+  * Check CRC: checked
+  * AFSK AX.25 300bd @ 850Hz
+Set modem 2 (slot 3) to:
+  * FX25 mode: none
+  * IL2P mode: IL2P only
+  * Send CRC: checked
+  * Check CRC: checked
+  * BPSK AX.25 300bd @ 2150Hz
+ARDOP can be decoded simultaneously with ''ardopf''. The slot 2 centre frequency - for ARDOP - is at a fixed 1500Hz offset. You need to run in limited bandwidth mode ARQBW 500MAX - maybe 1000 - need to test that.
+===== Note on software =====
-IL2P+CRC is favoured over IL2P since the data corruption rate with straight IL2P was unacceptably high in practice on HF.
+Please don't run Dire Wolf on HF - it lacks both ACKMODE - which is particularly problematic with longer transmit cycles since the node has no way to know when the modem is available to send - and also has no transmit bandwidth filtering - so will obliterate the other slots on transmit. We depend on good discipline to avoid interfering with each other in this very limited slice of bandwidth.