From 01ed64ad2d55da1e68b8d465b5e0420f9664af07 Mon Sep 17 00:00:00 2001
From: Neale Pickett
+ Resources
@@ -96,6 +93,13 @@
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E . | -I .. | -S ... | -H .... | -4 ....- | -
V ...- | -3 ...-- | -|||
U ..- | -F ..-. | -|||
- | 2 ..--- | -|||
A .- | -R .-. | -L .-.. | -||
- | ||||
W .-- | -P .--. | -|||
J .--- | -1 .---- | -|||
T - | -N -. | -D -.. | -B -... | -6 -.... | -
X -..- | -||||
K -.- | -C -.-. | -|||
Y -.-- | -||||
M -- | -G --. | -Z --.. | -7 --... | -|
Q --.- | -||||
O --- | -- | 8 ---.. | -||
- | 9 ----. | -
- This is a CW repeater, - named after Alfred Vail, - who may or may not have invented what's called "Morse code", - but clearly had some role in it. -
- -- Just like a radio repeater, - anybody can connect and start transmitting stuff, - and this will broadcast it to everyone connected. -
-- I needed a place to practice CW with actual human beings, - and I wanted it to be as close as possible to what I'd experience on a radio. - I also didn't have a lot of money to spend on equipment, but I did have a computer, phone, and gamepad. - Nothing else like this exists on the Internet, as far as I can tell. -
- -- It means this repeater doesn't repeat anything: - nothing you key in will be sent anywhere. - These are to help people practice and learn, - without worrying about anyone else hearing them fumble around. -
- -- This is the "drop tone", and will be accompanied by an error. -
-- This means the packet arrived so late, it can't be played in time. - In technical terms: the timestamp of the packet plus the receive delay - is less than the current time. - It can't be scheduled to play, because we can't go back in time. -
-- This could be happening for three reasons: -
-- Vail attempts to correct for clock differences, - but making sure your computer has correct time, - down to the millisecond, - can help with reliability. -
- -- Neale Pickett kd7oqi -
-- The Internet isn't exactly like radio waves: - it still goes at near the speed of light, - but there are multiple hops between endpoints, - which buffer up transmissions, and multiplex them onto a single uplink connection. - These repeaters (routers) - are also allowed to just drop things if they need to. - It's the responsibility of the communicating parties - to work out whether something needs to be retransmitted. - Because of this, - there's no telling how long it will take for a transmission to get to a destination. -
-- Each Vail transmission (packet) consists of: -
-- The repeater does nothing but broadcast everything it gets - to every connected Vail client, - including the one that sent the packet. - When your client gets back the exact same thing it sent, - it compares the current time to the time in the packet. - This is the round-trip time: - the time it takes for a packet to get from your computer to the repeater and back. -
-- When the client gets a packet it didn't send, - it adds the receive delay to the timestamp, - and schedules to play the tones and silences in the packet - at that time. -
-- By adding the maximum round-trip time to the longest recent transmission - (the length of a dah, hopefully), - your client can make a guess about how much time needs to be added to a received timestamp, - in order to have it play back in the future at the time it comes in. - This is just a guess. - If you're communicating with somebody with a higher round-trip time than you have, - you'll need to raise your receive delay to account for it. -
-