From 80a1deea65932ffc0feb6ea38551e7f6f1e787b8 Mon Sep 17 00:00:00 2001 From: Joe Taylor Date: Mon, 26 Feb 2018 17:56:18 +0000 Subject: [PATCH] Add basic protocol description for WSPR. git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8535 ab8295b8-cf94-4d9e-aec4-7959e3be5d79 --- doc/user_guide/en/protocols.adoc | 45 ++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/doc/user_guide/en/protocols.adoc b/doc/user_guide/en/protocols.adoc index 805ef2e3d..d6a10cebb 100644 --- a/doc/user_guide/en/protocols.adoc +++ b/doc/user_guide/en/protocols.adoc @@ -168,6 +168,51 @@ QRA64 presently offers no message averaging capability, though that feature may be added. In early tests, many EME QSOs were made using submodes QRA64A-E on bands from 144 MHz to 24 GHz. +[[WSPR_PROTOCOL]] +==== WSPR + +WSPR is designed for probing potential radio propagation paths using +low power beacon-like transmissions. WSPR signals convey a callsign, +Maidenhead grid locator, and power level using a compressed data +format with strong forward error correction and narrow-band 4-FSK +modulation. The protocol is effective at signal-to-noise ratios as low +as –31 dB in a 2500 Hz bandwidth. + +WSPR messages can have one of three possible formats illustrated by +the following examples: + + - Type 1: K1ABC FN42 37 + - Type 2: PJ4/K1ABC 37 + - Type 3: FK52UD 37 + +Type 1 messages contain a standard callsign, a 4-character Maidenhead +grid locator, and power level in dBm. Type 2 messages omit the grid +locator but include a compound callsign, while type 3 messages replace +the callsign with a 15-bit hash code and include a 6-character locator +as well as the power level. Lossless compression techniques squeeze +all three message types into exactly 50 bits of user +information. Standard callsigns require 28 bits and 4-character grid +locators 15 bits. In Type 1 messages, the remaining 7 bits convey the +power level. In message types 2 and 3 these 7 bits convey power level +along with an extension or re-definition of fields normally used for +callsign and locator. Together, these compression techniques amount to +“source encoding” the user message into the smallest possible number +of bits. + +WSPR uses a convolutional code with constraint length K=32 and rate +r=1/2. Convolution extends the 50 user bits into a total of (50 + K – +1) × 2 = 162 one-bit symbols. Interleaving is applied to scramble the +order of these symbols, thereby minimizing the effect of short bursts +of errors in reception that might be caused by fading or interference. +The data symbols are combined with an equal number of synchronizing +symbols, a pseudo-random pattern of 0’s and 1’s. The 2-bit +combination for each symbol is the quantity that determines which of +four possible tones to transmit in any particular symbol +interval. Data information is taken as the most significant bit, sync +information the least significant. Thus, on a 0 – 3 scale, the tone +for a given symbol is twice the value (0 or 1) of the data bit, plus +the sync bit. + [[SLOW_SUMMARY]] ==== Summary