Wednesday, December 13, 2017

Meteor Scatter

Wow ,  discovered MSK144 and Meteor Scatter quite by accident this evening!    There looked to be a bit of Sporadic E on 6m so I I joined the FT8 party.   Signals were fading in and out as is usual with a weak E opening but there was something else going on...there was sudden ,  sometimes very short burst of really strong signals.   I knew that the Giminid shower was ongoing saw some really good ones last eve from the hot tub before work.   I was looking at QRZ DX spotting network and observed some activity at 50.260 MHz ....beside the post it said " MSK144 " .     Dialed over to the freq and was quite surprised when there was a strong bust of data sound to be around a 1kb data rate!  Checked the WSJT program and sure enough there was a " MSK144" mode.   Dialed it in and before I could blink I was decoding the data.    Googled " MSK144 " found a quick primer and before I knew it I had logged a QSO bouncing signals off of the ionized trails of what use to be a meteor ...how cool is that?

Was using 30 Watts into a Fan Dipole.  Below is my QSO with VE2XK
























PSK Reported data the flags that are time stamp are folks that received me and reported it to the Internet.   The  " L" flags are stations that I heard.




















Here is the skinny on MSK144 .....

MSK144 is a high speed data mode introduced into WSJT-X to replace FSK441 for meteor scatter (MS) and other paths where short-term burst openings are likely to occur. Unlike all the other modes within the WSJT suite, MSK144 does not rely upon pure frequency shift keying to convey information symbols, but on a more efficient coherent modulation type called Minimum Shift Keying. Messages sent using MSK144 utilise the same compressed format as most of the other WSJT type messages, ie two callsigns and a report or locator; callsign plus CQ or other messages, or 13 characters of plain text. WSJT-X also introduces one or two other message types. The message is compressed down to 72 source bits to which an 8 bit checksum is appended to (virtually) eliminate false decodes. The 80 resulting source bits are then expanded using a Low Density Parity Code (LDPC) to 144 one-bit channel symbols before modulating an audio tone at 2000 baud for upconversion in an SSB transmitter. 144 symbols at 2000 baud means the entire message is sent in a burst just 72 milliseconds long. Bursts are repeated end-to-end for fixed Tx/Rx durations of 5 , 10, 15 or 30 seconds each. For reception, just one complete burst (which can have a number of symbols in error) is all that is necessary for a complete decode.





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