[amsat-bb] WSJT-X FT8 QSO confirmed between W2JAZ and W5RKN on FO-29

Ronald G. Parsons w5rkn at w5rkn.com
Tue Oct 17 17:28:07 UTC 2017

First of all, let me apologize for any disruption I may have caused by my tests (experiment, interference, ...).

Last evening around 0120Z  I was indeed transmitting MSK144 on a downlink frequency of 435.878 (at the satellite) on a pass of FO-29 with a 4 degree max elevation at my location with the satellite over the Atlantic. The pass was monitored by a station in Virginia as a test of using MSK144 at low angles. I deliberately transmitted near the upper end of the passband. I continuously monitored the passband on my panadapter and there were quite a few QSOs on that pass, all well below my frequency. 

I also did a test around 0300Z as shown in your link (http://druidnetworks.com/w5rkn-msk144-fo29.jpg)

If I interfered with any of those QSOs, I am sorry. The test confirmed that MSK144 could be decoded at weak signal levels even in the face of Doppler shift.

As far as the AO-7 incident you mention below, I did on a couple occasions inadvertently cause a mode switch. I was certainly not the only station to cause this action. Because I knew how that action could accidently be caused, I did make a couple posts to AMSAT-BB to help others avoid this mistake.

Again, I am sorry for any problems this may have caused.


From: David Swanson 
Sent: Monday, October 16, 2017 11:03 PM
To: Ronald G. Parsons 
Subject: Re: [amsat-bb] WSJT-X FT8 QSO confirmed between W2JAZ and W5RKN on FO-29

On the FO29 pass at 0155z this evening, I noticed a very hard time getting into the transponder. The pass was nearly overhead, and the 3w-4w that is normally sufficient was barely cutting it. I also noticed it was 'up and down' alot, whereas some moments it was easy to get in, then it would be nearly impossible. There were also pockets of 'noise' all over the transponder, that sounded somewhat digital, but I just couldn't place them. I found W5PFG in the passband (who was portable in a rare grid in western Texas) and he commented on the difficulty of working an otherwise easier bird tonight as well. I checked the screen, and no other birds were obviously in range, so I started scanning around the passband to see what I could hear. Up around 435.870 I found (or rather heard) what I was looking for. I fired up my recorder and captured this:


For those not familiar, that is the telltale sound of MSK144. I work a fair amount of Meteor Scatter in addition to operating satellites, and the noise is unmistakable. Since my shack PC has wsjt-x installed, I quickly fired it up and went to the msk144 mode and after some quick tweaking started decoding the signal. This is a screenshot of what I saw:


This signal continued for at least 8 minutes (that I recorded) in a 5 second T/R cycle while FO29 was passing high over North America. Every 5 second the digital signal would get transmitted, and all other SSB qsos would start to fail. You might call this an experiment, but I call it intentional QRM. 

*For the record* You are not the first person to play with wsjt-x modes on the linear satellites. Some months ago during the late night hours on the XW's and FO29 when the footprint was primarily over the desert southwest and south pacific, I to "experimented" with FT8 and MSK144. I purposely ran my transmitted signal thru over 100ft of low grade coax to attenuate my uplink to ~1.5w ERP. I made sure the entire transponder was empty before starting, announcing myself, then started the transmission. I decoded myself successfully, said "Well that was dumb" and never did it again. I purposely didn't announce what I had done to the world because I knew someone would think they were being cool too, and would fire up a 2700hz wide 50% duty cycle mode on a high US pass and QRM people trying to make QSOs out of existence, because said individual would lack even basic situational awareness and courtesy to others. What is extra hilarious about the fact that it is you being the responsible party for destroying a pass, is your constant whining to this mailing list about people using too much power on AO-7, when you're one of the worst offenders. On July 16th this summer, I was roving in EM35 and you called me on the 2155z pass of AO7, and you got the first 3 letters of your callsign out before you killed the bird. I know it was you, because I had already made 3 QSOs right at my AOS with other stations using a reasonable amount of power, and as soon as you key'd up the whole bird started FMing and croaked before you even finished your call. You didn't get that grid that day, and after the stunt you pulled this evening - you won't be getting any grids from me in the future either.  

-Dave, KG5CCI

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