Using FT4 (Weak Signal Digital Mode) on Satellites

[Burns FISHER]

I’ve had some fun this week figuring out how to use FT4 on satellites.  FT4 is a weak signal mode.  There are many of them, but this one trades off a relatively fast QSO with requiring a slightly stronger signal.  FT4 seems to be getting popular on at least satellite RS-44, but the reason I wanted to use it is because I helped build satellite AO-109, and 109 has blown one of its two PA chips and is very weak (8mW!).  We are going to recommend using FT4 or CW with it, but I thought I would try it first.  I have not used 109 yet, but I thought I would report on my experience on RS-44 to help people get started with YET ANOTHER amateur activity!

First, FT4 is available, along with a number of other weak signal modes, in the software suite called WSJT-X (those of you who just took the technician class/license exam may remember that name 🙂 )  You can download it from https://physics.princeton.edu/pulsar/k1jt/wsjtx.html, and it appears to be available on PC, Mac, and Linux.  (I used PC).

I recommend this video by Ant Levebre N1UW for setting up your system if you are using SatPC32 to track the satellite and an IC9700 radio:  https://www.youtube.com/watch?v=QhfUSRUP910

If, like me, you are using MacDoppler, follow pretty much the same procedure except first you should get the newest MacDoppler (2.40 beta 19 or later).  In this, Don Agro, the developer, was kind enough to add radio modes JA D and B D.  (This is my main complaint about MacDoppler that it uses the old fashioned satellite mode names).  But anyway JA D is 2m uplink, 70cm downlink with sideband modulation through the data port.  B D is 70cm up and 2m down.

I won’t try to teach you how to use WSJT-X here (still learning myself) but one important thing I discovered.  N1UW emphasizes that WSJT-X does not know the frequency or satellite that you are using and thus does not make valid logs.  However, the logs are MOSTLY right.  If you click “log it” after completing a QSO, it puts the log info into an ADIF file, which you can later import into MacLogger for your permanent record and for uplink to LOTW.  Just remember to edit the QSO line in MacLogger to get the right frequency, band, and satellite.  The ADIF file will have the time and call sign, and you can also right click and ask it to look up the contact’s name.

Have fun!

[Burns FISHER]

Just a note several years later.  AO-109 either just did or is about to re-enter and burn up.  Of course you can still use FT4 on other linear satellites (the ‘standard’ is at the low end of the passband; same with CW).

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