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RTTY DX work with Wide Splits and One Slice

Larry Loen  WO7R
Larry Loen WO7R Member ✭✭
edited February 2020 in SmartSDR for Windows
Like others, I have struggled to do RTTY with Smart SDR.  One problem is that my preferred (if aging) software, MixW2, seems to not understand how infinite the bandwidth is on the Flex.  My other favorite, Fldigi, isn't much smarter.  They presume the usual 3K bandwidth or so of an SSB channel.

I had been having some success using BOTH Fldigi and MixW2 with two slices, one for transmit, one for receive, but I have recently discovered a workable solution which, while not perfect, is at least workable.

Basic idea:  Toggle between RIT on and RIT off.

1.  Figure out from the panadapter where, generally, the DX seems to be listening.  Set your base frequency 2000 or 3000 cycles _above_ the DX to bring you within that range.  If it is 5000, then use that.  Whatever it takes.  Set the RIT to -2000 or -3000 as needed to match that base frequency you selected.  Listen to the DX with the RIT on.  On MixW2, which allows me to monitor multiple listening locations (pseudo slices), this scheme works well and easily.  On Fldigi, it's a little more complex, because you can briefly "right click" to listen on a secondary frequency, which is a bit tricky for time and for accidentally moving.

2.  When the DX makes it clear that he/she has selected a station, turn RIT off (I usually do this just before the DX finishes its message).  You are now "on frequency" well above the DX and where you expect the DX is listening.  This is also your "generic" transmit frequency which is offset wherever you want to put it by clicking on the RTTY software's waterfall.

3.  You have limited time, but locate where the winner of the moment is coming back.  Quickly make this "the simplex frequency" (as far as MixW2 or Fldigi is concerned).  Then decide whether to use that frequency or go up or down a bit.  Plan yourself on _that_ frequency even if the winner isn't done transmitting. 

4.  Enable RIT and hear the DX station finish the QSO and then the DX will call QRZ.

5.  Transmit on the frequency selected in 3 and see if you win.  If not, repeat 2 through 4 until you do.  You may have to change the offset from -2000 to -4000 or whatever it takes for a given pileup as the DX drifts up the band.  That may mean you lose a call or two, but so what.  It beats not working the DX at all.

6.  What do you do in 3 if the pileup is so large, there are two or three plausible winners all with about the right timing?  One idea is to decide which one (by timing) was most likely to be responding to the DX as opposed to just mindlessly calling.  I then pretend that's the winner (there may not be time to plant there and decode) decide whether to move up or down a bit, and hope.  Nowhere near as good as when you really do identify the winner, but some chance beats none.  If there is time to plant somewhere (if you aren't frozen by indecision) then by all means plant there and see if you are right.  If not, you can save a few electrons and wait for the next round because it was one of the other two and maybe it isn't worth the trouble to guess.  You must plant and decode some of the time if you really want to win, because you have to at least be in the 3K passband wherever the DX is listening.

Notice that on this scheme, you are always ready to transmit.  It is the DX that you "pop" in and out from being heard as you switch from the DX' transmit frequency to what you hope is he DX' receive (your eventual transmit).  The goal is to be within the 3K window as much as possible.


  • Mark Erbaugh
    Mark Erbaugh Member ✭✭
    edited February 2020
    Interesting strategy. Has anyone tried running two instances of MixW with two different slices and DAX channels? MixW has a dual channel mode, but I think that only works if the two audio channels are on the left and right channels of the audio input, and that's something I haven't been able to figure out with SSDR.
  • Sergey R5AU
    Sergey R5AU Member ✭✭
    edited April 2017
    i am usually turn on 2 slices with 2 different DAX channels, and selecting different devices for In and for Out in DIGI Appl. however this is very easy with Profiles in my F6700 but need more manipulations in DIGI Appl and has no well interoperability with DXcluster 

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