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Q's about SSB, fldigi and IC-7300

Discussion in 'Working Different Modes' started by KM6RNF, Apr 10, 2020.

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  1. KM6RNF

    KM6RNF Ham Member QRZ Page

    I've only ever used VHF (local repeater FM) and small CW kits, so SSB on HF is a new thing to me. I recently got an IC-7300 to work SSB and digital modes. What I'm seeing is unexpected.

    First, when I flip between LSB and USB on the Icon, signals will shift by 3KHz on the Icom's waterfall. I might have expected sounds above and below the center line to disappear, but not to move. It appears that the Icom's mixing frequency is actually about 1500Hz off of the center line and that flipping between LSB and USB flips that frequency about the center line. Does this sound correct?

    You might wonder why I care about that, but this brings up the second question or issue. When I use fldigi (with flrig), while it follows the radio very well, the transmission looks strange. The frequency of the radio (say 7070KHz) will match fldigi perfectly as well as the mode (say USB-D). But when I click on the waterfall (say at 7070.5), the transmission will not occur at 7070.5 but instead at 7069. Transmission at 7071.5 occurs at 7070. I first noticed the problem on the Icom's waterfall, but it has been verified by a third party.

    I would have expected fldigi to simply put out a 500HZ tone (for example), and for the Icom to mix it up to 7070 + 500HZ. This is one of the niceties of USB, right? But instead, it seems to be 7070 + 500Hz - 1500Hz. This could cause someone to transmit outside of a band!

    Does anyone know what's up? Everything seems to be configured correctly except for this issue, so I'd like to get it sorted and get on the air more.


    (I'm using fldigi 4.1.11 for what its worth.)

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