ICOM 7300 shifts down 500Hz on transmit in FT8

Discussion in 'Working Different Modes' started by M0AGP, Dec 29, 2020.

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  1. M0AGP

    M0AGP Ham Member QRZ Page

    Searching the interwebs, someone else asked this question on a forum and everyone misunderstood the guy's question - my question is nothing to do with being able to tick "Hold Tx Freq" or setting the Tx and Rx frequencies independently.

    When I am in FT8 mode, using WSJT-X with the IC-7300, and the Tx and Rx frequencies are for example both set to 1000 Hz, and the transmitter in receive mode is showing 14.074.00, when the rig goes into Tx mode the frequency readout moves down to 14.073.500, which I assume means I am transmitting 500Hz lower.

    Is this normal? I have the feeling it didn't previously do this, but I can't remember if I checked the transmit frequency previously.

    I have been on FT8 since xmas and have made hundreds of successful FT8 and FT4 contacts btw, so this is not an initial set-up issue.
  2. W1VT

    W1VT Ham Member QRZ Page

    In the Settings menu there is a "Split Operation" setting. This is used to keep your transmit audio frequency near the center of the passband. Many rigs roll off the voice audio at high and low frequencies. This can only be done by moving the carrier frequency.
    WD4ELG likes this.
  3. M0AGP

    M0AGP Ham Member QRZ Page

    Thanks - Ok - so if I understand this, it would only kick in if one is near the high or low end of the passband. But this happens at 1000 Hz, near the center of the passband. I had followed someone's setup process for the 7300 on FT8 and one of the things to do was to set split operation to "fake it" for the 7300.

    I would be interested in hearing if other 7300 users also have this downshift on transmit with the same Split Operation setting.
  4. KM8V

    KM8V Premium Subscriber QRZ Page

    Yes, with split operation (which you should use) this is normal and desirable for the reasons mentioned by W1VT.
  5. KE5MC

    KE5MC Premium Subscriber QRZ Page

    Likely your 7300 has a RIT / XIT function. Both allow reception and transmissions to be deviated +/- from your frequency dial setting. Not commonly used together, but one at a time when the other party is running an older rig with less than optimal on frequency receive and transmit. Or when in a net with others and everyone is not on the same frequency.

    I'm not saying it not a 'split mode' setting in WSJT-X, just another possible source. Typically RIT/XIT are set to 000 and stay that way until needed, which I have found to be seldom.
  6. W1VT

    W1VT Ham Member QRZ Page

    Split may not be necessary if you can set up your 7300 for a flat audio passband. A flat passband may be accessible via a data mode setting.
    You can test this if you have a wattmeter with sufficient precision for your needs.
    Check to see that the power output doesn't change as you move across the FT8 waterfall on transmit.

    A user group with several thousand users may be the best place to discuss the optimum settings for a particular radio. Some of us don't make enough money to keep up with the latest rigs.

    Zak W1VT
    WD4ELG likes this.
  7. M0AGP

    M0AGP Ham Member QRZ Page

    Thanks to all for your comments, but the rig has now stopped doing this... ?!? I haven't touched the settings in WSJT-X or the rig. Well I guess if you put a computer into something (like a radio) then you should expect it to act weirdly... Problem solved I guess! Hmm...
  8. WD4ELG

    WD4ELG Ham Member QRZ Page

    I only see it happen if I am TX below 1300 Hz (IIRC)
    M0AGP likes this.
  9. AE0GL

    AE0GL XML Subscriber QRZ Page

    From section 4.2 of the user's manual:
    • Split Operation: Significant advantages result from using Split mode (separate VFOs for Rx and Tx) if your radio supports it. If it does not, WSJT-X can emulate such behavior. Either method will result in a cleaner transmitted signal, by keeping the Tx audio always in the range 1500 to 2000 Hz so that audio harmonics cannot pass through the Tx sideband filter. Select Rig to use the radio‚Äôs Split mode, or Fake It to have WSJT-X adjust the VFO frequency as needed, when T/R switching occurs. Choose None if you do not wish to use split operation.
    K3RW and M0AGP like this.
  10. M0AGP

    M0AGP Ham Member QRZ Page

    Thanks guys - I just came cross this myself now too.

    If I understand correctly, when I was thinking I was being clever by choosing an offset of like 500, where there was nobody transmitting, the rig was undoing this effort by shifting the base frequency from like 21.074.00 to something like 21.073.00, and and pushing me back up between 1500 and 2000! This could explain my difficulty in making FT8 contacts - I would see someone as +3 and they could not hear me even though I *thought* I was transmitting in the clear. The rig would set me right back in the very busy 1500-2000 region where there is lots of QRM!

    Please correct me if I am misunderstanding here

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