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PSK31 Tuning for Transmit

Discussion in 'Working Different Modes' started by KF5PFP, Dec 22, 2020.

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  1. KF5PFP

    KF5PFP XML Subscriber QRZ Page

    I have started using FLDIGI and PSK-31. I have a question about setting up the transmit so I don't overdrive the signal.

    My setup is an Icom 7100 (max 100W) and a Vibroplex 40/20/10 end fed half wave (max 25W). Most advice I have seen is 'turn the radio all the way up and use the software to make sure the ALC barely registers'. For my situation does 'turn the radio all the way up' mean 100W or 25W? If I turn the radio to 100W how do I know I am not sending too much power through the antenna, other than watching the SWR meter?

    I have the radio set at 25W and the ALC is above the minimum but not hitting the max. I have gotten good signal reports from my QTH in North Texas to Florida (SN 31dB, IMD -31dB) and North Carolina. A Ham in Florida sent me screenshots from FLDIGI of my signal and it looked really good.

    Thanks in advance for your help.
  2. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    Radio at 100W output

    Use the sound level adjustments from the OS device level and fldigi to control your output power.

    There should be *no* ALC indication and any rig should be able to do nearly 100W without *any* ALC action.

    You really shouldn’t run more than 50W due to the duty cycle and most are running 25-30W.

    Run into a dummy load, set rig for 100W output power.

    In fldigi in the far lower right there is the attenuator box, set that to 0db.

    In the operating system, go to the sound control panel and find the Icom sound card device, set it to 0 for level. (If the OS level isn’t there, if it’s fixed, then in the menu of the Icom there is a level adjustment, do the adjustment from there instead)

    In fldigi, click the “tune” button.

    Go to the operating system sound device (or the menu adjustment for it on the rig) and slowly bring up the level and look at your power output level on the meter. Bring up the drive until you see 50W out.

    Now, you can control power output by just using the attenuator level in the bottom right hand corner of fldigi. Drop it down from there to 25W.

    Now, you are set to run whatever power up to 50W and without any ALC compression making your transmitted signal dirty and harder to decode.
    KF5KWO likes this.
  3. G0GSR

    G0GSR Ham Member QRZ Page

    Its not so much duty cycle as the peak to mean power ratio of the PSK31 signal.
    This is 4:1 so 25W average power is 100W PEP.

    KC2RGW likes this.

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