kopia lustrzana https://github.com/jamescoxon/dl-fldigi
75 wiersze
3.1 KiB
Plaintext
75 wiersze
3.1 KiB
Plaintext
/**
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\page tune_page TUNE - Transmit a single tone carrier.
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\tableofcontents
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\section tune TUNE Mode
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Too often you see an overdriven signals on the digital sub-bands;
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multiple audio sidebands on PSK, splatter from overdriven MFSK and
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RTTY. There is absolutely no reason for a transceiver driven
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by fldigi to exhibit this type of performance. You can set up
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your computer / transceiver for good solid performance without excessive
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drive.
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<br>
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The "TUNE" button generates a continuous single frequency audio signal
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at the exact frequency to which the waterfall cursor has been set. The peak
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amplitude of this signal is the peak amplitude of every modem signal
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generated by fldigi. None will exceed this value, even the simultaneous
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multi-tone modes like Throb. Every modern SSB transmitter uses some automatic
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level control ALC for preventing overdrive for SSB voice. A little overdrive
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on a voice channel can be tolerated to a degree. In fact, that is what
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an analog RF compressor does, overdrive and then subsequent filtering.
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But you absolutely cannot tolerate that with the digital modes. Here is the
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way to set up your transceiver for a clean signal. I recommend starting out
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with a dummy load, but an "off hour" for a band might work just as well if
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you do not have a dummy load.
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<br>
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<ul>
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<li>For Windows users</li>
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<ul>
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<li>Set your sound card output level to the minimum on the Windows
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mixer</li>
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</ul>
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<li>For Linux users</li>
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<ul>
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<li>Set your PCM level to about 80%</li>
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<li>Set your Transmit Level control for minimum output level.</li>
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</ul>
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<li>Enable the "Tune" mode in fldigi ... you do have CAT or PTT set up ...right?</li>
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<li>Make sure your transceiver's speech compression control is OFF</li>
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<li>Slowly bring up the Mixer audio out until your rig's ALC just starts
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to function (a light blinking or a meter showing this condition).</li>
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<li>Reduce the Mixer audio output until the ALC is disabled.</li>
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<li>You are now transmitting at maximum output power without distortion.</li>
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</ul>
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You can use any level below this and be assured that your output signal
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will be clean. All digital signals that fldigi generates will be limited to
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this peak-to-peak voltage. You should always use the minimum power necessary
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to maintain good comms, remember that even if you are clean at 100 W you
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signal will be so strong among the QRP signals that it will overpower the
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AGC on many receivers that are working another digital station within the
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same SSB bandwidth that you are on. You will appreciate this the first
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time that you are working a weak PSK DX station and someone blasts through
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and captures your AGC.
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<br>
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You should try the the above adjustments at different audio
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frequencies. Transceivers that achieve the SSB filtering with crystal or
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mechanical filters will have a considerable amount of variation across the
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passband of the filter. This will show up as a varying amount of ALC that is
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dependent on the audio frequency. Once you are comfortable with the process
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you can very quickly repeat the "Tune" and set the power for the frequency
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to which the waterfall is set.
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<br>
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\ref tune_page "Return to Top of Page"
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<br>
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\ref main_page "Return to Main Page"
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*/
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