I agree with Gary that something is causing a voltage drop or a power issue at the 13.8 volts.? CW uses another output for the sidetone and unbalances the first mixer to allow the Si5351 frequency to go to Q90.? Though small, a slight uptake in power is required.? The symptoms suggest a possible thermal shutdown of the LM7805.? You can check to see if it is getting excessively hot (you can not hold your finger on it).
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In addition to monitoring the power supply, also try different bands.
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There is another LM78xx regulator (U2) for the IRF510 bias that is off until transmitting.? If that regulator is the issue, it should not matter whether the transmitter is in CW or SSB mode.
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You could also try one or two diodes to see if that makes a difference.? A variable bench power supply would be ideal.
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You can always accept that the radio must have 12 volts or less.
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73
Evan
AC9TU
