Re: [wsjt-devel] Does the FT8 signal spike at the beginning of each transmission?

[Reino T. <rei...@ko...>]

>1.  The power spike problem can be “avoided” through keeping the xmtr power low at the beginning of each cycle and then  gradually increasing it.  I have bit of auxiliary code in Xojo which can do this, ramping power up during the first 5 seconds of the cycle.  

Is it known what actually causes power spikes? WSJT-X as such is not the reason, but some control in radio adjusts audio path gain. If the radio audio path is set linear in the sense gain is the same independent of time, then there should not be any extra spike due to ‘stepwise’ start of audio tone. In most radios audio path gain is changed due to ALC actions. How fast ALC cuts off extra output power depends on the radio design; in worst case the ALC control may even ‘oscillate’.
There could other reasons that also affect output power at the beginning of transmission, such as a drop of power supply voltage, may not be typical in modern radios; or a speech processing action. 
It would be interesting to see what kind of power spikes are generated, if any, when a stepwise audio is fed into radio at various power level (audio levels).

If the power needs to bring up slowly lasting 5 s, then that radio may not work properly at CW or voice. In any case it would degrade decoding performance. Perhaps ramp up time could be 5 ms to 50 ms.

73, Reino oh3ma