Re: Transmit Output Power (CW) #v5

Joe Puma

Thanks Evan. I have done the power mod on V3 and also used different sized bias resistors which worked better for my board.  My power out on CW is slightly higher then on SSB and it’s not because of the CW carrier. My emails are along the 331 emails as I was asking questions so I am familiar with Allison’s mod and comments about the differences between power out on CW And SSB. I know if you’re going to do the mod. It’s best to test your SSB out and use the CW carrier. 


On Mar 12, 2020, at 9:02 AM, Evan Hand <elhandjr@...> wrote:


To the best of my knowledge, the v5 boards have the upgrades in the sections prior to the first mixer (upgrading the 2n3904 to BFR93W) related to SSB performance.  The upgrades that are not done are in the driver and predriver stages where the 2n3904s are suggested to be replaced with 2n2222a or better devices.  Those sections are the same for both CW and SSB and can be modified for more consistent performance per Allison/KB1GMX in messages over a year ago.  The original work was done on the v3 and v4 boards, which then brought up the harmonics and spurs issues.  This lead to the v5 fixes that solved them through both redesign of the output filter sections of the board and the addition of a 45 MHz low pass filter between the 45 MHz IF stage and the first mixer T2.  The 40 meter power "dip" has not been addressed.  I believe that the v5 boards are not as bad as some of the prior boards.  I conjecture that one of the issues was incorrect turns or spacing of the 40 meter lpf inductors that seems to have reduced the problem, but not eliminate it.

To get more information of what has been tried to balance power out across bands I would read through the 331 messages that start with this one from Allison:
Message #49729

There has not been a significant change to the uBitx in the stages from Q90 through the output lpf, so there is some opportunity to improve, though the output that Rob listed is not as bad as some that have been posted on this message board.

Above are just suggestions, conjecture, and beliefs on my part.  Please take that into account and please excuse any errors or misconceptions on my part.


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