Re: Many uBitx's have reduced power on 40m CW

Jerry Gaffke


I have no idea if you will have trouble with IMD on 80m.
Increasing R83 would cure IMD and also further improves the impedance seen by the filter,
but reduces power on all bands.

Could just rotate RV1 for suitable 80m power levels.

Could use TXC (turns on the 80m LFP) to turn on a FET which attenuates the signal at RV1

Could add something at Q911,912 that reduces gain at low frequencies similar to C81,R83
Having Q90 as a buffer should give the filter and mixer a proper load impedance.

Jerry, KE7ER

On Thu, Apr 8, 2021 at 09:41 AM, Evan Hand wrote:

I did not think of the LPF causing the dip on 30meters.  That makes sense.

I will check the SSB signal on 80meters with my RSP1A and the SA software.  The choice would then be to change R83 to a higher value like in the v3 10ohms.  Maybe 6.8ohms?

Guess I am not finished yet.

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