When transmitting in CW mode, the uBitx disables clk0 and clk1,
Clk2 into the D1,D2 mixer is at the operating frequency.?
There is nothing for clk2 to intermodulate with, so CW transmissions are clean?so long as
the transmit LPF's have been taken care of.
There is no need to add a 45mhz crystal filter if you only plan to operate CW.
Some mods proposed here for adding the extra 45mhz crystal filter will disable CW mode,
since they do not provide a DC path for the CW-KEY signal to unbalance the D1,D2 mixer.
IMD (Inter-Modulation-Distortion) when transmitting SSB signals is an issue,
this will create splatter into adjacent channels.? It gets worse as you up the mike gain.
The causes include non-linearities in the IF amps, non-linearities in the four power amp stages,
signal levels into the mixers being too strong, and local oscillators into the mixers not being strong enough.
These issues are known and it should be possible to resolve them in v5.
It remains to be seen if there is an easy fix for v3/v4 boards that sufficiently cures the?IMD issue.
For example, perhaps stronger local oscillators from the si5351 using external buffers may help.
Unlike the spurs and harmonics previously discussed, IMD is close in to your?
transmitted signal, and is something?that other operators nearby in the band may notice.
If you do operate in SSB mode, do not use the uBitx with a high powered amp.
Be ready to acknowledge reports that your signal is splattering into adjacent channels.
Whether or not it is reasonable to operate at 5 or 10 watts with some IMD is up for debate,
I don't recall any reports in the forum of others in the band complaining of splatter.
Jerry, KE7ER?
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On Tue, Sep 11, 2018 at 04:43 PM, Bill Cromwell wrote:
with rearranged low pass filters and the additional 45 MHz filter, CW operation is healthy enough to operate.
