Warren did us a service by showing that IMD on the uBitx is worse than it should be
and where that is coming from.?
I agree it should be fixed.
However,? some IMD and some residual carrier are relatively minor sins
compared to strong harmonics and out-of-band spurs.
Looking at Warren's screen shots, the two highest peaks are 1khz apart,
and in a perfect rig are the only peaks that would be in the display.
We see one fairly strong peak 1khz beyond on each side,? and some lesser peaks
20dB down from those strong unwanted peaks.
As shown, that signal is taking up less bandwidth than an AM phone signal.?
At QRP power levels, some will consider this acceptable.
Warren's screen shots only show as far as the D1,D2 mixer,
not shown is how much worse this gets after going through the power amp.
He has reported that "On 40 meters the best IMD achievable was 12 dB"
That was likely with RV1 gain set quite low, not much power out.
But if those lesser peaks remain 20dB below the strongest unwanted peaks,
then the uBitx likely remains within the acceptable bandwidth of an AM phone signal.
For now, evaluate your rig carefully for splatter, especially if goosing the mike gain.?
Acknowledge reports that your signal is splattering into adjacent channels,
and perhaps report such events to the forum.
Do not use an external high power amp with the uBitx, keep it at 5 or 10 Watts.
We should all find the time to fix the transmit LPF's somehow, perhaps just
adding an external filter in line with the antenna.
Also do the simple 45khz filter fix for spurs once a preferred mod is arrived at.
With that, it appears this rig may be ok wherever AM phone is legal.?
Especially when operating at QRP levels.
Jerry, KE7ER
On Wed, Sep 12, 2018 at 08:59 AM, iz oos wrote:
ndeed it shows some mess on the SSB mode. It is not a K3. I am curious how the MFJ SSB hf transceivers, like the 9420 which have a powerful average power, behave on this respect (IMD). And also how ham transceivers behave with external speech boxes.
