While I've not used the QCX I know its progenitor the KK7B MiniR2, R2pro, MicroR2
very well and yes?the direct conversion image rejecting RX sounds very very good.
I've useed that for SSB TX too.
The need for quadrature LO has always been an issue with those and generally a
pain of done analog.
A decade back I did a design using miniR2/T2 as an upconverting 6M radio.
The uR2 works as well at 1mhz as 200 same performance.? So why not use it??
at higher?? ?No reason not to.? While its full analog its not hard to get I/Q?
LO right when its fixed.? Sideband selection is at audio.? Narrow filters,
do it at audio.
In process is a HF upconverting radio using the microR2/MicroT2
?as the IF (basically half the uBITX) with one mod rather than running
them with a VFO at 40M I moved them to?36mhz(fixed) and upconvert
to that.? As a wide tuning RX its simpler than uBitx as only two
oscillators are needed and one can be a crystal as its a common
frequency.? The other is one conversion.? For TX I did not go wide
band as I only wanted to TX on the standard bands (80,40,20,15,10)
so band pass after conversion and lowpass on TX.
How this is relevant.? My experience with 36mhz down converting TX showed
the image and spur issue and filters were planned anyway so it was a not a
lock out.? However moving the micrR2 and T2 to 64mhz or higher is fairly
trivial as its a fixed frequency and 64mhz crystals (for the LO) are common
or the Si5351.? ?With that in place and some simplification a wide 1.8-30mhz
tuning upconverting TRX is now a known thing.? No crystal filters and a whole
lot less RF hardware.? Its superhet but bridges the usual issues of mushy filters
and tuning the IQ LO.? The 5351 solves the issue of a lo from 64mhz to 94mhz.
While those radios were specifcally for SSB based work CW can be done the
same way as the ubitx, inject DC into the TX mod and carrier out. Add sidetone
and move the TX frequency (down converting LO) for the correct offset and go.
The QCX is an example of how non-superhet radios can make inroads when?
the quadrature LO or any LO solution is as simple as a Arduino and 5351.
Some would argue code is complex but once done its always reusable.
Rick Campbell and Dan Tayloe and others gave us a better set of tools to
solve the issue.
Allison
Craig Wadsworth