Oh no! NOW you tell me that all these years that I have believed that I
have been operating CW, it's really SSB!
(Disclaimer to avoid the otherwise inevitable explanations that a pure
audio tone transmitted via SSB is identical with CW: I know that).
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 8 Apr 2019 08:24, Wayne Burdick wrote:
Hi Phil,
In the K2 the sidetone starts off as a squarewave created by the
microcontroller. This is then shaped and injected into the AF
amplifier. The sidetone is turned on/off at the same time as the
carrier, which is generated by the LO (PLL synth) mixing with a gated
TX BFO signal.
In our DSP-based radios (K3/K3S and KX2/KX3), both the audio sidetone
and the 15 kHz 2nd IF carrier are created by the DSP. Their rising
edges are shaped mathematically using what's called a "raised cosine"
or sigmodal waveform. We experimented to find the ideal waveform
equation, the result being the cleaned signal possible, with
virtually no key clicks. The DSP can of course do other things like
apply amplitude or frequency modulation, generate voice and data mode
signals, apply ALC and audio EQ, etc. CW is just the simplest case of
what can be done.
From the DSP, the digitized audio signal codes to a DAC (part of the
audio CODEC IC), which then converts it to analog for injection into
the AF amp.
The 15 kHz 2nd IF carrier in the K3/K3S goes to a transmit mixer on
the KREF4 module where it's up-converted to about 8215 kHz. It is
then routed to the first IF mixer. The 8215 kHz signal passes through
two crystal filters enroute mixer. In the KX2/KX3, the 15 kHz IF
signal is converted to a pair of IQ signals (90 degrees out of phase
with each other) to directly modulate a quadrature up-converter. The
other input to the up-converter is a pair of balanced LO signals,
again separated by 90 degrees. A result of IQ modulation is that one
sideband is cancelled out, resulting in a single RF carrier at the
desired frequency.
In all cases, the rest of the T/R sequencing involves the usual
amplifiers, PIN diodes, filter switching, etc.
73, Wayne N6KR
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
