Matt,
You will not see analog I/Q signals in the K3 - the 2nd mixer's 15kHz
output feeds an Analog to Digital converter and the I and Q signals only
exist in the digital realm.
In transmit, the same thing happens in reverse - the mixer sees the 15
kHz output of a DAC.
73,
Don W3FPR
On 12/12/2015 2:10 PM, Matt Maguire wrote:
In the K3 schematic, I don’t see any quadrature path starting from the second mixer
in the RX path — the two signals lines coming out of that 2nd RX mixer are a
balanced (differential) output, not in-phase and quadrature signals. On the TX
side, the DSP seems to produce I&Q outputs, but it seems the I signal is not
used for anything and only the Q signal is used as an input to the TX mixer.
This is in contrast to the KX3 where there are I&Q signals used between true
quadrature mixers and the DSP. The IF of the KX3 can be 0Hz (direct conversion),
8KHz (single conversion), or as you point out, in the case of SSB weaver
demodulation the 0Hz mark can be placed in the centre of the signal passband, then
the I/Q signals are passed through the optional roofing low pass filter before
being unfolded/shifted in the DSP.
--
73 de Matt VK2RQ
On 12 décembre 2015 at 10:55:59 PM, David Woolley ([email protected])
wrote:
I don't think these descriptions are accurate, particularly the K2
versus K3 one.
The K3 has a double conversion superhet architecture, with an HF first
IF and an extremely low second one. There is a selectable crystal
filter (using commercial sub-assemblies) in the first IF, which provides
coarse selectivity. The final IF processing is digital. There is a
quadrature path starting from the second mixer, analogue at that stage.
Combined with digital processing, this creates an analogue of a
phasing design receiver to suppress the final IF image, rather than the
audio image. As the signal continues in quadrature, the digital
processing may also act analogously to a phasing receiver to do the
final conversion and audio image stripping, but it may be that the
internal logic is more complex than that - the fine details are a trade
secret, although they may or may not have release information about that
part of it.
The K3X, for CW at least, implements a hybrid analogue/SDR direct
conversion, phasing design. For SSB it may do the same, but it is also
possible that it actually implements a final passband centre at 0Hz, and
then does a final frequency shift to move the centre of the passband to
the correct audio frequency (i.e. they could have implemented it as a
single conversion architecture). Selectivity is provided entirely by
digital processing.
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