[Elecraft] Receivers?

[Hajo Dezelski]

Hi,

the block diagram of the K2 can be found in the owners manual page 148.
http://www.elecraft.com/manual/E740001_K2%20Owner's%20Manual%20Rev%20I.pdf

73 de Hajo DL1SDZ

Gruss
Hajo

---
Cela est bien dit, mais il faut cultiver notre jardin.

On Sat, Dec 12, 2015 at 12:55 PM, David Woolley <forums at david-woolley.me.uk>
wrote:

> I don't think these descriptions are accurate, particularly the K2 versus
> K3 one.
>
> The K2 is a fairly conventional, single conversion, analogue design.  As
> stated, it uses the crystal filter for primary selectivity.  It typically
> has up to two crystal filter options, one hard wired, and the other as an
> integral part of the SSB adapter.  The hard wired one is adjustable, and
> the SSB one is fixed.  The filters are constructed by the final assembler,
> from individual crystals.  Although there is a DSP option, it works purely
> on the audio.
>
> The K3 and K3X are software defined radios (SDRs) of the non-direct
> sampling variety.  I use SDR in the technical sense, not in the amateur
> radio community sense; the latter requires the digital processing to be
> performed on a PC.  This means they have an analogue front end with at
> least one analogue mixer, but the final processing is done digitally.
>
> 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 K3 also does digital processing on the recovered audio, but this is
> done within the same digital processor as the final IF processing.
>
> 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.
>
> For both the K2 and K3, first mixer image rejection is provided by a
> combination of band pass filters, optimised for each band, and a low pass
> filter, also optimised for the band.  For the KX3, the image is the one
> removed by the phasing, although there is also analogue band and low pass
> filtering - I'm not sure whether this is switched, or there is a single,
> compromise, filter.
>
> Block diagrams for all three are fairly easy to find.  I have the K2, so
> did that from memory, but the K3 one is at <
> http://www.qsl.net/wb4kdi/Elecraft/K3/K3_Block.png> and the KX3 at <
> http://www.elecraft.com/manual/KX3%20Manual%20Block%20Diagram.pdf>. There
> are likely other places, including a better K3 image.
>
> --
> David Woolley
> Owner K2 06123
>
> On 11/12/15 21:40, Ron D'Eau Claire wrote:
>
>> The K3 and K2 and conventional superhetrodyne formats with an Intermediate
>> Frequency in the H.F. range and crystal filters to set the passband. The
>> K2
>> has an adjustable crystal filter and the K3 uses fixed crystal filter
>> bandwidths. The basic K2 bandwidth is established by the crystal filter
>> while the K3 adds an adjustable DSP filter after the crystal filter. (The
>> K2
>> has an optional audio DSP for enhanced filtering.)
>>
>
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