[Elecraft] KX3 direct conversion system

[須崎 純一]

Many thanks for OT's comment on this system.
I don't understand the process within the multiplexer chip in detail, however, I think it's basically PSN.
In Japan, Kenwood adopted PSN in it's first SSB transmitter TX-15 about 45 years ago.
US manufactures were more advanced at that time.
It's my pleasure Elecraft has now established it's unique position.

73, Jun JI1TLL 

> From: ron at cobi.biz
> To: elecraft at mailman.qth.net
> Date: Wed, 15 Aug 2012 19:46:10 -0700
> Subject: Re: [Elecraft] KX3 direct conversion system
> 
> Us OTs recognize this system as the reverse of the phasing system of generating SSB that was popular in the 1950's. Phasing lost popularity as low-cost and high-quality crystal filters became available because, like the KX3, they depended upon highly accurate phase shift and gain control over the entire bandwidth of the audio channel to cancel the opposite sideband. (Remember, everything then was analog, meaning building wide-band analog phase shift networks that remained stable from discrete components.) Back in the "day" it wasn't easy to do and achieve more than 20 or perhaps 30 dB of attenuation. That was adequate in the 50's when almost all 'phone' stations were using double-sideband a.m. occupying 6 kHz of bandwidth. 
> 
> In the KX3 it appears to be returning with substantially greater phase and gain accuracy, and so opposite sideband suppression, than we could achieve back then.
> 
> 73, Ron AC7AC
> 
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Wayne Burdick
> Sent: Wednesday, August 15, 2012 9:07 AM
> To: ji1tll at jarl.com
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] KX3 direct conversion system
> 
> 須崎 純 (Jun) wrote:
> 
> > I built KX3 kit (S/N830) up last week after fixing some errors.
> > As soon as trying some functions, I found it's really a direct 
> > conversion system.  A weak leaked signal was observed with another 
> > receiver just on the watching frequency.
> 
> You can reduce the KX3's VFO signal leakage to another receiver nearby by setting MENU:RX ISO to ON.
> 
> Yes, it is similar to direct conversion, except that there are two channels (I and Q, like other SDRs), allowing for image rejection. The
> KX3 uses this architecture rather than superhet to provide the SDR feature, as well as to reduce the number of stages, allowing the unit to be very compact.
> 
> 73,
> Wayne
> N6KR
> 
> 
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