[Elecraft] Understanding the KX3 Block Diagram

[Wayne Burdick]

Igor Sokolov wrote:

> Is roofing filter switched out when dual RX is enabled in KX3?

The wider of the two roofing filters (FL2) is usable with dual RX if  
the distance between VFO A and B is small (about 2 kHz). Beyond this  
the filters are switched out, leaving the "native" I.F. bandwidth of  
about 15 kHz (FL1).

(The K3, with its true sub receiver, has a definite filtering  
advantage over the KX3's dual watch feature. But it's also six times  
bigger :)

As mentioned in the manual, this is one of several cases where the  
roofing filters must be bypassed. The others are AM, FM, ESSB, and  
with some wide-band noise-blanker settings.


> What limits dual RX to +/- 10 kHz? Is it ADC or something else?

Sampling rate, mostly, and some existing firmware constraints. +/- 15  
kHz may be possible later.

Wayne
N6KR


>
> 73, Igor UA9CDC
> ----- Original Message ----- From: "Wayne Burdick" <n6kr at elecraft.com>
> To: "Matt Maguire" <vk2acl at gmail.com>
> Cc: "Elecraft Reflector" <elecraft at mailman.qth.net>
> Sent: Thursday, March 08, 2012 10:20 AM
> Subject: Re: [Elecraft] Understanding the KX3 Block Diagram
>
>
>> Also keep in mind those roofing filters. This is a substantial
>> departure from other SDRs. Wasn't easy, either :)
>>
>> Wayne
>>
>> On Mar 7, 2012, at 8:17 PM, Matt Maguire wrote:
>>
>>> Here is a presentation by G8VOI which talks about some of the
>>> concepts used in radios like the KX3.
>>> http://www.pe0fko.nl/g8voi/SDR_1.pdf
>>>
>>> The presentation uses a softrock radio as a concrete example, so
>>> where the presentation talks about PCs and soundcards, keep in mind
>>> that for the KX3 this corresponds to the A/D & D/A convertors and
>>> DSP/microcontroller that are built into the KX3 itself.
>>>
>>> 73, Matt VK2ACL.
>>>
>>>
>>> On 08/03/2012, at 2:19 PM, David Stratton wrote:
>>>
>>>> Hoping that I may not be the only Ham puzzled by the block diagram
>>>> of the
>>>> KX3 I am asking that someone please explain it because it is so
>>>> different
>>>> from the superheterodyne radio concept I have become accustomed  
>>>> to in
>>>> current amateur radios. I understand direct conversion radios but
>>>> what is
>>>> all the stuff that's there besides the mixer-oscillator and audio
>>>> amplifier
>>>> needed by a direct conversion radio? It seems to me the KX3 block
>>>> diagram
>>>> looks a lot like radios put forth some time ago by Rick Campell
>>>> KK7B. Pardon
>>>> my saying so but the KX3 radio looks like it has a weak front end
>>>> and a
>>>> heavy back end that hopes to make up for the weak front end!
>>>>
>>>> Dave - KO4KL
>>>>
>>>>
>>>>
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