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KX3 and Quadarature down-sampling

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Gary D Krause

KX3 and Quadarature down-sampling

I've been wondering what Quadarature down-sampling is? This is the first that
I have heard of it.

Gary,
N7HTS

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Alan Bloom

Re: KX3 and Quadarature down-sampling

On Tue, 2011-07-26 at 08:44 -0600, Gary D Krause wrote:
> I've been wondering what Quadarature down-sampling is? This is the first that
> I have heard of it.

It's like a two-channel direct-conversion receiver. The two channels
are on the same frequency but use local oscillators that are 90 degrees
out of phase. With suitable processing, the in-phase (I) and quadrature
(Q) mixer outputs give both the amplitude and phase of the signal.
Among other things, that makes it possible to suppress the unwanted
sideband of an SSB signal without a crystal filter.

Alan N1AL

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Johnny Siu

KX3 and Quadarature down-sampling

Hello Alan,

I have limited knowledge of radio.

Is that the operation theory of quadarature down-sampling something similar to the image rejection mixer in the IC7800?

Excuse me if I ask a stupid question.

TNX & 73,

Johnny VR2XMC

從︰ Alan Bloom <[hidden email]>
收件人︰ Gary D Krause <[hidden email]>
副本(CC)︰ Elecraft <[hidden email]>
傳送日期︰ 2011年07月26日 (週二) 11:08 PM
主題︰ Re: [Elecraft] KX3 and Quadarature down-sampling

On Tue, 2011-07-26 at 08:44 -0600, Gary D Krause wrote:
> I've been wondering what Quadarature down-sampling is? This is the first that
> I have heard of it.

It's like a two-channel direct-conversion receiver. The two channels
are on the same frequency but use local oscillators that are 90 degrees
out of phase. With suitable processing, the in-phase (I) and quadrature
(Q) mixer outputs give both the amplitude and phase of the signal.
Among other things, that makes it possible to suppress the unwanted
sideband of an SSB signal without a crystal filter.

Alan N1AL

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Gary D Krause

(no subject)

In reply to this post by Gary D Krause

Thanks for the explanation, Alan. So, my next question is, how does it compare
with a crystal filter? It is better? Does it give you more flexibility with
filtering?

Thanks,
Gary, N7HTS

On Tue, 26 Jul 2011 08:08:38 -0700
Alan Bloom <[hidden email]> wrote:

On Tue, 2011-07-26 at 08:44 -0600, Gary D Krause wrote:

I've been wondering what Quadarature down-sampling is? This is the
first that I have heard of it.

It's like a two-channel direct-conversion receiver. The two channels
are on the same frequency but use local oscillators that are 90 degrees
out of phase. With suitable processing, the in-phase (I) and quadrature
(Q) mixer outputs give both the amplitude and phase of the signal.
Among other things, that makes it possible to suppress the unwanted
sideband of an SSB signal without a crystal filter.

Alan N1AL

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Don Wilhelm-4

Re: Quadrature down-sampling

Gary,

That part has nothing to do with the filtering - the next step is to
convert both the I and Q signals to digital and do the manipulation
mathematically - that includes filtering, detection, and most other
signal processing functions. The result is then converted to an analog
audio signal for the final amplification.

Yes, the amount of flexibility is limited only by the amount of DSP code
and speed of the DSP processing - all manner of "magic" can be performed
once the signal is placed into the digital "number soup".

That is the normal process for a Software Defined Radio - some use a
computer soundcard to do the digital/analog conversion and the processor
does the computation, but there is no reason why that process cannot be
done using a dedicated processor. The K3 already works the same way,
but the frequency for the ADC is higher - that really makes little
difference. Using the mixer to convert directly to baseband is quite
common in SDR receivers. While we are getting close to the time when
direct digital sampling from the antenna is feasible, it is not yet
available at a price we would want to pay.

73,
Don W3FPR

On 7/26/2011 11:43 AM, Gary D Krause wrote:

> Thanks for the explanation, Alan. So, my next question is, how does it compare
> with a crystal filter? It is better? Does it give you more flexibility with
> filtering?
>
> Thanks,
> Gary, N7HTS
>
>
> On Tue, 26 Jul 2011 08:08:38 -0700
> Alan Bloom<[hidden email]> wrote:
>
> On Tue, 2011-07-26 at 08:44 -0600, Gary D Krause wrote:
>
> I've been wondering what Quadarature down-sampling is? This is the
> first that I have heard of it.
>
>
> It's like a two-channel direct-conversion receiver. The two channels
> are on the same frequency but use local oscillators that are 90 degrees
> out of phase. With suitable processing, the in-phase (I) and quadrature
> (Q) mixer outputs give both the amplitude and phase of the signal.
> Among other things, that makes it possible to suppress the unwanted
> sideband of an SSB signal without a crystal filter.
>
> Alan N1AL
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Alan Bloom

Re: KX3 and Quadarature down-sampling

In reply to this post by Johnny Siu

Hi Johnny,

I'm not familiar with the IC7800, but in general an image-reject mixer
uses the same basic principle. It's the same as the "phasing" method of
SSB generation used 50 years ago, except that they didn't use the word
"quadrature" or "I/Q" in those days.

Alan N1AL

On Tue, 2011-07-26 at 23:31 +0800, Johnny Siu wrote:

> Hello Alan,
>
> I have limited knowledge of radio.
>
> Is that the operation theory of quadarature down-sampling something
> similar to the image rejection mixer in the IC7800?
>
> Excuse me if I ask a stupid question.
>
> TNX & 73,
>
>
> Johnny VR2XMC
>
> 從︰ Alan Bloom <[hidden email]>
> 收件人︰ Gary D Krause <[hidden email]>
> 副本(CC)︰ Elecraft <[hidden email]>
> 傳送日期︰ 2011年07月26日 (週二) 11:08 PM
> 主題︰ Re: [Elecraft] KX3 and Quadarature down-sampling
>
> On Tue, 2011-07-26 at 08:44 -0600, Gary D Krause wrote:
> > I've been wondering what Quadarature down-sampling is? This is the first that
> > I have heard of it.
>
> It's like a two-channel direct-conversion receiver. The two channels
> are on the same frequency but use local oscillators that are 90 degrees
> out of phase. With suitable processing, the in-phase (I) and quadrature
> (Q) mixer outputs give both the amplitude and phase of the signal.
> Among other things, that makes it possible to suppress the unwanted
> sideband of an SSB signal without a crystal filter.
>
> Alan N1AL
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>