> Could some DSP guru please provide some hints to
> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
> design for which the input data streams (I, Q) are synchronized with a
> 1 MHz clock. In this case
> what should be the carrier frequency ? I understand that the Nyquist
> criteria must hold, and so in this case what should be the carrier
> signal frequency ? Any hints would be valuable - thnks in advance.
Impossible to say given the information you've provided. Often times just the
fact that you've got complex IQ samples and not real samples means you've
already downconverted to a lowpass signal, but that's not always the case.
Why not examine the spectrum of a few thousand samples and see?
--
Randy Yates % "My Shangri-la has gone away, fading like
Digital Signal Labs % the Beatles on 'Hey Jude'"
yates@digitalsignallabs.com %
http://www.digitalsignallabs.com % 'Shangri-La', *A New World Record*, ELO
Reply by Avier●December 18, 20102010-12-18
>On 12/17/2010 12:53 PM, Eric Jacobsen wrote:
>> On Fri, 17 Dec 2010 12:36:10 -0600, Vladimir Vassilevsky
>> <nospam@nowhere.com> wrote:
>>
>>>
>>>
>>> Daku wrote:
>>>
>>>> Could some DSP guru please provide some hints to
>>>> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
>>>> design for which the input data streams (I, Q) are synchronized with
a
>>>> 1 MHz clock. In this case
>>>> what should be the carrier frequency ?
>>>
>>>
i hope you want to make aloopback
sampling >>>>>mod>>>up conversion >>>>>>down conversion
>>>>>>demod>>>sampling
you can start with generating a carrier ,,,,your concern should be the
carrier freq and sampling rate by this i mean that suppose you have a
carrier of 64 khz the max samples you can have in your sine/cos wave
generation for carrier will be 16(16x64=1 MHz)but you can also use less
samples ...it all depends on you ,,,,,oyu can use different combinations
like 128 khz with 8 samples ,,,,\\
the first thing you should do is to make a whole system design interms of
sampling rate ,,,keeping in view your dsp specs ,,,,,and then defining your
system
Reply by Tim Wescott●December 17, 20102010-12-17
On 12/17/2010 12:53 PM, Eric Jacobsen wrote:
> On Fri, 17 Dec 2010 12:36:10 -0600, Vladimir Vassilevsky
> <nospam@nowhere.com> wrote:
>
>>
>>
>> Daku wrote:
>>
>>> Could some DSP guru please provide some hints to
>>> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
>>> design for which the input data streams (I, Q) are synchronized with a
>>> 1 MHz clock. In this case
>>> what should be the carrier frequency ?
>>
>> Try the frequencies of 0, -1, and +/- j
>>
>>> I understand that the Nyquist
>>> criteria must hold, and so in this case what should be the carrier
>>> signal frequency ? Any hints would be valuable - thnks in advance.
>>
>> Don't poke your nose into the things far beyond your comprehension.
>>
>> VLV
>
> That sort of comment has no apparent redeeming value and has been
> causing the entire group harm by way of damaged reputation. It'd be
> appreciated if you could dial it back a bit.
Thanks Eric -- for the sentiment, and for wording it diplomatically.
Vladimir: he's right. You weren't born knowing everything; you seem to
forget that.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by Eric Jacobsen●December 17, 20102010-12-17
On Fri, 17 Dec 2010 12:36:10 -0600, Vladimir Vassilevsky
<nospam@nowhere.com> wrote:
>
>
>Daku wrote:
>
>> Could some DSP guru please provide some hints to
>> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
>> design for which the input data streams (I, Q) are synchronized with a
>> 1 MHz clock. In this case
>> what should be the carrier frequency ?
>
>Try the frequencies of 0, -1, and +/- j
>
>> I understand that the Nyquist
>> criteria must hold, and so in this case what should be the carrier
>> signal frequency ? Any hints would be valuable - thnks in advance.
>
>Don't poke your nose into the things far beyond your comprehension.
>
>VLV
That sort of comment has no apparent redeeming value and has been
causing the entire group harm by way of damaged reputation. It'd be
appreciated if you could dial it back a bit.
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
Reply by Jerry Avins●December 17, 20102010-12-17
On Dec 17, 1:36�pm, Vladimir Vassilevsky <nos...@nowhere.com> wrote:
> Daku wrote:
> > Could some DSP guru please provide some hints to
> > my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
> > design for which the input data streams (I, Q) are synchronized with a
> > 1 MHz clock. In this case
> > what should be the carrier frequency ?
>
> Try the frequencies of 0, -1, and +/- j
>
> > I understand that the Nyquist
> > criteria must hold, and so in this case what should be the carrier
> > signal frequency ? Any hints would be valuable - thnks in advance.
>
> Don't poke your nose into the things far beyond your comprehension.
Oh come on, Vlad. It's called "jumping in with both feet." I learned
electronics (after building a superregenerative receiver from plans)
by tearing out the guts of a Magnavox (or was the first one a
Capehart?) and reorganizing the old components, cutting distortion and
improving frequency in the process. Although built in quantity in the
middle 1940s, those console radios had been designed before WWII. By
1950, enough more had been learned so it was easy to do better.
Jerry
--
Engineering is the art of making something decent out of what came in
the box.
Reply by Vladimir Vassilevsky●December 17, 20102010-12-17
Daku wrote:
> Could some DSP guru please provide some hints to
> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
> design for which the input data streams (I, Q) are synchronized with a
> 1 MHz clock. In this case
> what should be the carrier frequency ?
Try the frequencies of 0, -1, and +/- j
> I understand that the Nyquist
> criteria must hold, and so in this case what should be the carrier
> signal frequency ? Any hints would be valuable - thnks in advance.
Don't poke your nose into the things far beyond your comprehension.
VLV
Reply by Tim Wescott●December 17, 20102010-12-17
On 12/17/2010 08:11 AM, Daku wrote:
> Could some DSP guru please provide some hints to
> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
> design for which the input data streams (I, Q) are synchronized with a
> 1 MHz clock. In this case
> what should be the carrier frequency ? I understand that the Nyquist
> criteria must hold, and so in this case what should be the carrier
> signal frequency ? Any hints would be valuable - thnks in advance.
> Could some DSP guru please provide some hints to
> my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
> design for which the input data streams (I, Q) are synchronized with a
> 1 MHz clock. In this case
> what should be the carrier frequency ? I understand that the Nyquist
> criteria must hold, and so in this case what should be the carrier
> signal frequency ? Any hints would be valuable - thnks in advance.
Do you mean the I and Q streams are _sampled_ at 1MHz, or that the
sampling is done at some lower rate and the samples happen at the clock
edges?
With I, Q data, the carrier frequency after sampling can be just about
anything you want* -- you've got enough information in your pair of
signals to change the frequency from anything to anything within the
interval [-Fs/2 Fs/2].
For that matter, with decent down-conversion, you're going to capture
the carrier and it's close-by spectrum with good fidelity, as long as
you don't alias far-away spectrum onto your signal.
So the question you _should_ be asking is how fast can your data rate
be, and what sort of pulse shaping should you be using.
* Although wanting to keep the after-sampling carrier frequency = 0, to
avoid making your brain hurt, is a laudable desire.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by Daku●December 17, 20102010-12-17
Could some DSP guru please provide some hints to
my problem - my DSP is a bit rusty ? I am experimenting with a QPSK
design for which the input data streams (I, Q) are synchronized with a
1 MHz clock. In this case
what should be the carrier frequency ? I understand that the Nyquist
criteria must hold, and so in this case what should be the carrier
signal frequency ? Any hints would be valuable - thnks in advance.