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Need of Eqaulization ?

Started by mite_learner ●September 27, 2013
Dear Members,

I am experimenting on digital 4-FSK (orthogonal) communication system.   On
the demodulation side, I am using AGC and then 4 filters to detect tones
and then using symbol timing.  My question is how can I know that I need
equalization looking at the signal if I transmit and receive the signal
over the air?  How can I verify that my signal is being affected by
multipaths ?

--
Mite	 

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Reply by Tim Wescott ●September 27, 20132013-09-27
On Fri, 27 Sep 2013 07:39:48 -0500, mite_learner wrote:


> Dear Members,
> 
> I am experimenting on digital 4-FSK (orthogonal) communication system.  
> On the demodulation side, I am using AGC and then 4 filters to detect
> tones and then using symbol timing.  My question is how can I know that
> I need equalization looking at the signal if I transmit and receive the
> signal over the air?  How can I verify that my signal is being affected
> by multipaths ?


Does the on-air signal show significantly more intersymbol interference 
than the signal when you do bench testing?  If so, then equalization may 
help (and you may have multipath).

Do some tones get significantly attenuated with respect to the other 
tones when you are on-air vs. bench testing?  If so, then you may have 
multipath.

It's not an easy question for me to answer; my knowledge of this subject 
is more on an intuitive "show me the signal" sort of level.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Vladimir Vassilevsky ●September 27, 20132013-09-27
On 9/27/2013 7:39 AM, mite_learner wrote:

> Dear Members,
>
> I am experimenting on digital 4-FSK (orthogonal) communication system.   On
> the demodulation side, I am using AGC and then 4 filters to detect tones
> and then using symbol timing.


Very stupid system.


>  My question is how can I know that I need
> equalization looking at the signal if I transmit and receive the signal
> over the air?  How can I verify that my signal is being affected by
> multipaths ?


If you can't tell if equalization is needed, then you don't need 
equalization.

VLV
Reply by mite_learner ●September 27, 20132013-09-27
>On 9/27/2013 7:39 AM, mite_learner wrote:
>> Dear Members,
>>
>> I am experimenting on digital 4-FSK (orthogonal) communication system.  

On

>> the demodulation side, I am using AGC and then 4 filters to detect

tones

>> and then using symbol timing.
>
>Very stupid system.
>


Why its a very stupid system ? And if that is a stupid system. Can you
please help me model a better one? I 'll appreciate that.  

Mite


>>  My question is how can I know that I need
>> equalization looking at the signal if I transmit and receive the signal
>> over the air?  How can I verify that my signal is being affected by
>> multipaths ?
>
>If you can't tell if equalization is needed, then you don't need 
>equalization.
>
>VLV
>
>	 


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Reply by mite_learner ●September 27, 20132013-09-27
<snip>

>> I need equalization looking at the signal if I transmit and receive the
>> signal over the air?  How can I verify that my signal is being affected
>> by multipaths ?
>
>Does the on-air signal show significantly more intersymbol interference 
>than the signal when you do bench testing?  If so, then equalization may 
>help (and you may have multipath).
>

How can I check ISI for FSK system ? 
 

>Do some tones get significantly attenuated with respect to the other 
>tones when you are on-air vs. bench testing?  If so, then you may have 
>multipath.
>


I'll check this, thanks for your answer.

--
Mite


>It's not an easy question for me to answer; my knowledge of this subject 
>is more on an intuitive "show me the signal" sort of level.
>
>-- 



>
>Tim Wescott
>Wescott Design Services
>http://www.wescottdesign.com
>
>	 


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Reply by Vladimir Vassilevsky ●September 27, 20132013-09-27
On 9/27/2013 12:12 PM, mite_learner wrote:

>> On 9/27/2013 7:39 AM, mite_learner wrote:
>>> Dear Members,
>>>
>>> I am experimenting on digital 4-FSK (orthogonal) communication system.
> On
>>> the demodulation side, I am using AGC and then 4 filters to detect
> tones
>>> and then using symbol timing.
>>
>> Very stupid system.
>>
>
> Why its a very stupid system ?


AGC is unnecessary and even harmful in this setup.
There are better ways to build system rather then 4FSK with filters.


> And if that is a stupid system. Can you
> please help me model a better one? I 'll appreciate that.


Of course. I accept appreciation in the form of paycheck.

VLV
Reply by Randy Yates ●September 27, 20132013-09-27
"mite_learner" <94814@dsprelated> writes:


> Dear Members,
>
> I am experimenting on digital 4-FSK (orthogonal) communication system.   On
> the demodulation side, I am using AGC and then 4 filters to detect tones
> and then using symbol timing.  My question is how can I know that I need
> equalization looking at the signal if I transmit and receive the signal
> over the air?  How can I verify that my signal is being affected by
> multipaths ?


Did you mean AGC in front of your ADC?

By the way, ignore Vlad. He's made a career out of calling people idiots
- doesn't mean they are.
-- 
Randy Yates
Digital Signal Labs
http://www.digitalsignallabs.com
Reply by ●September 27, 20132013-09-27
On Friday, September 27, 2013 1:22:57 PM UTC-4, mite_learner wrote:

> <snip>
> 
> >> I need equalization looking at the signal if I transmit and receive the
> 
> >> signal over the air?  How can I verify that my signal is being affected
> 
> >> by multipaths ?
> 
> >
> 
> >Does the on-air signal show significantly more intersymbol interference 
> 
> >than the signal when you do bench testing?  If so, then equalization may 
> 
> >help (and you may have multipath).
> 
> >
> 
> How can I check ISI for FSK system ? 
> 
>  
> 


A simple way is to look at the eye pattern with an oscilloscope.

Clay
Reply by Vladimir Vassilevsky ●September 27, 20132013-09-27
On 9/27/2013 1:24 PM, Randy Yates wrote:

> "mite_learner" <94814@dsprelated> writes:
>
>> Dear Members,
>>
>> I am experimenting on digital 4-FSK (orthogonal) communication system.   On
>> the demodulation side, I am using AGC and then 4 filters to detect tones
>> and then using symbol timing.  My question is how can I know that I need
>> equalization looking at the signal if I transmit and receive the signal
>> over the air?  How can I verify that my signal is being affected by
>> multipaths ?
>
> Did you mean AGC in front of your ADC?
>
> By the way, ignore Vlad. He's made a career out of calling people idiots
> - doesn't mean they are.


No matter how to call it, idiots are idiots. Let them make careers.
I design DSP systems which work. And I do it very well.


Vladimir Vassilevsky
DSP and Mixed Signal Designs
www.abvolt.com
Reply by Randy Yates ●September 27, 20132013-09-27
Vladimir Vassilevsky <nospam@nowhere.com> writes:


> On 9/27/2013 1:24 PM, Randy Yates wrote:
>> "mite_learner" <94814@dsprelated> writes:
>>
>>> Dear Members,
>>>
>>> I am experimenting on digital 4-FSK (orthogonal) communication system.   On
>>> the demodulation side, I am using AGC and then 4 filters to detect tones
>>> and then using symbol timing.  My question is how can I know that I need
>>> equalization looking at the signal if I transmit and receive the signal
>>> over the air?  How can I verify that my signal is being affected by
>>> multipaths ?
>>
>> Did you mean AGC in front of your ADC?
>>
>> By the way, ignore Vlad. He's made a career out of calling people idiots
>> - doesn't mean they are.
>
> No matter how to call it, idiots are idiots. Let them make careers.
> I design DSP systems which work. And I do it very well.


And you went from birth to designing DSP systems in, what, 15 minutes?
-- 
Randy Yates
Digital Signal Labs
http://www.digitalsignallabs.com