Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/17/2010 03:05 PM, Steven Clark wrote:
>
> On Wed, Nov 17, 2010 at 2:45 PM, Marcus D. Leech  > wrote:
>
> On 11/17/2010 12:43 PM, Marcus D. Leech wrote:
>
>
>
> What I'm seeing is that the magnitudes (as seen in the number
> sink) coming off the source, even with roughly  75dB of gain ahead
>  are roughly 0.002 to 0.003 when I'm using 400KHz sampling,
> and roughly 0.0006 to 0.0007 when the bandwidth is 250KHz.  If you
>  process the numbers as voltages, then we're talking a roughly
> 10dB drop in apparent average power level by reducing the
> bandwidth
>  by less than 3dB.  Both 400Khz and 250KHz use a decimation
> that is both even, and a multiple of 4, so they should be
> using exactly
>  the same filter sequence in the decimator, correct?
>
> Marcus, you're a blithering idiot who should routinely be denied
> air.  You have clearly conflated the decimation/bandwidth numbers and
>  erroneously come to the conclusion that they should use the same
> half-band filter lineup.  They don't, you stupid, sorry excuse for
>  an advanced lifeform you. God, can you even tie your shoes
> reliably?  Let's see, 250KHz uses a decimation of 400, which uses both
>  half-bands in the FPGA because it's both even and a multiple of
> 4, whereas 400KHz uses a decimation of 250, which is even, but not a
>  multiple of four, and so only uses a single half-band.  So
> *naturally*, the numbers won't "add up" between the two bandwidths.
>
> Frikkin' hell man, get a clue would you?  Before I come over there
> and whack you upside the head with a gnarly-great clue-by-four.
>
> :-) :-) :-)
>
>
> Don't be so hard on yourself...many of us would have still been stumped :)
> It's definitely not obvious/intuitive (to me, at least) that changing
> the decimation rate just slightly results in adding a whole 'nother
> additional set of filtering.
>
> Shouldn't the half-band filters have unity-gain in the pass-band?
>
> -Steven
Yes, they definitely should have unity-gain within the passband, but
they have a Bessel-like response
   as far as I recall. The edges have a 10dB roll-off, so my guess is
that the convolution of the
   response of those (extended) edges gives us the apparent 8-10dB
difference in average
   power level between 400KHz and 250KHz (or more generally,
decimination-by-factor-of-four vs
   decimation-by-other-even factor).  The difference in detected power
that one would "expect" for
   this bandwidth difference is roughly 2dB, all else being equal. 
Clearly, "all else isn't equal".

Matt would know for sure.

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Steven Clark]

On Wed, Nov 17, 2010 at 2:45 PM, Marcus D. Leech  wrote:

> On 11/17/2010 12:43 PM, Marcus D. Leech wrote:
>
>>
>>
>> What I'm seeing is that the magnitudes (as seen in the number sink) coming
>> off the source, even with roughly  75dB of gain ahead
>>  are roughly 0.002 to 0.003 when I'm using 400KHz sampling, and roughly
>> 0.0006 to 0.0007 when the bandwidth is 250KHz.  If you
>>  process the numbers as voltages, then we're talking a roughly 10dB drop
>> in apparent average power level by reducing the bandwidth
>>  by less than 3dB.  Both 400Khz and 250KHz use a decimation that is both
>> even, and a multiple of 4, so they should be using exactly
>>  the same filter sequence in the decimator, correct?
>>
>>  Marcus, you're a blithering idiot who should routinely be denied air.
>  You have clearly conflated the decimation/bandwidth numbers and
>  erroneously come to the conclusion that they should use the same half-band
> filter lineup.  They don't, you stupid, sorry excuse for
>  an advanced lifeform you. God, can you even tie your shoes reliably?
>  Let's see, 250KHz uses a decimation of 400, which uses both
>  half-bands in the FPGA because it's both even and a multiple of 4, whereas
> 400KHz uses a decimation of 250, which is even, but not a
>  multiple of four, and so only uses a single half-band.  So *naturally*,
> the numbers won't "add up" between the two bandwidths.
>
> Frikkin' hell man, get a clue would you?  Before I come over there and
> whack you upside the head with a gnarly-great clue-by-four.
>
> :-) :-) :-)
>
>
Don't be so hard on yourself...many of us would have still been stumped :)
It's definitely not obvious/intuitive (to me, at least) that changing the
decimation rate just slightly results in adding a whole 'nother additional
set of filtering.

Shouldn't the half-band filters have unity-gain in the pass-band?

-Steven
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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/17/2010 12:43 PM, Marcus D. Leech wrote:



What I'm seeing is that the magnitudes (as seen in the number sink) 
coming off the source, even with roughly  75dB of gain ahead
  are roughly 0.002 to 0.003 when I'm using 400KHz sampling, and 
roughly 0.0006 to 0.0007 when the bandwidth is 250KHz.  If you
  process the numbers as voltages, then we're talking a roughly 10dB 
drop in apparent average power level by reducing the bandwidth
  by less than 3dB.  Both 400Khz and 250KHz use a decimation that is 
both even, and a multiple of 4, so they should be using exactly

  the same filter sequence in the decimator, correct?

Marcus, you're a blithering idiot who should routinely be denied air.  
You have clearly conflated the decimation/bandwidth numbers and
  erroneously come to the conclusion that they should use the same 
half-band filter lineup.  They don't, you stupid, sorry excuse for
  an advanced lifeform you. God, can you even tie your shoes reliably?  
Let's see, 250KHz uses a decimation of 400, which uses both
  half-bands in the FPGA because it's both even and a multiple of 4, 
whereas 400KHz uses a decimation of 250, which is even, but not a
  multiple of four, and so only uses a single half-band.  So 
*naturally*, the numbers won't "add up" between the two bandwidths.


Frikkin' hell man, get a clue would you?  Before I come over there and 
whack you upside the head with a gnarly-great clue-by-four.


:-) :-) :-)




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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/17/2010 02:20 AM, Matt Ettus wrote:


Decimation is filtering.  When you decimate by 512 you are reducing 
noise by a factor of 512 (27dB).  Since you are using a BasicRX, there 
will be very little noise, and 27dB less after decimation.  In fact, 
there is so little noise that the output of the filters is a constant 
0 once it is rounded to 16 bit ints.  That is why the FFT results 
essentially show negative infinity.


The solution is to decimate less in hardware and more in software, or 
to use more amplification.


Matt


OK, to follow-up after a few experiments this morning.  I added roughly 
40dB of gain (in addition to the 35dB or so that was already there)
  of well-filtered gain in front of the USRP2/Basic_Rx.  That appears 
to have caused <400KHz to start working, so I got caught up by
  a red-herring of decimation=256 -- that was a coincidence, but *my oh 
my* what a coincidence!


So, I have over 70dB of gain in front of the USRP2+Basic_Rx combination, 
and I have a stripped-to-the-bones app for investigating things
  that consists of a UHD source, and FFT sink block, and also a 
complex-to-mag block with a number sink.


What I'm seeing is that the magnitudes (as seen in the number sink) 
coming off the source, even with roughly  75dB of gain ahead
  are roughly 0.002 to 0.003 when I'm using 400KHz sampling, and 
roughly 0.0006 to 0.0007 when the bandwidth is 250KHz.  If you
  process the numbers as voltages, then we're talking a roughly 10dB 
drop in apparent average power level by reducing the bandwidth
  by less than 3dB.  Both 400Khz and 250KHz use a decimation that is 
both even, and a multiple of 4, so they should be using exactly

  the same filter sequence in the decimator, correct?


What surprises me is how *tiny* these numbers are--I'm connected to an 
antenna outdoors, and the system can easily "see"
  distant CB stations, for example (I use stuff on the CB bands as a 
kind of gross sanity test for sensitivity).


So now, I'm wondering how things are scaled between the ADC and the 
host.  The ADC is 14 bits twos-complement signed, then it goes
  into the FPGA--do you do 32-bit arithmetic inside the FPGA and then 
re-scale back to 16-bits?


Then those 16-bits get squirted over the GiGe, where UHD picks them up, 
and re-scales them into +/- 1.0 floating point numbers, yes?






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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/17/2010 02:20 AM, Matt Ettus wrote:
>
>
> Decimation is filtering.  When you decimate by 512 you are reducing
> noise by a factor of 512 (27dB).  Since you are using a BasicRX, there
> will be very little noise, and 27dB less after decimation.  In fact,
> there is so little noise that the output of the filters is a constant
> 0 once it is rounded to 16 bit ints.  That is why the FFT results
> essentially show negative infinity.
>
Well, OK, I'll buy that.  But there's a significant change below
decimation=256. A non-linear
  jump from "reasonable-looking data" to "negative infinity".

I'm seeing a jump from a level of around -20dB to "negative infinity" by
changing decimation from
  256 to 260, which is a noise bandwidth change of something like 0.04dB.

So while I'm totally willing to believe that a gross change from 400KHz
to 200KHz might cause a
  bit of weirdness, it seems highly counter-intuitive that a small
change as implied by
  decimation=256 to decimation=260 would cause a huge nonlinear leap in
filter output in
  the decimator.

-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Tom Rondeau]

On Tue, Nov 16, 2010 at 11:15 PM, Marcus D. Leech  wrote:
> On 11/17/2010 02:00 AM, Tom Rondeau wrote:
>>
>> WBX with latest firmware downloaded from Ettus Monday.
>>
>>
> That's the 20100901 firmware or something more recent?

Yes, that's the firmware date I'm using (firmware and FPGA).

Tom


>>> And you're running latest GnuRadio and UHD?
>>>
>> Working from next and pulled from uhd/master yesterday.
>>
>> Tom

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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Matt Ettus]

On 11/16/2010 11:13 PM, Marcus D. Leech wrote:

On 11/17/2010 02:00 AM, Tom Rondeau wrote:


WBX with latest firmware downloaded from Ettus Monday.



Hmmm, I'm using Basic_Rx.  That should make *zero* difference.

I discovered that there's a "magic" break at any sample rate that
requires a decimation>256.
   So *somewhere* is having a hard time with greater-than-eight-bit integers.



Decimation is filtering.  When you decimate by 512 you are reducing 
noise by a factor of 512 (27dB).  Since you are using a BasicRX, there 
will be very little noise, and 27dB less after decimation.  In fact, 
there is so little noise that the output of the filters is a constant 0 
once it is rounded to 16 bit ints.  That is why the FFT results 
essentially show negative infinity.


The solution is to decimate less in hardware and more in software, or to 
use more amplification.


Matt

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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/17/2010 02:00 AM, Tom Rondeau wrote:
>
> WBX with latest firmware downloaded from Ettus Monday.
>
>   
That's the 20100901 firmware or something more recent?

>> And you're running latest GnuRadio and UHD?
>> 
> Working from next and pulled from uhd/master yesterday.
>
> Tom
>
>
>   


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/17/2010 02:00 AM, Tom Rondeau wrote:
>
> WBX with latest firmware downloaded from Ettus Monday.
>
>   
Hmmm, I'm using Basic_Rx.  That should make *zero* difference.

I discovered that there's a "magic" break at any sample rate that
requires a decimation >256.
  So *somewhere* is having a hard time with greater-than-eight-bit integers.




-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Tom Rondeau]

On Tue, Nov 16, 2010 at 8:42 PM, Marcus D. Leech  wrote:
> On 11/16/2010 11:34 PM, Tom Rondeau wrote:
>> On Tue, Nov 16, 2010 at 6:13 PM, Marcus D. Leech  wrote:
>>
>> No answer or insight, just another data point. I've been running UHD
>> apps today at 200 KHz sample rates with not problem.
>>
>> Tom
>>
>>
>>
> Hmm, that *is* interesting.  What daugthercard?  What firmware?

WBX with latest firmware downloaded from Ettus Monday.

> And you're running latest GnuRadio and UHD?

Working from next and pulled from uhd/master yesterday.

Tom

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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/16/2010 11:34 PM, Tom Rondeau wrote:
> On Tue, Nov 16, 2010 at 6:13 PM, Marcus D. Leech  wrote:
>   
> No answer or insight, just another data point. I've been running UHD
> apps today at 200 KHz sample rates with not problem.
>
> Tom
>
>
>   
Hmm, that *is* interesting.  What daugthercard?  What firmware?

And you're running latest GnuRadio and UHD?

I haven't run my hardware under 400KHz for several weeks, and then a
coupla days ago,
  after updating UHD and GnuRadio, it starts showing the "-410dB"
behaviour.  Even in a simple,
  simple flow-graph.  But anything >= 400Khz, and it's fine and dandy again.





-- 
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Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Tom Rondeau]

On Tue, Nov 16, 2010 at 6:13 PM, Marcus D. Leech  wrote:
> On 11/14/2010 02:28 PM, Marcus D. Leech wrote:
>>
>> I did a "git pull" for both UHD GnuRadio yesterday.  I'm on the "next"
>> branch for gnuradio, and on
>>  "master" for UHD.
>>
>> Since doing a rebuild yesterday, bandwidths below 400KHz no longer work
>> on the USRP2.
>>
>> I did a test with a dead-simple flowgraph:
>>
>> UHD single source-->multi-const x 32767-->FFT
>>
>> For bandwidths>= 400KHz, the resulting FFT, with my existing RF
>> front-end with 40dB gain feeding
>>   the BASIC_RX on my USRP2, the FFT looks just fine (showing a level
>> around -40dB).
>>
>> But anything below 400KHz bandwidth (I tried various bandwidths between
>> 200KHz and 400KHz),
>>   produces an FFT with nothing useful in it, and a "level" around -400dB.
>>
>> This used to work just fine below 400KHz. What happened?
>>
> So, nobody has answered my question yet.
>
> Even with the "latest and freshest UHD (master) and GnuRadio (next)", Rx
> bandwidths below 400KHz don't appear to work correctly on a USRP2
>  with UHD, giving a flat-line at -410dB in the FFT display.

No answer or insight, just another data point. I've been running UHD
apps today at 200 KHz sample rates with not problem.

Tom

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Re: [Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

On 11/14/2010 02:28 PM, Marcus D. Leech wrote:

I did a "git pull" for both UHD GnuRadio yesterday.  I'm on the "next"
branch for gnuradio, and on
  "master" for UHD.

Since doing a rebuild yesterday, bandwidths below 400KHz no longer work
on the USRP2.

I did a test with a dead-simple flowgraph:

UHD single source-->multi-const x 32767-->FFT

For bandwidths>= 400KHz, the resulting FFT, with my existing RF
front-end with 40dB gain feeding
   the BASIC_RX on my USRP2, the FFT looks just fine (showing a level
around -40dB).

But anything below 400KHz bandwidth (I tried various bandwidths between
200KHz and 400KHz),
   produces an FFT with nothing useful in it, and a "level" around -400dB.

This used to work just fine below 400KHz. What happened?


So, nobody has answered my question yet.

Even with the "latest and freshest UHD (master) and GnuRadio (next)", Rx 
bandwidths below 400KHz don't appear to work correctly on a USRP2

  with UHD, giving a flat-line at -410dB in the FFT display.





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[Discuss-gnuradio] bandwidths< 400Khz no longer work with USRP2

[Marcus D. Leech]

I did a "git pull" for both UHD GnuRadio yesterday.  I'm on the "next"
branch for gnuradio, and on
 "master" for UHD.

Since doing a rebuild yesterday, bandwidths below 400KHz no longer work
on the USRP2.

I did a test with a dead-simple flowgraph:

UHD single source-->multi-const x 32767-->FFT

For bandwidths >= 400KHz, the resulting FFT, with my existing RF
front-end with 40dB gain feeding
  the BASIC_RX on my USRP2, the FFT looks just fine (showing a level
around -40dB).

But anything below 400KHz bandwidth (I tried various bandwidths between
200KHz and 400KHz),
  produces an FFT with nothing useful in it, and a "level" around -400dB.

This used to work just fine below 400KHz. What happened?


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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