Re: [Flexradio] Flex 6000 Family Dynamic Range

[Stephen Hicks, N5AC]

Clay,

Just in rough numbers, you get a 1/2-bit for every divide-by-two decimation
you do.  If you are looking at dynamic range in a 500Hz bandwidth (this is
what we typically do).  The math I generally use to get there is
log(f1/f2)/log(2)/2.  I just think this way as a programmer (do everything
in base 2). So if you take log(245.76E6/500)/log(2)/2 you get 9.4 extra
bits when added to the 16 gives you 25.5 bits (152.7dB dynamic range).
 This assumes all 16-bits of the ADC are "good" which is probably not a
good assumption.  I'd have to pull out the notes and look at the data sheet
again, but this should give you a rough idea.  Hopefully I haven't made an
additional "duh" today myself!

Bottom line -- there's plenty of dynamic range.

Also, if you are interested, we are using Xilinx DSP48E1 blocks which use
an 18x25 multiplier and so Xilinx tools generate the on-board DDS as a
25-bit DDS by default --- again to preserve the SFDR of the receiver.  We
could add extra bits, but 25 are fine for the same reason.

Steve

Stephen Hicks, N5AC, AAR6AM
VP Engineering
FlexRadio Systems™
4616 W Howard Ln Ste 1-150
Austin, TX 78728
Phone: 512-535-4713 x205
Email: st...@flexradio.com
Web: www.flexradio.com



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On Fri, May 18, 2012 at 6:33 PM, Clay W7CE  wrote:

> Hi Bob,
> If it's OK with everyone, I'd like to count this as my "oh duh" moment for
> today (my target is no more than one per day).  I wasn't thinking about
> decimation.  However, assuming a bandwidth of 192 kHz and a sample rate of
> 245 MHz, doesn't that only give an extra 5 bits or so of effective
> resolution?  That still leaves us 3 bits short of the 5000A ADC, which
> still means 18 dB less dynamic range.
>
> Maybe I missed it in the PDF file, but I didn't see a dynamic range spec.
>
> 73,
> Clay  W7CE
>
>
>
> On 5/18/2012 3:44 PM, Robert McGwier wrote:
>
>>
>> Clay :
>>
>> The difference is more than made up in the the fact that the new AD
>> operates at 245 MHz and the old AD is 200 kHz and you get huge processing
>> gain in the downsample and filter process greatly increases the dynamic
>> range.
>>
>> Bob
>>
>> On May 18, 2012 4:46 PM, "Clay W7CE" > w...@curtiss.net>> wrote:
>>
>>Did anyone else notice that the receivers on the 6500 and 6700 use
>>a 16-bit ADC rather than 24-bit like the 5000A?  That reduces the
>>dynamic range by up to 48 dB (same dynamic range as the 1500).
>> That will probably be fine on HF, but I already have occasional
>>problems with ADC saturation on 6M when locals (within 25 miles)
>>running 1500 watts are transmitting in the 96 or 192kHz bandpass
>>of my current frequency.  Of course, I can eliminate the
>>saturation by turning off my preamp, but then I can't hear the
>>weak station I was trying to work.
>>
>>73,
>>Clay  W7CE
>>
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Re: [Flexradio] Flex 6000 Family Dynamic Range

[Clay W7CE]

Hi Bob,
If it's OK with everyone, I'd like to count this as my "oh duh" moment 
for today (my target is no more than one per day).  I wasn't thinking 
about decimation.  However, assuming a bandwidth of 192 kHz and a sample 
rate of 245 MHz, doesn't that only give an extra 5 bits or so of 
effective resolution?  That still leaves us 3 bits short of the 5000A 
ADC, which still means 18 dB less dynamic range.


Maybe I missed it in the PDF file, but I didn't see a dynamic range spec.

73,
Clay  W7CE


On 5/18/2012 3:44 PM, Robert McGwier wrote:


Clay :

The difference is more than made up in the the fact that the new AD 
operates at 245 MHz and the old AD is 200 kHz and you get huge 
processing gain in the downsample and filter process greatly increases 
the dynamic range.


Bob

On May 18, 2012 4:46 PM, "Clay W7CE" > wrote:


Did anyone else notice that the receivers on the 6500 and 6700 use
a 16-bit ADC rather than 24-bit like the 5000A?  That reduces the
dynamic range by up to 48 dB (same dynamic range as the 1500).
 That will probably be fine on HF, but I already have occasional
problems with ADC saturation on 6M when locals (within 25 miles)
running 1500 watts are transmitting in the 96 or 192kHz bandpass
of my current frequency.  Of course, I can eliminate the
saturation by turning off my preamp, but then I can't hear the
weak station I was trying to work.

73,
Clay  W7CE

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No virus found in this message.
Checked by AVG - www.avg.com 
Version: 2012.0.2176 / Virus Database: 2425/5007 - Release Date: 05/18/12



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Re: [Flexradio] Flex 6000 Family Dynamic Range

[Brian Lloyd]

On Fri, May 18, 2012 at 1:45 PM, Clay W7CE  wrote:

> Did anyone else notice that the receivers on the 6500 and 6700 use a
> 16-bit ADC rather than 24-bit like the 5000A?  That reduces the dynamic
> range by up to 48 dB (same dynamic range as the 1500).


No. Learn about decimation.

-- 
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
br...@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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Re: [Flexradio] Flex 6000 Family Dynamic Range

[Robert McGwier]

Clay :

The difference is more than made up in the the fact that the new AD
operates at 245 MHz and the old AD is 200 kHz and you get huge processing
gain in the downsample and filter process greatly increases the dynamic
range.

Bob
 On May 18, 2012 4:46 PM, "Clay W7CE"  wrote:

> Did anyone else notice that the receivers on the 6500 and 6700 use a
> 16-bit ADC rather than 24-bit like the 5000A?  That reduces the dynamic
> range by up to 48 dB (same dynamic range as the 1500).  That will probably
> be fine on HF, but I already have occasional problems with ADC saturation
> on 6M when locals (within 25 miles) running 1500 watts are transmitting in
> the 96 or 192kHz bandpass of my current frequency.  Of course, I can
> eliminate the saturation by turning off my preamp, but then I can't hear
> the weak station I was trying to work.
>
> 73,
> Clay  W7CE
>
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> Knowledge Base: http://kc.flexradio.com/  Homepage:
> http://www.flexradio.com/
>
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