[TenTec] Fwd: [External] Re: OT: 7300 buy back program

[Gary Follett]

>  
> From Flex, my questions in red:
> "A number of people have asked how you can get more than 96 dB of instantaneous dynamic range out of a 16-bit A/D converter.  You may think that one can only achieve 6 dB per bit, which would be 96 dB.  Technically the theoretical maximum limit is 6.02n +1.67 dB (wheren is the number of bits).[1,2] What many people fail to understand is that dynamic range is a meaningless term without knowing the final detection bandwidth (i.e. 500 Hz CW filter). Indeed narrowing the final detection bandwidth reduces noise as well. That was true with analog filters too. The only problem with this approach in analog signal filtering was that added electronic again was required to offset the filter loss, often with an INCREASE in overall noise due to the added noise from the amplifier’s noise figure. DSP filtering does not suffer in this regard.
> 
> Instantaneous dynamic range increases with decreasing bandwidth by a factor of 10*log*(bandwidth change).  That means that a 50 Hz filter will provide 10 dB higher dynamic range than a 500 Hz filter.  That is why you hear less noise in the smaller filter.  The actual receiver noise figure (NF) of the radio has not changed but the detection bandwidth has.  Thus the SNR and dynamic range improves accordingly. Within the bandwidth being detected! Therefore, yes, the dynamic range does improve at narrower bandwidths if the dynamic range is noise limited. This would, of course, be true on 40 meters in the summer. However, unless I messed something, this answer does not address the problems that take place when a signal whose amplitude is 148 dB above the LSB (least significant bit) voltage. An A/D converter has a voltage change for each bit. If the span of the A/D is 10 volts, then each bit in a 16 bit A/D accounts for a change in amplitude of 10V/65536 = 0.0015 V/bit (1.5 mV/bit). If you assume that a signal on the antenna of 1 uV is “copyable” in CW, and is thus at least a few dB above the noise floor, S1, for example, on a quiet band, then there would need to be some sort of gain stage (~1000X or 30 dB) to bring this up to one least significant bit. Alternatively, you design so that the LSB step size is 1/1000 of 10 volts or 10 mV. That is allowing only 1 bit to give you your CW signal. Realistically you need 4 bits to give a readable signal on CW, about 6 to 8 bits for SSB. So when you are detecting this 1 uV signal with a 50 Hz filter in place, all is well and you have good instantaneous dynamic range.
> 
>  
> 
> However, the A/D is simultaneously looking at the entire HF spectrum all of the time. It is digitizing that entire spectrum all of the time at twice (or more) the Nyquist frequency, and is extracting each individual signal using the DSP to unravel the complex waveform (which is the Fourier transform of the entire waveform that is digitized). If a signal appears anywhere between 0 and 30 MHz with an amplitude greater than 96 dB above 1 uV, with a 16 bit A/D, you have a problem. A signal 148 dB greater than 1 uV, quite often the case for the large shortwave station down the block, presents a signal voltage of 25 volts. Houston, we have a problem.
> 
> The law of linear superposition, essential for any of this stuff to work, simply states that the instantaneous value of any sampled point is the linear sum of all of the components at the sampling point. Thus, the 25 volt signal from that shortwave station rides on top of the 1 uV signal you are trying to hear. In reality, this will be well outside the“ maximum peak signal handling capability” of the A/D converter.
> 
>  
> 
> When you get outside the“ maximum peak signal handling capability” of the A/D converter, the law of linear superposition is still true, but the A/D cannot measure that signal because it is out of range. Very non-linear things happen when an A/D converter gets outside the“ maximum peak signal handling capability”. That would be known in analog days as “overload” or “blocking”.
> 
>  
> 
> The dynamic range of any ADC is normally assumed to be specified over the Nyquist bandwidth, which is equal to 1/2 of the converter’s sampling rate.  With the ADC used in the FLEX-6000 series, the Nyquist bandwidth is 122.88 MHz.  To calculate instantaneous dynamic range, one needs to know the converter’s specified signal to noise ratio (SNR), maximum peak signal handling capability, sampling rate, and final detection bandwidth.  There are many application notes available from Analog Devices, Linear Technology, Texas Instruments, etc. that aid in these calculations.  It is beyond the scope of this newsletter to provide the detailed education and analysis."
> 
> Sent from my iPad
> 
> On Aug 16, 2016, at 7:59 AM, Barry N1EU <barry.n1eu at gmail.com> wrote:
> 
> You don't need a PC.  You can use Maestro or an iPad.
> 
> Violated the laws of mathematics?  I suggest reading this:
> https://www.flex-radio.nl/flex-6000-serie/dynamicrange/
> 
> Barry N1EU
> 
> On Tue, Aug 16, 2016 at 8:55 AM, Gary J FollettDukes HiFi <
> dukeshifi at comcast.net> wrote:
> 
> 
> Flex has never been shy about touting their own perfection, ala' the 2
> hour on-air infomercials on 20 meters every Saturday afternoon.
>  
> And you still need a PC to run one…
>  
> Apparently someone has devised a way to get more than 96 dB dynamic range
> out of 16 bits and my congratulations to them for having successfully
> violated the laws of mathematics.
>  
> I wish they would apply that to the sub-par Compact Disk format with which
> we are stuck…
>  
> Gary
>  
>  
>  
>  
> On Aug 16, 2016, at 4:25 AM, Barry N1EU <barry.n1eu at gmail.com> wrote:
>  
> The argument that the current 16-bit digital sampling offerings (Flex 6K,
> ANAN-100/200, MB-1, etc) are insufficient in bit depth and sampling rate
> doesn't hold water IMHO.  Besides my own experience of no observable
> overload during major DX and 160M contests, here are a few more tidbits
> to
> consider:
>  
> http://www.eham.net/ehamforum/smf/index.php/topic,110479.0.html
>  
> https://community.flexradio.com/flexradio/topics/adc-
> overload-myths-debunked
>  
> etc etc
>  
> Barry N1EU
>  
> On Tue, Aug 16, 2016 at 7:43 AM, rick at dj0ip.de <Rick at dj0ip.de> wrote:
>  
> EXCELLENT Gary.  Thanks.
>  
> I only disagree on the timeline.  I don't think it will take so long.
>  
> The MB-1 from Sun SDR or Sun Expert (not sure which brand they are
> pushing) "claims" to be what you described, but it costs $5K.  However
> prices will drop rapidly as soon as competition is there.
>  
> Within 3 years we will have it.
>  
> In the year 2020, SDR with knobs a'plenty.  (no computer required)
>  
> BTW, has anyone actually seen or used the MB-1?
> I haven't heard a single user review yet.
>  
> 73 - Rick, DJ0IP
> (Nr. Frankfurt, Germany)
>  
>  
>  
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Gary J
> FollettDukes HiFi
> Sent: Tuesday, August 16, 2016 7:23 AM
> To: Discussion of Ten-Tec Equipment
> Sub