Noise figure paradox
 

"Jim Lux" wrote in message
...
For example, an Agilent N5181 looks like the noise floor is
around -160dBc/Hz well away from the carrier (e.g. 10MHz). That's probably
representative of the overall noise floor with the carrier at some level
like 0dBm. If we take that level, then it's 14 dB above kTB of -174 dBm/Hz

Thanks. Presumably then if you dial the carrier power down much below -14dBm
you're then going to have a -174dBm/Hz noise floor due to the output
attenuators as Owen mentioned...

---Joel

Noise figure paradox
 

"Owen Duffy" wrote in message
...
Joel, you misunderstood my calc.

Yeah, Ian pointed that out to me. My apologies...

Noise figure paradox
 

On Mon, 23 Mar 2009 23:39:42 GMT, Owen Duffy wrote:

My observation is that convention is the use the antenna connector or w/g
flange as a reference point for such calcs. It may even be laid down in
standards... but I am not sure. Someone else may know?

Hi Owen,

What you describe is typically called the "reference plane" in
metrology. This is a term that is found in many standard methods of
RF measurement. Most often it is a point that is neutral to the
introduction of new variables (and concommittant error). To achieve
this neutrality, it must be an access point that is reproducible -
hence the association with the connector or flange as these are
controlled points of access. Connectors can be measured separately to
validate their contribution to error and variability as they can
typically be mated to instrumentation whose own connectors have been
validated by more rigorous means.

There are other issues with the reference plane, one of which is heat
transfer through it which should ring bells here.

73's
Richard Clark, KB7QHC

Noise figure paradox
 

Hi Richard,
"Richard Clark" wrote in message
...
Deep space communications proceeds many dB below the noise floor
enabled through technology that has become ubiquitous in cell phones -
Spread Spectrum.

Aka, "averaging" (for the direct-sequence style of spread spectrum, ala CDMA
or GPS).

Still, AFAIK all that averaging can do is to effectively lower the noise floor
at the expense of bandwidth (effectively data rate), and the more benefit
you'd like to get from that averaging, the more important your sample points
become, which gets back to needing as little phase noise as possible on your
oscillators. Is there some other angle here?

---Joel

Noise figure paradox
 

On Mon, 23 Mar 2009 15:28:51 -0700, "Joel Koltner"
wrote:

I realized awhile back that noise is the primary factor that limits how far
you can transmit a signal and still recovery it successfully. (Granted, these
days it's often phase noise in oscillators rather than the noise figures in
amplifiers that determines this, but still.)

Hi Joel,

This is an antiquated consideration limited to amplitude modulation,
the same specie as noise. I suppose there are noise products that
fall into the phase/frequency category that lay claim to "primary
factor," but that is a rather limited appeal.

Deep space communications proceeds many dB below the noise floor
enabled through technology that has become ubiquitous in cell phones -
Spread Spectrum. I have developed pulsed measurement applications for
which any single pulse has a poor S+N/N, but through repetition
improves S+N/N response with the square root increase of samples
taken.

73's
Richard Clark, KB7QHC

Noise figure paradox
 

Deep space communications proceeds many dB below the noise floor
enabled through technology that has become ubiquitous in cell phones -
Spread Spectrum. I have developed pulsed measurement applications for
which any single pulse has a poor S+N/N, but through repetition
improves S+N/N response with the square root increase of samples
taken.

73's
Richard Clark, KB7QHC

And others call it autocorrelation?

W4ZCB

Noise figure paradox
 

On Tue, 24 Mar 2009 23:47:52 GMT, "Harold E. Johnson"
wrote:

Deep space communications proceeds many dB below the noise floor
enabled through technology that has become ubiquitous in cell phones -
Spread Spectrum. I have developed pulsed measurement applications for
which any single pulse has a poor S+N/N, but through repetition
improves S+N/N response with the square root increase of samples
taken.

73's
Richard Clark, KB7QHC

And others call it autocorrelation?

Which?

73's
Richard Clark, KB7QHC

Noise figure paradox
 

On Tue, 24 Mar 2009 16:08:46 -0700, "Joel Koltner"
wrote:

Still, AFAIK all that averaging can do is to effectively lower the noise floor
at the expense of bandwidth (effectively data rate), and the more benefit
you'd like to get from that averaging, the more important your sample points
become, which gets back to needing as little phase noise as possible on your
oscillators. Is there some other angle here?

That was a curious objection to a solution answering a problem as it
was specifically stated. Are there angles to showing noise being
overcome by several means when you offered none?

noise is the primary factor that limits how far
you can transmit a signal and still recovery it successfully.

Again, "qualified" statements such as that should be able to support
themselves with quantifiables.

What "noise" were you speaking about when through the course of this
thread it has most often been confined to kTB than, say, cross-talk,
splatter, spurs, whistlers, howlers, jamming, and a host of others?

What constitutes "successfully?" Is this a personal sense of well
being, or is it supported by a metric?

What constitutes "far"ness? At one point you offered from hilltop to
hilltop with antennas combining to 60dB directivity (but curiously
expressed as SNR). Lacking any quantifiable of what size hills,
shouting can be competitive at some range, and reasonably assured of
being understood to the first order of approximation without need for
averaging.

Spread Spectrum is so ubiquitous that waiting on anticipated exotic
failures of phase noise, on the face of an overwhelming absence of
problems, is wasted time indeed. Communication problems via the Cell
technology are more likely packets going astray on the network than
through the air. Perhaps it is with the clock chips of network
routers where phase noise fulfill this perception of sampling error -
but even there, collision is more likely and the system merely
abandons retries for the sake of economy not for overwhelming noise.

As to sampling error via the net. Time was when 16x over-sampling for
RS-232 was the norm. Going to one sample and transmitting at the base
frequency didn't help until quadrature and more complex phase systems
emerged. Same infrastructure, same noise, faster and more efficient
(not less) communication. Shannon wrote about the bit error rate in
the presence of noise, modulation techniques have improved throughput,
not lowered it.

73's
Richard Clark, KB7QHC

Noise figure paradox
 

On Mar 24, 9:45*pm, Richard Clark wrote:
On Tue, 24 Mar 2009 23:47:52 GMT, "Harold E. Johnson"

wrote:
Deep space communications proceeds many dB below the noise floor
enabled through technology that has become ubiquitous in cell phones -
Spread Spectrum. *I have developed pulsed measurement applications for
which any single pulse has a poor S+N/N, but through repetition
improves S+N/N response with the square root increase of samples
taken.

73's
Richard Clark, KB7QHC

And others call it autocorrelation?

Which?

73's
Richard Clark, KB7QHC

Radar people for one, also known as pulse-pair radar where data from
multiple returns are compared. The data can be from multiple hits on a
target using the same radar or the data can come from multiple radars.
MDS level improvement below the noise level can be achieved. Its also
used for transmitting data.One other specific use I am familiar with
involves transmition of radar data via radio. So the radar uses it as
well as the mode of transmission of the radar data from the radar to
the user.




Jimmie

Noise figure paradox
 

On Fri, 20 Mar 2009 19:46:53 -0700, "Joel Koltner"
wrote:

Say I have an antenna that I know happens to provide an SNR
of 60dB...

Returning to one of the few quantifiables, it would be instructive to
judge why it is so astonishing as a point to begin a dive into the
discussion of noise figure. In other posts related to deep space
probe's abilities to recover data from beneath the noise floor, much
less cell phones to operate in a sea of congestion, I encountered the
economic objection that such methods cost too much - expense of
bandwidth.

Well, not having seen anything more than yet another qualification -
how much is "too much?" It is time to draw back and ask how much is
enough? What would NOT be too expensive? Replacing qualitative
objections with quantitative objections sometimes evokes a horse laugh
when the magnitude of the qualitative issue ceases to exhibit much
quality.

I won't open this round of enquiry with exotic Spread Spectrum which
portends the objection of phase issues with clocks (even knowing that
such modulation techniques automatically incorporate slipping to
adjust for just such problems). Instead I will slip back some 60
years to the seminal paper published by Claude Shannon who figured
this all out (with H.W. Bode) and quote some metrics for various
coding (modulation) schemes. Search for "Communication in the
Presence of Noise." When you google, search in its image data space
for the cogent chart that I will be drawing on, below. Obtaining the
paper may take more effort (or simply email me for a copy).

Starting with BPSK and a S+N/N of roughly 10.5 dB, the bit error rate
is one bad bit in one million bits. This is probably the most
plug-ordinary form of data communication coming down the pike; so one
has to ask:
"is this good enough?"
If not, then "SNR of 60dB" is going to have to demand some really
astonishing expectations to push system designers to ante up the
additional 49.5 dB.

Well, let's say those astonishing expectations are as wild as
demanding proof that you won't contribute to global warming if you
chip an ice cube off of a glacier - such are the issues of scale when
you chug the numbers for BPSK.

OK, so as to not melt down the planet, we step up the complexity of
modulation to better than the last solution for "good enough." Let's
take the Voyager probes of the deep planets where at a S+N/N of 2.53
dB (in what is called 8 dB coding gain) the same error rate of 1 bit
in 1 million is achieved. One has to ask:
"is this good enough?"
If not, then "SNR of 60dB" is going to have to demand some really
astronomical expectations.

OK, perhaps this is a problem demanding really deep pockets that
exceed the several $Trillion being spent on the past 8 years of
Reaganomic neglect. (Why else pound the desk for that extra 57 dB?)
Let's go the full distance to the Shannon limit. It will give us that
same 1 bit error for every 1,000,000 at -1.5 dB S+N/N. If this isn't
below the noise floor, then the problem demanding 60 dB will never
find the solution to positively answer:
"is this good enough?"

73's
Richard Clark, KB7QHC