Re: [time-nuts] Sinlge ADC multi-band receiver

[jimlux]

On 4/10/17 2:08 PM, Eric Scace wrote:

   This approach is known as “security through obscurity”, and is deprecated in 
the professional of information security. What one invents, another can 
discover.

   The most secure systems use well-documented algorithms with open-source 
software — widely scrutinized for bugs or implants, and therefore with 
well-understood performance limitations. The secrecy comes from good crypto key 
management.



The M-code is described in a fair amount of detail here:
www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA456656


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Re: [time-nuts] Sinlge ADC multi-band receiver

[Alex Pummer]

depend how much in-band loss could you afford it is relative easy to 
make cavity filters if you have a network analyzer available


73

Alex


On 4/10/2017 9:11 AM, Attila Kinali wrote:

On Sun, 9 Apr 2017 18:13:48 -0400
Bob kb8tq  wrote:


The beauty of the system would be that you don't need a SAW filter
at all. If the input stage (LNA + mixer) has a high enough dynamic
range, then the (first) IF filer alone can remove all those out of
band interference.

Why would you substitute an expensive IF filter for a cheap front end filter?

Availability: Although there are L1/L2 filters available, they are not
easy to get unless you buy them in bulk. The standard L1 filters you
can buy are rather narrow band (just 2-4MHz) and don't allow the
reception of the modern signals. L5 filters are very rare and E5 filters
simply do not exist yet.

And keep in mind that the IF filter does not need to be a special
ultra-steep filter. The high sampling rate of the ADC allows to place
the input signal such, that the stop band can be quite far from the
pass band. Also, the filter is only really necessary to filter out
narrow band interference, which is hopefully far from the signal anyways.
Having a bit of noise fold in is, as Jim noted earlier, not a problem at all.

Attila Kinali


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Re: [time-nuts] Sinlge ADC multi-band receiver

[Eric Scace]

   This approach is known as “security through obscurity”, and is deprecated in 
the professional of information security. What one invents, another can 
discover.

   The most secure systems use well-documented algorithms with open-source 
software — widely scrutinized for bugs or implants, and therefore with 
well-understood performance limitations. The secrecy comes from good crypto key 
management.

— Eric

> On 2017 Apr 10, at 13:58 , Attila Kinali  wrote:
> 
> And they also learned
> that not documenting it is the best protection against people using it.



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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Mon, 10 Apr 2017 09:00:17 -0400
Bob kb8tq  wrote:


> > 
> > Only if you *need* the Galileo E5.
> 
> The other point with E5 is the nature of the data on the various sub signals. 
> Galileo has three classes of service and only one of them is free (open).

Yes. Thats why we do not talk about E6, or E1 PRS.
On E5 there are OS signals and CS signals. More accurately, the F/NAV data
which is part of the OS signal, is on E5a, and the I/NAV data, which is
both part of OS and CS is on E5b. Additionally, there is a dataless pilot
on both E5a and E5b.

As far as I am aware of, neither the CS nor the PRS specifications are
public yet. If someone has any information on those, I would be interested.

> As with traditional  L1 / L2 survey receivers, you don’t *have* to recover
> full data from a signal for it to be useful.

Yes. But semi-codeless tracking only works because:
1) A lot of the signal structure is known and it is actually such
that you can correlate quite a bit of it without knowing the P(Y) code.
2) The P(Y) code is send out on both L1 and L2, which allows correlating
both signals possible.

Without these two points, the use of L2 would not have been possible.
And yes, the US military learned from this and made the M code without
the strucutre that helped correlating it in 1). And they also learned
that not documenting it is the best protection against people using it.
Though I wonder how long it will take until someone figures out what
the signal structure is.

> That said, the free (open) service is only on one of the two sub signals.

No. See above.

> If you are building a L1 / L2 / L5 GNSS receiver, you might 
> well opt to only grab the lower part of the E5 signal. 

E5a overlaps with L5, The center frequncy of L2 is a mere 20MHz
from the E5b center frequency. So, if you are building an L1/L2/L5
receiver, there is very little point in not investing a little bit
in getting E5b as well.

> You might also decide on a setup that only used two of the three bands.
> That would give you all the data and ionospheric correction. It is a bit
> unclear what the third band would add other than a “cool factor” 

E5 allowes, due its large bandwidth, a supperior multi-path supression.
But Galileo is not yet fully functional, so using L1 C/A & L2C for now is
the best option. Supporting L5 is a good idea, to make the receiver
future proof (again supporting a large bandwith for multi-path supresion)
but it is not yet known, when L5 will reach full constellation (there 
only 12 satellites transmitting, yet). Also L2 was only recently marked
as GNSS band and thus there are still radar systems working in this band,
causing interferences.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Mon, 10 Apr 2017 07:00:27 +0200
Magnus Danielson  wrote:

> God Morgon Attila,
> 
> On 04/09/2017 10:28 PM, Attila Kinali wrote:
> > On Tue, 4 Apr 2017 17:58:11 -0700
> > jimlux  wrote:
> >
> > The beauty of the system would be that you don't need a SAW filter
> > at all. If the input stage (LNA + mixer) has a high enough dynamic
> > range, then the (first) IF filer alone can remove all those out of
> > band interference. And at the same time, because the IF frequency
> > being low, you don't need any specialized filter components that
> > might not be available in a couple of months.
> >
> > Of course, this doesn't really work that way when significantly
> > wider signals (E5) have to be caught together with "narrow band"
> > signals (L1 C/A or L2C).
> 
> You got it backwards.
> 
> You need to protect your LNA and mixer from other signals, not to be 
> blocked out by out of band signals which is strong. That's why you have 
> SAW filters to start with. This has become a larger issue these days.

I don't think they are necessary anymore. Todays LNAs have a very high
IP3 (in the order of 10-30dBm) and even IP1dB is usually around 0-10dBm.
Ie unless there is a very strong, narrow band interference, the LNA will
not cause any problems. Same goes for modern mixer.

Or, to make it a bit more practical: if you take an RTL-SDR dongle,
then you have a cheap, zero-IF system that has no frontend filter
and relies solely on selectivity of the antenna (which is often
a cheap puck without any filter) and its IF low-pass filters.
I have used this a few times and have not seen it fail. I took my
bladerf a few times and looked at the spectrum around 1575GHz and
haven't seen any strong interferer yet.


> > Unfortunately, the AD9361 does not offer the IF bandwith necessary.
> > Even though it has a high sample rate and can offer high bandwidth
> > capture of signals, the zero-IF nature of its design doesn't work
> > for this design approach. The IF of the AD9361 has a low pass filter
> > of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
> > frequency space (using both I and Q channels). But the above approach
> > would need an IF of >200MHz, but it would be enough to only have a
> > single channel.
> 
> Only if you *need* the Galileo E5.

With only L1 and L2 it is still ~180MHz. The two bands are ~350MHz appart.
You cannot get around that without introducing a second down-mix step.


Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Mon, 10 Apr 2017 08:08:10 +0100
"David J Taylor"  wrote:

> Thanks for that pointer!  Most interesting.  I wonder whether anyone has an 
> updated document detailing the different systems and their current state, as 
> that information is approaching 10 years old?

As far as I am aware of, that is the current state.
The GPS/Galileo was signed slightly before that thesis, IIRC.
The L2C and L5C signals are "old-school" LFSR generated PSRN BPSK
signals. The only "special" signals are L1C, E1 OS and E5.

QZSS uses GPS L1 C/A signals, IIRC
Beidu and IRNS I don't know.

If I am not mistaken, navipedia is up to date with everything,
but I have not read everything, nor checked against the standards
what I have read there.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Sun, 9 Apr 2017 18:13:48 -0400
Bob kb8tq  wrote:

> > The beauty of the system would be that you don't need a SAW filter
> > at all. If the input stage (LNA + mixer) has a high enough dynamic
> > range, then the (first) IF filer alone can remove all those out of
> > band interference.
> 
> Why would you substitute an expensive IF filter for a cheap front end filter?

Availability: Although there are L1/L2 filters available, they are not
easy to get unless you buy them in bulk. The standard L1 filters you
can buy are rather narrow band (just 2-4MHz) and don't allow the
reception of the modern signals. L5 filters are very rare and E5 filters
simply do not exist yet.

And keep in mind that the IF filter does not need to be a special
ultra-steep filter. The high sampling rate of the ADC allows to place
the input signal such, that the stop band can be quite far from the
pass band. Also, the filter is only really necessary to filter out
narrow band interference, which is hopefully far from the signal anyways.
Having a bit of noise fold in is, as Jim noted earlier, not a problem at all.

Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Magnus Danielson]

Hi,

On 04/10/2017 03:00 PM, Bob kb8tq wrote:

Hi


On Apr 10, 2017, at 1:00 AM, Magnus Danielson  
wrote:

God Morgon Attila,

On 04/09/2017 10:28 PM, Attila Kinali wrote:

On Tue, 4 Apr 2017 17:58:11 -0700
jimlux  wrote:

The beauty of the system would be that you don't need a SAW filter
at all. If the input stage (LNA + mixer) has a high enough dynamic
range, then the (first) IF filer alone can remove all those out of
band interference. And at the same time, because the IF frequency
being low, you don't need any specialized filter components that
might not be available in a couple of months.

Of course, this doesn't really work that way when significantly
wider signals (E5) have to be caught together with "narrow band"
signals (L1 C/A or L2C).


You got it backwards.

You need to protect your LNA and mixer from other signals, not to be blocked 
out by out of band signals which is strong. That's why you have SAW filters to 
start with. This has become a larger issue these days.

So, considering that you already have them, then what good do they do for the 
different scenarios.


Unfortunately, the AD9361 does not offer the IF bandwith necessary.
Even though it has a high sample rate and can offer high bandwidth
capture of signals, the zero-IF nature of its design doesn't work
for this design approach. The IF of the AD9361 has a low pass filter
of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
frequency space (using both I and Q channels). But the above approach
would need an IF of >200MHz, but it would be enough to only have a
single channel.


Only if you *need* the Galileo E5.


The other point with E5 is the nature of the data on the various sub signals. 
Galileo has three
classes of service and only one of them is free (open). As with traditional  L1 
/ L2 survey receivers, you
don’t *have* to recover full data from a signal for it to be useful. That said, 
the free (open) service
is only on one of the two sub signals. If you are building a L1 / L2 / L5 GNSS 
receiver, you might
well opt to only grab the lower part of the E5 signal.

You might also decide on a setup that only used two of the three bands. That 
would give you all
the data and ionospheric correction. It is a bit unclear what the third band 
would add other than a “cool factor”
if traditional criteria are used for the receiver design. There are various 
arguments for L1 / L5 and L1 / L2. One
could even make a case for L2  /  L5.


L2 and L5 is so close, that bringing them down together is relatively 
simple.


If you make a receiver today, it should be able to use any set of bands, 
including L2 only or L5 only. Even more refined than that, any set of 
signals. One should attempt to get any of the transmitted signal, so 
there might be L1 from one, L2 and L5 from one, L1 and L5 from one etc. 
Each signal contributes. Signal pairs and tripples allow for ionospheric 
estimation, with the added benefit.



Even if ionospheric correction is not a bit issue in your design, jamming 
probably should be for a design
targeted to run for many years into the future.. A broadband jammer 
(intentional or accidental) can fairly
easily take out one of the bands. It’s quite a bit harder to take out all of 
them at once. A lot would depend
on just how nasty an environment you intend to operate in, and how sensitive 
you are to occasional issues.

Lots of choices ….


Indeed. I have been advocating for use of multiple bands, besides L1, 
and for multiple GNSS. This helps to build signal redundancy. Such 
receivers should not be too expensive eventually.


Cheers,
Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Björn Gabrielsson]

Hi Bob,

> It is a bit unclear what the third
> band would add other than a "cool factor"

Even quicker RTK convergence.
   
http://www.navipedia.net/index.php/Carrier_phase_ambiguity_fixing_with_three_frequencies

--

Björn


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Re: [time-nuts] Sinlge ADC multi-band receiver

[Bob kb8tq]

Hi

> On Apr 10, 2017, at 1:00 AM, Magnus Danielson  
> wrote:
> 
> God Morgon Attila,
> 
> On 04/09/2017 10:28 PM, Attila Kinali wrote:
>> On Tue, 4 Apr 2017 17:58:11 -0700
>> jimlux  wrote:
>> 
>> The beauty of the system would be that you don't need a SAW filter
>> at all. If the input stage (LNA + mixer) has a high enough dynamic
>> range, then the (first) IF filer alone can remove all those out of
>> band interference. And at the same time, because the IF frequency
>> being low, you don't need any specialized filter components that
>> might not be available in a couple of months.
>> 
>> Of course, this doesn't really work that way when significantly
>> wider signals (E5) have to be caught together with "narrow band"
>> signals (L1 C/A or L2C).
> 
> You got it backwards.
> 
> You need to protect your LNA and mixer from other signals, not to be blocked 
> out by out of band signals which is strong. That's why you have SAW filters 
> to start with. This has become a larger issue these days.
> 
> So, considering that you already have them, then what good do they do for the 
> different scenarios.
> 
>> Unfortunately, the AD9361 does not offer the IF bandwith necessary.
>> Even though it has a high sample rate and can offer high bandwidth
>> capture of signals, the zero-IF nature of its design doesn't work
>> for this design approach. The IF of the AD9361 has a low pass filter
>> of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
>> frequency space (using both I and Q channels). But the above approach
>> would need an IF of >200MHz, but it would be enough to only have a
>> single channel.
> 
> Only if you *need* the Galileo E5.

The other point with E5 is the nature of the data on the various sub signals. 
Galileo has three 
classes of service and only one of them is free (open). As with traditional  L1 
/ L2 survey receivers, you
don’t *have* to recover full data from a signal for it to be useful. That said, 
the free (open) service
is only on one of the two sub signals. If you are building a L1 / L2 / L5 GNSS 
receiver, you might 
well opt to only grab the lower part of the E5 signal. 

You might also decide on a setup that only used two of the three bands. That 
would give you all 
the data and ionospheric correction. It is a bit unclear what the third band 
would add other than a “cool factor” 
if traditional criteria are used for the receiver design. There are various 
arguments for L1 / L5 and L1 / L2. One 
could even make a case for L2  /  L5. 

Even if ionospheric correction is not a bit issue in your design, jamming 
probably should be for a design
targeted to run for many years into the future.. A broadband jammer 
(intentional or accidental) can fairly 
easily take out one of the bands. It’s quite a bit harder to take out all of 
them at once. A lot would depend
on just how nasty an environment you intend to operate in, and how sensitive 
you are to occasional issues. 

Lots of choices ….

Bob

> 
>> I looked up the prices for the components and figured that the prices for
>> mixer and IF amplifiers are actually quite low (a 2-4 USD per IC) so it
>> isn't that much more expensive to build such a system than using a 3 tuner
>> approach (eg using MAX2120 as Peter Monta did with the GNSS Firehose).
> 
> Cheers,
> Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[David J Taylor]

BTW: Rodriguez' PhD thesis[2] (which is the basis of navipedia) gives a very
nice overview of the trade-off's that went into the Galileo signals and
gives a few hints where future GNSS signals could further improve things.

Attila Kinali

[2] "On Generalized Signal Waveforms for Satellite Navigation",
by José Ángel Ávila Rodríguez, 2008
https://athene-forschung.unibw.de/node?id=86167


Thanks for that pointer!  Most interesting.  I wonder whether anyone has an 
updated document detailing the different systems and their current state, as 
that information is approaching 10 years old?


Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] Sinlge ADC multi-band receiver

[Magnus Danielson]

God Morgon Attila,

On 04/09/2017 10:28 PM, Attila Kinali wrote:

On Tue, 4 Apr 2017 17:58:11 -0700
jimlux  wrote:

The beauty of the system would be that you don't need a SAW filter
at all. If the input stage (LNA + mixer) has a high enough dynamic
range, then the (first) IF filer alone can remove all those out of
band interference. And at the same time, because the IF frequency
being low, you don't need any specialized filter components that
might not be available in a couple of months.

Of course, this doesn't really work that way when significantly
wider signals (E5) have to be caught together with "narrow band"
signals (L1 C/A or L2C).


You got it backwards.

You need to protect your LNA and mixer from other signals, not to be 
blocked out by out of band signals which is strong. That's why you have 
SAW filters to start with. This has become a larger issue these days.


So, considering that you already have them, then what good do they do 
for the different scenarios.



Unfortunately, the AD9361 does not offer the IF bandwith necessary.
Even though it has a high sample rate and can offer high bandwidth
capture of signals, the zero-IF nature of its design doesn't work
for this design approach. The IF of the AD9361 has a low pass filter
of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
frequency space (using both I and Q channels). But the above approach
would need an IF of >200MHz, but it would be enough to only have a
single channel.


Only if you *need* the Galileo E5.


I looked up the prices for the components and figured that the prices for
mixer and IF amplifiers are actually quite low (a 2-4 USD per IC) so it
isn't that much more expensive to build such a system than using a 3 tuner
approach (eg using MAX2120 as Peter Monta did with the GNSS Firehose).


Cheers,
Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Magnus Danielson]

Hi Attila,

On 04/09/2017 10:29 PM, Attila Kinali wrote:

On Wed, 5 Apr 2017 10:37:07 +0200
Magnus Danielson  wrote:


Also, you don't really need to keep the bands fully separate in their
mixed-down form, since they do not correlate except for the P(Y), but
keeping enough frequency difference, such that doppler shift does not
remove correlation margin, they remain uncorrelated. Some of the
literature pay much attention to the band not wrapping around the
band-edge, but I'm not convinced it is such a big issue.


If part of the signal wraps because you are at the bandedge,
then you lose this part of the signal and the part it wraps over.
This is due to the signal coherently overlapping in frequency space.
As far as I understood the math, there isn't a way to seperate them
again (at least there isn't any I am aware of). Thus this signal energy
is lost for the decoding process.


Your generated signal would have the same wrapping. A single bit sampler 
would be feasible to loose in, but for multibit ADCs I'm more skeptic.


Cheers,
Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Bob kb8tq]

> On Apr 9, 2017, at 4:29 PM, Attila Kinali  wrote:
> 
> On Wed, 5 Apr 2017 08:27:58 -0400
> Bob kb8tq  wrote:
> 
>> Galileo E5 is a bit of a strange case. It’s really E5a and E5b.
>> You can either grab it all as one giant signal or as two separate signals.
>> You may (or may not) care about the data on E5a or b depending on what you
>> are trying to do. Getting the entire very wide signal likely has some 
>> interesting benefits when it comes to working out very small differences
>> in location or … errr… time. 
> 
> I wouldn't call it strange, but rather neat :-)
> The E5 signal is created as a single, 8-PSK signal(see [1]), which is
> modulated such, that the positive and negative frequency parts get
> a specific signal structure. This is done in order to allow an extremely
> wide band signal to be demodulated in parts. I guess they feared that a
> receiver for a 50MHz wide signal would be too expensive for the
> commercial market and made it possible to process the signal as two
> 20MHz wide pieces. There is a slight loss in correlation energy in this
> case, but for most applications it should not matter. The bigger issue
> is that the path delays for the two receiver channels would need to be
> calibrated and tracked during operation in order to make full use of
> the E5 signal. 
> 
> BTW: I have been told, that using the full E5 signal makes the use
> of any other signal kind of unnecessary as its extremely wide bandwidth
> allows a very fine tracking of the signal. Thus the use of any other signal
> (e.g. E1 OS) would actually degrade the receivers timing performance than
> improve it.

Without a “second frequency” you can’t do local ionosphere corrections. That’s 
true regardless of the bandwidth of the signals …..

Bob

> 
>> 
>> One way to do the E5 signal would be a dual (duplicate) IF ISB 
>> downconverter. 
>> How practical that turns out to be is an open question. The more conventional
>> approach is to take a monstrous chunk of L band down to a high speed 
>> sampler. 
> 
> As I have written above, to be able to do this is the reason for the E5's
> signal structure. And apparently the designers thought that this would be
> the way how most users would decode it. I am currently not aware of any
> commercial E5 receiver that is already on the market, so it is kind of moot
> to ask what the common way to decode E5 is.
> 
> BTW: Rodriguez' PhD thesis[2] (which is the basis of navipedia) gives a very
> nice overview of the trade-off's that went into the Galileo signals and
> gives a few hints where future GNSS signals could further improve things.
> 
>   Attila Kinali
> 
> [1] Galileo OS SIS ICD Issue 1 Revision 2, 
> Section 2.3.1.3 "Equivalent Modulation Type"
> 
> [2] "On Generalized Signal Waveforms for Satellite Navigation",
> by José Ángel Ávila Rodríguez, 2008
> https://athene-forschung.unibw.de/node?id=86167
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Bob kb8tq]

HI

> On Apr 9, 2017, at 4:28 PM, Attila Kinali  wrote:
> 
> On Tue, 4 Apr 2017 17:58:11 -0700
> jimlux  wrote:
> 
>>> The advantage of such a system would be that there is only a single
>>> path through the system for all signals, especially through the filters.
>>> Thus the variability of the differential phase shift between the
>>> frequency bands would be significantly reduced, which would result
>>> in better stability.
>> 
>> Oh, I'm not sure about that. It would depend on the filter kind and 
>> topology.
>> 
>> If it's a SAW or BAW filter, it's all one "brick", but I think you'd 
>> still need to calibrate the differential phase shift vs temp.  And it 
>> might be very predictable in a "measure 10 of them, and now you know the 
>> characteristics of the next 1000"
> 
> The beauty of the system would be that you don't need a SAW filter
> at all. If the input stage (LNA + mixer) has a high enough dynamic
> range, then the (first) IF filer alone can remove all those out of
> band interference.

Why would you substitute an expensive IF filter for a cheap front end filter?

Bob


> And at the same time, because the IF frequency
> being low, you don't need any specialized filter components that
> might not be available in a couple of months.
> 
> Of course, this doesn't really work that way when significantly
> wider signals (E5) have to be caught together with "narrow band"
> signals (L1 C/A or L2C).
> 
> 
>> 
>>  Of course, that's the theory. Whether things work
>>> out this way in reality is a different question. What can be said for
>>> sure is, because of the high IF frequency of >200MHz, the standard tuner
>>> chips cannot be used anymore and the RX chain has to be build from
>>> "discrete" components,
>> 
>> There's a ton of integrated demodulator/ADC parts out there these days 
>> that go up to 6GHz.
>> AD9361 for example
>> 
>> it will do 56 MHz BW through the IF, with 12 bit ADC feeding a 128 tap 
>> FIR filter, etc.
> 
> Unfortunately, the AD9361 does not offer the IF bandwith necessary.
> Even though it has a high sample rate and can offer high bandwidth
> capture of signals, the zero-IF nature of its design doesn't work
> for this design approach. The IF of the AD9361 has a low pass filter
> of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
> frequency space (using both I and Q channels). But the above approach
> would need an IF of >200MHz, but it would be enough to only have a
> single channel. 
> 
> I looked up the prices for the components and figured that the prices for
> mixer and IF amplifiers are actually quite low (a 2-4 USD per IC) so it
> isn't that much more expensive to build such a system than using a 3 tuner
> approach (eg using MAX2120 as Peter Monta did with the GNSS Firehose).
> 
>   Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Wed, 5 Apr 2017 08:27:58 -0400
Bob kb8tq  wrote:

> Galileo E5 is a bit of a strange case. It’s really E5a and E5b.
> You can either grab it all as one giant signal or as two separate signals.
> You may (or may not) care about the data on E5a or b depending on what you
> are trying to do. Getting the entire very wide signal likely has some 
> interesting benefits when it comes to working out very small differences
> in location or … errr… time. 

I wouldn't call it strange, but rather neat :-)
The E5 signal is created as a single, 8-PSK signal(see [1]), which is
modulated such, that the positive and negative frequency parts get
a specific signal structure. This is done in order to allow an extremely
wide band signal to be demodulated in parts. I guess they feared that a
receiver for a 50MHz wide signal would be too expensive for the
commercial market and made it possible to process the signal as two
20MHz wide pieces. There is a slight loss in correlation energy in this
case, but for most applications it should not matter. The bigger issue
is that the path delays for the two receiver channels would need to be
calibrated and tracked during operation in order to make full use of
the E5 signal. 

BTW: I have been told, that using the full E5 signal makes the use
of any other signal kind of unnecessary as its extremely wide bandwidth
allows a very fine tracking of the signal. Thus the use of any other signal
(e.g. E1 OS) would actually degrade the receivers timing performance than
improve it.

> 
> One way to do the E5 signal would be a dual (duplicate) IF ISB downconverter. 
> How practical that turns out to be is an open question. The more conventional
> approach is to take a monstrous chunk of L band down to a high speed sampler. 

As I have written above, to be able to do this is the reason for the E5's
signal structure. And apparently the designers thought that this would be
the way how most users would decode it. I am currently not aware of any
commercial E5 receiver that is already on the market, so it is kind of moot
to ask what the common way to decode E5 is.

BTW: Rodriguez' PhD thesis[2] (which is the basis of navipedia) gives a very
nice overview of the trade-off's that went into the Galileo signals and
gives a few hints where future GNSS signals could further improve things.

Attila Kinali

[1] Galileo OS SIS ICD Issue 1 Revision 2, 
Section 2.3.1.3 "Equivalent Modulation Type"

[2] "On Generalized Signal Waveforms for Satellite Navigation",
by José Ángel Ávila Rodríguez, 2008
https://athene-forschung.unibw.de/node?id=86167
-- 
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the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Wed, 5 Apr 2017 10:37:07 +0200
Magnus Danielson  wrote:

> Also, you don't really need to keep the bands fully separate in their 
> mixed-down form, since they do not correlate except for the P(Y), but 
> keeping enough frequency difference, such that doppler shift does not 
> remove correlation margin, they remain uncorrelated. Some of the 
> literature pay much attention to the band not wrapping around the 
> band-edge, but I'm not convinced it is such a big issue.

If part of the signal wraps because you are at the bandedge,
then you lose this part of the signal and the part it wraps over.
This is due to the signal coherently overlapping in frequency space.
As far as I understood the math, there isn't a way to seperate them
again (at least there isn't any I am aware of). Thus this signal energy
is lost for the decoding process.


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

On Tue, 4 Apr 2017 17:58:11 -0700
jimlux  wrote:

> > The advantage of such a system would be that there is only a single
> > path through the system for all signals, especially through the filters.
> > Thus the variability of the differential phase shift between the
> > frequency bands would be significantly reduced, which would result
> > in better stability.
> 
> Oh, I'm not sure about that. It would depend on the filter kind and 
> topology.
> 
> If it's a SAW or BAW filter, it's all one "brick", but I think you'd 
> still need to calibrate the differential phase shift vs temp.  And it 
> might be very predictable in a "measure 10 of them, and now you know the 
> characteristics of the next 1000"

The beauty of the system would be that you don't need a SAW filter
at all. If the input stage (LNA + mixer) has a high enough dynamic
range, then the (first) IF filer alone can remove all those out of
band interference. And at the same time, because the IF frequency
being low, you don't need any specialized filter components that
might not be available in a couple of months.

Of course, this doesn't really work that way when significantly
wider signals (E5) have to be caught together with "narrow band"
signals (L1 C/A or L2C).

 
> 
>   Of course, that's the theory. Whether things work
> > out this way in reality is a different question. What can be said for
> > sure is, because of the high IF frequency of >200MHz, the standard tuner
> > chips cannot be used anymore and the RX chain has to be build from
> > "discrete" components,
> 
> There's a ton of integrated demodulator/ADC parts out there these days 
> that go up to 6GHz.
> AD9361 for example
> 
> it will do 56 MHz BW through the IF, with 12 bit ADC feeding a 128 tap 
> FIR filter, etc.

Unfortunately, the AD9361 does not offer the IF bandwith necessary.
Even though it has a high sample rate and can offer high bandwidth
capture of signals, the zero-IF nature of its design doesn't work
for this design approach. The IF of the AD9361 has a low pass filter
of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
frequency space (using both I and Q channels). But the above approach
would need an IF of >200MHz, but it would be enough to only have a
single channel. 

I looked up the prices for the components and figured that the prices for
mixer and IF amplifiers are actually quite low (a 2-4 USD per IC) so it
isn't that much more expensive to build such a system than using a 3 tuner
approach (eg using MAX2120 as Peter Monta did with the GNSS Firehose).

Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Magnus Danielson]

Hi,

There are many things to be done before attempting the full E5 approach 
anyway, so I would not have make it a make or break for a first design.


Cheers,
Magnus

On 04/05/2017 02:27 PM, Bob kb8tq wrote:

Hi

Galileo E5 is a bit of a strange case. It’s really E5a and E5b. You can either 
grab it all as one
giant signal or as two separate signals. You may (or may not) care about the 
data on E5a or
b depending on what you are trying to do. Getting the entire very wide signal 
likely has some
interesting benefits when it comes to working out very small differences in 
location or … errr…
time.

One way to do the E5 signal would be a dual (duplicate) IF ISB downconverter. 
How practical that turns out
to be is an open question. The more conventional approach is to take a 
monstrous chunk of
L band down to a high speed sampler.

Bob


On Apr 5, 2017, at 4:37 AM, Magnus Danielson  wrote:



On 04/05/2017 01:21 AM, Attila Kinali wrote:

On Tue, 4 Apr 2017 06:55:24 -0700
jimlux  wrote:



So those folks were trying to use 1 ADC for all three bands, so they had
to choose a sampling rate that lets them separate the signals later in
software.

But that ADC is a MAX104 - a 1GSPS, 8 bit converter - that draws 5 Watts!!!

I'm not sure that's a good trade against a 1 or 2 bit converter for each
band, in terms of the downstream data rate and processing.


Honestly, I don't think the direct sampling approach is a good idea.
It folds a lot of noise into the signal band. I'd rather use a single
heterodyne with an LO frequncy of around 1000MHz, or something between
L2 and E5, such that the bands stay still seperated. Here I would add
a filterbank to get rid of as much noise as possible. And after that
use an ADC sampling frequency to fold the signals down again.
(Effectively forming a super-heterodyne receiver)


Regardless you already have SAW filters on the LNA to provide selectivity.

Also, you don't really need to keep the bands fully separate in their 
mixed-down form, since they do not correlate except for the P(Y), but keeping 
enough frequency difference, such that doppler shift does not remove 
correlation margin, they remain uncorrelated. Some of the literature pay much 
attention to the band not wrapping around the band-edge, but I'm not convinced 
it is such a big issue.

A direct sampler of 100 MHz would work well for GPS for instance, but not for 
GLONASS, but 90 MHz would work there. The S/H would need to have the BW of the 
top frequency, but then the S/H action will act as the first mixer.


The advantage of such a system would be that there is only a single
path through the system for all signals, especially through the filters.
Thus the variability of the differential phase shift between the
frequency bands would be significantly reduced, which would result
in better stability. Of course, that's the theory. Whether things work
out this way in reality is a different question. What can be said for
sure is, because of the high IF frequency of >200MHz, the standard tuner
chips cannot be used anymore and the RX chain has to be build from
"discrete" components, which increases the BOM cost quite considerably.


Since you don't really need to keep signals very separated, you can pack them 
relatively tight. It's the E5 of GALILEO which is wide.

Using a 1,4 GHz range LO1 to pick L1 and L2 has been known to be used before. 
There is even existing chips which uses 1.4 GHz on LO1, which with a different 
set of filters could almost support L2, will have to check the details. While 
that front-end would be neat, I would not use that chip since it is no longer 
in production.

The fun thing about these types of receivers, is that there is so many ways to do it, 
that it allows for many different approaches to be tried as technology develops. There is 
no single one "right" way of doing it.

Cheers,
Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Bob kb8tq]

Hi

Galileo E5 is a bit of a strange case. It’s really E5a and E5b. You can either 
grab it all as one
giant signal or as two separate signals. You may (or may not) care about the 
data on E5a or 
b depending on what you are trying to do. Getting the entire very wide signal 
likely has some 
interesting benefits when it comes to working out very small differences in 
location or … errr…
time. 

One way to do the E5 signal would be a dual (duplicate) IF ISB downconverter. 
How practical that turns out
to be is an open question. The more conventional approach is to take a 
monstrous chunk of
L band down to a high speed sampler. 

Bob

> On Apr 5, 2017, at 4:37 AM, Magnus Danielson  
> wrote:
> 
> 
> 
> On 04/05/2017 01:21 AM, Attila Kinali wrote:
>> On Tue, 4 Apr 2017 06:55:24 -0700
>> jimlux  wrote:
>> 
>> 
>>> So those folks were trying to use 1 ADC for all three bands, so they had
>>> to choose a sampling rate that lets them separate the signals later in
>>> software.
>>> 
>>> But that ADC is a MAX104 - a 1GSPS, 8 bit converter - that draws 5 Watts!!!
>>> 
>>> I'm not sure that's a good trade against a 1 or 2 bit converter for each
>>> band, in terms of the downstream data rate and processing.
>> 
>> Honestly, I don't think the direct sampling approach is a good idea.
>> It folds a lot of noise into the signal band. I'd rather use a single
>> heterodyne with an LO frequncy of around 1000MHz, or something between
>> L2 and E5, such that the bands stay still seperated. Here I would add
>> a filterbank to get rid of as much noise as possible. And after that
>> use an ADC sampling frequency to fold the signals down again.
>> (Effectively forming a super-heterodyne receiver)
> 
> Regardless you already have SAW filters on the LNA to provide selectivity.
> 
> Also, you don't really need to keep the bands fully separate in their 
> mixed-down form, since they do not correlate except for the P(Y), but keeping 
> enough frequency difference, such that doppler shift does not remove 
> correlation margin, they remain uncorrelated. Some of the literature pay much 
> attention to the band not wrapping around the band-edge, but I'm not 
> convinced it is such a big issue.
> 
> A direct sampler of 100 MHz would work well for GPS for instance, but not for 
> GLONASS, but 90 MHz would work there. The S/H would need to have the BW of 
> the top frequency, but then the S/H action will act as the first mixer.
> 
>> The advantage of such a system would be that there is only a single
>> path through the system for all signals, especially through the filters.
>> Thus the variability of the differential phase shift between the
>> frequency bands would be significantly reduced, which would result
>> in better stability. Of course, that's the theory. Whether things work
>> out this way in reality is a different question. What can be said for
>> sure is, because of the high IF frequency of >200MHz, the standard tuner
>> chips cannot be used anymore and the RX chain has to be build from
>> "discrete" components, which increases the BOM cost quite considerably.
> 
> Since you don't really need to keep signals very separated, you can pack them 
> relatively tight. It's the E5 of GALILEO which is wide.
> 
> Using a 1,4 GHz range LO1 to pick L1 and L2 has been known to be used before. 
> There is even existing chips which uses 1.4 GHz on LO1, which with a 
> different set of filters could almost support L2, will have to check the 
> details. While that front-end would be neat, I would not use that chip since 
> it is no longer in production.
> 
> The fun thing about these types of receivers, is that there is so many ways 
> to do it, that it allows for many different approaches to be tried as 
> technology develops. There is no single one "right" way of doing it.
> 
> Cheers,
> Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[Magnus Danielson]

On 04/05/2017 01:21 AM, Attila Kinali wrote:

On Tue, 4 Apr 2017 06:55:24 -0700
jimlux  wrote:



So those folks were trying to use 1 ADC for all three bands, so they had
to choose a sampling rate that lets them separate the signals later in
software.

But that ADC is a MAX104 - a 1GSPS, 8 bit converter - that draws 5 Watts!!!

I'm not sure that's a good trade against a 1 or 2 bit converter for each
band, in terms of the downstream data rate and processing.


Honestly, I don't think the direct sampling approach is a good idea.
It folds a lot of noise into the signal band. I'd rather use a single
heterodyne with an LO frequncy of around 1000MHz, or something between
L2 and E5, such that the bands stay still seperated. Here I would add
a filterbank to get rid of as much noise as possible. And after that
use an ADC sampling frequency to fold the signals down again.
(Effectively forming a super-heterodyne receiver)


Regardless you already have SAW filters on the LNA to provide selectivity.

Also, you don't really need to keep the bands fully separate in their 
mixed-down form, since they do not correlate except for the P(Y), but 
keeping enough frequency difference, such that doppler shift does not 
remove correlation margin, they remain uncorrelated. Some of the 
literature pay much attention to the band not wrapping around the 
band-edge, but I'm not convinced it is such a big issue.


A direct sampler of 100 MHz would work well for GPS for instance, but 
not for GLONASS, but 90 MHz would work there. The S/H would need to have 
the BW of the top frequency, but then the S/H action will act as the 
first mixer.



The advantage of such a system would be that there is only a single
path through the system for all signals, especially through the filters.
Thus the variability of the differential phase shift between the
frequency bands would be significantly reduced, which would result
in better stability. Of course, that's the theory. Whether things work
out this way in reality is a different question. What can be said for
sure is, because of the high IF frequency of >200MHz, the standard tuner
chips cannot be used anymore and the RX chain has to be build from
"discrete" components, which increases the BOM cost quite considerably.


Since you don't really need to keep signals very separated, you can pack 
them relatively tight. It's the E5 of GALILEO which is wide.


Using a 1,4 GHz range LO1 to pick L1 and L2 has been known to be used 
before. There is even existing chips which uses 1.4 GHz on LO1, which 
with a different set of filters could almost support L2, will have to 
check the details. While that front-end would be neat, I would not use 
that chip since it is no longer in production.


The fun thing about these types of receivers, is that there is so many 
ways to do it, that it allows for many different approaches to be tried 
as technology develops. There is no single one "right" way of doing it.


Cheers,
Magnus
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Re: [time-nuts] Sinlge ADC multi-band receiver

[jimlux]

On 4/4/17 4:21 PM, Attila Kinali wrote:

On Tue, 4 Apr 2017 06:55:24 -0700
jimlux  wrote:



So those folks were trying to use 1 ADC for all three bands, so they had
to choose a sampling rate that lets them separate the signals later in
software.

But that ADC is a MAX104 - a 1GSPS, 8 bit converter - that draws 5 Watts!!!

I'm not sure that's a good trade against a 1 or 2 bit converter for each
band, in terms of the downstream data rate and processing.


Honestly, I don't think the direct sampling approach is a good idea.
It folds a lot of noise into the signal band.


in most of the designs, the noise is from the LNA, and is band limited, 
so the additional noise from the amplifier chain is less. COnsider if 
the LNA has 40dB gain and a 2 dB NF. Let's say all the other amps in the 
chain have 5 dB NF.


The thermal noise into the next amp is -132 dBm/Hz.  In order for the 
5dB NF noise (-169 dBm/Hz) to get up high enough to be noticeable, say, 
30dB, you'd have to fold 1000 times the sampling bandwidth. if the 
sampling bandwidth is 40 MHz, to get the noise up high enough it would 
have to extend to 40 GHz... I'll bet it doesn't





You don't need a 1Gsps ADC for that, but if you want to keep all
frequency bands completely seperate, even after sampling, a relatively
high sampling rate is necessary. L1C/E1OS needs at least 14MHz,
L2C needs 2MHz, E5 needs 50MHz.


I don't think keeping the bands together buys you much - you don't need 
a multibit ADC for a signal that is below the noise floor. (unless 
you're trying to reject strong interference signals, but that's a 
different kind of receiver).






The advantage of such a system would be that there is only a single
path through the system for all signals, especially through the filters.
Thus the variability of the differential phase shift between the
frequency bands would be significantly reduced, which would result
in better stability.


Oh, I'm not sure about that. It would depend on the filter kind and 
topology.


If it's a SAW or BAW filter, it's all one "brick", but I think you'd 
still need to calibrate the differential phase shift vs temp.  And it 
might be very predictable in a "measure 10 of them, and now you know the 
characteristics of the next 1000"



 Of course, that's the theory. Whether things work

out this way in reality is a different question. What can be said for
sure is, because of the high IF frequency of >200MHz, the standard tuner
chips cannot be used anymore and the RX chain has to be build from
"discrete" components,


There's a ton of integrated demodulator/ADC parts out there these days 
that go up to 6GHz.

AD9361 for example

it will do 56 MHz BW through the IF, with 12 bit ADC feeding a 128 tap 
FIR filter, etc.



 which increases the BOM cost quite considerably.



Attila Kinali



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