I don't think there is anything else.

I have a light aircraft with a combined L1/L2/IMMARSAT/THURAYA/IRIDIUM
rooftop antenna, but have not found anybody making an L2 GPS receiver
for the civilian market.

I think L2 can be used in a manner which supplements L1, for accurate
survey stuff, but I just want a 'box' which connects to an L2 antenna
and outputs straight NMEA.

On Apr 24, 8:05*am, Peter <peter0o0...@peter2-0-o-0.c0.uk> wrote:
> I don't think there is anything else.
>
> I have a light aircraft with a combined L1/L2/IMMARSAT/THURAYA/IRIDIUM
> rooftop antenna, but have not found anybody making an L2 GPS receiver
> for the civilian market.
>
> I think L2 can be used in a manner which supplements L1, for accurate
> survey stuff, but I just want a 'box' which connects to an L2 antenna
> and outputs straight NMEA.

I have never seen reference to anything like that. There would be a
major issue selling such a receiver to the civilian sector. All 31
healthy satellites send the L2 legacy military P code but it's
encrypted. The eight newest healthy satellites also send a modernized
military code plus the modernized civil code (L2C). L2C messages
aren't currently formatted with positioning data and eight satellites
cannot provide coverage.

--- CHAS

Alan Browne <(E-Mail Removed)> wrote

>On 2011-04-24 08:05 , Peter wrote:
>> I don't think there is anything else.
>>
>> I have a light aircraft with a combined L1/L2/IMMARSAT/THURAYA/IRIDIUM
>> rooftop antenna, but have not found anybody making an L2 GPS receiver
>> for the civilian market.
>>
>> I think L2 can be used in a manner which supplements L1, for accurate
>> survey stuff, but I just want a 'box' which connects to an L2 antenna
>> and outputs straight NMEA.
>
>L2C - it is smack dab in the middle of L2 - should be available on one
>satellite beginning in 2014 with more, of course, to follow. From there
>your antenna will be usable with the appropriate receiver.
>
>Novatel (and presumably others) make civil receivers that use L2.
>http://www.novatel.com/products/gnss...v-receivers/##
>
>Current L2 is encrypted (Y) so its use would be restricted to processes
>akin to survey. (Codeless processing (phase)).
>
>Presumably with a base station on the ground you could post process to
>very accurate relative positions; or have a datalink to the aircraft and
>a lot of processing to do same in real time. You could get relative
>position accuracies of better than 1 - 10mm per km between the base
>station and the airborne receiver. eg: at 100 km distance you could
>have an error of 10 cm - 1 meter. Not shabby at all.
>

That was my understanding...

What suprises me is that military receivers have not "escaped into the
wild". They must be widely used by troops etc. I recall reading a book
about the 1st war in Iraq and they had them in 1991, made by Magellan,
so this stuff is really very old. Maybe they quickly become useless.
How often are the keys changed?

Alternatively, is there some way to run off L1 and if L1 disappears
then one could run off L2, at least for say some minutes or tens of
minutes?

I ask this, as a private pilot, seeing various notams warning about
intentional GPS jamming. This is quite serious stuff, because GPS is
the only means of area nav. Here in the UK, we have poor VOR coverage
at low levels and we have to fly low to remain below various bits of
Class A. INS is obviously not feasible (FOGs are another military
technology, though big jets use them, and way too expensive), solid
state gyros are a couple of orders of magnitude not good enough (lots
and lots and lots of people are looking at this) and a backup would be
very handy because if you bust some controlled airspace you won't get
any credit for being unable to use GPS because they will just say you
should have been reading a map like our grandfathers did in WW1 and
WW2 and we beat the Germans on both occassions so it must be good....

On 2011-04-24 12:00 , Peter wrote:
>
> Alan Browne<(E-Mail Removed)> wrote
>
>> On 2011-04-24 08:05 , Peter wrote:
>>> I don't think there is anything else.
>>>
>>> I have a light aircraft with a combined L1/L2/IMMARSAT/THURAYA/IRIDIUM
>>> rooftop antenna, but have not found anybody making an L2 GPS receiver
>>> for the civilian market.
>>>
>>> I think L2 can be used in a manner which supplements L1, for accurate
>>> survey stuff, but I just want a 'box' which connects to an L2 antenna
>>> and outputs straight NMEA.
>>
>> L2C - it is smack dab in the middle of L2 - should be available on one
>> satellite beginning in 2014 with more, of course, to follow. From there
>> your antenna will be usable with the appropriate receiver.
>>
>> Novatel (and presumably others) make civil receivers that use L2.
>> http://www.novatel.com/products/gnss...v-receivers/##
>>
>> Current L2 is encrypted (Y) so its use would be restricted to processes
>> akin to survey. (Codeless processing (phase)).
>>
>> Presumably with a base station on the ground you could post process to
>> very accurate relative positions; or have a datalink to the aircraft and
>> a lot of processing to do same in real time. You could get relative
>> position accuracies of better than 1 - 10mm per km between the base
>> station and the airborne receiver. eg: at 100 km distance you could
>> have an error of 10 cm - 1 meter. Not shabby at all.
>>
>
> That was my understanding...
>
> What suprises me is that military receivers have not "escaped into the
> wild". They must be widely used by troops etc. I recall reading a book

Military receivers are not all that common and usually quite expensive.
Their distribution is quite controlled even though an unkeyed receiver
can't be used beyond C/A - and a keyed receiver falls back to CA after
less than 1 week (maybe up to 2 if the succeeding week's key was also
loaded - not sure if that's feasible).

> about the 1st war in Iraq and they had them in 1991, made by Magellan,
> so this stuff is really very old. Maybe they quickly become useless.
> How often are the keys changed?

I would bet that in the 1st Iraq war soldiers were equipped with
civilian receivers over military receivers at a ratio approaching
1000:1. Possibly higher. Mothers were mailing GPS receivers to their
sons. I don't recall Magellan making P/Y code receivers. At the time
of the 1st Iraq war, I'm not sure if the majority of satellites were
broadcasting Y code in any case.

Keys are distributed in 1 week chunks. I don't recall if the receivers
could hold more than 1 week of code (or current + next).

> Alternatively, is there some way to run off L1 and if L1 disappears
> then one could run off L2, at least for say some minutes or tens of
> minutes?

No. The C/A code contains a handover word with an index to the time
position in the P/Y code. This is because correlation search would be
very long over a 7 day long code. So the HOW tells processor what
position in the sequence the receiver should use to load the correlator.
Without the current key, of course, the receiver can't compute the
proper correlation code to load into the correlator. No tracking.

Survey receivers, on the other hand, track the carrier phase. With an
encrypted signal there is a trivial hardware solution (I don't recall
the details but something simple in hardware can 'rectify' (wrong term)
the signal so that its phase can be accurately tracked. With that, and
a reference station, the phase difference between the two can be very
accurately computed, and thence very accurate position differences
computed. Note the term: _position differences_. This is highly usable
for survey but impractical and expensive for navigation.

(I probably have muffed a lot of the detail above wrt survey receivers)

> I ask this, as a private pilot, seeing various notams warning about
> intentional GPS jamming. This is quite serious stuff, because GPS is
> the only means of area nav. Here in the UK, we have poor VOR coverage
> at low levels and we have to fly low to remain below various bits of

NDB's are usually better at low alt and you can use commercial AM
stations for reference as well. Not as easy to navigate as VOR, esp. in
cross track winds, but still a good orientation device.

The NOTAM's are over generous in the seriousness of the amount of test
jamming strength, coverage area and duration. eg: abundance of caution.
Don't give up your VOR/NDB skills and procedures just yet. (Is it me
or procedure turns are disappearing from most approaches?).

> Class A. INS is obviously not feasible (FOGs are another military
> technology, though big jets use them, and way too expensive), solid
> state gyros are a couple of orders of magnitude not good enough (lots
> and lots and lots of people are looking at this) and a backup would be
> very handy because if you bust some controlled airspace you won't get
> any credit for being unable to use GPS because they will just say you
> should have been reading a map like our grandfathers did in WW1 and
> WW2 and we beat the Germans on both occassions so it must be good....

ILS was invented at the beginning of WW II and is still the basis for
almost all CAT II and all CAT III approaches. Of course you also need a
very good inertial integration for CAT III and beyond, not to mention
crew training.

--
gmail originated posts filtered due to spam.

This
http://www.kvh.com/Commercial-and-OE.../CNS-5000.aspx

looks good but the price tag?

On 2011-04-24 16:06 , Peter wrote:
> This
> http://www.kvh.com/Commercial-and-OE.../CNS-5000.aspx
>
> looks good but the price tag?

Not cheap. But it is assumed to be ITAR proof:

"...the rugged CNS-5000 meets COTS requirements, minimizing
the operational complexities for customers whose products
cross international boundaries."

Note that it uses a GPS module from Novatel as I mentioned in the first
reply.

Of course then you have to integrate into your aircraft which is another
kettle of fish.

--
gmail originated posts filtered due to spam.

On Apr 24, 9:05*am, Peter <peter0o0...@peter2-0-o-0.c0.uk> wrote:
> I don't think there is anything else.
>
> I have a light aircraft with a combined L1/L2/IMMARSAT/THURAYA/IRIDIUM
> rooftop antenna, but have not found anybody making an L2 GPS receiver
> for the civilian market.
>
> I think L2 can be used in a manner which supplements L1, for accurate
> survey stuff, but I just want a 'box' which connects to an L2 antenna
> and outputs straight NMEA.

L2C and L5 civilian signals are still in their operational infancy.
Both signals are being broadcast with an MT0 (message type zero) which
is the last stage of testing before a signal becomes fully available.
But that MT0 signal is enough to cause most GPS receivers to ignore
those satellites.
Hopefully the current slow pace of GPS IIF launches are caused by the
unresolved signal issues (some signal issues can't be fixed at all
after the satellite is launched).
IIF signals are within the specifications, but far short of what was
expected by the civilian GPS scientists.
I say that, since if USAF starts launching 3 IIF birds per year, in
just 3 years we would have minimum L2C signal availability for an IOC
(initial operational capability) status - 18 satellites.
Plus if Japan's QZSS program stays on track, in a few years there will
be 3 extra L1/L2C/L5 ranging sources over Japan/Australia and region.
Notice that all IFR/certified usage of L2C signals is essentially
forbidden by the FAA and EAA, since L2 is not an aviation protected
band. The only usage they might not frown upon would be in handhelds/
VFR only panel mounts.
L5 is expected to be useable much sooner, since Galileo doesn't
support L2C (but supports L1 C/A, L5, plus a few more signals), and L5
is an aviation protected band.
Also all WAAS/EGNOS/MSAS GEOs broadcast an L5 signal, although that
signal is considered unhealthy for end user utilization (even though
its very much used by WAAS closed loop GEO monitoring system, go
figure !).
Hopefully in a few years USAF will realize that L2C and L5 signals are
useful even without a complete coverage for standalone navigation. If
a GPS receiver has 6 L1 C/A ranging sources with 3 of those having an
associated L2C signal, position/time can be calculated a whole more
accurately than 6 L1 C/A ranging sources alone.
I wish FAA got out of their "certified to perfection" or nothing
mentality and realized that all GPS signals are useful, and that L2C
should utilization should be allowed and encouraged as a secondary
signal (L1+L2C or L5+L2C ok, but L2C alone=forbidden), even for WAAS
LPV200 landings. Triple frequency GPS is far more accurate and robust
than dual frequency GPS. Triple frequency GPS accuracy + WAAS accuracy
is measured in millimeters even for fully dynamic (in flight)
utilization, while dual frequency GPS + WAAS accuracy won't get better
than a few inches. Accuracy <> WAAS calculated protection envelope
which is about 10x bigger than actual measured accuracy.

Marcelo Pacheco PP-IFR + GPS enthusiast

> L2C - it is smack dab in the middle of L2 - should be available on one
> satellite beginning in 2014 with more, of course, to follow. From there
> your antenna will be usable with the appropriate receiver.

L2C is available right not, but with MT0 test message, on 7 IIR-M plus
one IIF satellite plus QZSS. SVN49/PRN1 has L2C, but is has the same
L1 C/A accuracy issues, so that's not considered here.
The issue is until MT0 test message gets removed, there will be zero
mass market manufacturer interest in shipping a receiver that can
receive L2C signal.
MT0 should be an all or nothing proposition. The reason MT0 is there
is because: 1-There are less than 18 GPS satellites with L2C
capability in orbit 2-The current ground monitoring network can't
receive L2C signals (OCX will help that).
Plus since Galileo won't support L2C, the main justification for
having an L2C signal at all was the reduced power requirements +
reduced circuit costs associated with the L2C signal 1MHz bandwidth
versus L5 signal 10MHz bandwidth.
Today that's quickly becoming a non-issue with the ever shrinking
chips (and the resulting reduction in power consumption).
So there's a huge risk L2C will be relegated for usage only by premium
priced triple+ frequency GPS receivers.
Specially if Galileo launch schedule delays are minimal (since it
should quickly become the second most important GNSS constellation and
it won't support L2C at all).
Bottom line is there isn't much motivation today towards using dual
frequency GPS receivers outside of aviation. If there were, we would
see an effort to use dual frequency GPS receivers with SBAS
corrections to produce much better street maps, current ones are too
low accuracy to justify car GPS receivers with dual frequency
capability.
But all of that can change, if in a year or two the Car GPS market
gets stagnant, and the economy is booming, we might see suppliers
offering dual/triple frequency GPS receivers to try to revive sales.
If a couple heavyweight GPS suppliers decide to invest on L2C, perhaps
their clout might be enough to make USAF to remove MT0 from L2C
signals.

Marcelo Pacheco

Alan Browne <(E-Mail Removed)> wrote

>On 2011-04-24 16:06 , Peter wrote:
>> This
>> http://www.kvh.com/Commercial-and-OE.../CNS-5000.aspx
>>
>> looks good but the price tag?
>
>Not cheap. But it is assumed to be ITAR proof:
>
> "...the rugged CNS-5000 meets COTS requirements, minimizing
> the operational complexities for customers whose products
> cross international boundaries."
>
>Note that it uses a GPS module from Novatel as I mentioned in the first
>reply.
>
>Of course then you have to integrate into your aircraft which is another
>kettle of fish.

If there was a box which had an RF connector for a GPS antenna (active
or passive, but the active ones are much more common) and had an RS232
NMEA output, and *internally* ran an INS with GPS corrections, that
would be a completely usable product because you could run some moving
map application (e.g. Oziexplorer) on some tablet computer, and you
are sorted.

It does not need integration into the aircraft; a totally portable
solution would be just fine. In any case, virtually no panel mounted
(IFR certified) GPS has an external NMEA input.

Very interesting replies Marcelo - many thanks.

However I am not sure Galileo is of much help against a DIY/Ebay type
jammer which will probably wipe out 1575MHz, leaving L2 intact
"because nobody uses L2".

Perhaps there is just no solution short of that GPS+INS box.

I agree re the aviation issues. That whole business is way behind the
technology, especially here in Europe where EGNOS has only just been
approved for "safety of life" applications, and there are no LPV
approaches, and EASA wants 4 figures for an approved flight manual
supplement authorising them because it is a Major mod They played
the same game for the AFMSs for straight NP GPS approaches until
somebody told them that GPS approaches are dead in the water in Europe
unless they treat the AFMS as a Minor mod.