My LNAV (Rev4.2) needs GPRMB (destination) and GPRMC (position)
sentences. PCAIB sentence is optional.
I think that any GPS with Waypoint/ GOTO functionality provides the
GPRMB and GPRMC sentences.
I am currently replacing the brick in my cockpit (GPSMAP195) which has
been feeding the LNAV for years, with a smaller GPS.

The PCAIB sentence is Cambridge proprietary and contains waypoint name
and waypoint elevation.
This is used for automatic final glide calculation.
If you are using a non-Cambridge GPS, which will lack the PCAIB
sentence, you will still get the wind calculation, but for final glide
you have to enter your arrival MSL altitude (+margin) manually.
Very inconvenient.

It would not be too difficult to have any of the PDA/PNA soaring
packages to output these 3 sentences based on the selected waypoint.
I was using SoarPilot on the Palm platform.
Paul Gleeson build me a version with these outputs, but my Tungsten
gave up and I could not test it.
In the mean time I switched to the Ipaq310 PNA platform and I am still
trying to convince some developers to output these sentences for
connection to the LNAV through BlueTooth.
Yes, I know that the PNA/PDA also has final glide calculation.
Still nice to have another reference at nearly no additional cost.
The whole point here is NOT to have to spent $2500 for the 302, when
you have an LNAV that is still working alright.
Approved logging is not relevant for me. (Just OLC acceptance of the
PNA IGC files is fine for me)

Hans Van Weersch



On Apr 25, 1:08*pm, Martin Gregorie
wrote:
On Sat, 25 Apr 2009 17:28:51 +0100, soaringtheskies wrote:
I have a Cambridge LNAV and I want to replace my LX400, which is
currently being used purely as a GPS receiver, with something else to
provide a GPS feed to the LNAV, preferably without taking up a space on
my instrument panel.

What NMEA sentences does it need?

Why does it need a GPS? Just for wind calcs or do you want it to do more?

The NMEA sentence information will hopefully be in its manual. Knowing
that will help you select a suitable GPS.

I just went though a similar exercise when I replaced my Garmin GPS II+
with a Binatone PNA running XCSoar. This has no way to output GPS data.

Anyway, I wanted my SDI C4 vario to still calculate wind, so I connected
a blind GPS that I hid behind the panel: I have room on my panel for the
GPS II+ OR the PNA and no spare slots. Like all blind GPS receivers mine
only outputs GPRMC sentences, which is the same as a GPS II+ does without
an active waypoint or task. However, the C4 also needs destination
sentences (GPRMB, GPWPL and GPR00) to calculate wind, so all the blind
GPS is doing right now is draining my battery.

The point being, that, if the LNAV needs destination data to calculate
wind, you'll not be able to use a blind GPS. You'll need one that you can
enter a waypoint or a task into, so it will probably occupy panel space.

Your LNAV may be the same. If you can't find anything in the manual for
the LNAV or the LX400, and nobody else on r.a.s knows what sentences it
needs, there are a couple of other ways to find out:

- connect the LX400 to a laptop with a serial port set to 4800 baud,
* 1 stop bit and 8 data bits/no parity and run any program that can
* display or capture the data coming down the serial line.

* Alternatively, borrow a datascope, and use that to show you what
* the LX400 outputs.

- Another way is to borrow a Garmin GPS II+ or a 12XL, connect it to
* the LNAV. If the LNAV is like my C4, it will not calculate wind until
* you put a waypoint into the GPS.

Of course, there is another way: accept that the LNAV will become a
simple TE compensated averaging vario, buy a PNA and run XCSoar on it.
XCSoar is both a moving map navigation system and a glide computer. Its a
cheap solution: XCSoar is free Open Source software and will run on any
PNA with an SD card slot and Windows Mobile 5. PNAs are inexpensive: my
Binatone X.350 cost £50 (about $US 75) plus £5 ($US 7.50) for a 2GB SD
card.

HTH

--
martin@ * | Martin Gregorie
gregorie. | Essex, UK
org * * * |