Re: EGNOS/ESTB

asdf wrote...
>> I have left my monochrome etrex Vista (sofware version 3.60) powered up
>> on its windscreen mount for almost the last 24hrs. Just came out of work
>> (car parked pointing West) and noticed that the right hand pair of
>> satellite indicators were cycling through sats 33, 37 & 39 only
>> (strangely 33+37 or 37+39 but never 33+39). I was not getting any
>> signal, but all three satellites were indicated in sensible southern
>> positions on the skyview
>
> Locking process does not work as with regular GPS satellites. With patch
> antennas, you must be pointing more or less toward North (so that the
> screen and antenna point to the south) or a GPS must be flat horizontal so
> that the patch antenna can read the singal comming from the South (S-SW).
> In car it may be difficult with buildings around. Until now, I did not
> have any luck in car while driving (even on open road), but only
> stationary with open view to the south sky. And, it is best to stnad still
> until lock is obtained (actually, not a full lock, but until differential
> data is recived)
>
> You can not use other sattelites since two others are emiting pure EGNOS
> signal which is not yet marked as availalbe, and only 33 sends EGNOS/ESTB
> signal, open to the public. Satelite bar remains hollow, but other
> sattelites get D to show that the GPS recieves Differential data for these
> sattelites. GPS list all WAAS/EGNOS sattelites in the almanac, and it does
> so apparantly each time.
>
>> If I get time over the weekend I'll take the Vista to the top of the
>> Malvern Hills, where it should get as perfect a view of sat 33 as is
>> possible at this latitude, and see if that makes any difference.
>
> I have no problem reading sat 33 from any bit larger (at least several
> hunderd meters open to the south) par area in my city.

What a pointless and self-indulgent post!

You carefully snipped my next sentence "When I held the receiver out of the
window appropriately angled towards south I immediately received fairly
strong signals (grey bars) from 33 (~75%) and 39 (~60%)" and then went on
patronisingly to explain that I should have done exactly that!

The point of my message was that I had been receiving very strong signals
from sat33 for a long period of time but apparently no differential
corrections were being obtained (or accepted) by the receiver, since it kept
cycling away from this SV to monitor 37 & 39, which I am perfectly aware are
not broadcasting usable corrections (although a strong signal was also being
received from 39). This was suggesting that either sat 33 was not
broadcasting diff data at that time or else the Vista was rejecting data
with the test bit set, as has been suggested in the past.

Large car parks actually tend to be quite good for reception since the
highest object likely to obscure the signal is probably a people-carrier!
You just have to be aware that the geo sat has an altitude of approx 30
degrees from this part of the world. In fact yesterday afternoon I again
noticed reception from sat 33 whilst parked facing north in a supermarket
car park. This time the Vista was holding on to sat 33 so it appeared to be
receiving valid diff data. After holding the receiver out of the window,
facing S, for about 15 minutes it finally reported differential corrections
on all visible satellites and an EPE of just 2metres.

Obviously I lost the signal from sat 33 when I replaced the receiver on its
windscreen mount and all the Ds immediately disappeared from the satellite
display. However the receiver continued to report an enhanced EPE for at
least 5 minutes, as I was driving home, before drifting up to a more usual
value. (I haven't examined the tracklog data to see whether this enhanced
EPE was meaningful in terms of accuracy).

On returning home I again obtained a strong signal from sat 33 but even
after leaving the receiver propped up on the roof of my car for about half
an hour I could not again obtain any differential corrections.

Does this imply that the Vista is indeed rejecting test transmissions but
that ESA are playing games turning the test bit on and off or is there some
other reason why my Vista could be reporting a strong signal from the geo
sat but failing to accept any valid diff data?

David






.

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