Rapco 1804M - serial problems?
I've just got a Rapco 1804M and while it works, within the limits of my
antenna placement, the RS-232 serial out doesn't read very well, and seems
to have incorrect characters. The voltage levels look OK, and the
terminal emulation program is set to 4800 baud, 8-bit, no parity, one stop
bit, no flow control. I've tried other combinations. As near as I can
measure, the baud rate is 4800.
Here's some sample output:
UTC Time : 16:65:19 16/10?1q
UTC Time : 16:25:20 16/10/11
Position : 53 54.406 N 002 12.075 W 0239 M
PDOP : 02
Sat PRN : 28,19,32,01,11<22
Sat levål : 00,12,13,06,05,03
Fix, Mode : 2D , Coarse
UTC Time : 16:25:21 16/10/11
UTC Time : 16:25:22 16/10/11
UTC Time : 16:25:23 16/10?11
UTC Time : 16:25:24 16/10/11=
UTC Ti}e : 16:25:25 16/10?11
UTC Time : 16:25:26 16/10?11
The same serial port works correctly with 9600 baud Garmin signal, and I
don't have any other available computers with spare RS-232 ports I can
test against.
Am I missing the obvious, or is there something wrong with the serial
port? I do appreciate that the serial port isn't critical to the correct
operation of the 1804M, but this has cast doubts about this particular
unit into my mind!
Thanks,
David GM8ARV
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Le 16/10/2011 18:34, David J Taylor a écrit :
I've just got a Rapco 1804M and while it works, within the limits of
my antenna placement, the RS-232 serial out doesn't read very well,
and seems to have incorrect characters. The voltage levels look OK,
and the terminal emulation program is set to 4800 baud, 8-bit, no
parity, one stop bit, no flow control. I've tried other
combinations. As near as I can measure, the baud rate is 4800.
Here's some sample output:
UTC Time : 16:65:19 16/10?1q
UTC Time : 16:25:20 16/10/11
Position : 53 54.406 N 002 12.075 W 0239 M
PDOP : 02
Sat PRN : 28,19,32,01,11<22
Sat levål : 00,12,13,06,05,03
Fix, Mode : 2D , Coarse
UTC Time : 16:25:21 16/10/11
UTC Time : 16:25:22 16/10/11
UTC Time : 16:25:23 16/10?11
UTC Time : 16:25:24 16/10/11=
UTC Ti}e : 16:25:25 16/10?11
UTC Time : 16:25:26 16/10?11
The data is nearly all good, so probably not a rs232 rate issue. Looking
at the transformations in the above data,
/ => ?
1 =>q
, => <
CR => =
m => }
they are all single/multiple bit flips in the top nibble of the
character hex value. Maybe it's a UART that has hickups.
I couldn't find a schematic, but may be worth looking to see what's
connected to the RS232 tranceiver chip..
The same serial port works correctly with 9600 baud Garmin signal, and
I don't have any other available computers with spare RS-232 ports I
can test against.
Am I missing the obvious, or is there something wrong with the serial
port? I do appreciate that the serial port isn't critical to the
correct operation of the 1804M, but this has cast doubts about this
particular unit into my mind!
Thanks,
David GM8ARV
The data is nearly all good, so probably not a rs232 rate issue. Looking
at the transformations in the above data,
/ => ?
1 =>q
, => <
CR => =
m => }
they are all single/multiple bit flips in the top nibble of the
character hex value. Maybe it's a UART that has hickups.
I couldn't find a schematic, but may be worth looking to see what's
connected to the RS232 tranceiver chip..
Mike,
Many thanks for your investigation. I can confirm that the device has a
Z85230 serial chip, and I took a look at the soldering on the topside of
the board, and it all looked fine. I had wondered about taking the
processor board out and checking the underside soldering, but that
involved disturbing so much that I've ruled that out for the moment.
The box was supplied with a generic GPS puck antenna by the eBay seller,
and it's not that sensitive so I've ordered a better puck antenna (for the
moment, I don't want the complexity of an outdoor antenna) and when that
arrives and I have a better GPS signal I'll visit the box again. No
urgency right now.
I have checked the 5 MHz using the RWM calibration of my R8500 receiver,
and it's spot-on as near as I can tell which is likely good enough for me.
Thanks,
David
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
David,
I'm in a similar position to you regarding GPS aerials, may I ask where you obtained your 'better puck'?
John H.
On 17 Oct 2011, at 15:45, David J Taylor wrote:
......................
The box was supplied with a generic GPS puck antenna by the eBay seller, and it's not that sensitive so I've ordered a better puck antenna (for the moment, I don't want the complexity of an outdoor antenna) and when that arrives and I have a better GPS signal I'll visit the box again................
The box was supplied with a generic GPS puck antenna by the eBay
seller, and it's not that sensitive so I've ordered a better puck
antenna (for the moment, I don't want the complexity of an outdoor
antenna) and when that arrives and I have a better GPS signal I'll
visit the box again................
David,
I'm in a similar position to you regarding GPS aerials, may I ask where
you obtained your 'better puck'?
John H.
John,
It's ordered, but not yet received (and it has to come from the USA - no
UK supplier?). See the comparison between the supplied GA 27C and their
antenna:
http://www.gilsson.com/external_gps_antenna_comparison.htm
I'll report back when it arrives. At the moment, I'm getting lock about
half the time, but at least with the unit permanently on I trust the
frequency in holdover mode (constant control voltage) to be far better
than anything else I have.
Cheers,
David
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
David,
I'm in a similar position to you regarding GPS aerials, may I ask where
you obtained your 'better puck'?
John H.
John,
I'm currently trying this unit from londoncolour:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250687616146
and it produces a consistently higher total satellite strength reading, a
consistently higher number of satellites with non-zero strength readings,
the maximum number of reported fixes per minute has been consistent over
the last 90 minutes, but the PDOP while more consistent is still at 4 or
5, rather than the 2 required for the unit to re-define its average
position away from its original location in London!
Cheers,
David
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
David,
Given your results and the price, the londoncolour antenna is a 'must try'. Also the extra cable length will get the puck to a window which should also help. The 1804M has already shown how stable my old HP107BR quartz standard really is. Not being a software person I must now go and learn about RS232s and terminals, (:-)
Thanks for your help,
John.
On 19 Oct 2011, at 17:15, David J Taylor wrote:
David,
I'm in a similar position to you regarding GPS aerials, may I ask where you obtained your 'better puck'?
John H.
John,
I'm currently trying this unit from londoncolour:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250687616146
and it produces a consistently higher total satellite strength reading, a consistently higher number of satellites with non-zero strength readings, the maximum number of reported fixes per minute has been consistent over the last 90 minutes, but the PDOP while more consistent is still at 4 or 5, rather than the 2 required for the unit to re-define its average position away from its original location in London!
Cheers,
David
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
David,
Given your results and the price, the londoncolour antenna is a 'must
try'. Also the extra cable length will get the puck to a window which
should also help. The 1804M has already shown how stable my old HP107BR
quartz standard really is. Not being a software person I must now go and
learn about RS232s and terminals, (:-)
Thanks for your help,
John.
John,
I think I was unlucky with the RS-232. Every indication is that people
usually have no problems, and my own case may have been due to having to
cobble together a 9-pin null modem lead from a variety of other leads.
(Null modem swaps the send and receive leads, so that you can connect two
"terminals" or two "computers" together, Normally, the computer transmit
(TX) lead is connected to the terminal receive (RX) lead, and the computer
RX is connected to the terminal TX. Three wire - TX, RX and ground - is
enough for the 1804.
I've now written a small plotting program to show the PDOP, satellite
signal strength, inactive/coarse/fine lock mode etc. This ideally needs
to run for several days with the box connected to each puck in turn, but
preliminary results show that the unit achieved "fine" lock several times
with the new antenna, but never with the old. The reported signal
strength and number of active satellites appears more consistent as well.
The extra cable length meant that I could bypass a short BNC patch lead I
had, so at least reducing the number of connectors.
I also compared the new antenna with a Lowe antenna from some years back
on a GPS 12 XL, and it produced a worthwhile improvement. It may only be
the extra gain and slightly higher signal level, but that does seem to
help. I have the unit outside on a SSW-facing window, with rather more
than 135 degrees of clear view.
Cheers,
David
SatSignal software - quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk