[time-nuts] Rapco 1804M - serial problems?

David J Taylor david-taylor at blueyonder.co.uk
Thu Oct 20 10:49:08 UTC 2011


> 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 at blueyonder.co.uk 




More information about the time-nuts mailing list