T&T: Connecting new GPS with older Raytheon radar

[Bob McLeran]

Sanderling's current radar is a Raytheon R40 raster scan radar that was 
installed on the boat in 1990. Although it doesn't have a lot of bells 
and whistles compared to a new model of any kind, it functioned 
perfectly for us last summer in foggy Rhode Island Sound, Maine and the 
Bay of Fundy - we couldn't have asked for a better display of our 
surroundings, which even included lobster pot markers and birds in the 
water at the 1/4 mile range when we couldn't see more than a hundred 
yards - and I'm not interested in replacing the radar with a new one 
that will provide only slightly more functionality.

However, I would like to take advantage of functionality that seems to 
be built into the radar which could be awakened with NMEA data from our 
GPS chart plotter. With NMEA data the radar can display position, SOG, 
target and waypoint information (as well as some other NMEA-based info). 
The display unit has a connection on the back of the display for a BNC 
connection which the user's manual indicates is to accept NMEA data from 
a Loran C and refers to NMEA 0183 with GLL, GTD, VTG and BWC sentences. 
Specifically, the manual states:

"The R40 is programmed to accept data from the Loran in the NMEA 1082 
and NMEA 1083 formats . . . The NMEA 1083 data standard will, in most 
cases, provide Lat/Long, TD course and speed data for the radar display 
. . .The connection to the R50 Display Unit is made with a common BNC 
connector. RG 58 A/U Coax cable of any length may be used to complete 
the interconnection to the Loran C. A two wire, shielded cable may be 
used in place of the RG 58 coax if necessary. . . ."

Two questions come to mind:

(1) Is the  NMEA 1083 sentence format from a GPS now the same as it was 
back in 1989 from a Loran C when this unit was made? (I realize the data 
stream may contain more information now than it did in 1989, but are 
GLL, GTD, VTG and BWC sentences now the same as they were back in 1989?)

(2) Can any decent-sized wiring be used other than shielded cable as 
long as I can attach a BNC connector at the display unit end? (The NMEA 
data from the GPS comes from an 18 or 20 guage wire, and I'd prefer to 
just run a little heavier wire and end it with a BNC connector if that 
were possible.)

I'd appreciate any thoughts you might have regarding this lash-up.

-- 
<><><><><><><><><><><><>Mozilla Thunderbird<><><><><><><><><><>
Bob McLeran and Judy Young                  Manatee Cove Marina
MV Sanderling                               Patrick Air Force Base
DeFever 41 Trawler                          Melbourne, Florida