GPS-A vs. GPS

[Dean AE7Q]

Questions:

1. I understand that the main reason that GPS-A is generally preferred over GPS mode is that GPS-A includes a CRC, while GPS only includes a XOR checksum.  Also, clearly from the D-PRS calculation page, the XOR checksum does not include the actual GPS position data (since it is pre-computed).  My question is, does the GPS-A CRC include the GPS position data?

2. I understand that one advantage of using GPS mode over GPS-A, is that the GPS data can be pickup up and displayed by the older D-Star radios, like the IC-91AD.  Are there any other advantages to using GPS mode over GPS-A?

[Pete AE5PL]

Questions:

1. I understand that the main reason that GPS-A is generally preferred over GPS mode is that GPS-A includes a CRC, while GPS only includes a XOR checksum.  Also, clearly from the D-PRS calculation page, the XOR checksum does not include the actual GPS position data (since it is pre-computed).  My question is, does the GPS-A CRC include the GPS position data?

2. I understand that one advantage of using GPS mode over GPS-A, is that the GPS data can be pickup up and displayed by the older D-Star radios, like the IC-91AD.  Are there any other advantages to using GPS mode over GPS-A?

1. Each GPS string carries its own checksum per the NMEA specifications.  The CRC in GPS-A is for the entire line which includes everything including position data.

2. No other benefit.  GPS is longer (more subject to bit errors) than GPS-A and less accurate (as you noted, checksums vs. CRC).

Hope this helps.

73,

Pete AE5PL

[Dean AE7Q]

... one advantage of using GPS mode over GPS-A, is that the GPS data can be pickup up and displayed by the older D-Star radios, like the IC-91AD.  Are there any other advantages to using GPS mode over GPS-A?

...
2. No other benefit. ...
Pete AE5PL

I think you forgot one:  altitude reporting!  However, one additional disadvantage of std. GPS over GPS-A, is that if you want to manually change the comment field "on the fly" (like mobile), you don't have a handy calculator for the XOR checksum (unless you know the ASCII alphanumeric bit codes by heart like I do).