John,
It's common to see either 4 or 5 digit numbering, where "chain 9940" and
"GRI of 99400 µs" are equivalent. The former is short-hand; the latter
uses proper SI units. If that looks odd, see some GRI examples:
"FS700 LORAN-C frequency standard"
https://www.thinksrs.com/downloads/PDFs/Catalog/FS700c.pdf
"New Life for LORAN" (2004)
https://www.loran-history.info/George/George-Appel-New-Life-for-Loran-1.pdf
https://www.loran-history.info/George/George-Appel-New-Life-for-Loran-2.pdf
A funny quote from the document above is:
> The entire process repeats over again in what is called the Group
Repetition Interval (GRI).
> To confuse novices to LORAN terminology, the GRI is given in tens of
microseconds.
> Thus, a GRI of 99,400 microseconds is known as "LORAN rate 9,940."
> It is the GRI that the LORAN receiver uses to identify the chain to
which it's locked on.
More examples:
"Loran-C and Loran-D Systems or Radio Navigation" (1972)
<https://media.defense.gov/2017/Jul/03/2001772426/-1/-1/0/1972_LORAN-C&LORAN-DENGINEERINGRPT.PDF>
See table 1 on page 9.
"Timing With LORAN-C"
https://www.febo.com/time-freq/loran/index.html
"Austron 2100F Loran-C Frequency Monitor"
http://www.leapsecond.com/museum/au2100f/scope.htm
/tvb
On 8/7/2020 3:13 AM, John Ponsonby wrote:
When I designed and built my LORAN-C receiver, for navigation not precise time,
it was my understanding that all GRI's (Group Repetition Intervals) were
expressed as four digit numbers. I designed my receiver accordingly. The number
was the repetition time in units of 10 microsecs. This is the period of one
cycle of the RF signal. so the RF is coherent from group to group. (The groups
are not all identical. There are alternately A groups and B groups.) I notice
that in the present discussion the GRI is given to five digits. Does any one
know if the change to five digits, which are presumably the time in microsec,
is so to speak official?
John P
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