Peter Duniho wrote:

What LORAN receiver do you have? My Northstar M1 LORAN exhibits neither of
those problems.

I have the Foster LRN-501.

What it *does* do is suffer significant errors in position on occasion,
which I haven't gotten a good explanation for. The errors are up to 20
miles off at times, and I have only noticed them when flying near home (but
of course, this is where I do most of my flying, so that may not indicate
anything).

From the Foster manual. There are 6 LORAN chains in the U.S. (4 in the lower 48) and
more outside, and each is made up of a "master" transmitter and two or three "slave"
transmitters. These are synchronized and transmit timing info as part of the signals.
The receiver figures out where you are by calculating the difference between the
three transmitters and triangulating. Significant position errors can result when the
master and either of the slave stations are in line with your aircraft (you're
between them or they are both off to one side).

I do notice that when I fly long cross-country flights, I don't
have to go very far (50-100 miles) before the LORAN wants to change from one
GRI (or is that just my LORAN's way of saying "grid"? I can't remember) to
another.

GRI is "Group Repetition Interval', but basically it's saying it wants to change
chains.

Maybe I'm right on the edge of reception for the one that the
LORAN unit wants to use (or on the edge of multiples, for all I know).

Yep. Mine wants to change chains about the North Carolina/South Carolina border.
Reception sucks sometimes in Knoxville, and that's on a border as well. IIRC, you're
in Washington State? If so, you're at the boundary of the U.S and Canadian West Coast
chains. To make matters worse, the slave in your area (located in the middle of the
State) is shared by both chains.

I doubt that this issue is a programming problem though. More likely a
fundamental limitation of the ground-based radio chain.

Yep again. Programming would never enter into the situation. A faster CPU would,
however, result in the unit refreshing its idea of your position more rapidly after a
change of course (or your speed after leveling off, etc.).

George Patterson
If you don't tell lies, you never have to remember what you said.