GPS loss of signal explanation

In article ,
"Peter Duniho" wrote:

In addition to Jon's nice explanation of DME, I'd like to point out that
because DME is an active receive-and-reply system, it can get saturated when
too many aircraft are using the same DME site. A pilot using DME in busy
airspace should keep this in mind, in case some funny numbers start getting
spit out, or the DME just stops giving any indications.

I admit, I've never actually seen this happen, but it is theoretically
possible.

Interesting. I hadn't thought about the interrogator before. But It's more
likely that the ground station will reduce the sensitivity to the point that
it doesn't transmit that many replies - thereby reducing the probability
the DME will be listening to a reply intended for someone else.

For a DME interrogator that already acquired the ground station and
is tracking, it's extremely unlikely that its tracking algorithm will drift
off. Remember that the interrogations are psuedorandom, there are
only 30 interrogations per second (IIRC), and they are short.

--
Bob Noel
Looking for a sig the
lawyers will hate

"Bob Noel" wrote in message
...
Interesting. I hadn't thought about the interrogator before. But It's
more
likely that the ground station will reduce the sensitivity to the point
that
it doesn't transmit that many replies - thereby reducing the probability
the DME will be listening to a reply intended for someone else.

That would cause the DME in the airplane to stop providing DME information,
which is one of the consequences I mentioned. I admit, I wasn't precise
about which "DME" would stop giving nay indications...it's the one in the
airplane I was talking about.

For a DME interrogator that already acquired the ground station and
is tracking, it's extremely unlikely that its tracking algorithm will
drift
off. Remember that the interrogations are psuedorandom, there are
only 30 interrogations per second (IIRC), and they are short.

I agree it's less likely you'll get erroneous data from the DME. It'd be a
pretty rare situation in which that happens, assuming it has ever happened
at all anywhere. My main point is just that pilots should be aware of the
limitations of DME (I guess we could mention slant-range here too, but I
think we were just talking about the radio signal itself? I've lost track
).

Pete