DME operates by transmitting to and receiving paired pulses from the
ground station. The transmitter in the aircraft sends out very narrow
pulses at a frequency of about 1,000 MHz. These signals are received at
the ground station and trigger a second transmission on a different
frequency. These reply pulses are sensed by timing circuits in the
aircraft's receiver that measure the elapsed time between transmission
and reception. Electronic circuits within the radio convert this
measurement to electrical signals that operate the distance and ground
speed indicators.

Jon Kraus
'79 Mooney 201
443H @ UMP

..Blueskies. wrote:
wrote in message ...
: On Fri, 04 Aug 2006 09:37:44 -0400, Jonathan Goodish
: wrote:
:
: In article .com,
: "Jay Honeck" wrote:
: http://www.scn.org/~bk269/gps.html
:
: This is an interesting site that explains why some pilots (seemingly
: mostly running Garmin-brand portable GPS units) are having trouble with
: losing satellite lock.
:
:
: We had a problem in our PA28 with a Skymap II (panel mounted GPS) when
: using an antenna on the top of the instrument panel. The culprit was
: the Narco IDME 825 and depended which frequency the DME was tuned. The
: DME transmitter blocked the GPS receiver. There was a considerable
: improvement when we fitted an external roof antenna. We have now
: fitted a Skymap IIIc GPS which is understand has a better receiver
: and so far appears ok.


Didn't know DME transmitted...