View Full Version : Dmeeee

14th Sep 2008, 11:35
Has anybody ever heard of 100 aircraft interrogating the same DME, and a 101th aircraft being not able to recieve?

rhythm method
14th Sep 2008, 14:01
Are you sure it shouldn't be a 101st aircraft? :} (Sorry, couldn't resist!)
Anyway, I'm pretty sure you are correct, but who could prove it?

Loose rivets
14th Sep 2008, 19:02
When it first came on trial, the number was very low. More like ten, and things would go awry.

14th Sep 2008, 21:04
When I was on my ATC non-tech Navaids course, [many moons ago], I am sure that 200 was the number mentioned, but as we were also told... "It is ONE beam per DEGREE"..so I will ask my "friendly" Tels man on Tuesday, if I remember :ok:

2 sheds
14th Sep 2008, 21:14
About 200 is the figure that I recall. Can't see what degrees have got to do with it.

Arm out the window
14th Sep 2008, 22:32
**Caution - aviation-related content**

Yeah, I think one beam per degree is a bit of a furphy - like:

Q: Why does the windscreen heat use a square wave?
A: So it can reach into the corners.

If you're talking about VOR radials (nice thread creep there), the equipment measures the time difference between an omnidirectional reference signal and a sweeping directional signal (the old lighthouse analogy) to work out how far round the compass rose you are, ie what radial you're on.

The DME is a bit like SSR in reverse, ie your airborne set sends out a pulse, the ground station replies with a matching signal and the time taken for that all to happen tells the set how far away you are.

Or so I recall through the fog of time and alcohol-related brain deterioration...

14th Sep 2008, 22:36
It's a long time ago but I seem to recall the number being 200 and above that the Transponder reduced sensitivity, therefore reducing range, and those nearest to the ground station and most "in need" received the better service. But that could also be ATC Transponder and I am getting muddled. No books here and Rioja interferes !

Pontius Navigator
14th Sep 2008, 23:09
I seem to recall Wodrick is right.

This seemed to be true of TACAN and was not unlikely in days of yore when 200 aircraft airborne in one part of the UK might have been trying to interrogate one beacon.

DME Basics (http://www.avweb.com/news/avionics/183230-1.html)
This refers to the desensitisation but not absolute numbers.

This one does:
(WO/2008/065328) METHOD AND APPARATUS FOR DETERMINING DME REPLY EFFICIENCY (http://www.wipo.int/pctdb/en/wo.jsp?IA=GB2007003887&WO=2008065328&DISPLAY=DESC) and says 100 as does this one:


15th Sep 2008, 09:08
Yessss indeed,

in the NZ theory books 100 is the stated number. I guess it varies.

And yes I did mean 101st! Although 101th just sounds better. ahha :8

15th Sep 2008, 10:02
I'll be quite happy at 100, it's 33 years since I did my License and things fade, it's not the sort of thing you remember when all you have to do is slam a new box in ! but it must have been in there somewhere.

Romeo India Xray
15th Sep 2008, 10:37
Yes, it was still 100, 20 years ago when I was training - would be good to hear from a ground equipment specialist as to weather it is possible to have more interrogating aircraft these days.