London coverage

Jeremy · July 16, 2009, 06:25:20 PM

Thanks Support.
I have an outside aerial, no pre-ap, and a polor diagram that covers the whole UK.
I am getting puzzled between ADS-B and Mode-s signals. I thought a mode-s signal was a 'packet' within ADS-B.
Is it p[ossible to switch off the priority so I can see either one or the other, without discon the aerial?
Surely, everybody must suffer this at the edges of their receive coverage but they do not know it?
J.

DaveReid · July 16, 2009, 10:09:01 PM

Quote from: Jeremy on July 16, 2009, 06:25:20 PMI am getting puzzled between ADS-B and Mode-s signals. I thought a mode-s signal was a 'packet' within ADS-B.

Other way round.

Jeremy · July 16, 2009, 10:59:30 PM

Explain?
J.

DaveReid · July 17, 2009, 05:53:37 AM

ADS-B data is contained in a 'packet' within a Mode S transmission.

CoastGuardJon · July 18, 2009, 08:53:39 PM

Hi Dave, I'm sure you, Allocator or Tarbat will be able to answer this one (I've tried Search for it, but haven't come up with the answer) - at the bottom of Mylog, it shows number of messages per sec. - what exactly does a message consist of - a certain number of bits/bytes or what? What constitutes a "packet"

Allocator · July 18, 2009, 09:13:21 PM

A short explanation from AirNav in this thread:

http://www.airnavsystems.com/forum/index.php?topic=271.0

CoastGuardJon · July 18, 2009, 09:31:53 PM

Tried that link, clear as mud to me! Exactly what data is passed and encoded, sorry if this seems a dumb-arse question, but I'm having a job trying to understand this info., as sometimes it can be tens or even hundreds/.........

DaveReid · July 19, 2009, 07:42:40 AM

Quote from: CoastGuardJon on July 18, 2009, 09:31:53 PM
Tried that link, clear as mud to me! Exactly what data is passed and encoded, sorry if this seems a dumb-arse question, but I'm having a job trying to understand this info., as sometimes it can be tens or even hundreds/.........

See ICAO Annex 10, Volume IV - Surveillance and Collision Avoidance Systems.

Pages 1-268 :-)

OKC-Steve · July 19, 2009, 04:16:01 PM

Quote from: Jeremy on July 16, 2009, 06:25:20 PM
Is it possible to switch off the priority so I can see either one or the other, without discon the aerial?
Surely, everybody must suffer this at the edges of their receive coverage but

Obviously you can filter what you hear, but you can't get everyone to stop transmitting. They all transmit on the same frequency. ADS-B is an extended Mode-S feature, where the airplanes broadcast their lat/lon and other goodies. Meanwhile the little puddle jumpers are transmitting Mode-A and Mode-C, and a bunch are transmitting Mode-S without the extended ADS-B.

You could open your window and shout: "Shut Up!" Youre neighbors might call the hospital on you though...

CoastGuardJon · July 19, 2009, 09:25:25 PM

Hi Dave, thanks for the reference, but £112 for the info. is a bit too much, a couple of quid, yes, but I'm not £112 worth curious!

http://www.afeonline.com/shop/product_info.php?products_id=492

CoastGuardJon · July 20, 2009, 03:04:28 PM

Many thanks for that link Steve. I've saved it as a pdf, so I can read at my leisure and (best of all) no cost!!!

OKC-Steve · July 20, 2009, 03:12:22 PM

No problem. A lot of the stuff can be ignored, like the 20 pages of altitude bit code and the Collision and Avoidance bo-jive chapter at the end.

Allocator · July 28, 2009, 07:48:29 PM

Traffic in 3 of the 4 holds for EGLL at the moment!

Filters in to only show traffic below 15,000 ft