I installed a Mode S (it was 'mandated' at the time) when refitting my a/c and have yet to see any benefit over mode C.
I have observed several times on the FIS frequencies in Germany calls like "D-EXXX if you are listening on this frequency, you are in restricted airspace, turn left heading 270 immediately". This is not to punish them (radar tracks are sufficient) but to help them and get them out without prosecution.
The privacy issue is also important for tracking movements for financial gain, for example a business is looking to acquire a company, they don't want it known that their corporate aircraft just landed at an airport where a for sale company is based. Celebrities don't want their movements tracked and so on.
That doesn't make sense. Who operates a business jet flight without ATC services? The US are pretty weak on protecting personal information. While flightaware is a great resource, I am glad that such information is not available in Europe. None of anyone's business when I fly where and even though we have mandatory Mode S, the information about our flights is less available than in the US. And in case I am really concerned about privacy, I stay out of the transponder mandatory airspace or I ask ATC for an exemption (which I have always been granted in the past).
Conversely, aircraft below those thresholds are required to NOT have Enhanced Mode S (they have to use Elementary Mode S) which prohibits radiating the extra parameters.
I still think you are wrong on this Peter. All certified Mode S transponders officially contain ADS-B position reporting when connected to a GPS. This functionality is part of the certification and it is described in the installation manual of the transponder and the applicable STCs. When performing the transponder installation according to the EASA approved installation manual, I can enable this functionality. Therefore it is perfectly legal. Your 2007 document is very ambiguous. The avionics shop I used (one of the largest in Europe) saw absolutely no issue enabling this feature.
I have observed several times on the FIS frequencies in Germany calls like "D-EXXX if you are listening on this frequency, you are in restricted airspace,
I don't think this ever happens in the UK because most ATC units do not have the equipment to display the aircraft reg.
All certified Mode S transponders officially contain ADS-B position reporting when connected to a GPS
I don't think so. The capability is there, but is not used. ADS-B radiates the information continuously i.e. without being triggered by ATC radar. Large aircraft (20T+?) must have that. Enhanced or Elementary Mode S radiates nothing unless pinged by ATC secondary (SSR) radar. At least I think that is the description of a GTX330, unless ADS-B is explicitly enabled.
It's certainly true that there is very little difference between a Mode S aircraft whose transponder gets lat/long fed to it from the GPS (and which then radiates it at every SSR interrogation) flying in a radar-rich environment, and the same aircraft having ADS-B.
That 2007 document could well be de facto obsolete now, and I cannot imagine anybody caring one little bit to enforce such garbage given that every plane not based in the EU will be radiating everything anyway, but it has driven a large number of avionics installations over the years to not have GPS etc connected to the transponder, so the bulk of the UK GA fleet is stuck with that. I would have no issue with radiating everything...
Many used a squat switch, or an air pressure switch, to do the GND/AIR auto switching. I have a differential pressure switch, switching at 0.8" excess on pitot over static pressure. Some years ago an avionics shop wired up the KLN94 GS to do that job but it never worked.
Who operates a business jet flight without ATC services?
The issue I think is that there is a big difference between (a) some anorak listening locally on VHF, picking up just local traffic, collating the info (which is just an audio track) and furiously typing it into a flight database, and (b) somebody sitting a thousand miles away with an ADS-B receiver seeing where all the jets belonging to Company X are flying and the data being automatically recorded and distributed instantly, which is what one has in Europe now.
Interestingly, the ADS-B boxes use an internet "network" of many boxes to exchange time-stamped data and use this to triangulate the position of Mode S traffic which does not emit lat/long. That is how everybody can see e.g. my TB20 everywhere I go, and my reg is displayed next to the blip.
Prague CTA does have mode S equipment, too. On a short bimble last year, I relied on my GPS to stay OCAS and, being unaware it was switched to the minimum detail mode, clipped a corner of the Prague CTR. Upon return, I was met by our local FISO who said Prague Info had phoned him about me, and I'd better call them back and apologise. No official repercussions followed, but I have since made a rule not to fly without radio communication anymore, no matter how short and trivial the flight is.
but I have since made a rule not to fly without radio communication anymore, no matter how short and trivial the flight is.
Wow...
Please forgive my naivety but how do the integrated TCAS systems different from devices like the ZAON MRX type which detect radar interrogation bounces? I often see a number of aircraft, some quite close, and they arent detected by the MRX. The other aircraft cant all have their transponders switched off (well....) but I wondered if the integrated ones had some kind of radar as they seem to show much more traffic.
Integrated just detect the transponder positions.
Please forgive my naivety but how do the integrated TCAS systems different from devices like the ZAON MRX type which detect radar interrogation bounces? I often see a number of aircraft, some quite close, and they arent detected by the MRX. The other aircraft cant all have their transponders switched off (well....) but I wondered if the integrated ones had some kind of radar as they seem to show much more traffic.
The ZAON and similar products are passive receivers. They rely on transponder emissions from targets which have been pinged by SSR radar. They have several problems
The "active" systems from e.g. Avidyne or Garmin transmit SSR-like pulses, uniformly in all directions, and then collect the responses from the targets. From the time delay they can determine the range pretty accurately, and using an array of (normally) four antennae mounted externally and the relative signal levels from them they can determine the azimuth (to maybe 10-20 degrees). And because they tap into into your transponder RF cable and also connect into your DME, they sidestep picking up your own transponder emissions that were triggered by SSR radars.
There is a x10 difference in cost 
In all cases the relative altitude is determined by comparing your own pressure altitude with the target's Mode C returned pressure altitude.
Mode S transponders don't reply with position information. The main difference between mode S transponders and mode A/C transponders is that the mode S transponder has a unique 24 bit address and can be interrogated individually. The mode S transponder can receive (1030 MHz) and transmit (1090 MHz) a digital message up to 54 bits or 108 bits. This permits exchanging more data than the squawk code and the altitude. Each transmission uses the aircraft ID, but after the first transmission, the parity is Xor'ed with the ID.
Mode S can also broadcast a message (1090 MHz) without being interrogated. The radar term for this is called a squitter. In the basic mode S, the squitter is used to broadcast the fact that it is nearby. A mode S radar will pick this up and realize that the transponder is in its airspace and therefore add it to its interrogation table. A full TCAS system will also receive the broadcast and is able to exchange information via the squitters between two aircraft that have TCAS. Because of mode S being individually addressable, the ground radar system can operate more efficiently and the capacity of the system is enhanced, particularly in congested airspace.
There are two levels now in use by the standard mode S, ELS (Elementary Surveillance) and EHS (Enhanced Surveillance). ELS only replies with the ID, altitude, ident status, and squawk code. EHS provides more information by adding selected altitude, roll angle, roll angle, true track angle, magnetic heading, ground speed, indicated airspeed, and baro climb/descent rate.
ADS-B does not use the reply messages, it only uses the squitters. Because it needs more data, it uses Extended Squitters (108 bits) and this includes position data and other data such as position integrity and accuracy codes. So, without ADS-B or 1090ES capability, the mode S transponder does not transmit its position.
Mode S is an interesting technology invented by the MITRE corporation to be backward compatible with the mode A/C transponders. To get the mode A/C transponders to ignore the longer mode S messages and to avoid interference from mode A/C transponders stepping on the mode S transmissions a technique known as side lobe suppression is employed. Mode A/C transponders receive the interrogations from the radar antenna as it sweeps by the azimuth of the aircraft, but it will also receive an interrogation when the antenna is pointed 90 degrees from the azimuth to the aircraft. This spurious signal is called a side lobe and is unwanted. If the mode A/C replies to the side lobe, then the radar will think it is in the direction that the antenna is pointed and will displace it 90 degrees. To avoid this, one pulse in the preamble to the inquiry is transmitted using a non directional antenna, but at a distinctly lower amplitude. The other pulse is sent only by the directional antenna. If a mode A/C transponder sees the non directional pulse and it is smaller in amplitude than the directional pulse, it assumes this is normal and replies. If instead it detects the two pulses similar in amplitude or the directional pulse being smaller, it assumes it is from the side lobe and goes to sleep for a short while. MITRE used this characteristic and encodes the mode S transmission with the directional pulse deliberately at a lower amplitude so that any mode A/C transponder will go to sleep for a while. It then continues on with a higher amplitude pulse in a later time slot so that the mode S transponder can check for the side lobe. The maximum length of the inquiry and reply messages are based on the time that the mode A/C transponders are required by the TSO to be asleep for the side lobe suppression. The side lobe suppression is checked every time the transponder is recertified. In the US this is every two years.
Great explanation, NCYankee!
I don't doubt NCYankee's explanation because I know he knows the subject, but I don't think that is entirely how Mode S is operated in Europe.
Firstly, if one does a search of a GTX330 installation manual for "Elementary" or "Enhanced", one finds nothing. At least not in the IM I have. That's because these are European creations, done without reference to actual equipment that exists.
Elementary Mode S emits the 24 bit ID and also some sort of flag indicating the speed range of the aircraft, which i recall is configured in the GTX330 as being above or below 150kt or something like that.
Enhanced Mode S returns whatever you feed to the GTX330. There is no config in the GTX330 for elementary v. enhanced. It will just transmit on 1090ES everything connected to it via RS232 or ARINC429.
Also, a GTX330 won't radiate anything at all unless interrogated by SSR radar.
ADS-B has to be enabled separately and then it will radiate the various input data without being interrogated by SSR.
Is that incorrect?
