Peter,
Thanks for your reply.
To simplify my problem here is an example. A radar controller tells a plane with a mode c transponder to squawk say 3666. When the pilot applies this code to the transponder the squawk appears on a radar screen as I understand it.
Surely then even mode c transponders must transmit this code, and possibly it could be a unique number which no other
aircraft is squawking. It is worth keeping this info and even reporting it so a pilot can infer that the threat aircraft might or might not be on the same frequency.
Phil
Hi again Phil,
You are correct about Mode C Aircraft transmitting their Squawk in response to interrogation by ATC RADAR, however the problem lies in the phrase ’... and possibly it could be a unique number which no other aircraft is squawking.’
Unfortunately in practice, in the GA world this only occurs when the aircraft concerned is transitting, or about to transit, controlled airspace and has been allocated a unique Squawk for the transit by the local ATC. During the transit, we of course already know what frequency it will be on and ATC will ensure effective separation.
In the vast majority of cases outside controlled airspace, GA aircraft will be transmitting a ‘Common Squawk’ such as 7000, the local ‘Listening Squawk’ (again common to all ‘listening’ aircraft) or a generic Squawk used by for example Scottish or London Information. Also, the digital code which produces the Squawk is in many cases exactly the same as that for the equivalent altitude. The code for ‘7000’ for example is exactly the same as that for ‘7000 ft’. As I have said previously, with Mode C there is no Hex ID or other reliable marker available to allow us to easily collate received data to an individual aircraft or easily separate between a Squawk and an Altitude transmission. In order to make this possible at all, Lee has had to develop extremely complicated detection and comparison algorithms. In some cases this comes down to monitoring the signal codes over a period as the altitude will vary over time, whereas the Squawk will generally remain constant.
As I said previously, the lower section of the Traffic Screen is the area where all the recording and comparison to make this happen is displayed, which is why this section of the table is so fluid. As far as ‘users’ are concerned, this screen is part of the internal working of PilotAware. It is made available to users for background information
only and should
not be used for aircraft awareness.
These detection and comparison algorithms have been even further refined in the newest software, which we have now been testing for some time and which should be due for release shortly. Believe me when I say that getting to this point with Mode C has been an extremely hard slog and is the result of over 2 years of ongoing development.
We are always open to ideas and suggestions for improvement.
Fly Safe!
Best Regards
Peter