Transponder keys are automotive ignition keys with signal-emitting circuits built inside. The circuit has no battery; it is energized by the radio signal itself.
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This should only be operated upon ATC request. Airborne Collision Avoidance System ACAS operation requires that both aircraft - the interrogator and the target - are equipped with operating transponders. An aircraft equipped with ACAS will receive the following information depending on the type of transponder with which the target aircraft is equipped:. Later the transponder aircraft identifying field became 12 bits, and the octal convention was maintained.
It is a convention, and it has been maintained. Supplemental: I remember a transponder which had 6 toggle switches for entering the code, prior to the 12 bit standard.
The switches were marked by threes with underneath them. Back prior to computer literacy of the masses, once can speculate the the selection of digits, rather than for example, hex, entered into consideration as IFF and transponder technology developed. A VFR squawk code could be entered as a 12, which would have most significant 1 switch up, and the least significant 2 switch up.
I recall that secondary radar show that the same as , even though it came from a transponder without the 12 bit standard. The 12 bits were set by the system timing and accuracy of pulse generation and processing technology available at the time. So to keep things simple they used Octal with 4 simple, 8 position switches. In computer systems, everything is binary.
This is due to the logic circuitry only having 2 states, high and low voltage. Because of this, decimal wouldn't be as simple to convert to binary as octal or hex are. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more.
Why is the range of transponder digits 0 to 7 rather than 0 to 9? Ask Question. Asked 4 years, 6 months ago. Active 1 year, 11 months ago.
Viewed 17k times. Improve this question. Greg Bacon 5, 4 4 gold badges 30 30 silver badges 83 83 bronze badges. Hugo Woesthuis Hugo Woesthuis 1, 2 2 gold badges 14 14 silver badges 29 29 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. Lnafziger Lnafziger Using octal dials, you cannot select outside the valid range of Since user doesnt do any math with such addresses, there is no drawback at all.
Show 1 more comment. As an example, let's group by 2 bits and use Greek letters for the required 4 symbols: We would be poor designers to produce this except for a remake of Airplane! In case your are interested by the details of how octal is used, I propose details below. Let's illustrate with some values: We can add as many 0 on the left as we want e. Octal and hexadecimal representations of binary numbers For convenience, we usually replace groups of bits by some equivalent to reduce the number of signs used.
It's common to use groups of 3 and 4 bits: Octal : A group of 3 bits can generate 8 combinations, we can easily replace this group by a single figure in radix 8 to cover these combinations.
Back to our examples, replacing the bit groups by their equivalents in radix 8 and Select which radix to use What have we got so far? There are many designs to do this, one is to use brushes rotating over a disc with printed conductive tracks: Source The switches provides directly the binary group.
It's as easy to use 3 hexadecimal wheels with 4 contacts. Why not 10 symbols? Here is the result: The minimization allowed to reduce the number of terms hence gates to That's assuming you can even source the parts - the 74S chip is long out of production, though there are more modern equivalents.
BTW a "simple keypad and micro-controller" are more expensive than you think in the aviation world, you have to make them certified. This is not a world where you can phone Apple to tell them you have a problem. When I answer a question, I use the complexity appropriate to the original question, and the wording of his question made it seem like he didn't need this level of detail. Good info for others though, and I certainly up-voted this answer to show appreciation for the info and effort that he put into it!
Background Mode A and Mode C compatible transponders use bit identity or beacon codes. The Sweet Spot Considering it the other way, we have four groups of three bits. All digits are familiar 0 through 7, so Dial inputs have only eight positions or Eight buttons suffice. All four-digit pilot inputs are representable in Mode A or Mode C. Greg Bacon Greg Bacon 5, 4 4 gold badges 30 30 silver badges 83 83 bronze badges.
But all computers are still binary.
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