Transponder

[gramps]

Hello,

Can anyone tell me why a transponder only goes up to 7 and not 9?

Thanks,

Gramps

[Bright-Ling]

From a poor memory:

If I remember rightly it is because it works of binary data.

There was only space for 12 characters. Each squawk number was made of binary (1's or 0's). As there are only characters able to be transmitted, that meant you only had a max of three digits for each squawk number.

With me so far??

As the max number of representations in binary using three digits is 8, (000, 001, 010, 011, 100, 101, 110, 111), the number of usable numbers in a squawk are 0, 1, 2, 3, 4, 5, 6, 7

So, a squawk of 4125 would be represented as

100,001,010,101

(in fact there may be 15 total characters including the spacers (the commas in the binary example)

If 0-9 were used in binary, then 4 binary digits would be needed, which would mean only three characters, leading to a max number of squwks of 999, as opposed to the 4096 that are currently available.

This is all from memory when at the College of Air Traffic Control. So it is may be wrong. If it is right, thanks to Pedro!!!:)

[Little One]

This doesn't really belong here but thought I'd share a funny story anyway:p

We give vfr flights that are not on FPL sequential squawks with each sector being assigned certain numbers ie 2604 to 2607.

One ATC having more than the usual amount of vfr in thier sector gave a very timid sounding pilot the squawk of 2608 without thinking and forgot that they were octaganal. After a few minutes of him trying to dial in this he replied " Sorry but my transponder seems to be broken cause it only goes to 7. Can you give me another number please." Apparantly he also asked the AMO to replace the Transponder when he landed.

I wonder if others have been caught out like this??:confused:

[chiglet]

Yup,
A very large British [International] Airline confused "slot time 1812" with his squawk 0612 :rolleyes:
we aim to please, it keeps the cleaners happy