Silly Transponder Stuff

Ravioli

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Saturday morning I called up for flight following and a practice approach to KXYZ.

Departure said: Squawk 4646 and ident

Well... the 4 button on my xponder didn't work. WTF? Tried again... no joy.

Departure, Bug Destroyer 666 unable 4646, can I have a different code?
Negative BD666, all of our local codes start with 4.

ARGH.

So he quite nicely let us stay on 1200 using the ADSB signature and cleared us for the Bravo and approved the practice approach. All was good.

I called about the flat repair from Garmin for a GTX327. $700 and a few weeks. Double ARGH!

I found a GTX on my field (not literally) for $600. Bought it. Slid it in. Seemed okay. I'm testing all the numbers and the 8 and 9 didn't seem to work. WTF. I went from one bad digit to 2 bad digits? Somethings wrong.

I called @AggieMike88. He knows him some stuffs, I'll tell ya. He managed not to call me an idiot while reminding me that the codes use 0-7 (some kind of math thing) and the 8 and 9 are there for two reasons: Confuse me, and entering tail numbers and the like.

Anyway, everything is working, and a halfway funny story to boot.

Thanks Mike!
 
Looking forward to the day where buying a 430W on ebay is cheaper than the flat rate. :D

P.S. I love my 327. Rock solid.
 
I was pleased to see your name on the caller ID when you phoned. But gotta say, I wasn’t expecting to discuss inop 4’s and why 8’s and 9’s are included on that transponder.
 
If you still have your old transponder, you might fix it by spraying electronic contact cleaner around the button then blowing it out.

BTW, 0 through 7 are used because it is base 8(octal) code that is used for the sqwauk code. As Mike said the 8 & 9 buttons are used for other purposes where normal base 10 numbers are used in setup.
 
Also, some time back @RyanB and I were pondering why the numbers go 0-9 (left to right) instead of 1-0. Being octal explains that as well, since the 8 characters used are together instead of skipping over the two that are not.

So it seems I fixed something and learned something yesterday. I think I'll take the rest of week off.
 
As someone who did assembly language programming while the dinosaurs were still roaming the Earth, the math of this is second nature. At one point mathematically I thought in octal and hex more than base 10. ANY number system, hex, octal or decimal begin with zero. That’s why the nineteen hundreds were called the twentieth century. Think about it.
 
Wow! If they are able to reinvent octal math with an electronic device, that deserves an engineering award!
 
Now I’m wondering why it has been Octal all this time versus decimal.
 
I don’t know, but being an electronics guy from that period, Digital electronics were all the rage in the sixties and seventies. Octal was quite popular in that period before microprocessors came along and most all operated with Hex in the beginning. In the very beginning octal. Base 10 doesn’t lend itself to a digital system. Base 8 and base 16 were most popular. Something digital in those days utilized digital systems like octal or hex for all their logic and number crunching. Decimal was typically only used for interfacing with us lowly humans.
 
Now I’m wondering why it has been Octal all this time versus decimal.
Because the squawk is 12 bits (i.e. 4096 code) and mapping BCD into 12 bits is awkward. You'd only end up with 1000 discrete decimal combinations vs 4096 from octal.
 
In WWII there was a system called Identification Friend or Foe (IFF). It was an octal code that was displayed on a radar screen as three rasters each one be narrow or wide. A narrow was a zero and a wide was a one making for seven possible codes. There was a code of the day which would be zero though 7. The aircraft had transponders that transmitted that code. The radar had a unit that deciphered it. I fully expect that our transponders came from those roots.

As a radar repairman in the Army circa 1970 we still had these ancient tube type IFF units that fed the signal to our radar. For the time, our radar looked clean and modern. The ancient IFF units looked as if they had been carried in the back of a truck ever since the war.
 
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