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Ditch digger circuit

Anyone ever hear of a ditch digger circuit? That would be outside the context of where it exists -- in aircraft transponders, for side lobe suppression re interrogation pules transmitted by FAA's ATCRBS directional antenna, rotating along with the primary radar.

Just curious, because it's odd that FAA long ago put out a technical spec which says don't respond to a side lobe, and then competing manufacturers design a circuit each calling it ditch digger. Clever but simple circuit, but why the need for the odd name which doesn't quite fit what it does, unless it was a known name for that type circuit. Side lobe suppression circuit would work if you're not trying to impress outsiders, and it really functions as a sort of comparator (originally effected with vacuum tubes).

Fred F.

Reply to
TxSrv
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I'm not sure I understand your question.

I am familiar with "ditch digger" circuits in the context of aircraft trasponder side lobe suppression circuit.

What is your question?

Mark

Reply to
Mark

I think the OP wants to know where the term "ditch digger" came from in this context.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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>> Insert witty message here
Reply to
Paul Hovnanian P.E.

Yup, just curious if the insular avionics industry invented the term, or it existed outside. If the former, then it's odd to read the typical aircraft transponder service manual, and see that odd term like you're supposed to know what they're talking about.

Fred F.

Reply to
TxSrv

I don't KNOW, but I would guess the term ditch digger came not from the function of the circuit but from the waveform seen on a scope when it was in operation. The SLS function was implemented using a simple cap charging up to the level that represented the RF level of the pulse. This voltage would then decay over time (looks like a ditch on the scope. If the SLS pulse exceeded this decaying threshold value, then the SLS pulse was detected and the interrogation was from a side lobe. If the SLS pulse remained below this decaying threshold, it was not detected and the next valid pulse was detected as a true interrogation.

The scope waveform of the capacitor voltage resembled an inverted ditch that was dug out by each pulse.

Thats my guess. Mark

Reply to
Mark

Whew! Glad to hear that. It would have been scary if all the PhD engineers at Boeing were stumped by this problem and the ditch digger sketched the solution on the white board during a lunch break (like the janitor in Good Will Hunting).

;-)

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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If the first attempt at making a drawing board had been a failure,
what would they go back to?
Reply to
Paul Hovnanian P.E.

Maybe the hatchlock for the cargodoor on boeing 747-122 that landed in honolulu after haveing several meters of the plane ripped away together with some passengers were constructed the same way.. :)

When I saw how it was constructed. I was amazed how poorly engineered it was. To begin with the electrical motors used to open the cargodoor is supposed to be unpowered dureing flight, didn't happen switch was faulty per design.. Then the worst.., the locking mechanism is such that it doesn't take momentum into consideration such that it may open inadvertly. If a simple plug in a hole had been used instead. It would been very unlikely to open when not supposed to.

In previous versions the door was open inwards, but then bean counters decided it was more profitable to do it the less secure way.. I certainly don't trust their engineering skills anymore..

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pbdelete

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