KT78A transponder
Thread Starter
Joined: Jul 2010
Posts: 2,807
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From: Ansião (PT)
KT78A transponder
My secondhand plane had a transponder installed, and how impressive I found that! It is labelled KT78A, I take that to indicate (Bendix-)King.
Now that the time has come to actually fly, I am looking into this transponder, and have some questions. And of course there is no manual, though there was one for the altitude encoder.
-) no amount of websearching found me a manual, I only came up with a 2-page pdf describing installation and cabling. But perhaps there is not much to say, beyond that?
-) apparently, there are 3 similar models: 76A, 76C, 78A - what are the differences?
-) when I switch the transponder on, in its normal "alt" mode, the orange indicator flickers busily, even on the ground. I suppose every flicker indicates an interrogation, but are these really so frequent? Even on the ground, outside most radar station's range?
Now that the time has come to actually fly, I am looking into this transponder, and have some questions. And of course there is no manual, though there was one for the altitude encoder.
-) no amount of websearching found me a manual, I only came up with a 2-page pdf describing installation and cabling. But perhaps there is not much to say, beyond that?
-) apparently, there are 3 similar models: 76A, 76C, 78A - what are the differences?
-) when I switch the transponder on, in its normal "alt" mode, the orange indicator flickers busily, even on the ground. I suppose every flicker indicates an interrogation, but are these really so frequent? Even on the ground, outside most radar station's range?
Joined: Jan 1999
Posts: 6,209
Likes: 2
From: north of barlu
Basically it's a lower specification KT76 A with lower power output and it is unable to code mode C above 15000ft.
I would guess that it was built as a low cost unit to use parts that work but don't meet the spec for being fitted to a KT76A, King also did this with the KN62 DME, when unit failed meet the KN62 power out put they badged it as a KN64.
If you got lucky your KN64 had only missed the spec by a few watts and you had very good DME in terms of output for a budget price.
I would guess that it was built as a low cost unit to use parts that work but don't meet the spec for being fitted to a KT76A, King also did this with the KN62 DME, when unit failed meet the KN62 power out put they badged it as a KN64.
If you got lucky your KN64 had only missed the spec by a few watts and you had very good DME in terms of output for a budget price.
Joined: Jun 2007
Posts: 862
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From: Swindon, Wiltshire
76C is digital (buttons and a display) - the other two have mechanical selectors.
78A is less powerful (100 ish watts instead of 200 watts) and is limited to a certain height. It's effectively the 'VFR' model.
It's quite normal for the light to flash almost constantly on the ground - just depends where you are in relation to the radar stations.
78A is less powerful (100 ish watts instead of 200 watts) and is limited to a certain height. It's effectively the 'VFR' model.
It's quite normal for the light to flash almost constantly on the ground - just depends where you are in relation to the radar stations.
Joined: Jun 2008
Posts: 519
Likes: 16
From: Luton
Don't TCAS equipped commercial aircraft also interrogate transponders? Your transponder will flash when responding to TCAS equipped aircraft in the vicinity - even when out or range of a ground based secondary radar system.
