Here is the deal, both the primary and the secondary detectors need to be adjusted. Significant in Tom's set of requirements for the transponder test equipment is that it need not be required to produce the P0 pulse in the test interrogation. Here is an engineering question: How do you even adjust the secondary?B. Keith Peshak
512-863-0994
keith.peshak@gtwn.netOK, here is the answer, given to me by the FAA when I started as a bench technician at a Certified Repair Station. We'll do this for the 3A primary detector and 3A alternate detector, but it is the same story for the 3C primary detector and 3C alternate detector. We'll do this for the Narco AT-150, but it is the same for virtually all transponders that don't eliminate all of the analog components (there are only two that eliminate all of the analog components).
Interrogate with a twin pulse pair, 0.8 microseconds in duration, spaced 8.0 microseconds on 1030 MHz. Adjust R473 until the transponder replies to the interrogation. Tweak R473 until you can change the 8.0 microseconds as low as you can high before the transponder fails to reply on each side. Typical window will be 1.6 microseconds, so tweak the range for 7.2 to 8.8 microseconds. The primary is "tuned."
Put the scope on U420 pin 1, and look see the pulse length. Now adjust R469 to "tune" the alternate, by the following procedure.
Since there is no way to make the transponder alternate detector key the transponder reply, because there is no P0 pulse in the interrogation, because Tom McSweeny doesn't require the test equipment to be able to do that, you'll have to "fake it". Put the scope on U420 pin 2, and adjust R469 for the same pulse length. The alternate is now "adjusted", without ever firing a reply from the transponder under an interrogation preceded by a noise pulse (completely operation unverified).
You ASSUME that the value of component C440 EXACTLY equals the value of component C439 AND you ASSUME that the value of component R496 EXACTLY equals the value of component R495 AND you ASSUME that both inputs of U420A are symmetric (which is actually likely) AND you ASSUME that the up and down drives of U411A match identically the up and down drives of U412A (which is highly unlikely) AND you know that, in your entire career, you have NEVER seen any two analog components with the EXACT same value or behavior, not to mention entire analog chains).
You get the picture? Never has been "tuned" even though it has been "adjusted."
Here is the deal, all four detectors need to be tested to see what happens if there is a P4 2.0 microseconds after the P3 (an SLS command 2 microseconds into the 3 microsecond wait until reply. Significant in Tom's set of requirements for the transponder test equipment is that it need not be required to produce the P4 pulse in the test interrogation!!! Here is an engineering question: How could he have ever said: "FAA Aircraft Engineering Division personnel...attempted to verify...conducted an in depth study...found no evidence", when he never ever even required anybody ever check? Talotta checked, but McSweeny won't pay any attention, apparently, to his own technical people! Nobody even knows how to check. Here is a new instrument that, at least, tried!
Enough said?