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Thanks for the info. Our relationship with the avionics shop is relatively
new but they have been outstanding so far and came highly recommended both by fellow aviators and Garmin and King manufacturer reps My take on this subject is that I need to take it back and specifically have them bench test the xponder. (hmm, could it be time for that mode-s?) Thanks again, Eddie "dave" wrote in message news:lUn%b.126184$jk2.539089@attbi_s53... James M. Knox wrote: "eddie" wrote in om: We just had the pitot-static, encoder / transponder certification completed on 2/21. On 2/23 ATC repeatedly failed to receive the mode-c. Recycling didn't seem to help. What exactly did the shop "certify" when they certified the xponder/encoder? Was it the encoder calibration? They did three things. One - they checked the static system for integrity (i.e. it doesn't leak). Two - they checked the altimeter for accuracy. [They used to do this at the same time, but now they have to pull the altimeter and test it separately, as I understand the latest changes). And three - they put a small "ATC simulator" out by your aircraft and test the transponder. Basically this applies a small vacuum to your static system while they "ping" your transponder and listen for the replies. This tests the transponder system, including the encoder. BTW this has been a problem in the past too, so whatever they did didn't cause the problem but it didn't fix it or find it either. Now... what the transponder tests DON'T catch. 1. A weak transponder transmitter section. It works, but doesn't put out the full rated power. There are minimum requirements for passing the transponder power tests one is power. This is rated on the class of the transponder. 2. Bad cable or corroded connectors between the transponder and antenna. Quite often a corroded antenna connector can be caught during the transponder test as the transponder is quite often shifted off frequency. It can't test for intermitten connections. Again, power will also verify this problem. 3. Bad antenna, including bad connection to ground plane. See above 4. Poor positioning of the antenna, including areas subject to shadowing or too near other antennas. [If the system has NEVER seemed to work well, then this is a possibility.] Correct, but usually not a big problem. And lastly, of course, don't rule out ATC problems. They too have poor receivers, cables, antennas from time to time, and sometimes it can take years to get them to actually test/repair the problem. The usual symptom here is a) multiple people getting reports that their Mode-C isn't being received, and b) in other parts of the country you don't seem to have any problems. This is 100% correct!! Also, don't rule out that the person who tested the unit didn't do his job. The transponder test also do not catch problems which are caused by vibration or electronic parts of the transponder which degrade over time with heat. ----------------------------------------------- James M. Knox TriSoft ph 512-385-0316 1109-A Shady Lane fax 512-366-4331 Austin, Tx 78721 ----------------------------------------------- Dave www.craigmileaviation.com |
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