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#31
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On Tue, 9 Mar 2004 19:52:22 -0600, "Joe" wrote:
Why can't you just continue to use what worked? Namely the aluminum foil. Durability and maintainability are the main issues. This isn't tucked behind an instrument panel... the radios are mounted in an open-ended box on the floorboards, and the area is brushed by my right foot when I get into and out of the airplane. So it has to be something that doesn't tear easily. The current foil is basically just crumpled-on and duct-taped in place. If I have to remove it, it'll just come apart and I'll have to start from scratch. Plus, I think it was already starting to loosen, etc during the single flight...interference seemed to be coming back by the end of the test ride. I'd rather have something a bit more durable held on with tie-wraps and/or clamps. My thought is to bend up a hose clamp so it'll snug the new shielding tight around the square cross-section of the back of the radio, and tie-wrap it around the existing shielding on the wiring harness. Then, to remove the radio, all I'll have to do is loosen the clamp and slide back the shielding to get at the connectors, and slide it back into place and tighten the clamp when I'm done. If it were aluminum foil, I'd probably have to completely take it away and fit a new piece, every time. Finally... since I didn't build this airplane, I have to have an A&P do the annual inspection every year. He's eventually, essentially, going to have to sign off my installation as part of the annual. I'd just as soon present him with a professional-looking job. But you're right, I'm weird. :-) Ron "Pay no attention to Marvel Mystery Oil in the Crankcase" Wanttaja |
#32
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You may have the only known transponder of that variety that has ever been
designed. In the overwhelming predominant world, the test button tests the receiver only by injecting microwatts of oscillator into the front end. Jim (John) shared these priceless pearls of wisdom: -Humm, I forgot about that Jim. However most have a self test button -that causes the transponder to transmit some pulses. I know my 20 -year old Cessna ARC transponder transmits at a low rate when you push -the test button. Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#33
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So, what does the IDENT button do?
BTW, the comment about the balloon reminded me that what you really need to do is get your wife mad at you. The roses you have to buy will come in foil faced mylar already formed into the cone shape you need. Charlie Jim Weir wrote: You may have the only known transponder of that variety that has ever been designed. In the overwhelming predominant world, the test button tests the receiver only by injecting microwatts of oscillator into the front end. Jim (John) shared these priceless pearls of wisdom: -Humm, I forgot about that Jim. However most have a self test button -that causes the transponder to transmit some pulses. I know my 20 -year old Cessna ARC transponder transmits at a low rate when you push -the test button. Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#34
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Lets see if I got this correct. A micro power oscillator injects RF
pulses into the receiver which then thinks this is a radar interrogation pulse and fires out a normal TX pulse out of the transponder. This sounds very much like what I said befo " I know my 20 year old Cessna ARC transponder transmits at a low rate when you push the test button." The ARC RT-359A service manual says that the self test generates 60 MHz 1us pulses that is fed to the first IF amp and that the rest of the circuit behaves as if it was a normal radar reply. It also says that you must use a dummy load or an antenna or damage may occur because it is responding to the self test pulse by transmitting. I am not sure how King and Narco do the same function since I do not have a schematic to look at but most likely it is done the same way which is what you said. It looks like we were both correct. The end result is that it transmits when you push the self test button. On Wed, 10 Mar 2004 08:42:32 -0800, Jim Weir wrote: You may have the only known transponder of that variety that has ever been designed. In the overwhelming predominant world, the test button tests the receiver only by injecting microwatts of oscillator into the front end. Jim (John) shared these priceless pearls of wisdom: -Humm, I forgot about that Jim. However most have a self test button -that causes the transponder to transmit some pulses. I know my 20 -year old Cessna ARC transponder transmits at a low rate when you push -the test button. Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#35
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On Wed, 10 Mar 2004 20:18:37 -0600, Charlie England
wrote: BTW, the comment about the balloon reminded me that what you really need to do is get your wife mad at you. The roses you have to buy will come in foil faced mylar already formed into the cone shape you need. Geeze, Charlie, she's ALREADY mad at me for spending $2000 for a new transponder. Better be gold-faced mylar. :-) Ron "Doghouse" Wanttaja |
#37
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From my Terra TRT-250D repair/test manual:
******************************************* 18 Self Test. 18.1 Set interrogation RF level to -90dBm. Hold transponder "Test" switch in test for at least 4 seconds. 18.2 Observe replies being generated by transponder on % reply meter of the ATC-1400C/S-1403C. The replies should not exceed 75% over a 5 second period. 18.4 Also observe "T" on display indicating replies being generated. 18.5 Release "Test" switch. Replies should stop. *********************************************** My comments to clarify some of the above: 1) The ATC-1400C/S-1403C is a transponder test-set. 2) -90 dBm is a level that is well below the receiver threashold (ie, they don't want the transmitter to "squitter" during this test). It seems clear to me that the transmitter is indeed transmitting. Sid Knox Velocity N199RS Starduster N666SK KR2 N24TC W7QJQ Jim Weir wrote in message . .. (John) shared these priceless pearls of wisdom: -Lets see if I got this correct. A micro power oscillator injects RF -pulses into the receiver which then thinks this is a radar -interrogation pulse and fires out a normal TX pulse out of the -transponder. Nope. The transmitter's local oscillator (or a microfragment thereof) is injected into the receiver's front end. The receiver tests whether or not the microtransmitter was received. The transmitter is inhibited by a digital signal during test. You got it wrong. Sorry. If you want to carry on this conversation, post your real name and real email addy. Jim Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#38
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Jim:
I have the Cessna RT-359A service manual in front of me. There is NO disabling of the transmitter during self test. In fact several months ago I watched the voltage on the cathode of the transmitter tube with a scope and it pulses when the test switch is depressed. There are only 4 wires and a coax cable to the TX tube. These are Cathode, filament, anode , ground and RF out. The anode is +1400 volts DC, the filament is +6.3 volts and ground is of course at ground. The cathode is pulled to ground by an NPN transistor to transmit. On page 5-9 paragraph 5-10 step 2 the manual tells you to press the test switch to measure the TX peak power and frequency of the transmitter. King and Narco may or may not disable the transmitter for self test. I do not have schematics for these transponders so I can not say one way or the other but I see no reason to do this since it would add extra circuits and extra cost to do this. They may do this on the more modern units since the logic may be in an EPLD and no extra production cost would be incurred to add this small piece of VHDL code. I used to have my email address as part of the post but a few months ago I started to getting 20 to 60 bounced email messages per day that I had not sent from people I had never heard of. Apparently the spammers were not only using my email address to spam me at the rate of 30 to 40 per day they were also spoofing my address on the spam they were sending. Due to this I now no longer show even a human readable address but if you insist here it is: frerichsATroDOTcom. If you want my address and phone number look up airport identifier AL10. If you email me your phone number I will give you a call and we can talk about this. This all started over an EMC question and I am the EMI "expert" where I work. (The definition of expert is: A drip under pressure.) John On Wed, 10 Mar 2004 19:52:48 -0800, Jim Weir wrote: (John) shared these priceless pearls of wisdom: -Lets see if I got this correct. A micro power oscillator injects RF -pulses into the receiver which then thinks this is a radar -interrogation pulse and fires out a normal TX pulse out of the -transponder. Nope. The transmitter's local oscillator (or a microfragment thereof) is injected into the receiver's front end. The receiver tests whether or not the microtransmitter was received. The transmitter is inhibited by a digital signal during test. You got it wrong. Sorry. If you want to carry on this conversation, post your real name and real email addy. Jim Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#39
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Charlie England wrote in
: So, what does the IDENT button do? Just sets a flip/flop so that an extra bit is set on the next reply to an interrogation (which clears the IDENT flip flop). ----------------------------------------------- James M. Knox TriSoft ph 512-385-0316 1109-A Shady Lane fax 512-366-4331 Austin, Tx 78721 ----------------------------------------------- |
#40
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Jim...
As I recall, that flipflop triggers a timer (10 seconds???) that sends the ident bit until timeout. Bose' book confirms what I remember also. Jim "James M. Knox" shared these priceless pearls of wisdom: -Charlie England wrote in : - - So, what does the IDENT button do? - -Just sets a flip/flop so that an extra bit is set on the next reply to an -interrogation (which clears the IDENT flip flop). - ------------------------------------------------ -James M. Knox -TriSoft ph 512-385-0316 -1109-A Shady Lane fax 512-366-4331 -Austin, Tx 78721 ------------------------------------------------ Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
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