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#71
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Snowbird wrote: Mark Mallory wrote in message ... Isn't troubleshooting fun? ;^) Just Ducky (pun intended). So what do you suggest to distinguish? My ideas a 1) return to antenna farm w/ handheld and try to stay long enough to get a station ID, also confirm lat long coordinates if interference received: 2) fly w/out handheld in the plane if interference received: 3) remove #2 nav com and ELT from plane fly again if no interference: 4) put one back Sounds like a good plan. I would try disconnecting *all* the antennas on the plane except for the *good* com's (and the transponder's, which you need under the clsB and which IMO is unlikely to be the problem.) Note the results on the good com, then hook them back up one by one... I'm also thinking it might be worth a call to the TV station, to see if they have someone who cares because maybe they have better equipment and could check this out. (or maybe I can get the FAA guy to call...) Yes, I mentioned this in my first post... get in contact with their Engineering Department and explain the problem. They'd be *more* than interested, they're technically qualified guys, and they have the necesssary equipment. As a ham radio guy and former Broadcast Engineer myself (1970s), I know I'd be chomping at the bit to track it down! You mentioned the problem was considerably worse on *one* com than the other... if the problem IS in the plane, that's my guess as to the source (see my other post). Can you disconnect the antenna from *that* com, and fly with just the other one? No problem, but it would be easier (as well as owner-allowed maintenance) to just remove the radio -- if that would suffice? Or are you thinking it's the antenna/cable? Unless the problem is a corroded connector or such, probably not. I like the idea of disconnecting the BNC at the antenna because it eliminates as much as posible. IF it's the radio -- unfortunately it's a TKM. Are there bench checks our local avionics guy should be able to run to see if it's up to spec, before we ship it out to them? Possibly... if they're clever and have the equipment, they might be able to rig up two signal generators with a 3db hybrid combiner to simulate the two suspect interfering signals. Another idea that doesn't require any test equipment is as follows: go flying and check the frequency 119.5 (also 119.475 & 119.525) on all your radios, and see if you receive distorted TV audio. This is the second harmonic of ch. 2's aural carrier, and if something on the plane is generating second-order intermod (at 127.0), the same mechanism should generate the second harmonic as well. (Think of this as the sound carrier mixing with *itself*) It's likely that ch.2 has gone to pains to ensure their radiated 2nd harmonic is quite clean... so you DON'T hear it, it *might* mean that the problem is outside the airplane (or the interference is caused by some different mechanism.) If you drive back to the farm, you can check these frequencies with your handheld as well. Thanks! Sydney Good luck! Keep us posted... |
#72
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Mark Mallory wrote in message ...
I would try disconnecting *all* the antennas on the plane except for the *good* com's (and the transponder's) Well, but.. which is the good com? They both get the interference.. If you get the impression I'm not too thrilled about disconnecting all the antennae in the plane, you got that right. Removing avionics and leaving them on the ground is easy, for the most part (and legal for me to do AFAIK). Disconnecting some of our antennae is a cast-iron b**** and reconnecting them is worse. Notably, the VOR/glideslope antennae. Which brings me to ask...what does d/c'ing antennae get me that removing their avionics doesn't? I'm really hoping to hear from a couple of other folks on this one, notably Jim Weir since I took his advice, drove to the antenna farm, and found interference w/ my handheld. What do you suggest next, Jim? Yes, I mentioned this in my first post... get in contact with their Engineering Department and explain the problem. They'd be *more* than interested, they're technically qualified guys, and they have the necesssary equipment. Well, I did. I can't say they were "more than interested" in fact, they were initially interested in telling me my equipment was at fault because "we just had our equipment checked last Tuesday and we're absolutely clean". But I'm hopeful I eventually persuaded the guy I talked to that if I could drive up to the foot of other antenna and just get some strong RF noise on the aviation band, but drive up to the foot of his tower stick the ducky out the window and listen to a broadcast 5x5, maybe this bore investigation. At least he said he'd call me back in a couple days and gave me his direct number. We'll see... Cheers, Sydney |
#73
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Pull the darned radios. If the interference goes away, you at least know it was
ONE of the radios that did it. If you have dual coms, pull one, go fly, then pull the other one, put the first one in, and go fly. Jim (Snowbird) shared these priceless pearls of wisdom: -I'm really hoping to hear from a couple of other folks on this -one, notably Jim Weir since I took his advice, drove to the antenna -farm, and found interference w/ my handheld. - -What do you suggest next, Jim? Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#74
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On Mon, 10 Nov 2003 16:35:28 -0800, Jim Weir wrote:
Pull the darned radios. If the interference goes away, you at least know it was ONE of the radios that did it. If you have dual coms, pull one, go fly, then pull the other one, put the first one in, and go fly. Jim And if they're the same radios, switch trays, too. (Snowbird) shared these priceless pearls of wisdom: -I'm really hoping to hear from a couple of other folks on this -one, notably Jim Weir since I took his advice, drove to the antenna -farm, and found interference w/ my handheld. - -What do you suggest next, Jim? Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#75
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Roger Halstead wrote:
On Fri, 07 Nov 2003 12:39:37 -0800, Jim Weir wrote: Back in the old days we did it by trial and error and glommed onto what worked best. When the digital computer came along, we got a full blown printout of the inter/cross/spuri mod products across a frequency band and picked a frequency(ies) for the IF that produced minimum spurious products. Note the word MINIMUM. There has never been a receiver produced by the superheterodyne process that is totally free of spurious, including the magnificent Collins S-line or 51J series of receivers. And they were tube type equipment which I think did far better at rejecting intermod than transistors. OTOH todays FETs are pretty good. Of course a miser is a mixer is a mixer ... which was designed to mix the signals. It takes sojme careful design to prevent unwanted signals from getting into (and out of) the mixer. As you say, none of them are perfect. Roger Halstead (K8RI EN73 & ARRL Life Member) www.rogerhalstead.com N833R World's oldest Debonair? (S# CD-2) I am sorry that I missed the beginning of the thread. The King KX170 series is an excellent, if old, radio; and should be able to regect the FM and VHF-TV band signals from as near as a couple of miles. Nonetheless, your problem sounds like "front end overload" which is made worse if the receiver has become slightly detuned over time. Therefore, even though I usually assert that at least 80% of radio problems are really antennas and other airframe wiring, I really thing that you will end up sending the KX170 to the shop in order to solve this problem. Peter |
#76
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#77
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How are we doing on this now by the way?
Paul wrote in message ... What your drive to the antenna farm (with the handheld) "proved" is that the problem is still most likely garden variety intermodulation interference. |
#78
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"Paul Sengupta" wrote in message . ..
How are we doing on this now by the way? Thanks for asking! Well, DH set out on an "interference hunt" primed to selectively remove this and that from the plane -- and couldn't find any interference to remove. Haven't run into any since. So troubleshooting is on hold until the trouble shows up again -- the reason intermittant problems are such a bear. Sydney |
#79
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Ah. Maybe they've cleaned up the transmitter? Too much to
hope I guess... Paul "Snowbird" wrote in message om... Well, DH set out on an "interference hunt" primed to selectively remove this and that from the plane -- and couldn't find any interference to remove. Haven't run into any since. |
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