Let'sgoflying!
Touchdown! Greaser!
If it’s possible to narrow down the radio that any particular antenna is attached to solely using its external appearance, perhaps there is an illustrated compendium a student pilot could refer to?
Antennae appearance database
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Let'sgoflying!
Touchdown! Greaser!
The blades would probably be DME and transponder antennas. The "wire" may be ADF.
The little blades are hard because they can be so many things. Generally they're uhf... high frequency, short wavelength, short antenna. Transponder, dme, adsb.
The one with the heavy wire sticking out looks to me to be the right length to be a comm. They often put one on top and one on bottom. If you have two comm radios and only one comm antenna on top, that's my guess.
Adf is super low frequency, and usually the antenna was a wire from the top of the vert. stab. to the cabin.
The one with the heavy wire sticking out looks to me to be the right length to be a comm. They often put one on top and one on bottom. If you have two comm radios and only one comm antenna on top, that's my guess.
Adf is super low frequency, and usually the antenna was a wire from the top of the vert. stab. to the cabin.
donjohnston
Pattern Altitude
I always thought those types of questions were idiotic. Makes as much sense as requiring drivers license applicants to be able to identify the logos of all car manufactures.
ateamer
Pattern Altitude
It’s trivia that takes bandwidth from students who need it for flying, navigation skills and other things that actually need to be immediately recalled. Is there any situation in which a pilot needs to identify the type of antenna and he can’t take the time to look it up? Same kind of BS as TOMATO FLAMES or knowing tire pressures from memory.
I don't disagree. To play devil's advocate, you have to know where the antennas are to preflight them, and their purpose dictates their placement.
donjohnston
Pattern Altitude
First of all, the only thing a typical pilot can do to preflight an antenna is to make sure it's firmly attached. You don't need to know what the antenna does in order to do that. As for where an antenna is, I would submit that if you can't see an external antenna then you probably failed the vision test and shouldn't be flying.
Besides, you can't see antennas on all aircraft. Tell me where the transponder antenna is on this plane?
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donjohnston
Pattern Altitude
Or this one.
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Ran into an examiner in the E-3 that would ask examinees how many fasteners were on each mission crew console. I asked him why; it was not published in any documentation available to the aircrew member, nor was it part of any evaluated area.
His response was that he liked trivia. If true bureaucratic fashion , he was shortly upgraded to a new crew position and lost examiner and instructor status.
yeah, that.... a brain bandwidth distraction.
It tests if the candidate can prioritize issues and deal with distractions, etc...
It's also giving them a "teaching moment" that's not a test pass/fail variable
and it could be just a way to relax the moment through conversation
I remember my PPL examiner asking me about the V-shaped corrugations on the Cessna 152's control surfaces, while I was doing my preflight. "Why is it like that?"
& I can imagine some good in knowing which antenna does what...for troubleshooting as well as pre-flighting. Which are going to be critical to flight and which maybe not so much?
donjohnston
Pattern Altitude
The problem with that logic is that at that point in the game, you don’t know what things are “need to know”, “nice to know” or ”don’t need to know”. So most people will go with everything they’re told is “need to know”.
As for knowing what an antenna does for troubleshooting, 1) that’s what A&P’s and avionics techs are for and 2) I would save that knowledge for post PPL because it offers zero value when you are learning how to fly.
As for knowing what an antenna does for troubleshooting, 1) that’s what A&P’s and avionics techs are for and 2) I would save that knowledge for post PPL because it offers zero value when you are learning how to fly.
I'm planning to have my plane painted in a few months, and I intend to have the paint shop de-porcupine it for me by removing several antennas that are no longer used. The avionics were taken out long ago, but the antennas were left behind. I'm curious about some of them, though.
Anybody know what this is?
How about this one?
I'm pretty sure this one is a marker beacon antenna, right?
The plan is to leave the cabling in place and just cap the holes so antennas can be reinstalled later if desired, but for now I see no need to have them cluttering up the plane and adding drag.
Anybody know what this is?
How about this one?
I'm pretty sure this one is a marker beacon antenna, right?
The plan is to leave the cabling in place and just cap the holes so antennas can be reinstalled later if desired, but for now I see no need to have them cluttering up the plane and adding drag.
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Albany Tom
No idea what they are, but if they have coax feeds and someone has an antenna analyzer or a spectrum analyzer and a bridge they might be able to give you a rough idea of what they might be useful for? Don't think there are too many options - ADF, VHF nav/com, beacons, LORAN?
Let'sgoflying!
Touchdown! Greaser!
That reminds me, is it helpful, in the task of identifying antennae to disconnect the bnc connector that some have, then see which radio fails/underperforms?
Or does removing the load have the potential to damage the radio?
Or does removing the load have the potential to damage the radio?
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You can always disconnect the antenna of something that's receiving without causing harm. Some transmitters, more likely older ones, can be harmed by transmitting without an antenna, and I wouldn't do it on purpose with anything. So I wouldn't disconnect a transponder antenna without knowing if it was harmless to do so. Com or nav radio as long as you don't key it, or GPS or ADF? Sure.
Depends. Modern radios fold back power when presented with an improper load, but an older radio might be damaged.
Yes, if you can access the antenna connector you can check it that way. Or, if you have an oscilloscope, you can make a sniffer by putting a small loop of wire on the tip of a scope probe and holding it near each antenna while transmitting. The scope trace will show a large magnitude increase when the sniffer is next to the hot antenna.
Also, the possibility of damaging an older transmitter could be eliminated by connecting a dummy load.
Well, I think my #2 photo above is an ADF antenna, but I still have no clue about #1.
Likely also part of the ADF antenna, although I’ve never seen a base like that before.
Could you provide more details on the oscilloscope method? Eg., should both ends of the loop go to the + probe end, or one end to the + probe and the other to the ground clip. How many loops in the coil? Coil diameter? Other? Thanks
Real simple. You're not looking for an accurate measurement, just the presence of RF. Just make a loop of wire an inch or so in diameter and clip both ends to the probe tip. Don't worry about the ground wire. The RF will induce enough noise to see on the scope. You can experiment with the loop diameter a bit.
This is just a crude version of a commercial probe like this: https://www.testequity.com/product/...WiRPH_JnLJKP_xtQxMzlmsaPEvEb5AfBoCmzsQAvD_BwE
Commercial probes have shielding and are calibrated and band-limited and some have built-in preamps, but for just figuring out which antenna is emitting RF you don't really need those nuances. We used to do this when we were troubleshooting EMI emissions on missiles and needed to see where the RF leak was.
If you're interested here's a little light reading on the subject: https://www.unitest.com/pdf/ee_0287_berger.pdf .
Thank-you. And my apologies to the others for taking the thread on a tangent.
I did the oscilloscope test today and it worked to identify the antennas. My plane has an antenna switchbox in the coax from Com2. It switches out the Com2 radio and connects a handheld to the Com2 antenna when a coax from the handheld's antenna connection is plugged into the switchbox jack. With a portable oscilloscope on the ground near the lower VHF antenna and the wire coil held near the antenna tip, keying the radio produced a strong signal on the scope (in auto mode). Moving the oscilloscope and wire coil to the top of the plane near the top VHF antenna produced a much weaker signal when the handheld was keyed. Moving the oscilloscope coil from the top to the bottom while the handheld was transmitting resulted in a continuous increase in signal intensity as the coil was moved closer to the bottom antenna. So the top antenna must be Com1 and the bottom antenna Com2.
Simple, no? You might also key up your COM1 to confirm it uses the other antenna.
When I was replacing my COM1 radio a couple of years ago, the local avionics shop wanted to charge me for a couple of hours work to sort out which VHF antenna went to which coax, because they thought they'd have to pull the headliner and actually trace the cables. I told the shop owner about this little trick, he tried it and loved it, worked like a charm, and only took him a few minutes. Saved me a couple of hundred bucks!
