one of these coupled with a PLB (personal locator beacon), would be an acceptable solution for some.
ELT Antenna Location
- Thread starter bubb2
- Start date
one of these coupled with a PLB (personal locator beacon), would be an acceptable solution for some.
wireweinie
FOUNDER
Palmer, AK
How so?
Web
Web
RedOwlAirfield
Registered User
Nevada
I once had one activate when I tossed it on the kitchen table at the end of a long day. I had been disassembling a PA 16 project I had bought and put the ELT on the table. The Battery hadn't been replaced in 15 years so I expected nothing. About three in the morning the dog went nuts. The C.A.P are parked outside in their tracking truck. They found me! I had no idea what was going on until I went out to talk to them. I was surprised when they told me they were tracking an ELT - and it was coming from inside my house. I showed them the ELT with the sticker showing a 15 year old battery and they had no problem with it. But it was one of those things that sticks with you.
ROA
dabridgham
Registered User
Claremont, NH
People have brought up the idea that ELT antennas ought to be vertically polarized. When we were using 121.5 MHz and searchers were listening for you on their comm radios, which have vertically polarized antennas, this makes sense. Once we go to satellites being the primary receivers of the signal, not so much. The satellite's vertical and yours are seldom going to match up so either the satellites have circularly polarized antennas (best answer) or they just live with whatever they get.
wireweinie
FOUNDER
Palmer, AK
Explain how one antenna needs to be vertically oriented and another does not, when they are both vertically polarized. What's your engineering data? What install data are you referring to? How many different systems have you installed?
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dabridgham
Registered User
Claremont, NH
Assuming you, wireweinie, are talking to me, I'll explain a little more about antennas. First, an antenna isn't intrinsically vertically or horizontally polarized. It's linearly or circularly polarized and if it's circular, then it can be left-handed or right-handed. And then a linearly polarized antenna may be mounted vertically or horizontally (or in between) so the signal it puts out is vertically or horizontally polarized (or in between). If an airplane with a vertically oriented linearly polarized antenna (like an ELT antenna) is lying on its side, it's putting out a horizontally polarized signal.
If the transmit and receive antennas are cross-polarized, 90 degrees apart for linearly polarized antennas or left vs right for circularly polarized antennas, then the received signal will be very low. If one antenna is circular and one linear, then the received signal will be constant no matter the orientation in polarization of the linear antenna, though it will be half of what it would be for matched antennas.
Now consider satellites. What's vertical? The obvious answer is that it's a line from the satellite to the center of the Earth. For a satellite that's not directly overhead, that means your vertical and its are going to be different. If your antenna is vertical and its is too, you will be somewhat cross-polarized, how much depends on how far the satellite is from directly overhead. By the way, vertical antennas put out a lousy signal straight up so the situation where your verticals align is the worse case for other reasons. If the satellites have circularly polarized antennas then this problem goes away and the orientation of the ELT's linearly polarized antenna does not matter. Well, it doesn't matter to the satellite. As I said, searchers on the ground or air will also be using vertically polarized antennas so for them it's still beneficial if your ELT antenna is also vertical.
If the transmit and receive antennas are cross-polarized, 90 degrees apart for linearly polarized antennas or left vs right for circularly polarized antennas, then the received signal will be very low. If one antenna is circular and one linear, then the received signal will be constant no matter the orientation in polarization of the linear antenna, though it will be half of what it would be for matched antennas.
Now consider satellites. What's vertical? The obvious answer is that it's a line from the satellite to the center of the Earth. For a satellite that's not directly overhead, that means your vertical and its are going to be different. If your antenna is vertical and its is too, you will be somewhat cross-polarized, how much depends on how far the satellite is from directly overhead. By the way, vertical antennas put out a lousy signal straight up so the situation where your verticals align is the worse case for other reasons. If the satellites have circularly polarized antennas then this problem goes away and the orientation of the ELT's linearly polarized antenna does not matter. Well, it doesn't matter to the satellite. As I said, searchers on the ground or air will also be using vertically polarized antennas so for them it's still beneficial if your ELT antenna is also vertical.
121.5 to fulfill the FAR’s
PLB so someone can actually find you.
downsides to this setup:
must manually activate the PLB (problem here is if you are pinned and can’t get to it)
PLB gets damaged/lost in the accident
probably other issues, those are the big ones that come to mind
upsides:
cheaper (the unit and no installation costs)
more versatile (i.e. removable)
better than only having a 121.5
with that said - I have a 406, sat phone, and an inreach.
406 for a rescue
sat phone to call buddy for prop and struts
inreach to text the girlfriend
wireweinie
FOUNDER
Palmer, AK
I'll use English as we have company;
Generally speaking, we use two types of antennas on aircraft; Omni directional and directional. As their names indicate, omni antennas are designed to receive or transmit from any clock position. Com antennas are of the omni type. With the antenna properly installed, you can listen from or talk to a station regardless of the direction of the signal with respect to the aircraft. Directional type antennas either transmit or receive a signal in one direction. Unless you are using special mission equipment, we only use direction receiving antennas on aircraft. Nav antennas and ADF antennas are examples of this. When a signal is received, the receiving unit is able to 'see' the direction from the aircraft to that signals source.
ELT antennas are omni directional, transmitting antennas. We need to have a signal radiated in all clock positions to increase the odds of someone (now days a satellite) receiving that signal. They are also of the quarter wave design. At our level, this means that the antenna length is one quarter of the wavelength of the signal it's designed to work with. Not important to us, but what IS important is that quarter wave antennas require a ground plane to operate properly, so keep that in mind when installing. While it would be awesome to find an antenna that transmitted in a full sphere they don't exist in the aircraft world. Each kind of antenna has strong points and weak points. For us, using rod type antennas, they will transmit the strongest signal when the receiving antenna is oriented the same way as the transmitting antenna. I.e., They antenna at ATC is straight up and if ours is too, then we can communicate well. Have a buddy with a Bonanza with the com antenna in the wing tip? He still has to turn the aircraft 90º to the tower to talk at a distance. This is because the Bonanza's antenna is horizontal to the vertical antenna in the tower.
To visualize the signal put a donut (or a bagel if you prefer) on a rod antenna. That is what the signal looks like as it is transmitted. Just an every growing donut. (See the attached pic, the rod antenna would be along the Y axis) If you have another rod antenna, oriented vertically, the 'donut' will eventually cross that one and allow the radio to hear the signal. Now take the donut with the antenna in it's hole, and lay it on it's side. The signal still has the 'growing donut' shape, but now it's on it's side. The receiving antenna will have no trouble IF it is perpendicular from the transmitting antenna. But if the receiving antenna is off the tip or the base of the transmitting antenna, there will be almost no signal to be received.
No, we can't foresee all outcomes of a crash and therefore the final position of the ELT, but the antenna's installed position is designed to give the best chance of survival, to remain operational, after the crash.
Web
Generally speaking, we use two types of antennas on aircraft; Omni directional and directional. As their names indicate, omni antennas are designed to receive or transmit from any clock position. Com antennas are of the omni type. With the antenna properly installed, you can listen from or talk to a station regardless of the direction of the signal with respect to the aircraft. Directional type antennas either transmit or receive a signal in one direction. Unless you are using special mission equipment, we only use direction receiving antennas on aircraft. Nav antennas and ADF antennas are examples of this. When a signal is received, the receiving unit is able to 'see' the direction from the aircraft to that signals source.
ELT antennas are omni directional, transmitting antennas. We need to have a signal radiated in all clock positions to increase the odds of someone (now days a satellite) receiving that signal. They are also of the quarter wave design. At our level, this means that the antenna length is one quarter of the wavelength of the signal it's designed to work with. Not important to us, but what IS important is that quarter wave antennas require a ground plane to operate properly, so keep that in mind when installing. While it would be awesome to find an antenna that transmitted in a full sphere they don't exist in the aircraft world. Each kind of antenna has strong points and weak points. For us, using rod type antennas, they will transmit the strongest signal when the receiving antenna is oriented the same way as the transmitting antenna. I.e., They antenna at ATC is straight up and if ours is too, then we can communicate well. Have a buddy with a Bonanza with the com antenna in the wing tip? He still has to turn the aircraft 90º to the tower to talk at a distance. This is because the Bonanza's antenna is horizontal to the vertical antenna in the tower.
To visualize the signal put a donut (or a bagel if you prefer) on a rod antenna. That is what the signal looks like as it is transmitted. Just an every growing donut. (See the attached pic, the rod antenna would be along the Y axis) If you have another rod antenna, oriented vertically, the 'donut' will eventually cross that one and allow the radio to hear the signal. Now take the donut with the antenna in it's hole, and lay it on it's side. The signal still has the 'growing donut' shape, but now it's on it's side. The receiving antenna will have no trouble IF it is perpendicular from the transmitting antenna. But if the receiving antenna is off the tip or the base of the transmitting antenna, there will be almost no signal to be received.
No, we can't foresee all outcomes of a crash and therefore the final position of the ELT, but the antenna's installed position is designed to give the best chance of survival, to remain operational, after the crash.
Web
Attachments
wireweinie
FOUNDER
Palmer, AK
I'll agree with all of that except using something nearly worthless just to fulfill an faa requirement. If you fly around with something in your aircraft, make sure it has a good use.
Up here the sat phone extremely important!
Web
BC12D-4-85
SPONSOR
Fairbanks, AK.
This is well beyond topic, but if interested read Chapters 22/27 from this book: http://www.w3pga.org/Antenna Books/Reflections III.pdf
It describes the antennas used by Sat phones and satellites by one of the developers Walter Maxwell, plus other radio transmission/reception theory.
Gary
It describes the antennas used by Sat phones and satellites by one of the developers Walter Maxwell, plus other radio transmission/reception theory.
Gary
wireweinie
FOUNDER
Palmer, AK
Here is some info on the installation of an antenna.
The term 'ground plane' denotes a surface NOT an electrical attachment. Simply attaching a ground wire to a screw on the antenna base does not mean it has a ground plane. Read the attachment for AC43-13b, 310, (a) through (d). They call out mounting the antenna on a metal panel or using screen mesh to work as the antenna ground plane. For all you guys that have an antenna mounted on a 1" square tab, pay particular attention to paragraph (b), where it says to use a ground plane at least 24" across.
For you guys with composite structure, Look at the pic from the AC43-13b showing a metal tape ground plane. It may look a little cheesy but I've used it on fiberglass panels with very good results. Any kind of metal tape such as aluminum or copper seems to work well. Keep all legs of the 'asterisk' equal lengths for best results.
If you are mounting an antenna to a metal panel, read the two attachments, AC43-13b1 and AC43-13b2. This is a great rundown on how to prep a metal panel for getting the best ground plane effect. Remember; good metal to metal contact between the antenna and panel, so clean the paint from around the mounting holes and don't use a gasket.
And last but not least, read the four clips from ELT manufacturer's about orienting the antennas. They all say to keep the antenna vertical while in flight attitude. One of them even, specifically, warns against mounting an antenna inside conductive structure/fabric.
Web
The term 'ground plane' denotes a surface NOT an electrical attachment. Simply attaching a ground wire to a screw on the antenna base does not mean it has a ground plane. Read the attachment for AC43-13b, 310, (a) through (d). They call out mounting the antenna on a metal panel or using screen mesh to work as the antenna ground plane. For all you guys that have an antenna mounted on a 1" square tab, pay particular attention to paragraph (b), where it says to use a ground plane at least 24" across.
For you guys with composite structure, Look at the pic from the AC43-13b showing a metal tape ground plane. It may look a little cheesy but I've used it on fiberglass panels with very good results. Any kind of metal tape such as aluminum or copper seems to work well. Keep all legs of the 'asterisk' equal lengths for best results.
If you are mounting an antenna to a metal panel, read the two attachments, AC43-13b1 and AC43-13b2. This is a great rundown on how to prep a metal panel for getting the best ground plane effect. Remember; good metal to metal contact between the antenna and panel, so clean the paint from around the mounting holes and don't use a gasket.
And last but not least, read the four clips from ELT manufacturer's about orienting the antennas. They all say to keep the antenna vertical while in flight attitude. One of them even, specifically, warns against mounting an antenna inside conductive structure/fabric.
Web
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