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  #11  
Old 05-07-2019, 05:34 PM
Canadian_JOY Canadian_JOY is offline
 
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Location: Ontario, Canada
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Quote:
Originally Posted by lr172 View Post
the 151 signal, that needs the vertical orientation, isn't really used anymore.
Larry
Larry - I believe your post was intended to state the 121.5MHz signal is not used any more. Please allow me to correct this mistaken belief.

While it is absolutely correct that the 121.5MHz signal is no longer being monitored by satellites, it IS being monitored by many aircraft. More importantly it is also WIDELY used for the "last mile" efforts of ground search parties. I learned of a rescue last week that was successful only because the ground search party was able to home on the crashed aircraft stuck on the side of a mountain in a blinding snowstorm. The searchers homed using the 121.5MHz signal.

OK, back to our regular programming now...
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  #12  
Old 05-07-2019, 09:09 PM
rongawer rongawer is offline
 
Join Date: Dec 2007
Location: Brentwood, CA
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Quote:
Originally Posted by Brent View Post
If the DAR insists on it being mounted externally, then on the RV8 it would need to be mounted underneath. I don’t think that the vertical stab or rudder would be acceptable due to the lack of required ground plane. I intend to mount mine between the front and rear seats on a suitable mount.with ground plane. I can mount it almost vertically with a tether to bend it clear of the canopy.

Bearing in mind that if the aircraft turns over during a forced landing, mounting it externally on top doesn’t make a great deal of sense does it. If the aircraft remains upright, then presumably the pilot will be in a position to activate it himself, and can either open or jettison the canopy.
The RV8 empennage is metal airframe, so if you just get a good ground for the antenna to the airframe, it will be your ground plane. A good reference is AC 43.13-2B, section 3.

Generally, the safest place to install your ELT, hence antenna, is the empennage - which tends to be the most survivable portion of a crashed airframe. AC 91-44A is an excellent resource (with many referenced resources as well) for ELT installation.

While you can install an antenna internally, if it’s an Artex or ACK, it needs to be installed vertically; I suspect that is true for any other brand as well to ensure the best signal transmission.
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  #13  
Old 05-07-2019, 09:16 PM
AviatorJ AviatorJ is offline
 
Join Date: Feb 2015
Location: Oklahoma City
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Quote:
Originally Posted by majuro15 View Post
I know some have burried it in the vertical stabilizer fairing but that's not going to pass muster with the final inspection for airworthyness.
That’s where mine is located and tested out fine.
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  #14  
Old 05-07-2019, 09:33 PM
rongawer rongawer is offline
 
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Originally Posted by AviatorJ View Post
That’s where mine is located and tested out fine.
If you mounted it horizontally...well, I’m going to sound like broken record...it’s contrary to the installation instructions.

If it tested successfully via SARSAT, then you’re fortunate, however a local test with a transceiver won’t ensure the unit communicates with the satellite successfully.

To test and ensure your ELT communicates with the satellites, here’s the ELT test website and the test form to submit for SARSAT: https://www.sarsat.noaa.gov/Beacon%2...%20Policy.html
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  #15  
Old 05-07-2019, 11:06 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by Canadian_JOY View Post
Larry - I believe your post was intended to state the 121.5MHz signal is not used any more. Please allow me to correct this mistaken belief.

While it is absolutely correct that the 121.5MHz signal is no longer being monitored by satellites, it IS being monitored by many aircraft. More importantly it is also WIDELY used for the "last mile" efforts of ground search parties. I learned of a rescue last week that was successful only because the ground search party was able to home on the crashed aircraft stuck on the side of a mountain in a blinding snowstorm. The searchers homed using the 121.5MHz signal.

OK, back to our regular programming now...
Thanks for correcting; I was rushed. I am aware of the last mile usage. However, I don't believe that orientation of the antenna will make much difference at a one mile range. If that were the case, they would only find planes that land upright after the crash. That unit has enough power to send that signal up to satellites (several miles).

Larry
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  #16  
Old 05-08-2019, 06:36 AM
Canadian_JOY Canadian_JOY is offline
 
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Location: Ontario, Canada
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Larry - the 121.5MHz signal can be as small as 50mW... it's actually very little signal. Toss in some wet evergreen branches or some active precipitation and it becomes a challenge to receive it even at relatively short distances on the ground. While I agree that our aircraft are not guaranteed to crash "right side up", I also feel there is no sense in hampering the probability of an ELT performing by intentionally installing the antenna in a less-than-optimal fashion.
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  #17  
Old 05-08-2019, 07:09 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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Quote:
Originally Posted by cderk View Post
This is exactly why the DAR in my area won’t let me install it internally. He said that it needs to be installed per the instructions that come with the ELT.
Find a new DAR that has a clue on how antennas work - and how you match the antennas to the need. How many of you walk around with a full size antenna connected to your handheld radio because “it works better”?

Reviewing such “TSO installation requirements” I find great strides taken so that no matter what the circumstances the company paying the money to get a TSO cert can always point to their install instructions as proof “it was not our fault”.

You want a survivable install. It may not be the most perfect in terms of the last fraction of a dB of signal strength, but at least you will have a signal. And shoot fire - just go test whatever you end up with and show the results to the DAR.

Carl
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  #18  
Old 05-08-2019, 08:06 AM
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majuro15 majuro15 is offline
 
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No need to hit against the DAR. The experience they have and the been there done that can help all of us out.

I've done EPRB searches on 121.5 back in my days of CAP and yes the signal can be weak even on a good day. Planes don't always crash upright. It's all about mitigating risks and accepting levels comfortable and within the guidelines.

I am set on the DAR I'm using, so that identifies my limfacs as well as guidance from others. I'll put it in the overhead and if I don't get good test results (both 406 and 121) then I can easily mount it on the tail cone. I'll try and remember to update folks on my results.

Thanks!
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  #19  
Old 05-08-2019, 10:32 AM
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fl-mike fl-mike is offline
 
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keeping the coax intact between the ELT and the antenna is much more important than antenna location. The NASA crash tests showed COSPAS/SARSAT 406MHz reception from the antenna in the dirt. The ELTs with a broken cable?...nope.

https://www.youtube.com/watch?v=FsRwlr7RDkk

FYI, ED-62B adds firesleeve on the coax and includes the cable in the flame test. This is to help ensure that at least the first couple full 406 messages make it out.
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  #20  
Old 05-08-2019, 12:41 PM
Canadian_JOY Canadian_JOY is offline
 
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Quote:
Originally Posted by fl-mike View Post
keeping the coax intact between the ELT and the antenna is much more important than antenna location. The NASA crash tests showed COSPAS/SARSAT 406MHz reception from the antenna in the dirt. The ELTs with a broken cable?...nope.

https://www.youtube.com/watch?v=FsRwlr7RDkk

FYI, ED-62B adds firesleeve on the coax and includes the cable in the flame test. This is to help ensure that at least the first couple full 406 messages make it out.
A most excellent point! We've seen too many ELT's fail where the ELT broke free from its mount and sheered its coax cable, or the coax cable was poorly installed and sheered under crash forces. The ELT coax should be secured as though it were a fragile aluminum fuel line, with Adel clamps and grommets where necessary and with caterpillar grommet on the edges of lightening holes through which the coax passes plus standoffs to hold the coax away from structure. If you treat the coax like it was a fuel line it will most likely produce a much more crash-survivable installation.

Since the first valid 406MHz distress signal is only sent 50 seconds after ELT activation, the point on adding fire sleeve to the coax is definitely worthy of consideration.
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