ELT Antenna: vertical or horizontal?

[PBY Catalina]

Hello all,

CC provided a bracket to attach the antenna horizontally to the back of the extended bags.
Chuck, relayed by Dave, give excellent details about the horizontal installation in his post. He placed the bracket lower than CC suggested.

But Dave in his videos on Youtube said that the horizontal installation in several of his builds just don’t work (!!). I’m not so surprised by that, as my (too) old memories of my electromagnetism classes at the university, make me think that, to function properly, this antenna must be indeed installed vertically.

In the Kannad ELT’s Installation Manual (DOC09081E), we can read: “ELT antennas should be vertically polarized when the aircraft is in the normal flight attitude”.

Dave, on Youtube describes a vertical installation with an aluminum ground plane installed between the fairleads. As he said himself: “It isn’t pretty” ! In fact, in the Kannad Installation Manual, they also said: “ELT mounting surface should be able to whistand a static load equal to 100 times the antenna weight applied at the antenna mounting base in all directions”.

So my question is: what is for you the best method to install the RAMI whip antenna for the Kannad ELT in an EX2?

Y.

[Andy]

I'm more concerned about whether the carbon fibre seat and pilot's body block reception of GPS signals by the ELT. At 406 MHz the polarization will be randomly rotated as the signal passes through the ionosphere. I doubt the starting polarization will make much difference to signal reception as I suspect the SARSAT receiving antenna will be RHCP (right hand circular polarization).

As an aside - If you want an antenna to work then putting it inside a steel tube cage may not be ideal.

(GPS reception comment applies only to Kannad ELT with built in GPS receiver not to ELT models that receive GPS position over an RS-232 link)

[Daveembry]

There is a problem with this setup and Rami engineers (through Cubcrafters) say the Kannad has a grounding problem. I’ve gone through this extensively with Cubcrafter (when Jon was the kit manager) and he called Kannad and Rami to try and figure it out.

rather than go all through it again in detail, please go to this post https://forum.cubcrafters.com/showth...ll=1#post22084 and then there are 5 links to YouTube videos I did about it. Like I say there, start with the first 4 minutes of video 5 for a final explanation of what we found. Then the first 4 are very short showing the checks and solution I did which was a different ground away from the baggage compartment.

Every single plane I’ve built has had this problem. I wonder how many people actually notice the self test on the Kannad? Because it shows a problem with 3-5 beeps when doing the self test.

they say the Kannad is very particular to almost anything, in one case early on, I shorted the cable maybe 1/2” and it worked? They say the way it sends a signal down the cable and back that even that can change it. I really don’t know.

in the last one shown in the video, nothing worked until Rami said…. “Put it on a separate ground and see what happens”. It worked. Using the baggage sidewalls as a ground for some reason did not work. I don’t think I’ll use a Kannad any longer unless they come up with something more concrete. (Note, verticals or horizontal has never made a difference).

Here a cut and paste with the links….

Page 67, ELT ANTENNA INSTALLATION.

Looks like the antenna bracket number has changed to SC91033-001. I had to take my step drill and widen the hole just a tad for the antenna to go through the bracket.

I also have been mounting mine down lower on the back wall of the baggage area to make it more accessible from the bottom access panel that will be there in the fuse to more easily get to it.

NOTE: I WOULD CERTAINLY COMPLETELY HOOK UP THE ANTENNA AND COAX CABLE TO MY ELT AT THIS POINT AND TEST IT BEFORE COVERING. On my last build, the last thing I did probably was to put the 90 degree coax connector at the end of the antenna where it hooked up to the ELT under my seat and tested it. It came back with a negative test (see the Kannad manual if that's your model for error codes ...there are beeps and red flashing lights on power up/test) and I figured it was ANYTHING but the actual unit. Surely I didn't have a connector installed correctly or something. But after replacing and testing everything else, Mitch sent me another ELT unit and sure enough, it was just the unit!! SO TEST IT NOW!

HOWEVER, I DONT THINK THAT WAS REALLY THE REASON. IVE HAD THIS PROBLEM NOW WITH ALMOST EVERY KANNAD UNIT. I did some YouTube videos on this and explain this in detail. The problem seems to be with the Kannad 7nits and the grounding. Watch these YouTube videos I did explaining it and how if fixed it so far using a different mounting surface.

According to Rami Antenna engineers, the Kannad has a grounding problem and they just are not working right as mounted on the Carbon Cub. None have vee worked for me without a lot of work. They say even changing the length of the cable a very small amount (any amount) can change the way it works.

https://youtu.be/FvvY69ygRg4 Part 5. Watch the first 4 minutes of this Part 5 video first for a final explanation of what was discovered before watching the first 4. They are very short.

https://youtu.be/d10ukGUjQZE Part 1
https://youtu.be/7sslQlPF90s Part 2
https://youtu.be/PCqKSYMez8c Part 3
https://youtu.be/LQKy1EA27RU Part 4

Cubcrafters needs to come up with something for this for kannad or stop using them.

Hello all,

CC provided a bracket to attach the antenna horizontally to the back of the extended bags.
Chuck, relayed by Dave, give excellent details about the horizontal installation in his post. He placed the bracket lower than CC suggested.

But Dave in his videos on Youtube said that the horizontal installation in several of his builds just don’t work (!!). I’m not so surprised by that, as my (too) old memories of my electromagnetism classes at the university, make me think that, to function properly, this antenna must be indeed installed vertically.

In the Kannad ELT’s Installation Manual (DOC09081E), we can read: “ELT should be vertically polarized when the aircraft is in the normal flight attitude”.

Dave, on Youtube describes a vertical installation with an aluminum ground plane installed between the fairleads. As he said himself: “It isn’t pretty” ! In fact, in the Kannad Installation Manual, they also said: “ELT mounting surface should be able to whistand a static load equal to 100 times the antenna weight applied at the antenna mounting base in all directions”.

So my question is: what is for you the best method to install the RAMI whip antenna for the Kannad ELT in an EX2?

Y.

[ceslaw]

I'm more concerned about whether the carbon fibre seat and pilot's body block reception of GPS signals by the ELT.

(GPS reception comment applies only to Kannad ELT with built in GPS receiver not to ELT models that receive GPS position over an RS-232 link)

That is a very good point I had never considered. I wonder how one could find out the answer? I wonder if the Kannad self check cycle includes determining the presence of the GPS signal?

[Andy]

I watched the linked videos. I don't know why the installation passes test with the isolated ground plane but not with the factory standard ground plane.

However, your assumption that an antenna which shows "shorted" at DC is defective is completely invalid. It is very common for antennas to have some sort of internal matching network which has close to zero impedance at DC but which will have the design impedance at the antenna operating frequency. DC resistance is not the same as reactance and reactance is frequency dependent.

The characteristics of an antenna should be measured at the design operating frequencies not at DC. My main amateur radio transmitting antenna presents a DC short to the transmitter. It works as intended with over 500 W RF input.

It's quite possible the DC "short" at the antenna is incompatible with the Kannad RF output design. Typically the RF final amplifier stage is DC isolated from the antenna connector by either a capacitor or a matching transformer. I have no knowledge of the Kannad design.

FWIW the standard factory Kannad installation in my FX-3 passes self test.

[Andy]

I wonder if the Kannad self check cycle includes determining the presence of the GPS signal?

I asked the same question but I don't know the answer. It's something I have been meaning to follow up on and I decided not to crash until I find out.

[PBY Catalina]

... It's something I have been meaning to follow up on and I decided not to crash until I find out.

good decision !!!

[PBY Catalina]

... At 406 MHz the polarization will be randomly rotated as the signal passes through the ionosphere. I doubt the starting polarization will make much difference to signal reception as I suspect the SARSAT receiving antenna will be RHCP (right hand circular polarization).

Ok, but why is Kannad saying “ELT antennas should be vertically polarized when the aircraft is in the normal flight attitude”, then ?

As an aside - If you want an antenna to work then putting it inside a steel tube cage may not be ideal....

You are right but outside we should not use the "whip" antenna but the "blade" type then ?

Are you convinced that the std factory antenna installation remain valid, Andy ?

[Daveembry]

yes Andy. I’m well aware that that is normal for that antenna. That’s why I said go to video 5 first for the conclusion and that the first 4 parts were just working the problem which was the ground as stated and suggested by Rami.

On one build, everything worked. First on the bench, then in the fuse. Checked again after cover and paint. All good. Finished the airplane and it wouldn’t work. Something changed it. Electronics, wings, turtle deck etc, seats installed?????

Perhaps a different antenna than Rami should be used. I have no idea. Rami said the signal comes out of the unit to the antenna and back. The wave or whatever it sends out is very particular and the distance traveled can change that wave or something. I’m certainly not experienced on these except to the extent to try and make them work.

I watched the linked videos. I don't know why the installation passes test with the isolated ground plane but not with the factory standard ground plane.

However, your assumption that an antenna which shows "shorted" at DC is defective is completely invalid. It is very common for antennas to have some sort of internal matching network which has close to zero impedance at DC but which will have the design impedance at the antenna operating frequency. DC resistance is not the same as reactance and reactance is frequency dependent.

The characteristics of an antenna should be measured at the design operating frequencies not at DC. My main amateur radio transmitting antenna presents a DC short to the transmitter. It works as intended with over 500 W RF input.

It's quite possible the DC "short" at the antenna is incompatible with the Kannad RF output design. Typically the RF final amplifier stage is DC isolated from the antenna connector by either a capacitor or a matching transformer. I have no knowledge of the Kannad design.

FWIW the standard factory Kannad installation in my FX-3 passes self test.

[Andy]

Perhaps a different antenna than Rami should be used. I have no idea. Rami said the signal comes out of the unit to the antenna and back. The wave or whatever it sends out is very particular and the distance traveled can change that wave or something. I’m certainly not experienced on these except to the extent to try and make them work.

It's quite common for a transmitter to monitor the antenna matching. One way to do this is to measure reflected power with a directional coupler. A well matched antenna will have low reflected power and the transmitter will be happy. Too much reflected power and the transmitter may reduce output power ("fold back") or even shut off completely. Either condition could cause self test to fail.

Your video 5 says how you fixed the problem but I didn't see any indication that you had actually found what the problem was. Was it an antenna matching problem or was it the DC path that upset the Kannad? I deal with RF every day and it would have been an interesting problem to investigate. My standard installation passes self test but maybe when this hot weather ends I'll measure the characteristics of the installed ELT antenna.