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Where to fit the Mode S Transponder Antenna

P

Philly5G

Registered User
England
I’m in the process of fitting a Trig TT21 to my 12 and wondering where other folks have fitted the transponder antenna and what kind/size of ground plane works best?

The Trig book describes a square ground plane of minimum 120mm to “max” 700mm sides, the smaller size would allow one of the underneath panels to be used, but the larger size sounds like a plate and I’m guessing with a bend to fit the belly contours.

Thanks and happy holidays!!

Philly




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Started out with mine on the boot cowl and ended up moving it back to the tail mounted on the removeable bottom clean out to get rid of interference with the intercom.
 
I agree with the Comant 105 on the bottom of the boot cowl. Never had a problem.
 
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Has anyone installed a “diversity” antenna on the topside for satellite contact?


As for as the ground plane size, as big as you can, but at least 2.65 inches radius...
 
mam90 said:
View attachment 40567

Works well here.
Click to expand...

This is where I usually mount them. As said above, occasionally there can be noise issues but rarely enough that I deal with them on a case by case basis. The Comant antenna works great but is spendy. I've used the TED 104-12 antenna for many years and had great performance. Also, drill one hole and the TED is installed.

When any antenna is mounted on a metal surface, the ground plane issue is usually taken care of with no further 'additions' needed.

Web
 
fobjob said:
Has anyone installed a “diversity” antenna on the topside for satellite contact?


As for as the ground plane size, as big as you can, but at least 2.65 inches radius...
Click to expand...

The second (diversity) antenna is not for satellite contact. It is just a second transponder, L-band antenna, the same part number as the bottom antenna. It's installed to reduce antenna shading. That can happen when any part of the aircraft blocks the direct path of a signal from the antenna to the ground station.

I'm not a big fan of ADS-B up here, but if you need the system, I try to talk the owner into the diversity option, when available. Might as well make the system work as well as possible. As far as installation goes, it's just one extra antenna.

Web
 
With the new Iridium sat system monitoring ads-b , it was implied that if you want Nav Canada or atc monitoring your position in the wilds of BC or wherever....that a top mounted antenna (in addition to the bottom one) would be a really good idea. If certain attitudes or conditions cause you to lose radar contact with normal ground based radars, then it’s still a good idea, but rarely worth the trouble.
 
If you don't want to install a top antenna, then don't do it. It's your aircraft.

I want to make sure that everyone realizes that the top antenna has nothing to do with GPS or satellites. It is the exact same antenna as the standard bottom mounted ADS-B antenna. It operates at normal transponder frequencies such as 1090 or 978 mhz not the much higher satellite frequencies (think about ELT's at 121.5 mhz for ground base compared to 406 mhz for satellite). That top antenna is solely for uninterrupted ADS-B coverage. And the second antenna is only an option with certain model units.

I'm also curious about the statement 'it's rarely worth the trouble'.

Web
 
OLDCROWE said:
View attachment 40565
Click to expand...

I’ve got the same type of antenna as in OldCrowe’s pic above which I guess is the TED 104-12 as WireWeinie uses, I see the one on the boot cowl is a different type, I like the boot cowl mounting as possibly an easier install (at least as an initial “see if it works” install) ands sounds like WireWeinie has got multiple transponders working well with the TED antenna type on the boot cowl so I'll start off with this.

As the lower part of the boot cowl is basically fixed and sealed, I'm guessing I'll need to make an access hole in the forward floor if I can't somehow route the coax under the floor and down to the antenna hole, ASSUMING the coax will fit through the mounting hole? Any steers on this please?

PS As I often say, THANK GOODNESS for this forum and everyone that takes the time to contribute to supercub.org!!! :)


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OLDCROWE said:
View attachment 40565
Click to expand...

This may be an excellent very functional location for the transponder antenna. However you should consider how you use your airplane. Do you operate only on pavement or do you like to land out in the weeds on occasion? This type of antenna is ripe for departing the airplane in the first batch of weeds which pass under the tail. Even if you only operate on floats, this location would be susceptible to breakage. IF you choose to use this location I suggest that you use a blade type of antenna like the one below.

spinner2 said:
View attachment 40566
Click to expand...
 
Philly5G said:
I’ve got the same type of antenna as in OldCrowe’s pic above which I guess is the TED 104-12 as WireWeinie uses, I see the one on the boot cowl is a different type, I like the boot cowl mounting as possibly an easier install (at least as an initial “see if it works” install) ands sounds like WireWeinie has got multiple transponders working well with the TED antenna type on the boot cowl so I'll start off with this.

As the lower part of the boot cowl is basically fixed and sealed, I'm guessing I'll need to make an access hole in the forward floor if I can't somehow route the coax under the floor and down to the antenna hole, ASSUMING the coax will fit through the mounting hole? Any steers on this please?

PS As I often say, THANK GOODNESS for this forum and everyone that takes the time to contribute to supercub.org!!! :)


Sent from my iPhone using SuperCub.Org mobile app
Click to expand...

The TED antenna is a spike type and the Comant is a blade type. Electrically they function the same.

Most boot cowls can be accessed by removing the screws at the trailing edge of the lower section. Then open up the the false boot to give you some working room. If you're lucky the boot cowl already has screws that hold the fore/aft seam to allow good access. I've even seen access rings installed there, but don't install the antenna directly on the access cover.

Route the coax cable from the transponder, over the kick panel, and straight down, between the kick panel and the boot cowl. At the bottom of the kick panel there is a gap between the intersection of the floor/kick panel and the inside of the boot cowl. As you feed the coax down, have a buddy reach into the opening you've made at the lower training edge of the boot cowl. Just grab the coax and pull it to the antenna position. Make sure to use a 90 degree connector on the antenna as it will eliminate kinking of the coax cable when the boot cowl is buttoned up.

Web
 
wireweinie said:
The TED antenna is a spike type and the Comant is a blade type. Electrically they function the same.

Most boot cowls can be accessed by removing the screws at the trailing edge of the lower section. Then open up the the false boot to give you some working room. If you're lucky the boot cowl already has screws that hold the fore/aft seam to allow good access. I've even seen access rings installed there, but don't install the antenna directly on the access cover.

Route the coax cable from the transponder, over the kick panel, and straight down, between the kick panel and the boot cowl. At the bottom of the kick panel there is a gap between the intersection of the floor/kick panel and the inside of the boot cowl. As you feed the coax down, have a buddy reach into the opening you've made at the lower training edge of the boot cowl. Just grab the coax and pull it to the antenna position. Make sure to use a 90 degree connector on the antenna as it will eliminate kinking of the coax cable when the boot cowl is buttoned up.

Web
Click to expand...

FANTASTIC!! Thank you Web :)

I’m with the plane right now and hopefully these pics illustrate your description? There are fore/aft screws in the middle of the panel, but the sides SEEM to be riveted?

Is that the gap you mean between the firewall panel and floor? Certainly another reason to bring on the carpet replacement :)

IMG_4215.JPGIMG_4216.JPGIMG_4217.JPGIMG_4218.JPGIMG_4219.JPG




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That is the line of fore/aft screws. If you remove them along with the screws along the trailing edge of the boot cowl, you should have a little room to reach in and install the antenna.

As for the gap for routing the coax, it's between the kick panel and the boot cowl. Think about where your foot is on the rudder pedal. If the kick panel was not installed, you would see a gap between the edge of the floor board and the boot cowl. This is big enough to route the coax cable down below the floorboard.

Web
 
Don’t forget the doubler. That practice is enforced around here on planet Udah. If you are using a blade antenna on the cowl, realize that the side to side aero loads from the prop blast turbulence might require an especially robust doubler....
 
skywagon8a said:
This may be an excellent very functional location for the transponder antenna. However you should consider how you use your airplane. Do you operate only on pavement or do you like to land out in the weeds on occasion? This type of antenna is ripe for departing the airplane in the first batch of weeds which pass under the tail. Even if you only operate on floats, this location would be susceptible to breakage. IF you choose to use this location I suggest that you use a blade type of antenna like the one below.
Click to expand...
Just what should I be worried about BEE7E60C-EB50-4B39-8B50-6A2717132100.jpeg 18” clear in 3 point, it’s an airplane not a log skidder and in case I kick something up something landing on a gravel bar I would much rather it hit something that will bend.
 

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OLDCROWE said:
Just what should I be worried about View attachment 40625 18” clear in 3 point, it’s an airplane not a log skidder and in case I kick something up something landing on a gravel bar I would much rather it hit something that will bend.
Click to expand...
Whatever floats your boat. It is your airplane and antenna. I have seen this type of antenna get bent and broken in more protected locations than this.
 
hotrod180 said:
I've bent one of them with my head when crawling under the airplane.
They don't un-bend too well. :oops:
Click to expand...
I would contend they are more vulnerable under the boot cowl for just the reason you state than when mounted in the back and there is no annoying tic-tic-tic coming through the audio system with the extended separation from the rest of the EMS (electrical-magical-stuff). As to the type, I'll order a spare. Now go whack that blade antenna real good with a rock or a log and see if what happens to what its mounted to and if it still works, I'll keep mine disposable and yes they work when bent over but don't ask how I know that.
 
wireweinie said:
That is the line of fore/aft screws. If you remove them along with the screws along the trailing edge of the boot cowl, you should have a little room to reach in and install the antenna.

As for the gap for routing the coax, it's between the kick panel and the boot cowl. Think about where your foot is on the rudder pedal. If the kick panel was not installed, you would see a gap between the edge of the floor board and the boot cowl. This is big enough to route the coax cable down below the floorboard.

Web
Click to expand...

There is that exact gap between the floor and back of the firewall as in the pic, or is the back of the firewall, in front of the tubes holding the park brake cables, the kick panel?


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Philly5G said:
There is that exact gap between the floor and back of the firewall as in the pic, or is the back of the firewall, in front of the tubes holding the park brake cables, the kick panel?


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Click to expand...

What we call the 'kick panels' are the removable panels on the left and right, below and just forward of the instrument panel. It's the ones that your knees rub against and also where most guys mount a map pocket. They are just outboard of each rudder pedal.

Web
 
wireweinie said:
What we call the 'kick panels' are the removable panels on the left and right, below and just forward of the instrument panel. It's the ones that your knees rub against and also where most guys mount a map pocket. They are just outboard of each rudder pedal.

Web
Click to expand...

Do you mean these (white) fabriced panels? :)IMG_4101.JPG


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