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UAT Ant mount at rear of -14 fuse?

rockitdoc

Well Known Member
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The plans (page 10-23) have us route a UAT antenna cable from the very aft part of the fuse forward. I started thinking about antennas recently since the fuse is done and my wings will be late.

That UAT antenna is supposed to mount at a location where three holes are provided in the skin. Unfortunately, there is no doubler there to support an antenna, now. And, putting one in, now is going to be somewhat awkward, at best. Two questions come to mind:

1. Is this the best place for the UAT antenna?
I have read that a large 2' minimum ground plane is best for this ant. There's not even 1' of plane back there.
And, the Dynon and Garmin folks tell me that the shorter the coax cable to the ADSB unit, the better. So, why run the cable 15' from the tailbone to the panel?

2. If this is a good place for the ant, why didn't the plans have us put in the doubler and associated nut plates when we had better access?

I must be missing something here and would be interested in your opinions/answers.
 
Griund plane

The plans (page 10-23) have us route a UAT antenna cable from the very aft part of the fuse forward. I started thinking about antennas recently since the fuse is done and my wings will be late.

That UAT antenna is supposed to mount at a location where three holes are provided in the skin. Unfortunately, there is no doubler there to support an antenna, now. And, putting one in, now is going to be somewhat awkward, at best. Two questions come to mind:

1. Is this the best place for the UAT antenna?
I have read that a large 2' minimum ground plane is best for this ant. There's not even 1' of plane back there.
And, the Dynon and Garmin folks tell me that the shorter the coax cable to the ADSB unit, the better. So, why run the cable 15' from the tailbone to the panel?

2. If this is a good place for the ant, why didn't the plans have us put in the doubler and associated nut plates when we had better access?

I must be missing something here and would be interested in your opinions/answers.

The term is misleading. If the antenna is mounted and touching the aluminum, all the metal at the same potentail is a ground plane.

I suspect Vans missed it. Welcome to the club. Send a munchkin in there!
 
It is a perfect place for the ADS-B antenna. I do suggest making a small doubler.

For the SkyView install, mount the ADS-B receiver in the same spot. Run a four #22 conductor shielded wire from the receiver to the Skyview. You end up with just a few inches of coax between the antenna and the receiver.

I mounted the ADS-B antenna and receiver aft on all three of my RVs and will do so again.

Carl
 
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It is a perfect place for the ADS-B antenna. I do suggest making a small doubler.

For the SkyView install, mount the ADS-B receiver in the same spot. Run a four #24 conductor shielded wire from the receiver to the Skyview. You end up with just a few inches of coax between the antenna and the receiver.

I mounted the ADS-B antenna and receiver aft on all three of my RVs and will do so again.

Carl

Carl,

I'd be much obliged if you could take a photo of your install of the ADSB receiver and send it to me.

Scott
 
The term is misleading. If the antenna is mounted and touching the aluminum, all the metal at the same potentail is a ground plane.

I suspect Vans missed it. Welcome to the club. Send a munchkin in there!

Larry,
Get your mukluks out. Snows a comin!

Hope you got your groceries.

s
 
+1 on the installation location as per plans.

I went with the Delta Pop Low Drag Transponder antenna; my transponder is a Garmin GTX-345 so all the ADS-B, Transponder, 978/1090 signals use a common antenna.

The "ground plane" or counterpoise is the other leg in a dipole or monopole antenna type. I believe this antenna is a 1/4 wave monopole, so it only needs a ~2.8" diameter ground plane.

The amount of loss in RG-400 cable at these frequencies is pretty negligible. Think about how much of it is in a G-5 and then look at how small the RV is...
 
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It is a perfect place for the ADS-B antenna. I do suggest making a small doubler.

For the SkyView install, mount the ADS-B receiver in the same spot. Run a four #22 conductor shielded wire from the receiver to the Skyview. You end up with just a few inches of coax between the antenna and the receiver.

I mounted the ADS-B antenna and receiver aft on all three of my RVs and will do so again.

Carl

Carl,
Dynon’s instructions for the ADS-B say 3’ minimum for the coax to antenna connection. But, if you haven’t had any issues I will mount my ADSB next to my ELT.
S
 
+1 on the installation location as per plans.

I went with the Delta Pop Low Drag Transponder antenna; my transponder is a Garmin GTX-345 so all the ADS-B, Transponder, 978/1090 signals use a common antenna.

The "ground plane" or counterpoise is the other leg in a dipole or monopole antenna type. I believe this antenna is a 1/4 wave monopole, so it only needs a ~2.8" diameter ground plane.

The amount of loss in RG-400 cable at these frequencies is pretty negligible. Think about how much of it is in a G-5 and then look at how small the RV is...

Actually power loss is quite high at these freq's, Garmin recommends max 2 db loss in the STC IM (approx 9' RG400 with 2 connectors) for new generation xpdrs with high power. The older xpdrs were 1.5db max loss.

A 3db loss means only half the power from the unit actually makes it to the antenna.

(RG400 has a loss of approx 18.5db per 100' and each connector is avg at .2 db)

If you have 15' of RG400 on your xpdr (approx 3 db loss) you may have trouble passing the 91.413 check due to low power and sensitivity not to mention your range will be reduced. If you need this long of a cable you should use a lower loss coax.

Recommended ground plane for xpdr antenna is 8" dia not 2.8"
 
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Interesting - perhaps a change from when I did mine.

Carl

Prolly.

I'm still gonna mount my ADS-B next to the ELT in the tail. Then, just make the antenna cable 3' long and loop it to fit the distance between the antenna mount and the electronics mounted above. That way, in case of maintenance I have service loop. 2 birds.
 
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The F-01479 Skin piece is quite thick I suspect it does not need a doubler. It is probably a good Idea to mount the antenna before mounting the Horizontal Stab as there would be room to reach in from above. However it looks like if you do have the Tail feathers on you can still reach in through the two holes in the front part of the Aft deck.

.
 
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The F-01479 Skin piece is quite thick I suspect it does not need a doubler. It is probably a good Idea to mount the antenna before mounting the Horizontal Stab as there would be room to reach in from above. However it looks like if you do have the Tail feathers on you can still reach in through the two holes in the front part of the Aft deck.

.

I called tech. They said a doubler is recommended. We put in a 0.032" piece reaching in from the top as you suggested. It wasn't too bad. Dimpling the skin was the hardest part, but we managed with the Cleaveland close quarters tool using steel nails as mandrels. I broke every one but they made acceptable dimples. It's a two person job to rivet, but now I can rest assured the antenna will not be vibrating back there.
 
Vans sells a small doubler for the transponder type antenna. I bought two of them. Mine are installed just aft of the firewall. I couldn't reach to do the riveting singlehanded so I rigged up my backriveting plate with my floor jack pressing the plate up against the bottom skin of the plane. I backriveted them from the inside. Worked like a charm. You might be able to do something similar.
 
Actually power loss is quite high at these freq's, Garmin recommends max 2 db loss in the STC IM (approx 9' RG400 with 2 connectors) for new generation xpdrs with high power. The older xpdrs were 1.5db max loss.

A 3db loss means only half the power from the unit actually makes it to the antenna.

(RG400 has a loss of approx 18.5db per 100' and each connector is avg at .2 db)

If you have 15' of RG400 on your xpdr (approx 3 db loss) you may have trouble passing the 91.413 check due to low power and sensitivity not to mention your range will be reduced. If you need this long of a cable you should use a lower loss coax.

Recommended ground plane for xpdr antenna is 8" dia not 2.8"

Walt,

Thank you as always for keeping us honest. However, I do have a couple of points that need to be clarified/understood.

1/4 wave monopole antenna design use the formula of L = 234/Freq -> e.g. 234/1090, with 135° for the legs to achieve the correct impedance in air. I see in the Part 23 AML for the GTX 3x5, Garmin is calling for 12" for the ground plane; what gives here?

I also see the 2.0dB call out in the AML for maximum loss which is about 9' of RG-400 (18.5dB/100ft, + ~.2dB for each BNC). In the RV-14 with a panel mount GTX 3x5 it looks like you need about 16' of feedline. Van's specs RG-400 for this installation. What did you do in this case? Remote mount the 3x5 or use other feedline? Or just take the extra .5dB loss and ignore the AML...

Cheers!
 
Walt,

Thank you as always for keeping us honest. However, I do have a couple of points that need to be clarified/understood.

1/4 wave monopole antenna design use the formula of L = 234/Freq -> e.g. 234/1090, with 135° for the legs to achieve the correct impedance in air. I see in the Part 23 AML for the GTX 3x5, Garmin is calling for 12" for the ground plane; what gives here?

I also see the 2.0dB call out in the AML for maximum loss which is about 9' of RG-400 (18.5dB/100ft, + ~.2dB for each BNC). In the RV-14 with a panel mount GTX 3x5 it looks like you need about 16' of feedline. Van's specs RG-400 for this installation. What did you do in this case? Remote mount the 3x5 or use other feedline? Or just take the extra .5dB loss and ignore the AML...

Cheers!

Yes if you actually do the calculation at 960mhz (ADS-B in) comes out to about 6" minimum. Maybe Garmin prefers a 1/2 wavelength which would be 12".

If I was mounting the xpdr in the panel I would definitely find a location up front for the antenna, the other option (which I usually do) is remote mount the xpdr in the rear). No I would not accept the 1db loss for the extra 6 ft of cable.
 
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