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  #1  
Old 03-10-2021, 05:19 PM
rockitdoc's Avatar
rockitdoc rockitdoc is offline
 
Join Date: May 2020
Location: Fort COllins, CO
Posts: 236
Default UAT Ant mount at rear of -14 fuse?

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.
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14A
Begun 07-23-20
Emp Completed 11-12-20
Slo Fuse Completed 3-2-21
Wiring and Avionics Begun 3-3-21
QB Wings delayed until ?
Finish Kit expected 7-21
Thunderbolt EXP119 expected 7-21
2021 Dues Paid
Reserved: N52XL
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  #2  
Old 03-10-2021, 05:42 PM
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wirejock wirejock is offline
 
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 4,379
Default Griund plane

Quote:
Originally Posted by rockitdoc View Post
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!
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Estes Park, CO
http://wirejockrv7a.blogspot.com
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Donated 01/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
Empennage, wings, fuse, finishing kit, now FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #3  
Old 03-10-2021, 05:53 PM
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Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,947
Default

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

Last edited by Carl Froehlich : 03-11-2021 at 06:53 PM.
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  #4  
Old 03-10-2021, 06:07 PM
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rockitdoc rockitdoc is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
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
__________________
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Begun 07-23-20
Emp Completed 11-12-20
Slo Fuse Completed 3-2-21
Wiring and Avionics Begun 3-3-21
QB Wings delayed until ?
Finish Kit expected 7-21
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  #5  
Old 03-10-2021, 06:21 PM
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rockitdoc rockitdoc is offline
 
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Location: Fort COllins, CO
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Default

Quote:
Originally Posted by wirejock View Post
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
__________________
14A
Begun 07-23-20
Emp Completed 11-12-20
Slo Fuse Completed 3-2-21
Wiring and Avionics Begun 3-3-21
QB Wings delayed until ?
Finish Kit expected 7-21
Thunderbolt EXP119 expected 7-21
2021 Dues Paid
Reserved: N52XL
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  #6  
Old 03-11-2021, 05:46 AM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
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Default

+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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Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.

Last edited by bjdecker : 03-11-2021 at 05:55 AM.
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  #7  
Old 03-13-2021, 02:35 PM
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rockitdoc rockitdoc is offline
 
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Location: Fort COllins, CO
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Default

Quote:
Originally Posted by Carl Froehlich View Post
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,
Dynonís instructions for the ADS-B say 3í minimum for the coax to antenna connection. But, if you havenít had any issues I will mount my ADSB next to my ELT.
S
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14A
Begun 07-23-20
Emp Completed 11-12-20
Slo Fuse Completed 3-2-21
Wiring and Avionics Begun 3-3-21
QB Wings delayed until ?
Finish Kit expected 7-21
Thunderbolt EXP119 expected 7-21
2021 Dues Paid
Reserved: N52XL
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  #8  
Old 03-13-2021, 03:49 PM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by rockitdoc View Post
Carl,
Dynonís instructions for the ADS-B say 3í minimum for the coax to antenna connection. But, if you havenít had any issues I will mount my ADSB next to my ELT.
S
Interesting - perhaps a change from when I did mine.

Carl
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  #9  
Old 03-13-2021, 04:55 PM
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Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 6,018
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Quote:
Originally Posted by bjdecker View Post
+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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EXP Aircraft Services LLC
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Last edited by Walt : 03-13-2021 at 05:49 PM.
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  #10  
Old 03-14-2021, 04:01 PM
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rockitdoc rockitdoc is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
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.
__________________
14A
Begun 07-23-20
Emp Completed 11-12-20
Slo Fuse Completed 3-2-21
Wiring and Avionics Begun 3-3-21
QB Wings delayed until ?
Finish Kit expected 7-21
Thunderbolt EXP119 expected 7-21
2021 Dues Paid
Reserved: N52XL

Last edited by rockitdoc : 03-14-2021 at 04:02 PM. Reason: fix
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