FLARM A minimum spacing to ADS-B Antenna? 1 foot !?!?

Maybe this has been covered in RAS but I couldn't find it. I looked through two documents about the spacing of FLARM antennas, specifically the FLARM A and ADS-B antennas. Obviously, the thing to avoid is the transmitting of FLARM data (A antenna) interfering with ADS-B (or GPS) reception.

The FLARM document "PowerFLARM_Application_Note_ANTENNAS1.pdf"* has the following information about antenna spacing. It doesn't mention a minimum distance between the FLARM A and ADS-B antennas;

Keep antennas separated as far as possible!
Min. distance between RF antenna on FLARM A and FLARM B port: 1ft (0.3 m)
Min. distance between RF antenna on FLARM A port and GPS antenna: 1ft (0.3 m)
Min. distance between RF antenna on FLARM B port and GPS antenna: 4in (0.1 m)
Min. distance between ADS-B / XPDR antenna and GPS antenna: 4in (0.1 m)

The FLARM Core V2.0 manual** says the following in the section on ADS-B antennas;

"This antenna should be placed at least 30cm/1ft away from the FLARM antennas. The FLARM antennas have priority over this antenna for best placement."

1 foot (30cm) spacing within our tight glider cockpits is going to be a struggle. Based on the FLARM portable (might not be the best example) the two antennas are only 2.5" (0.06 m) apart.

Anyone have more information on this spacing conundrum?

Thanks, John "OHM"

* http://cumulus-soaring.com/flarm/Pow..._ANTENNAS1.pdf. I don't see it on the FLARM.org web site. Was it superseded?

** https://flarm.com/wp-content/uploads...anual-2.00.pdf

On Thursday, October 27, 2016 at 8:09:32 AM UTC-7, OHM Ω wrote:
Maybe this has been covered in RAS but I couldn't find it. I looked through two documents about the spacing of FLARM antennas, specifically the FLARM A and ADS-B antennas. Obviously, the thing to avoid is the transmitting of FLARM data (A antenna) interfering with ADS-B (or GPS) reception.

The FLARM document "PowerFLARM_Application_Note_ANTENNAS1.pdf"* has the following information about antenna spacing. It doesn't mention a minimum distance between the FLARM A and ADS-B antennas;

Keep antennas separated as far as possible!
Min. distance between RF antenna on FLARM A and FLARM B port: 1ft (0.3 m)
Min. distance between RF antenna on FLARM A port and GPS antenna: 1ft (0.3 m)
Min. distance between RF antenna on FLARM B port and GPS antenna: 4in (0.1 m)
Min. distance between ADS-B / XPDR antenna and GPS antenna: 4in (0.1 m)

The FLARM Core V2.0 manual** says the following in the section on ADS-B antennas;

"This antenna should be placed at least 30cm/1ft away from the FLARM antennas. The FLARM antennas have priority over this antenna for best placement.."

1 foot (30cm) spacing within our tight glider cockpits is going to be a struggle. Based on the FLARM portable (might not be the best example) the two antennas are only 2.5" (0.06 m) apart.

Anyone have more information on this spacing conundrum?

Thanks, John "OHM"

* http://cumulus-soaring.com/flarm/Pow..._ANTENNAS1.pdf. I don't see it on the FLARM.org web site. Was it superseded?

** https://flarm.com/wp-content/uploads...anual-2.00.pdf

Dave Nadler's published some guidance. Check the third article down on this link. http://www.nadler.com/public/NadlerSoaringIndex.html

Cheers,
Craig

Thanks ... but...

Dave contributed heavily to this in-depth FLARM® discussion on GliderPilot.org
Bad Link

FLARM antenna installation notes (replaces the FLARM Antenna Hall of Shame web page)
Same as the document I referenced in my original diatribe

Thanks, John "OHM"

I might have to disagree with FLARM's statement, "The FLARM antennas have priority over this [ADS-B] antenna for best placement."

I think that early detection of a 1,000 lb FLARM equipped glider closing at 100kts should probably take a back seat to early detection of a 62,000 lb ADS-B equipped 737 closing at 400kts. Just sayin'

There are caveats to that statement of course. There are low risk and high risk ADS-B traffic areas. But you aren't going to move your (FLARM and ADS-B) antennas around based on where you are flying this week. So I would think that you should place your antenna based on the worse case threat scenario = a high speed and hefty flying bomb. Just sayin'

My $0.02 - John "OHM"

On Thursday, October 27, 2016 at 2:00:03 PM UTC-7, OHM Ω wrote:
I might have to disagree with FLARM's statement, "The FLARM antennas have priority over this [ADS-B] antenna for best placement."

I think that early detection of a 1,000 lb FLARM equipped glider closing at 100kts should probably take a back seat to early detection of a 62,000 lb ADS-B equipped 737 closing at 400kts. Just sayin'

There are caveats to that statement of course. There are low risk and high risk ADS-B traffic areas. But you aren't going to move your (FLARM and ADS-B) antennas around based on where you are flying this week. So I would think that you should place your antenna based on the worse case threat scenario = a high speed and hefty flying bomb. Just sayin'

My $0.02 - John "OHM"

The reason the Flarm antennas are more critical is because the power of the flarm signal is very low compared to the ADS-B signal.

Richard
www.craggyaero.com

What Richard (Craggy Aero) said, and:

The placement of a transmit or transceiver antenna will almost always be more critical than a receive only antenna. This is due to obstructions or interference causing nulls (areas where the transmitted signal is suppressed or blocked) and impedance mismatch causing high SWR, i.e. power to be reflected back down the transmission line (coax) and wasted instead of being transmitted by the antenna. Thus antenna installation for the PF A antenna is extremely important as it has a minuscule output power of only a few milliwatts (I read 10 mw somewhere, but can't find it now).

On the other hand, you could probably hold up a paper clip and receive the ADS-B signal from even a small power aircraft that has a minimum power output of 75 watts, larger aircraft 125 watts minimum, up to 500 watts max. Optimal ADS-B installation in your glider, while important, would hardly be an issue.

Bump-man, Craggy,

I had no clue of the **VAST** power difference between FLARM and ADS-B. Something on the order of 1/10,000 the power (100w/10mw)?? Wow. Really brings home that the FLARM antenna placement needs to be as optimized as humanly possible.

Thanks, John "OHM"

On Friday, October 28, 2016 at 3:35:04 PM UTC-4, OHM Ω wrote:
Bump-man, Craggy,

I had no clue of the **VAST** power difference between FLARM and ADS-B. Something on the order of 1/10,000 the power (100w/10mw)?? Wow. Really brings home that the FLARM antenna placement needs to be as optimized as humanly possible.

Thanks, John "OHM"

In 27 and 29 I found high in the center above the glare shield gets the best result. Antenna lead wire to the rear is better than the side. Antenna mounted at aft edge of glare shield with 3/4 inch square Velcro. I don't like the view but have gotten to where I don't really notice it.
B antenna mounted on the aft canopy frame seems to also add to pattern. It is mounted with small Velcro squares and wire retained with 1/4 inch wide Velcro strips to allow pull away.
ADSB antenna up front under the glare shield.
FWIW
UH

If you are using the little dipole antennas, you can increase efficiency by shortening the coax instead of folding or coiling the extra. If you disassemble the antenna end, the coax shield (braid) is connected to one radial and the center conductor to the other. Unsolder, cut coax to more appropriate length, resolder (use heat sink [hemostats etc] on braid when soldering it to avoid heat damage to coax insulator).

bumper

Bumper- Good tip! Thanks!