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 Was it superseded?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.

Bumper- Good tip! Thanks!

If you're seeking to improve your Flarm range then moving to
a better aerial design is an option. In the crowded Alps you see
many installations using the "SuperFant" antenna; see link
below.
This aerial is both small and slim and so does not impede the
view when mounted on the front of the instrument panel, high
just under the canopy. My experience is that it has much
superior performance to the standard simple Flarm dipole. It's
available with custom length cable.
Of course the position of the Flarm aerial is critical! There are
some truly terrible installations out there....

http://www.gliderdesignparts.de/ant_flarm.html

I always found their service to be fast and relable; usual
disclaimers.

On Saturday, October 29, 2016 at 2:45:06 PM UTC-7, Dave Walsh wrote:
If you're seeking to improve your Flarm range then moving to
a better aerial design is an option. In the crowded Alps you see
many installations using the "SuperFant" antenna; see link
below.
This aerial is both small and slim and so does not impede the
view when mounted on the front of the instrument panel, high
just under the canopy. My experience is that it has much
superior performance to the standard simple Flarm dipole. It's
available with custom length cable.
Of course the position of the Flarm aerial is critical! There are
some truly terrible installations out there....

http://www.gliderdesignparts.de/ant_flarm.html

I always found their service to be fast and relable; usual
disclaimers.

Nice antenna frequency frequency different in Europe.

Richard

On Saturday, October 29, 2016 at 2:45:06 PM UTC-7, Dave Walsh wrote:
If you're seeking to improve your Flarm range then moving to
a better aerial design is an option. In the crowded Alps you see
many installations using the "SuperFant" antenna; see link
below.
This aerial is both small and slim and so does not impede the
view when mounted on the front of the instrument panel, high
just under the canopy. My experience is that it has much
superior performance to the standard simple Flarm dipole. It's
available with custom length cable.
Of course the position of the Flarm aerial is critical! There are
some truly terrible installations out there....

http://www.gliderdesignparts.de/ant_flarm.html

I always found their service to be fast and relable; usual
disclaimers.

Nice antenna frequency different in Europe.

Richard