Dual PowerFLARM Antennas: Teamwork or Duel?

[[email protected]]

Sorry, fun with words. :)

Does anyone know how PowerFLARM handles inputs from two antennas, "A" and "B"? Does it select the strongest signal source? Or, alternatively, does it somehow integrate inputs from two different antennas and use the combined information?

In an attempt to increase range, I installed a "B" dipole antenna (the receive-only port) on my Portable PowerFLARM and flew with it this weekend. The "A" antenna (transmit-receive) is the factory "stick" antenna that sits on the rear of the unit, which is mounted on the top of the glare shield.

With the stick antenna only, I had a big lobe out to the left side (per the range analyzer tool) and pretty unimpressive reception in all other directions. After I reset the software (see recent related thread), I temporarily installed the dipole low on the right side of the glareshield.

Success! Much better reception on the right side. No surprise--the mass of numerous instruments shields the left side of the dipole. What WAS a surprise was that the big lobe out to the left is now gone: i.e., reception there has gotten worse.

Overall I'm somewhat better off, though the marginal reception straight ahead hasn't improved.

Does it matter that the two antennas are of different types?

I've checked other threads and it seems like the brick owners are using two dipoles to cover different areas of the sky (left & right, front & rear, above & below). Underlying everything I've read is that two antennas are better than one, providing combined coverage. That's not exactly what appears to have happened in my case.

I've had experience in the past installing a homemade VHF dipole in the rudder of a glider where the existing factory antenna a few inches forward of it in the vertical fin apparently acted as a parasitic element and made the add-on antenna extremely directional. IIRC, the stick and dipole are perhaps 30 cm apart.

I should also mention that I have one of the three or so Schleicher gliders in the U.S. with the factory canopy wire (fence) deflector bars, with the front hoop of steel tubing arching over the cockpit just aft of the instrument panel. Another potential challenge for antenna positioning.

Finally, since the Portable is mounted on the glareshield, I'm very reluctant to mount a dipole in the nose (as the ASW 27/29 crowd have done) unless I can provide a friction-fit disconnect in the coax or insure the antenna itself will separate cleanly from the glider if I have to jettison the canopy.

Ideas?

Chip Bearden
ASW 24 "JB"

[[email protected]]

On Wednesday, August 10, 2016 at 3:20:21 PM UTC-4, wrote:
> Sorry, fun with words. :)
>
> Does anyone know how PowerFLARM handles inputs from two antennas, "A" and "B"? Does it select the strongest signal source? Or, alternatively, does it somehow integrate inputs from two different antennas and use the combined information?
>
> In an attempt to increase range, I installed a "B" dipole antenna (the receive-only port) on my Portable PowerFLARM and flew with it this weekend. The "A" antenna (transmit-receive) is the factory "stick" antenna that sits on the rear of the unit, which is mounted on the top of the glare shield.
>
> With the stick antenna only, I had a big lobe out to the left side (per the range analyzer tool) and pretty unimpressive reception in all other directions. After I reset the software (see recent related thread), I temporarily installed the dipole low on the right side of the glareshield.
>
> Success! Much better reception on the right side. No surprise--the mass of numerous instruments shields the left side of the dipole. What WAS a surprise was that the big lobe out to the left is now gone: i.e., reception there has gotten worse.
>
> Overall I'm somewhat better off, though the marginal reception straight ahead hasn't improved.
>
> Does it matter that the two antennas are of different types?
>
> I've checked other threads and it seems like the brick owners are using two dipoles to cover different areas of the sky (left & right, front & rear, above & below). Underlying everything I've read is that two antennas are better than one, providing combined coverage. That's not exactly what appears to have happened in my case.
>
> I've had experience in the past installing a homemade VHF dipole in the rudder of a glider where the existing factory antenna a few inches forward of it in the vertical fin apparently acted as a parasitic element and made the add-on antenna extremely directional. IIRC, the stick and dipole are perhaps 30 cm apart.
>
> I should also mention that I have one of the three or so Schleicher gliders in the U.S. with the factory canopy wire (fence) deflector bars, with the front hoop of steel tubing arching over the cockpit just aft of the instrument panel. Another potential challenge for antenna positioning.
>
> Finally, since the Portable is mounted on the glareshield, I'm very reluctant to mount a dipole in the nose (as the ASW 27/29 crowd have done) unless I can provide a friction-fit disconnect in the coax or insure the antenna itself will separate cleanly from the glider if I have to jettison the canopy.
>
> Ideas?
>
> Chip Bearden
> ASW 24 "JB"

B antenna on the bottom would avoid many of the issues you mention.
UH

[Dan Daly[_2_]]

On Wednesday, August 10, 2016 at 3:20:21 PM UTC-4, wrote:
> Sorry, fun with words. :)
>
> Does anyone know how PowerFLARM handles inputs from two antennas, "A" and "B"? Does it select the strongest signal source? Or, alternatively, does it somehow integrate inputs from two different antennas and use the combined information?
>
> In an attempt to increase range, I installed a "B" dipole antenna (the receive-only port) on my Portable PowerFLARM and flew with it this weekend. The "A" antenna (transmit-receive) is the factory "stick" antenna that sits on the rear of the unit, which is mounted on the top of the glare shield.
>
> With the stick antenna only, I had a big lobe out to the left side (per the range analyzer tool) and pretty unimpressive reception in all other directions. After I reset the software (see recent related thread), I temporarily installed the dipole low on the right side of the glareshield.
>
> Success! Much better reception on the right side. No surprise--the mass of numerous instruments shields the left side of the dipole. What WAS a surprise was that the big lobe out to the left is now gone: i.e., reception there has gotten worse.
>
> Overall I'm somewhat better off, though the marginal reception straight ahead hasn't improved.
>
> Does it matter that the two antennas are of different types?
>
> I've checked other threads and it seems like the brick owners are using two dipoles to cover different areas of the sky (left & right, front & rear, above & below). Underlying everything I've read is that two antennas are better than one, providing combined coverage. That's not exactly what appears to have happened in my case.
>
> I've had experience in the past installing a homemade VHF dipole in the rudder of a glider where the existing factory antenna a few inches forward of it in the vertical fin apparently acted as a parasitic element and made the add-on antenna extremely directional. IIRC, the stick and dipole are perhaps 30 cm apart.
>
> I should also mention that I have one of the three or so Schleicher gliders in the U.S. with the factory canopy wire (fence) deflector bars, with the front hoop of steel tubing arching over the cockpit just aft of the instrument panel. Another potential challenge for antenna positioning.
>
> Finally, since the Portable is mounted on the glareshield, I'm very reluctant to mount a dipole in the nose (as the ASW 27/29 crowd have done) unless I can provide a friction-fit disconnect in the coax or insure the antenna itself will separate cleanly from the glider if I have to jettison the canopy.
>
> Ideas?
>
> Chip Bearden
> ASW 24 "JB"

The CORE 3.41 manual, page 14, says "In
case you use two FLARM antennas, ensure they are separated by at
least 5ft."

The Portable 3.41 manual, page 13, says"If a second flat FLARM/PowerFLARM device
communications antenna with the extension cable
(used for reception of FLARM/PowerFLARM device
signals only, included in shipments to the USA) is
used, it should be connected to socket labelled
‘FLARM B’; ensure it is located at least 0.6 meters (2
ft) from the device."

Dunno why; perhaps the higher transmit power of the Core vs Portable.

You might try separating them a bit and see what happens.

[JS]

Chip:
If you want a clean canopy ejection, add an MCX connection to the cable of the antenna that will not go away with the canopy. The Core uses MCX for the GPS antenna, so you may have seen those connectors.
The OzFLARM I had a decade ago used an MCX disconnect for the remote FLARM antenna.
Have you done the same with power? PowerPoles will disconnect with a pull.
Jim

[[email protected]]

On Wednesday, August 10, 2016 at 4:40:12 PM UTC-4, JS wrote:
> Chip:
> If you want a clean canopy ejection, add an MCX connection to the cable of the antenna that will not go away with the canopy. The Core uses MCX for the GPS antenna, so you may have seen those connectors.
> The OzFLARM I had a decade ago used an MCX disconnect for the remote FLARM antenna.
> Have you done the same with power? PowerPoles will disconnect with a pull..
> Jim

Jim, Yes, my power leads (for Portable PowerFLARM and canopy-rail-mounted Dell Streak) are "pull apart" connectors. My old Cambridge GPS/NAV (with three connectors) is velcroed to the canopy rail so it should rip off, too. The antenna is the one I'm worried about: even the smaller diameter coax is strong enough that it might not break or pull out of the connector.

Thanks for the suggestion for the MCX connectors. My U.S. PowerFLARM has SMA connectors (normal and reverse) that are threaded. I've wondered if the coax would just tear out of the antenna itself under a sharp load but don't feel like destruction testing an antenna to find out :)

Chip

[[email protected]]

On Wednesday, August 10, 2016 at 4:03:35 PM UTC-4, Dan Daly wrote:

> Dunno why; perhaps the higher transmit power of the Core vs Portable.
>
> You might try separating them a bit and see what happens.

Interesting. I assume the Core dipoles are higher gain/more directional than the stock stubby antenna on the Portable. So perhaps that's another reason why the greater separation is required for the Core.

That said, I've seen more than one glider installation where the two Core antennas (dipoles) were MUCH closer than 5 feet.

UH, I'll communicate offline about moving one antenna to the bottom since you know '24s (and my glider) as well as anyone.

What to try next? Swap the stubby antenna for a dipole "A" antenna (requires an antenna with a reverse polarity connector for the Portable)? Or remove both the stubby "A" and dipole "B" and replace it with a single "A" dipole? Both require getting another antenna so I'm not sure it matters.

I'm better off now than a week ago so I guess I shouldn't complain. But I thought this would be so simple. :)

Chip Bearden
ASW 24 "JB"