December 28, 2021

Why do we need remote antennas?

Carry on devices are fine if they are used correctly. However, carry-on EC devices must be installed correctly. The main issue is obscuration (signal blocking) and attenuation (signal weakening). This affects all devices but is more prevalent amongst carry-on devices. The performance reduction is mainly caused by a combination of bad location, incorrect antenna orientation and poor GPS reception.  

The UHF radio signals, used by all EC devices, are obscured by radio opaque objects such as metals or carbon fibre. The engine and airframe are the biggest culprits. The primary effect of airframe obscuration is to prevent the radio waves transmitting in the direction of the obscuring object.  

For example, if you put an EC device on the rear shelf of a metal or carbon fibre aircraft such as a VANS, Sportscruiser or Sting, it will be completely obscured to the rear as the signal fails to pass through the metal or carbon fuselage. If the device is positioned low enough, it will also be blocked by the engine and firewall in the forwards direction. Fibreglass airframes such as the Europa or tube and fabric aircraft like the Eurofox will be less affected, but the engine and occupants will still block the signals in the forwards direction. There is a PilotAware YouTube video that describes this further.  

PilotAware Atom GRID Features and Obscuration  

The signals are also attenuated by dense objects and liquids such as the fuel in fibreglass or polypropylene fuel tanks and the water in the occupants bodies (70%). The effect of this is to weaken the signals, and hence reduce the effective design range of the device. Received signals are always weaker than transmitted signals.

These effects are well understood and performance is improved by placing remote internal antennas inside the aircraft at optimal positions or better still remote antennas outside of the aircraft. This is always done with transponders and VHF radios and therefore, is also the best option for the weaker signals used by Electronic Conspicuity devices.  

PilotAware and Obscuration

What Should be Expected of a Well Installed Carry on Device?

As mentioned earlier, there is nothing inherently wrong with a well-designed carry on device that has been installed properly. As shown this should  have a clear line of sight for both antennas, which will be vertically oriented and also a clear line of sight for the GPS. There will however, be obscuration and attenuation in some direction. This is inevitable because the carry on device is inside an aircraft that is possibly occupied by up to 4 or more people.  

The following PilotAware VECTOR polar diagram shows what a real world, well-positioned carry on PilotAware Rosetta EC device can achieve,  

This polar diagram, collected from several ATOM GRID stations, is from a Cabri G2 helicopter with a carry-on PilotAware Rosetta mounted in front of the dashboard. The polar diagram is analysed as follows. The air to ground range of the PilotAware unit is 50Kms + in all directions, except to the rear where there is significant obscuration. The obscuration is caused by the passengers, fuel and the engine to the rear of the aircraft. This obscuration could be reduced by the use of remote internal antennas or better still by using remote external antennas.

What Should be Expected from a Poorly Installed Carry on Device?

In the VECTOR polar diagram below you can see a much different picture

 

This polar diagram is taken from a carry on device installed in a PA28, probably fixed to a port window. It can be seen that the EC device has been occasionally detected at 25KMs to the front left but the main detections are much weaker with significant obscuration to the rear and the starboard side. This is most probably caused by airframe obscuration and occupant attenuation. This is not a PilotAware device. Again this poor performance could be improved by the use of remote internal antennas or better still by using remote external antennas if this option is available from the chosen device manufacturer.

What Should be Expected of a Well Installed Device using External Antennas.

Every installation will be different, but by using external antennas with a good ground plane 360° transmission and reception is eminently possible with PilotAware units. The following Polar Diagram shows a PilotAware unit fitted with external antennas on a metal aircraft.  

Here is the VECTOR polar diagram from a VANS RV7 aircraft using a PilotAware Rosetta EC device fitted with remote external antennas. Gathered from 5 flights and 11,416 detections the VECTOR software is building an excellent polar pattern with 360 degrees of transmission at an air to ground range of over 60Kms to available distant ATOM stations. Each radial ring represents 20Kms. This is a good example of the benchmark for a well-designed EC installation using external antennas.

What options are there for fitting remote antennas to PilotAware units?  

There are two remote antenna options. Remote Internal Antennas and Remote External Antennas.

Remote internal antennas  

Remote internal antennas are used by folks who do not want, or who cannot modify their aircraft for any reason. PilotAware remote internal antennas come with 2 metres of high grade RG316 coaxial cable so that they can be optimally positioned within the aircraft. For example in certified aircraft, such as a PA28 or a Cessna 152, a popular place to install the antennas is either side of the windscreen. Each antenna is provided with rubber suction mounts to do this. More permanent Scotch Tabs are also provided. The thin coaxial cable can also be routed behind the trim around the window and thus out of sight. The GPS mouse is then mounted on the centre of the dashboard giving a clear view of the required satellites.

For tube and fabric aircraft, remote internal antennas can be positioned high up and to the rear of the pilot and passengers or any other suitable place. The fabric of the aircraft is transparent to radio waves so a good radiation pattern should be achieved.

Remote internal antennas look like this.  

Remote External Antennas

Remote external antennas, mounted outside of the aircraft, will always give the best performance when correctly fitted. Remote external antennas differ from remote internal antennas in that they are monopole antennas and therefore require a ground plane to operate correctly. On metal aircraft the fuselage acts as a good ground plane and will give the results shown in the previous polar diagram. If the external antennas are mounted on a wooden, tube and fabric, fibreglass aircraft or the pod on a gyrocopter, or weight-shift microlight, then a metal ground-plane will be required. This will take the form of a thin sheet of aluminium about 20cm square. Antennas should be mounted a minimum of 15cm apart and at least 20cm away from the 1090MHz transponder antenna if fitted.

There are no hard and fast rules about where the external antennas are fitted. Underneath the aircraft, behind the front seats is a popular position as this site is far enough away from the engine to reduce the obscuration. Also, 230+ PilotAware ATOM GRID Ground Stations are now providing ground to air information and will provide more in the future.  An underbelly installation will also improve the air to ground capability.  Post a question on the PilotAware Forum to see how others have installed antennas in similar aircraft to the one that you fly.

Remote external antennas look like this.

To What Type of Aircraft Are You Fitting Remote Antennas?

You can install either internal or external antennas to LAA and BMAA permit to fly aircraft without a major modification. Just ask your inspector.  

However, for aircraft on the CAA or EASA registers it has not been so easy. It is possible to install antennas on EASA aircraft using the standard change CS-SC004a in CS STAN issue 3, or the minor change route could be used instead. However, I am told by those very helpful people in Cologne that help is at hand.  

Over the last 9 months EASA, has been working to extend the light touch regulation, currently available for the installation of remote external antennas for Flarm devices. This is soon to be changed to include other EC devices operating on a non-aviation frequency.  

The intention is that, “This template could be drastically simplified for the installation of an electronic conspicuity device. No flight test (no flight conditions, no permit to fly) is needed. A flight check is sufficient.” This will of course include PilotAware and other EC devices. EC devices operating on 1090MHz or 978MHz will not be included as they operate on an aviation frequency and will be subject to the full modification requirements for the filling of antennas. With the UK leaving the EU and EASA, the adoption of this light touch for aircraft on the CAA register, will depend on whether this is harmonised by the UK authorities or not.  

If you want to check the performance of your PilotAware installation then you can do this by using PilotAware VECTOR.

VECTOR is another free service from PilotAware that will report on the fidelity of any EC device, not just PilotAware. This will show you how good your installation is. Please see the following video on how VECTOR works.  

PilotAware VECTOR

To use PilotAware VECTOR you need to have made a flight or flights of about an hour in the last 30 days or so. You also need to have the correct ICAO code installed in all EC devices on board.


PilotAware Remote Internal and External Installation Kits  

To make life easy PilotAware has produced installation kits that use either internal or external antennas. These are available for sale on the PilotAware website.  

External Antenna Installation Kits

These are available from

https://www.pilotaware.com/product/external-antenna-installation-kit

If you just want the external antennas they are found here

https://www.pilotaware.com/product/aviation-grade-external-antennas

The installation instructions for Remote External antennas are found here

External Antenna Installation Instructions

Internal Antenna Installation Kits

These are available from,  

https://www.pilotaware.com/product/internal-antenna-installation-kit

If you just want the internal antennas or GPS Mouse they can be found here

https://www.pilotaware.com/product/internal-1090mhz-aerial

https://www.pilotaware.com/product/internal-869-5mhz-antenna

https://www.pilotaware.com/product/gps-mouse

The installation instructions for Remote Internal Antennas are found here

Internal Antenna Installation Instructions

Summary

The design criteria for PilotAware is for a transmit and receive performance, of a well installed carry on device of 30KMs. In practice this has been exceeded. Unfortunately, attenuation and obscuration will reduce or eliminate this. However by using remote internal or external antennas both obscuration and attenuation can improved and an optimum performance for your aircraft can be achieved.