MODE C AND S proximity alerts - Which Whip Aerial to instal below aircraft

[Gary Nelson]

Can anyone recommend a good monopole whip aerial to maximise reception of proximity alerts of Mode C and Mode S.  I am intending to install the aerial below the aircraft pointing directly downwards. Also should it ideally be 68.9mm in length for 1090MHz?

I ask as looking at the forum messages there never seems an ADS-B reception issue but a fair number saying they feel they see far less Mode C or S alerts than they would have expected for the number of GA and light aircraft they see passing en route.

NB Pilot Aware sell a P3i stubby tuned monopole whip. It is currently out of stock. If it were in stock would it work as well for picking up Mode C or S even though tuned for P3i.

 

[exfirepro]

Gaz,

It is actually unusual for us to experience any significant issues with Mode C/S or ADSB reception with PAW. When investigated, most of the reported Mode C/S reception 'issues' turn out to be down to bad configuration, such as range or altitude filter settings set too tight or Mode C/S simply not switched on in PAW or the Nav system, or visible aircraft either not transponder equipped, flying with their transponder turned off, or flying below radar interrogation altitude or in areas not effectively covered by primary radar.

GA Mode C/S generally runs between 70Watts and 250Watts out at best at the Transponder, with the Trig TT21 (an 'average' example) putting out around 125Watts in an 'ideal' installation and these transponders only 'transmit' when interrogated by either primary ground radar or CAT / Military aircraft TCAS. ADSB on the other hand transmits its position and altitude automatically without any need for Radar or TCAS interrogation. Whilst GA ADSB operates with similar transmit power to its base transponder, CAT ADSB generally runs about 500Watts out at the antenna, which is 1000 times the output power of PilotAware's own extremely reliable P3i signal.

Assuming you're fitting it to a metal bodied aircraft, or on a suitable 'ground plane', the PilotAware 1/4 wave monopole works fine for 1090 MHz reception, though you need to waterproof the connection e.g. with a smear of silicone or a suitable rubber washer. They aren't designed for external use in high speed aircraft, however, so if you have one of those and want a good external 1090MHz antenna, look at the ones sold for use with transponders, e.g.

https://www.gps.co.uk/harrys-hm109s-stub-transponder-dme-antenna/p-0-1894/ .

Any of these will work equally well for PilotAware 1090MHz reception. Just remember to keep it a sensible distance away from your own transponder antenna to avoid swamping (overloading) the PAW receiver.

Regards

Peter

[Al Charles]

Hi Peter

Looking to have the antennas fitted outside a PA28, can you please advise on suitable units for both the antennas and a GPS unit that could be fitted outside? Not tech so dont really understand the differance between the two antennas, guessing the dme antenna replaces the small antenna remote from the PAW unit ?

Do you have a best advise PDF for permanent fittment of antennas I can pass on to my engineer to carry out this work

Regards

[PaulSS]

For what it's worth (from a total non-expert), I've bought the following kit for my external antennas:

For the PAW side of things you need an 868 MHz aerial. There are plenty available if you look up Flarm antennas. I went for the GAV-868 but there are also the shark fin types available as well:

https://www.gps.co.uk/antenna-exterior-gav-868-flarm/p-0-2024/

For the ADSB you'll need a 1090 MHz antenna. I went for the 'TED' type but, again, the shark fin aerials are available for this purpose:

http://parts4aircraft.oxatis.com/ted-transponder-aerial-c2x9383447

On the main Pilot Aware website there is a list of documents and in that list is an article on how to permanently mount your PAW. This has advice on what extensions etc are required and how you might mount one sort of antenna externally:

http://www.pilotaware.com/documents/

There is also a document which talks about where to mount antennas for the best performance, which is worth a read.

Apart from that, one of the bits of information I have gleaned from this forum is the fact that you don't want your ADSB antenna too close to your transponder aerial. They both operate at 1090 MHz and your ADSB is receive only, whereas your transponder is TX/RX. Apparently, the transponder is quite powerful and it will drown out the receive-only capability of your ADSB antenna if it is too close.

[Paul_Sengupta]

You can't legally hard wire a PilotAware into a PA28... 

[PaulSS]

Doh 

Every day's a schoolday 

[Paul_Sengupta]

Though if you're just fitting a couple of antennas "for no reason" then it might be ok! 

[Keithvinning]

You can't legally hard wire a PilotAware into a PA28...

No.

Now this isn't an official Pilotaware view but.......

Its true that PilotAware is classed as carry on equipment and the enlightened folks at the LAA and BMAA recognise it as safety equipment so don't demand a modification or charge. EASA is different so PilotAware at the moment is not "certified" however does that mean that you can't drill holes in non load bearing bits the same as you can in permit aircraft to give your safety equipment a better view? Physically its the same?

I don't know the answer to this but the thought goes along the lines of you are not expecting it to be certified by doing so, so why not. Will the insurance be void because you have drilled a couple of 6mm holes in none structural aluminium plastic or sticking through some thin stitts? I don't know?

Of course this is not advice but check out with your engineer. You are not fitting certified equipment and don't want it certified. Is it in fact legal to use a mobile phone inn aircraft when to can broadband more cell sites than was expected in their design?

Technology in advance of standards. Great isn't it? 

Is their an EASA engineer out there who can put us right on the law and the pragmatic view.

[exfirepro]

Hi All,

Sorry Al, ....I wasn't ignoring you. I have been busy all week putting my plane back together after what started out as minor maintenance last weekend went awry - a long story, but now pretty much resolved, I'm glad to say.

The guys above have pretty much answered your question as far as I can see. I would agree that the best approach would be to speak to your (hopefully friendly and cooperative) engineer about fitting good quality external antennas for -  1090MHz (Mode C/S ADSB) and 868MHz (look at antennas intended for FLARM), ......rather than get into 'discussion' about 'installing' PilotAware. There are plenty of good quality antennas out there for the above frequencies designed for use in high performance aircraft. They are a bit pricier than I would be looking at for my flexwing, but much more likely to achieve approval for fitting to your aircraft.

WRT GPS antennas, you need to be a bit careful, as PilotAware will only operate with certain GPS units. I would suggest trying a PilotAware gps 'mouse' on your coaming first. This should work fine through the windscreen without being obtrusive. Just be careful to check that there is no adverse effect on your compass, etc. In the event that an external GPS/Antenna is required, you would need Lee's advice on whether any proposed unit would work.

Once the antennas and cabling are installed and approved, it should be a case of plugging your 'portable carry on' PilotAware into 'existing' antennas.

Regards

Peter

[JCurtis]

Things get a little murky when something is fitted to an EASA aircraft that cannot be taken out when the pilot leaves the cockpit.  Physically fitting an antenna is also linked to cable routing, potential impact of nearby items etc., and how can the engineer sign off the install without taking into account of what will be going in/out of the antenna.

I know from experience the fun and games getting EASA to accept a change never seen before, often if they have seen it they will not admit they have.  It has taken ages to finally get the paperwork sorted to permit my USB supplies to be fitted into EASA aircraft, the new CS-STAN regs have now made that easy and at a vastly reduced cost for customers (I don't charge a premium for the supply or for the paperwork, you just pay your engineer to fit according to the published MOD).

The key is to have a chat with your engineer and see how they feel about it, nothing will happen otherwise.

[exfirepro]

Hi Jeremy,

Very valuable info on your EASA approval 'hoops'.

Clearly supports the need to speak to your engineer and also why I suggested going for 1090 Mode S/ADSB and FLARM ('antenna') fit as there are already Mod procedures in place to allow the fitting of Transponders and FLARM in EASA aircraft, so that should hopefully be an easier route.

Regards All

Peter

[Gary Nelson]

Thanks for replies to date. I have 2 existing jig holes under the Eurostar SL that would be good to use for the 2 pilot aware tuned stubby aerials. These are (very appox) 70cm and 40cm away from my existing Funke mode C/S transponder aerial. Re "swamping" risk, is 70cm sufficient distance for the Pilot Aware ADS-B/Mode C/S receive aerial and does it matter if the Pilot Aware P3i transmit/receive aerial will therefore then end up being only 40cm away from the Funke transponder aerial?

If I use the above referred jig holes, then the 2 Pilot Aware aerials will end up being about 75cm from each other