Author Topic: P3I Antenna Location in metal aircraft  (Read 5875 times)

Robski

P3I Antenna Location in metal aircraft
« on: October 10, 2016, 04:28:26 pm »
Hi all.

I have an RV-6. I have put the PAW with the P3I antenna on the coaming as suggested to get it as high as possible with as clear a view as possible. However I get screening from the rear fuselage so my flying chums, also with PAW units, cannot see me and I cannot see them when we are all on the same track. This is precisely the sort of scenario when we need to be able to see each other (1-5 miles apart, not close formation, all heading to the same destination).

An external antenna would seem to be the solution.
The offered one is this http://pilotawarehardware.com/product/tuned-monopole-whip/.

However the info on it is a tad scant, aside from it needing a ground plane (not an issue on an aly airframe).
Is it definitely weatherproof?
Does it include all mounting hardware?
Will it put up with high airspeeds (210mph for the RV-6's VNE, more for RV7s, 8s and 10s).
How long can the lead be?
What is the end connector?

Next question is whether to mount the above monopole on the topside or underside of the aircraft?
Has anyone tried either, and with what results?
Is both, diplexed, an option?

Anybody have experience/solutions for any of this?
I am reluctant to drill holes in the plane without any kind of idea as to whether it is a good position or not.
Presumably other RV's, Sport Cruisers, Zenairs and other low wing, highish turtledeck metal aircraft have similar issues.
Rob
If the good Lord had intended man to fly He would have given him more money.

Keithvinning

Re: P3I Antenna Location in metal aircraft
« Reply #1 on: October 11, 2016, 02:18:43 pm »
Hi Rob

I have fitted PilotAware permanently in my Sports Cruiser which is similar construction but not as fast as the VANS. I have put a paper on this on the website at http://www.pilotaware.com/wp-content/uploads/2016/09/160915-Permanent-Installation.pdf have you seen this?

It makes it really convenient, just hit the master switch, wait for the iPad to log onto the WiFi select Skydemon etc and go. The range on 3PI is over 30Km and the ADSB insane at 200Km plus,  absolutely useless of course but nice to see. Antennas are located underneath the aircraft.



The offered one is this http://pilotawarehardware.com/product/tuned-monopole-whip/.

However the info on it is a tad scant, aside from it needing a ground plane (not an issue on an aly airframe).
Is it definitely weatherproof?
Does it include all mounting hardware?
Will it put up with high airspeeds (210mph for the RV-6's VNE, more for RV7s, 8s and 10s).
How long can the lead be?
What is the end connector?

Cant say its definitely waterproof but I use petroleum jelly on the interface as a barrier.
It doesn't include the mounting hardware but this is in the list above.
I use an aluminium ground plane about 6*8cm to spread the load on the inside and a penny washer on the outside. The airframe is then the earth plane as you say and is brilliant.

You can get the extension leads from pilotawarehardware.com and one should be long enough. Its in the list

The end connector is SMA

Speed. If you are flying at this kind of speed then you may want to log at a more flexible antenna which will bow slightly with the friction but works well. There are available from Paddy Magee <paddy@industrial-remotes.com> Paddy will build you  tuned antennas one for pilotAware 869.5MHz and one for 1090MHz. They are very good.


Next question is whether to mount the above monopole on the topside or underside of the aircraft?
Has anyone tried either, and with what results?
Is both, diplexed, an option?

Bottom works great for me and makes the cable runs easy also keep it out of the wet somewhat.

I don't know about duplexed - I haven't done it - would this not affect the output impedance? It would be great if you could as this would improve efficiency in all directions.

Anybody have experience/solutions for any of this?
I am reluctant to drill holes in the plane without any kind of idea as to whether it is a good position or not.
Presumably other RV's, Sport Cruisers, Zenairs and other low wing, highish turtledeck metal aircraft have similar issues.

I would have no hesitation to drill the holes as the results are very worthwhile, but make sure you get the right authorisation from the LAA if that is your licensing authority.


Cheers

Keith




Robski

Re: P3I Antenna Location in metal aircraft
« Reply #2 on: October 11, 2016, 03:16:12 pm »
Thanks for the post. I will proceed accordingly!

Speed I mentioned is VNE. Don't normally go that fast - just once a year for the flight test. Still don't want damage from that one occasion, though.
Normally cruise between 140-160 mph, depending on mood, schedule, daylight and fuel burn.
Rob
If the good Lord had intended man to fly He would have given him more money.

JCurtis

Re: P3I Antenna Location in metal aircraft
« Reply #3 on: October 11, 2016, 06:32:05 pm »
The underlying RF chipset used in the Bridge does have support for antenna diversity, although the module currently used doesn't itself support it. This takes the RX from two antennas and chooses the strongest signal at any given time, an RF solid state switch is used to determine which antenna is used to transmit. So if you had antenna top and bottom you could transmit alternately between the two antenna.

You can't really just hook up two antenna directly, as you would need to disconnect one when the bridge transmits.
Designer and maker of charge4.harkwood.co.uk, smart universal USB chargers designed for aviation.  USB Type-A and USB-C power without the RF interference. Approved for EASA installs under CS-STAN too.

Ian Melville

Re: P3I Antenna Location in metal aircraft
« Reply #4 on: October 11, 2016, 09:29:53 pm »
That sounds interesting for perminant installations.

Richard W

Re: P3I Antenna Location in metal aircraft
« Reply #5 on: October 12, 2016, 12:09:33 am »
The underlying RF chipset used in the Bridge does have support for antenna diversity, although the module currently used doesn't itself support it.
...
You can't really just hook up two antenna directly, as you would need to disconnect one when the bridge transmits.

JC, that is very interesting. Please could you elaborate as to why it is not possible to TX to two antennae. Is it phasing?

JCurtis

Re: P3I Antenna Location in metal aircraft
« Reply #6 on: October 12, 2016, 10:11:38 am »
The underlying RF chipset used in the Bridge does have support for antenna diversity, although the module currently used doesn't itself support it.
...
You can't really just hook up two antenna directly, as you would need to disconnect one when the bridge transmits.

JC, that is very interesting. Please could you elaborate as to why it is not possible to TX to two antennae. Is it phasing?

There is phasing, splitting of power, loss of effective radiated power at both antenna, altering the load the transmitter actually 'sees' etc.
Then look at what the receiver 'sees', rather than a single stream there will be issues with the phase at the TX antenna, plus the different distance between the transmit antenna and the receiver also introduces phasing.

The main reason for diversity is to help with frequency-selective fading due to multipath propagation, where the signal is bounced around.  This is what MIMO systems do, they have multiple antenna but the TX transmit the same data but with a very slight delay between them, so help counter the fading from the signal bouncing around. 

Generally in the air there is no issue with buildings and walls creating lots of multi-path signals to worry about - only the potential of an airframe. 

Remember that an antenna top or bottom of metal skin aircraft only attenuates the signal for someone directly above or below, as soon as the other aircraft is a short distance away the area of reduced reception reduces.  All that really happens is that reception at range decreases, you would 'see' another aircraft when they got closer.

The world of RF is a complex beast, I spend time generally trying to avoid turning things into transmitters.  I'm sure there will be some RF types on here who can describe the complexities far better than me!
Designer and maker of charge4.harkwood.co.uk, smart universal USB chargers designed for aviation.  USB Type-A and USB-C power without the RF interference. Approved for EASA installs under CS-STAN too.

Richard W

Re: P3I Antenna Location in metal aircraft
« Reply #7 on: October 13, 2016, 12:25:11 am »
Thanks for that JC, very helpful.

T67M

Re: P3I Antenna Location in metal aircraft
« Reply #8 on: October 13, 2016, 01:19:19 pm »
MIMO actually transmits different data from the various antennas with very complex encoding so that the entire message can be decided from "a bit of this and a bit of the other". It's not just the same data with a time delay - that's TxDiversity, not MIMO.

Robski

Re: P3I Antenna Location in metal aircraft
« Reply #9 on: November 22, 2016, 02:56:58 pm »
The world of RF is a complex beast...
I do understand, hence asking the questions in the first place.

I used to play with CB radios (27 Mhz) when I was a kid, making longwire antennas etc.
It taught me a moderate amount (SWR, propagation patterns, polarisation etc) but opened my eyes to just how much I didn't know (such as the way the characteristics of transmitters and antennas change with frequency).

Thanks to everyone for the input!

Going to resist the urge to get the drill out for now and try the dipole up higher in the screen near (not next to!) the roll-over bar and strut. That location has worked very well for GPS antennas.
Rob
If the good Lord had intended man to fly He would have given him more money.