PilotAware
British Forum => Technical Support => Topic started by: RobertPBham on August 31, 2016, 12:09:34 am
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Hi folks,
I fly various aircraft from the club and this was one of the reasons I wanted a portable traffic solution and hence PilotAware.
One item I've struggled with is testing the functionality and install. Is there anyway of testing if I have the antennas positioned in the optimal way? On flights I detect traffic but don't know if it is picking up 360 degree traffic or if one of the antennas is shielded by something in the plane.
Thanks
Rob
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Rob,
I am not sure that there is an easy way to do that. At best you would need a second aircraft to fly around you at a set distance, but you won't know who has the shielding issue, if it is observed. You could also do a flat 360 version, at your level by using a second PAW a few miles away, and rotating the aircraft 360 degrees on the ground. But the ground and other objects can mess that up.
Theoretically, if you plot all your track logs on top of each other over a long period, and gaps will show up. To be correct the plot would have to be relative to your heading, and be done in height bands.
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Hi
It's almost a certainty that unless you have an antenna mounted in such a way that it has a clear 360 deg view of the sky from above and below you will have areas of signal attenuation. I would personally be concentrating my efforts to ensure as far as possible that the forward 180/240 deg were going to receive the strongest signal. That's where the most imminent danger is most likely to approach from. Anything from behind is likely to be closing slower. The biggest destroyers of radio signal are large lumps of metal (engines) and bags of water (pilot & passengers), keep as much of these out of the line of sight of your antenna and you should not go too far wrong. As Ian says you still have the problem of the other guys set-up over which you have no control.
Hence all the warnings on the website and in the user manual that PAW is only an aid to your visual lookout.
Regards
Alan
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Hi Ian and Alan,
Thank you for the replies and advice - you have confirmed what I suspected - it's not an easy task to achieve! :-)
But great advice on the position of the antennas - I currently have them hanging over the back seats (PA28) but from your information below there is a good chance that the pilot, passenger and engine will be shielding the signal from the front. I think I'm going to investigate some magnetic Velcro that I can stick to the ceiling - this will then allow me to attach the ADS-B antenna and GPS antenna (I bought the one with a long wire) to the ceiling and hence give a good front view. Although I guess the engine would still be the problem when a plane is in front and below the aircraft.
Is it the ADS-B antenna that detects the Mode C and Mode S? I'm just thinking that I might only need to attach the ADS-B antenna to the ceiling?
Thanks for all your help - great product and support!
Rob
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Rob,
Yes, it is the thinner/ shorter ADSB antenna that does all the 1090 MHz stuff including Modes C and S. It can be shortened (carefully) to about half its length and the PAW made into a more compact package which will fit on most coamings. See here...
http://forum.pilotaware.com/index.php/topic,438.msg5661.html#msg5661
...though there are other alternative threads on this subject.
Have you read the antenna guide here.....
http://forum.pilotaware.com/index.php/topic,400.0.html
Good background for antenna selection and location. Try to keep the antennas as vertical as possible (except the gps which should lie flat with as a good a view of the sky as possible - the coaming is good). There are lots of other good options, e.g using suckers to hold one of PilotAware Hardware's 'Horn Dipoles' onto your glazing for the P3i side of things, which allows this antenna to be easily moved between planes.
Worth a read round to help find your perfect solution.
Regards
Peter
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Hi Peter,
That's really helpful - thank you. I've read the guides and forum post and will review some of the other forum posts that you mention.
In regards to keeping the aerials vertical - I'm sure upside down is fine - ie Velcro strip and then stuck to the ceiling. If I was to use the suckers for the side window in the rear, that would make the antenna vertical - would this cause a significant issue or just best practice? I'm also assuming that it doesn't matter where the Pi unit is located - the aerials (ADS-B specially) being the important factor?
Really appreciate the input.
Thanks
Rob
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Yes, upside down will make no difference. Just try to keep them as near vertical as possible. IIRC from my ham radio, transmit and receive antennas 90 degrees out of alignment theoretically halves the received signal strength - which could have a serious effect on the Mode C/S danger alert thresholds. The location of the PAW itself isn't significant. I have mine mounted up inside my flexwing pod, but use remote antennas (including a remote GPS). WRT the ADSB being more important, remember 1090MHz transponders / ADSB is transmitted at relatively high power, but PilotAware P3i only transmits at 1/2 a watt, so good P3i antenna placement is very important if you want to see and be seen by other PAWs.
Regards
Peter
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Hi Peter,
That's great - thank you! I'll invest in some Velcro and a magnet to mount the ADS-B antenna on the ceiling of the aircraft.
I look forward to spotting some other P3i users out there - there is one very close to Wellesbourne but the signal always shows on the ground - gave me a quick scare when I thought I'd missed something on my visual scan. :-)
Thanks
Rob
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Hi Rob,
Yes, we have quite a few people operating PAWs as Ground Stations, so you need to take care to check the relative altitude. Thankfully you should see them from a fair distance away, so gives you plenty of time to assess the situation.
Regards
Peter
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Rob,
Be careful if you use magnets. Your compass etc......!
Tony
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Good point Tony. There are several posts suggesting removing the magnet (fairly easily done by carefully peeling off the stuck on foil) and using sticky Velcro instead. You could at the same time carefully shorten the antenna coax if you need to - method also described here somewhere.
Regards
Peter
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Great points - thanks.
I'm planning on having the antennas and device in the back of the plane (rear seats) and don't believe the magnetic force would be strong enough to effect the compass in the front. Famous last words! :-)
Thanks
Rob
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As you say, I don't think you'll have any magnetic problems from the back seat Rob. As Tony says, always worth checking though. I remember when I fitted my first 'gps' a Memory Map simple moving map with no alerts whatever running on a car Road Angel unit. All was fine until I turned on the external power and saw my compass turn through about 50 degrees!!
Regards
Peter
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Having the antennae sitting on the coaming is as good a place as any I would suggest. I have my whole unit up there, antennae included.
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Hi to all the Radio Experts,
Would it be possible to have two antenna connected together somehow - One on the top of the fuselage and one underneath the fuselage. What would be the technical difficulties?
Thanks - Great product.
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You can phase two antennas by feeding each antenna to a tee with 75ohm coax (multiple of odd 1/4 wavelength lengths of coax).
From the tee, use 50 ohm coax to the transmitter or RX.
But the question is, with PAW do you need to?
I was getting Pi3 traffic reports at 30KM+ with the standard antenna sat on the dash.
ATB
Deker
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I think the idea is that by using two antenna, they can be placed to cover blind spots due to engine and the bag of water.
Never tried what you suggest, but am very weary of faffing around with stuff that transmits. Get it wrong and pop goes your bridge unit.
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Hi Guys,
Deker is correct in his advice. I did quite a bit of 'fiddling' with multiple stacked 'yagi' antennas in my Ham Radio competition days. In those days I was regularly playing with 400Watts of RF at HF, VHF and UHF. I still have some of the hi-tech matching units in the shed that we built to combine the antennas. Unfortunately, the maths to build them properly is fairly complex and you need to get it just right to ensure a correct impedance match to the output stage of the transmitter or all is for naught!
As you say Deker, with P3i reception from up to 30k out with a simple antenna fit, you would need to be very unlucky for a rogue aircraft to approach all the way in with your engine(s) / body(ies) between your respective antennas.
Regards
Peter
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Having had my PAW for a while I thought it was time I got it fitted and took it airborne?
Looks like the link to the antenna placement guidance is broken, but from a quick look/read
around it seems a simple test would be to use a portable battery pack with it all sat on the top of
the coaming (top of instrument panel?) with the small aerial stuck down (with a velcro pad)
in the middle of the top of the panel and with both aerials vertical? Hopefully this won't be in the
way too much!
I have a fixed wing microlight (EuroFOX) so have limited space and want to find a home for it
where it doesn't get booted everytime I climb in and out!
On a different note, I have noticed when ground testing that the ADS-B 'counter' shown on the web
interface sometimes freezes - when I unscrew the aerial a bit and retighten it, it starts counting again,
is my aerial stuffed?? I like the idea of shortening the cable and the aerial but don't want to start cutting
anything until I have seen it all working - I was hoping that I could have a look at my recorded track on
FlightRadar24 or have I missed the point somewhere? Is this only possible when you are hooked up to
the transponder and transmitting your position? (which might be another issue as I have a Funke TRT800
and I am not sure if this will work with the PAW?)
Regards
Chris Parsons
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Having had my PAW for a while I thought it was time I got it fitted and took it airborne?
Looks like the link to the antenna placement guidance is broken, but from a quick look/read
around it seems a simple test would be to use a portable battery pack with it all sat on the top of
the coaming (top of instrument panel?) with the small aerial stuck down (with a velcro pad)
in the middle of the top of the panel and with both aerials vertical? Hopefully this won't be in the
way too much!
I have a fixed wing microlight (EuroFOX) so have limited space and want to find a home for it
where it doesn't get booted everytime I climb in and out!
Hi Chris,
Pretty much all correct. Remember the aerials need to be vertical, but can be hung from the roof, or in the Eurofox will probably work fine fitted in the cockpit behind you. In fact with a front mounted engine, higher up and further back is usually better.
On a different note, I have noticed when ground testing that the ADS-B 'counter' shown on the web
interface sometimes freezes - when I unscrew the aerial a bit and retighten it, it starts counting again,
is my aerial stuffed??
The ADSB counter will stop if you are not receiving any aircraft transmissions. This can be for many reasons e.g. there just aren't any ADSB aircraft within reception range and does not necessarily mean there is any problem with your system.
I like the idea of shortening the cable and the aerial but don't want to start cutting
anything until I have seen it all working
Good call - no problem in trimming the 1090MHz antenna and cable but make sure everything is working well first
- I was hoping that I could have a look at my recorded track on
FlightRadar24 or have I missed the point somewhere? Is this only possible when you are hooked up to
the transponder and transmitting your position? (which might be another issue as I have a Funke TRT800
and I am not sure if this will work with the PAW?)
Regards
Chris Parsons
Correct - you will only appear on FR24 if you are transmitting Mode 'S' from a transponder - and then only if you are in an area where FR24 has effective 'multilateration' known as MLAT, which means multiple receiving stations so they can triangulate your estimated position from your Mode 'S' signal - or if you are TRANSMITTING ADSB - which PilotAware does NOT do directly, though it can be used to supply a GPS signal to your Mode 'S' transponder to make this ADSB out. Pretty sure you will be OK - try doing a search on 'TRT800' from the forum Home Page - lots there to read.
Regards
Peter