Author Topic: external antennae  (Read 407 times)

skyboy999

external antennae
« on: January 05, 2022, 02:23:18 pm »
Vector currently shows poor coverage in 8 o'clock to 2 o'clock area which is consistent with where my classic unit is presently mounted. As a result, I am considering external aerial(s). Couple of questions to help me:
1) I'm showing perfect ADS-B coverage but, presumably, this is from my transponder rather than PAW?
2) However 'ModeS' option shows nothing which makes me question above?
3) If I go down the external aerial route, I would need a ground plane, and presumably, a different one to that which my transponder uses. Could I use a separate ground plane for both PAW aerials?
Thanks

neilmurg

Re: external antennae
« Reply #1 on: January 05, 2022, 03:29:58 pm »
1 - yes
2 - it doesn't for me either, I presume as Mode S has to be multilaterated, the display was discontinued as not provably accurate
3 - Aluminium aircraft use the aircraft skin, - so - I guess 1 ground plane is OK. Keep away from your ADSB aerial at, least 90cm, and away from each other

Others more qualified will be along with more definitive replies...

PaulSS

Re: external antennae
« Reply #2 on: January 05, 2022, 03:33:35 pm »
1) I'm showing perfect ADS-B coverage but, presumably, this is from my transponder rather than PAW? If you have ADSB Out through a Mode S transponder then, yes, it will use the transponder antenna. If you're talking about ADSB In (which you are when considering Vector) then, no, PAW won't use the transponder antenna but the ADSB antenna plugged into your PAW. ADSB are much stronger signals than PAW etc, so are easier to receive. If you only have the room for one external antenna then make it the PAW antenna (Tx/Rx) and leave the ADSB antenna (Rx only) where it is.
2) However 'ModeS' option shows nothing which makes me question above?ModeS doesn't show anything on Vector or the ATOM station for anyone. I think it's a facility that was included in the design of the app but not yet used.
3) If I go down the external aerial route, I would need a ground plane, and presumably, a different one to that which my transponder uses. Could I use a separate ground plane for both PAW aerials? Yes, you would need a separate one to the transponder because you want to distance the antennas as far as you're able from the relatively powerful transponder transmission. The two PAW antennas can use separate ground planes. One is for the PAW Tx/Rx and one is for ADSB Rx only. You want to get the ADSB Rx away from the transponder antenna because they're both using 1090 MHz and the transponder can swamp the ADSB Rx. They don't need to be massive distances (i've heard 20 cm bandied around) but the further the better. As a very, very rough example, I have PAW under the bum of the left seat of a Eurofox, the transponder under the right knee (ish) and the ADSB In under the bum of the right seat. They all have their own aluminium ground planes. 

skyboy999

Re: external antennae
« Reply #3 on: January 05, 2022, 03:58:31 pm »
All very helpful. Thanks guys.

Just to build on PaulSS' reply, I had assumed the 'ADSB' filter in Vector was showing the output from my transponder. Are you saying that it is showing the ADSB input to PAW from its ADSB ant?

neilmurg

Re: external antennae
« Reply #4 on: January 05, 2022, 04:27:12 pm »
Vector shows where signals are received by the ATOM Grid ground stations, with range and relative direction (from the aircraft point of view). ie
PAw, Flarm, ADS-B, CAP1391(SE2) output devices on the aircraft.
The main a/c I fly that doesn't have ADS-B out doesn't show any Vector ADS-B, it shows the CAP1391 that we have.
The other one that has ADS-B out does.

My Vector's tend to show poor detection behind, due to people in the way. I tune my antenna position for looking forward

PaulSS

Re: external antennae
« Reply #5 on: January 05, 2022, 07:38:03 pm »
No, sorry Skyboy, I can see how what I have written in 1. would cause confusion and sounds like the utter nonsense it is. That's the trouble when I am thinking of Vector and ATOM station coverage at the same time (I had literally been looking at my ATOM stats moments before). Please see what Neil wrote.

Vector will show your ADSB Out and this will be through your Mode S transponder (and, therefore, your transponder antenna) or from a dedicated ADSB unit. If you were ADSB Out via a CAP1391 device then, obviously, the performance of that will be shown on Vector under 'CAP1391'. This will not be through your transponder antenna.

skyboy999

Re: external antennae
« Reply #6 on: January 05, 2022, 08:54:30 pm »
Great. Thanks.
So if Vector reports strength of signals transmitted from my aircraft, do I just assume that any weak spots reported will similarly be weak spots for reception? If so, is there any way of checking the effectiveness of my PAW ADSB placement (without switching off my transponder which would be illegal)?

steveu

Re: external antennae
« Reply #7 on: January 05, 2022, 09:13:58 pm »
So if Vector reports strength of signals transmitted from my aircraft, do I just assume that any weak spots reported will similarly be weak spots for reception? If so, is there any way of checking the effectiveness of my PAW ADSB placement (without switching off my transponder which would be illegal)?

Vector will show FLARM(gliders only), ADS-B and PAW tx. Your ADS-B tx (transponder) will be from a different aerial to your ADS-B rx (PAW 1090). So the reciprocal can't be assumed. And they should be some distance apart...

You might have some idea of ADS-B rx by running your PAW log file through aircrew, but it won't give you that polar analysis. You'll also have some idea of ADS-B rx on the Radar screen.

The home screen on your PAW will tell you how many ADS-B rx hits there are...

But as ADS-B is so high power(260/130W), I doubt there will be an issue. The issue might be with CAP1391(20W), as they are much lower power, and the popular one does not have external aerials.

neilmurg

Re: external antennae
« Reply #8 on: January 05, 2022, 10:12:58 pm »
...CAP1391(20W), as they are much lower power, and the popular one does not have external aerials...
that's on my aircraft, I'm not a fan of it, better to get ADS-B for maximum visibility and use PAw for maximum awareness

exfirepro

Re: external antennae
« Reply #9 on: January 06, 2022, 10:17:58 am »
Hi skyboy,

Vector reports what we are seeing from your aircraft via the ATOM-GRID Ground Station Network.

The reports are based on data from the past 30 (?) days or so, unless you Filter any of the reporting dates out (which allows for comparison after setup changes). For best quality reports, you need to have been flying for as many days as possible out of the last 30, and ideally in range of as many Ground Stations as possible. The more Ground Stations and the broader distance and bearing range from each, the more detailed and reliable the report.

As advised above, ADSB is a DF17 report from a suitably equipped Mode S - ES transponder. DF18 devices (such as SkyEcho) are reported separately under the CAP1391 tab. Pure Mode S (i.e. No ADSB-Out) was reported when Vector was first developed, but we had to suspend this as it was taking up a massive amount of data storage and was having a negative effect on other parts of the network. P3i is reported from your PAW transmissions and Flarm from your Flarm transmitter if you have one.

You don’t say what type of aircraft you are flying. Even in my flexwing, I am getting significantly better reports since changing to external antennas mounted beneath my aircraft. As stated by the others these antennas do require a ground plane (which can be common to all, as in the skin of a metal bodied aircraft), but be careful when choosing positions to be aware of potential obscuration points - such as heavy metal undercarriage legs and try to keep the antennas as far apart as reasonably practicable.

If you let us know the aircraft type, we can probably help point you in the right direction and avoid any known pitfalls.

Best Regards

Peter

skyboy999

Re: external antennae
« Reply #10 on: January 06, 2022, 01:47:23 pm »
It's a Eurofox. I note PaulSS' placements but I have less space to play with due (912iS) fuel pumps and servos for autopilot occupying the space under P1 seat. My transponder ant lives under pax seat with it's ground plane. PAW is presently living near side window pax side on baggage bay slope. I'm thinking I could possibly accommodate a 200cm ground plane disk for the P3i further aft and leave the PAW ADSB stubby where it presently is (cross tubes top of baggage bay). This all based on evidence that my reception of other aircraft (when flying in loose formation) is sketchy especially for those without transponder.
I tried a P3i internal dipole stuck to windscreen pax side but this seems to be worse than the one which screws directly into the classic. I suppose I could try moving that around if anybody has had success in a Eurofox.

neilmurg

Re: external antennae
« Reply #11 on: January 06, 2022, 03:14:07 pm »
200cm!

PaulSS

Re: external antennae
« Reply #12 on: January 06, 2022, 06:45:02 pm »
Skyboy,

I have a Eurofox. Please check your PMs, as I have left you my number, where we can discuss it all in much more detail without typing  ;D

skyboy999

Re: external antennae
« Reply #13 on: January 08, 2022, 02:36:26 pm »
Thanks Paul for chat and all your help. As soon as it gets warmer, I'll have play and see how I can improve things.

....and it should, of course, have been 200mm

C172

Re: external antennae
« Reply #14 on: January 15, 2022, 02:46:54 pm »
Vector will show FLARM(gliders only)

Small point, but for the sake of accuracy RAF Prefects and some other training aircraft are FLARM equipped.