PilotAware
British Forum => General Discussion => Topic started by: PaulSS on February 06, 2018, 07:31:33 am
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Some time ago I bought one of these antennas for the ADSB reception side of things:
https://www.ebay.co.uk/itm/ADS-B-RadarBox-SBS-RTL-SDR-1090MHz-ADSB-Magnetic-Antenna-Aerial/391638799640?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908103841%26meid%3D67593422c47a48f18d150eb3f8870d9e%26pid%3D100227%26rk%3D1%26rkt%3D5%26mehot%3Dlo%26sd%3D391638799640%26itm%3D391638799640&_trksid=p2054502.c100227.m3827 (https://www.ebay.co.uk/itm/ADS-B-RadarBox-SBS-RTL-SDR-1090MHz-ADSB-Magnetic-Antenna-Aerial/391638799640?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908103841%26meid%3D67593422c47a48f18d150eb3f8870d9e%26pid%3D100227%26rk%3D1%26rkt%3D5%26mehot%3Dlo%26sd%3D391638799640%26itm%3D391638799640&_trksid=p2054502.c100227.m3827)
I got this because it has an SMA connector, which will go nicely with the Flight Aware ADSB dongle I have. SMA connectors were bought in order to ensure less risk of the connections coming apart, in what will be a permanently mounted PAW.
The antenna above is going to live inside the tail end of a fabric covered aircraft. It has a 30mm magnetic base.
My question is (drumroll), does this antenna need a ground plane to sit on? If so, I assume it will be about 140mm square (1/4 wavelength being 69mm).
I'm asking because I've become a bit confused with too much reading. I know I need a ground plane for a transmitting antenna (such as my transponder) but I really don't know if I need one for a receive-only antenna.
I've also been reading that the ground plane (when used) should have the same dimensions as the antenna length which, although a multiple, seems to be at odds with other wise words that counsel 1/4 wavelength.
I know I've done too much research and have just confused myself, so maybe someone could set me straight (using simple words). Thank you :).
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This antenna doesn't need a ground plane.
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Thanks Keith :)
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Sorry my previous post was short.
The antenna that you have bought is just a higher gain version of the one supplied with the PilotAware Classic but with an SMA connector rather than an MCX.
If you mount this vertically in the back of the Eurofox when you build it, you will, as The Who said see for miles and miles and miles and miles and miles. 1090MHz that is.
If anyone has a metal aircraft then a monopole is better as the whole aircraft acts as a ground plane. On my Sportscruiser I use a monopole tuned to 1090 and receive ADSB signals over 200Km away when I am in the hangar. Absolutely over the top for electronic conspicuity but great to know that you have a strong signal.
If anyone wants a 1090 tuned antenna for metal aircraft drop me a PM.
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No need to apologise; you did exactly what I asked, with a concise and accurate answer. I am grateful for that ;)
However, I do appreciate the extra information and the news that my proposed plan is a viable one. All my reading here has convinced me of the receiving capabilities of the powerful ADSB signals, so I think your Who reference may well prove true. The P3I antenna is going to be externally mounted and will have its own ground plane on the opposite side of the aircraft from the transponder antenna (basically, one underneath each seat). I realise there will be compromises to be made regarding the siting but I think this will be the best position I can manage, whilst ceding to my OCD which would prevent things being stuck on the windows :)
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Paul
That is exactly the correct thing to do. the bigger the ground pale the better. This is what I do in my sports cruise and get 40+Km on PAW and 200+ on ADSB more than enough for EC.
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Hello Paul,
Is that aerial you've bought from eBay a 5/8 over 1/4 wave co-linear? It looks like it from the photo on eBay. If so, then I am pretty sure it should be used with a groundplane as the radiation pattern will be severely affected without one. However as Keith mentioned, it will probably provide signals that are too far away to worry about for your purposes anyway.
Any groundplane should be a minimum of 1/4 wavelength at the operating frequency and the bigger the better within reason. A larger groundplane has the effect of lowering the radiation angle and effectively acts as a mirror for the radiating element. A groundplane is not just required for a transmitting aerial, but also for a receiving-only aerial as they both work in exactly the same way.
You mention that you are going to mount the P3I aerial on a groundplane, but I think I am right in saying that this aerial (if it's the one supplied with the purchased PA unit?) is a halfwave sleeve-dipole so doesn't need a groundplane. The same is also true for the supplied 1090MHz aerial as that's also a sleeve-dipole.
https://www.pulseelectronics.com/antenna_basic_concepts/
Frank,
G0CFD
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Hi Frank,
Thank you for your advice in my quest for knowledge. I'm afraid I have no idea of the type of antenna. It says it is tuned for 1090MHz but apart from that I am ignorant. I can't even look at it in detail because it currently resides at my sister-in-law's house in England, whilst I'm still in Oz. To be honest, I don't think making it a ground plane will be a problem as it'll give it something robust to sit on, rather than balancing on the steel fuselage frame. From what you've written and I've read previously, if it is mounted on a sheet of steel (for instance) then there is no need to ground the antenna shield to the ground plane as it is not transmitting. The ground plane is only been used to better reflect the wigglies into the antenna. So, I cut out a decent sized bit of metal and attach the antenna to it using its magnetic base and all will be well.
I am using a different antenna for the P3I. I'd read up all I could about dipoles, monopoles etc and the instructions for permanently mounting the PAW but decided to go for the antenna below as it is a very neat unit and is meant to perform well.
https://www.gps.co.uk/antenna-exterior-gav-868-flarm/p-0-2024/ (https://www.gps.co.uk/antenna-exterior-gav-868-flarm/p-0-2024/)
In the photo below you can see the ground plane that is normally used for the transponder. I shall have one of those for the transponder and another, under the left seat, for the P3I antenna.
Thanks again for your input; every day is a school day ;D
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Hello Paul,
OK being in Oz - we are suffering the depths of winter at the moment and the temperature here in south Lincolnshire is forecast to drop to about -5 degrees Celsius tonight!
The aerial certainly looks like a colinear-type and the magnetic-base electrically couples the earthy-side to the groundplane by capacitance. In this instance there is no need for a physical electrical connection, so just attaching it to a steel sheet is sufficient. The effect of the groundplane is exactly the same whether the aerial is for transmitting or receiving. The only real difference is that if it's used for transmitting, the electrical matching of the aerial (high VSWR) to the transmitter may be bad enough to damage the transmitter output stages. That's why you've seen comments that differ for transmitting and receiving aerials. For a receive-only setup, although the effect on radiation pattern and electrical matching is exactly the same, the receiver will still work but not optimally. It's surprising what you can use for an aerial to receive radio signals, but when you compare what you are receiving on a piece of "damp string" to a properly configured and tuned aerial there is usually a vast difference.
As for the GAV-868 aerial, I think it must be a shortened 1/4 wavelength - the website doesn't give much away other than the height of 70mm which is far too short for a 1/4 wavelength at 868MHz. A 1/4 wave at 868MHz is about 86mm uncorrected. That would mean it needs a groundplane, so yes, mounting it on an alloy groundplane is perfect. It appears to be designed to mount directly onto a typically metal airframe.
The GAV-868 seems expensive for what it is. A standard 1/4 wave aerial cut to the correct length (about 82mm corrected) would work just as well if not better than the GAV-868 (larger aperture), but then the GAV-868 can be fitted with no configuring and it's guaranteed to work out of the box.
You mention mounting the aerials within a couple of feet of each other, but I'm not sure about the minimum separation required between the transponder aerial and the P3I one. A transponder transmits typically 100 or 200 watts or so depending on model and class and I'm not sure if the P3I RF input stages could handle this sort of power close by repeatedly, so does anyone else reading this (Maybe Keith?) have any thoughts about aerial location/separation?
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Frank,
Sound advice! IIRC the general advice for antenna placement is 'at least a 1/4 wavelength apart' (which at the longest wavelength we are concerned with here is still actually pretty close).
I have never experienced any issues with running the P3i (869MHz) or 1090MHz SDR antenna within a few feet of my ADSB / Transponder antenna (approx 100watts out from a TT21), though when advising / assisting others I do try to keep them as far apart as I can (not easy in a flexwing) and would always suggest keeping them as far apart as is reasonably practicable, bearing in mind our other priorities and constraints.
Regards
Peter
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Thanks again chaps :) I have read and inwardly digested the advice on distancing antennas (both in this thread and the countless others I've interrupted) and will certainly try to space them as widely as possible. As ever, the constraints of mounting the ground plane etc leads to the inevitable compromise. The transponder and ADSB will be miles apart, so no snags with the transponder swamping the ADSB reception. Unfortunately the transponder (Trig TT21) antenna will be a lot closer to the P3I but I'm still pretty sure I can distance them by a little more than the 1/4 wavelength of the P3I, at approx 34.5cm. If I can get them further apart I will.
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Yet more antenna questions (not fixed installation) .
I'm contemplating changing the ADS-B antenna (standard PAW supplied one) for one of the antenna listed below:
NooElec ADS-B Discovery 5dBi (High Gain) Antenna Bundle - 1090MHz & 978MHz
19cm (7.5") long, 5dBi, with a VSWR of 1.5:1 or better
NooElec ADS-B Discovery 3dBi Antenna Bundle - 1090MHz & 978MHz
11cm (4.25") long, 3dBi, with a VSWR @ 978MHz of 2:1 or better.
In view of the relatively high power of 1090 MHz ADSB, Mode C and Mode S signals will the shorter
antenna (11cm (4.25") long, 3dBi) be a better choice?
Mike
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Mike,
Kind of depends on how you are connecting it to the PAW. If you intend to attach it direct, I'd go for the 3dBi which will be lighter and will therefore place less strain on the MCX connector on the SDR Dongle and the USB into the PAW. If you are putting it on an extension lead, this is less of an issue, though again the 3dBi version should be absolutely fine and will draw in aircraft from well past the distance we need to see them.
IMHO, at 1090 MHz, higher gain antennas are only necessary for the 'Plane Spotters' (no disrespect intended). Many of us have already cut down our existing 1090MHz antennas to 69mm or so without any detriment.
Regards
Peter
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Peter,
Many thanks for the valuable information. I will go ahead with the smaller antenna at 3dBi
Mike
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I think, yet again, that I may be over-complicating things so just want to confirm one point and ask another question.
Above I wrote of the plan to use a fancy ADSB antenna and discovered that it does need a ground plane. Then I was looking at Mike's post and thought of a different solution (at this point everyone slaps their foreheads). As I understand it (please let me know if I'm wrong) an end-fed dipole does not need a ground plane. I still intend to mount the ADSB antenna inside the rear of a fabric-covered fuselage but, instead of having a ground plane attached (somehow) to the frame and the fancy antenna on top of that, I thought an end-fed dipole could be vertically mounted so much easier with a clamp and would do the same job. Is this correct?
And then I read of a USB extension cable being used betwixt the PAW and an ADSB dongle and I thunk a bit more :o I have a Flight Aware ADSB dongle. At one end is the USB connector for the PAW and at the other is an SMA connector to the antenna. Does anyone know how a USB extension cable and a coax cable compare, since I thought of a couple of scenarios? In one scenario the ADSB dongle would plug into the PAW and the coax cable would then lead to the back of the aircraft and the antenna. In the second scenario, imagine a very short coax from the antenna to the ADSB dongle, which is now mounted close-by the antenna. From the dongle, instead of a coax running to the PAW (which is behind the panel), a long USB cable would be used.....I really should see if such a beast exists before I postulate further...... In my imagined scenarios, let's compare a 3m USB cable with a 3m coax cable, of the sort available in the PAW shop (which I just so happen to have). What have I got wrong this time ;D
They do exist: https://www.amazon.com/AmazonBasics-Extension-Cable-Male-Female/dp/B00NH12O5I/ref=pd_cp_147_2?_encoding=UTF8&pd_rd_i=B00NH12O5I&pd_rd_r=TA65QN3ADJ9BJH9DR0SB&pd_rd_w=XQzrO&pd_rd_wg=ZpLng&psc=1&refRID=TA65QN3ADJ9BJH9DR0SB (https://www.amazon.com/AmazonBasics-Extension-Cable-Male-Female/dp/B00NH12O5I/ref=pd_cp_147_2?_encoding=UTF8&pd_rd_i=B00NH12O5I&pd_rd_r=TA65QN3ADJ9BJH9DR0SB&pd_rd_w=XQzrO&pd_rd_wg=ZpLng&psc=1&refRID=TA65QN3ADJ9BJH9DR0SB)
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Paul, you can get some darn long USB leads. I use 20 and 20 metre leads in my job.
End fed dipole clamped to farme with no ground plane should be OK, provided the clamp holds it half wavelength, give or take a bit, away from any metal tubes.
OGN-R stations use a long(10m) USB lead. With the ADSB dongle mounted on the mast. Just a short coax clear to the antenna. This is for Weak FLARM and P3i signals. They are attenuated in the coax, but once digitalised, within reason can be set down any length of USB cable without loss. For ADSB I would prefer to make sure the dongle is accessible, but need not be directly connected to the PAW.
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Well, that's very interesting, so thank you Ian.
I was actually going to attach the clamp to one of the metal tubes of the fuselage, so that kind of scuppers the idea of an end-fed dipole. Back to Plan A with the fancy ADSB antenna and a ground plane I suppose.
I think it is very interesting to know about the difference in attenuation between the two cables and it certainly seems to favour the long USB cable. I can understand the need to have access to the ADSB dongle but it sounds from what you have written that having the signal digitised close to the antenna (by the dongle) and then using a high speed USB 3.0 cable would lead to a stronger signal into the PAW than if it travelled by coax and was then digitised closer to the PAW. One of the things that attracts me to this idea is the shielding on the USB appears to be less susceptible to interference from electric cables etc than coax. I will be trying my very best to ensure any coax cables (radio, transponder, P3I and PAW's ADSB) stay as far away from electrics as I can but this seems to be a neat way of managing the ADSB better.
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And then I read of a USB extension cable being used betwixt the PAW and an ADSB dongle and I thunk a bit more :o I have a Flight Aware ADSB dongle. At one end is the USB connector for the PAW and at the other is an SMA connector to the antenna. Does anyone know how a USB extension cable and a coax cable compare, since I thought of a couple of scenarios? In one scenario the ADSB dongle would plug into the PAW and the coax cable would then lead to the back of the aircraft and the antenna. In the second scenario, imagine a very short coax from the antenna to the ADSB dongle, which is now mounted close-by the antenna. From the dongle, instead of a coax running to the PAW (which is behind the panel), a long USB cable would be used.....I really should see if such a beast exists before I postulate further...... In my imagined scenarios, let's compare a 3m USB cable with a 3m coax cable, of the sort available in the PAW shop (which I just so happen to have). What have I got wrong this time ;D
Paul
Yes this can be done. This is in fact how we do some of the OGN installations when we have a long run and don't have thick CoAx. Using a short length of CoAx minimises attenuation and once the signal is digitised it can be regenerated. We use 10 Metres of USB extension cable to good effect.
However does the distance on your Eurofox justify this? Why not go the whole way and put the Pi in the back as well then you will can have 1 foot of CoAx and no attenuation problems. The 1090 MHz transmissions are very high and will basically be picked up by the proverbial piece of wet string (50ohms of course)
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Why not go the whole way and put the Pi in the back as well then you will can have 1 foot of CoAx and no attenuation problems
HMMmmm, now you've got me thinking ??? This is why I shouldn't read this forum or engage in correspondence; every timeI think I've got stuff sorted out in my head, someone comes up with another good idea.
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How are you going to ensure you have 5.0-5.1v at the Pi?
KISS
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I was thinking of something like the cable below from my Charge4 unit. I am definitely a KISS believer but just examining the different options. If there's a good reason, such as the charge cables being no good due the length, then I'm more than happy to bin an idea.
https://www.amazon.com/Anker-PowerLine-Micro-USB-10ft/dp/B012WHAG7K/ref=pd_sbs_147_5?_encoding=UTF8&pd_rd_i=B012WHAG7K&pd_rd_r=6CH58770N0PQX4MF4Z9B&pd_rd_w=COgyt&pd_rd_wg=6tTTT&psc=1&refRID=6CH58770N0PQX4MF4Z9B (https://www.amazon.com/Anker-PowerLine-Micro-USB-10ft/dp/B012WHAG7K/ref=pd_sbs_147_5?_encoding=UTF8&pd_rd_i=B012WHAG7K&pd_rd_r=6CH58770N0PQX4MF4Z9B&pd_rd_w=COgyt&pd_rd_wg=6tTTT&psc=1&refRID=6CH58770N0PQX4MF4Z9B)
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I was thinking of something like the cable below from my Charge4 unit. I am definitely a KISS believer but just examining the different options. If there's a good reason, such as the charge cables being no good due the length, then I'm more than happy to bin an idea.
https://www.amazon.com/Anker-PowerLine-Micro-USB-10ft/dp/B012WHAG7K/ref=pd_sbs_147_5?_encoding=UTF8&pd_rd_i=B012WHAG7K&pd_rd_r=6CH58770N0PQX4MF4Z9B&pd_rd_w=COgyt&pd_rd_wg=6tTTT&psc=1&refRID=6CH58770N0PQX4MF4Z9B (https://www.amazon.com/Anker-PowerLine-Micro-USB-10ft/dp/B012WHAG7K/ref=pd_sbs_147_5?_encoding=UTF8&pd_rd_i=B012WHAG7K&pd_rd_r=6CH58770N0PQX4MF4Z9B&pd_rd_w=COgyt&pd_rd_wg=6tTTT&psc=1&refRID=6CH58770N0PQX4MF4Z9B)
You don't really want to go over 1m of cable for the power to the PAW, even with a 20AWG cable. At 10 feet in theory the voltage would be down to 4.8 excluding connector losses (which are more than you would think). Charge2 & Charge4 are set to provide a nominal 5.25v, regardless of load, so it would be a bit touch and go IMHO.
That said I have made up some cables with much larger power conductors for testing - so there is potential to make something suitable if all else fails....
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You don't really want to go over 1m of cable for the power to the PAW, even with a 20AWG cable.
Thank you very much, that has put that idea to bed :) As I said; I'm more than happy to take the advice of those in the know and I'm not even going to think about questioning your credentials.
Plan 267: PAW is back behind the panel, with WIFI dongle. Charge4 is also under the panel and probably no more than 30cm from the PAW (maybe less). GPS mousey thing is on top of the coaming. Fancy ADSB antenna is on its ground plane in the boot. P3I antenna sticks out under the aircraft on its own ground plane and almost certainly the ADSB dongle will be behind the panel and plugged directly into the PAW....... but the long USB lead and the ADSB dongle near the fancy antenna does still intrigue me ;D
Okay, enough, I'll shut up now........but for how long ??? ??? ??? ??? ???
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I'd just run a long coax to the ADSB dongle, the loss will not be a problem given the power of the transmissions. That keeps all the active stuff in one place, if needed you could use a short USB extension lead for ADSB dongle and strap it to something for better cooling and separation from the WiFi dongle etc. That may actually help and make the cable routing easier, you can strap the coax, dongle, and usb to something as a unit to prevent issues with any minimum bend radius of the coax etc. and give better strain relief on the connections too.
Its the PAW coax you should try and keep short with good strain relief and ensuring it isn't kinked or bent below it's minimum radius (during or after install), they are the lowest power transmissions so the most care is needed there.
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Good advice and thanks for the short USB cable idea for the ADSB dongle. I agree that would be an elegant way of keeping the temperatures a bit lower around the PAW and making it more flexible in its location (plus less susceptible to wriggling out of the USB slot). All ideas are in the idea box :)
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You could screw one of these:
(https://images-na.ssl-images-amazon.com/images/I/71CNktgnmML._SL1500_.jpg)
Directly onto one of these:
(https://images-na.ssl-images-amazon.com/images/I/81EpXu1FZtL._SY355_.jpg)
Use the USB extension, then use some sort of clamp to mount the SDR thing in the right place, leaving the antenna free above it.
Just a thought.
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STOP IT!!! Now you've got me thinking again ;D ;D
Edited as it did get me wondering:
Ian advised before:
End fed dipole clamped to farme with no ground plane should be OK, provided the clamp holds it half wavelength, give or take a bit, away from any metal tubes.
If one of the end fed dipoles above was attached directly to the ADSB dongle, would it still need to be kept half a wavelength (14cm ish) from any metal tubes? I think it would but I'd just like confirmation. I see now why people like wood frames :-)
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Paul,
It would be fine if you fix (cable tie) the dongle to a horizontal tube, so that the antenna is proud of the tube and vertical.
Regards
Peter
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That sounds good to me and kind of what I was thinking until I read Lee's advice. I was then thinking of having the antenna sticking out on a prong away from the frame to satisfy the separation requirements, but if I could clamp an aluminium 'L' bracket to the frame and then mount the dongle/antenna combo onto that it would be great. Obviously the antenna would be vertical.
I really do need my machine so I stop just talking about this and get on with it!