best antenna

[F-EGLF1]

There is really little need for building (or buying) antennae with "gain"
Aircraft fly in essentially a hemisphere over your head...

Actually they don't fly in anything like a hemisphere, I can detect aircraft out to 300+nm in all directions other than straight up! I suspect that if they flew at that height the ISS would be considered a collision risk��
Antenna don't require much gain straight up as the distance to an aircraft overhead is much less than one on the horizon, that is where you need the gain.

[rederikus]

What you say is true for a ground plane antenna. If you used a simple dipole then it would be as you say, gain in one place would result in a loss in others. The classic cardioid pattern. The length of the antenna is critical because it resonates and the required frequency. In this case at 1090Mhz. This amplifies the signal just as a guitar string makes a noise of (mainly) one note as it is plucked on a particular fret. The amplification is not caused by an amplifier. It is only caused by resonance. It also rejects other frequencies (I am ignoring harmonics here) and so also acts as a filter. This is what you describe I think.

Consider a collinear antenna where there are multiple antennas all independently resonating and producing signal. The antenna is vertical so there is no loss of signal anywhere in the hemisphere. There is an effect wheregenerally the more elements you introduce, the larger your hemisphere becomes at somewhat the expense of nearer signals. Thus an antenna of this type can pick up signals from further away than a simple ground plane antenna with just one receiving element. This is expressed as dBi (decibels relative to isotropic radiator). An isotropic radiator is (I think) considered here as a point source and I assume carries a value of 1. The multiple element signals are additive and, naturally since bigger numbers are easier to sell the marketing people tend toward using dB instead of dBi as a "gain" figure.

I have built various 1090Mhz antennas and have had varying positive results when compared to the original non-ground plane. I first used a tomato can underneath the stick antenna. This worked much better when I connected the feeder shield to the can and formed a real ground plane - duh. I then made a spider. Better still. Better here is defined (by me) to mean increased range in all azimuths. I built an 8 element collinear and this first try increased my range by nearly double. It is still my best antenna. Encouraged I moved on to a 16 element collinear. Not so good as the original 8 element. Since then I have built several more collinears and none have given the range of my initial effort.

What it has done is to convince me that I can see aircraft further away with certain antennas than I can with other. My conclusion is that the better the antenna, the further I can see given the same antenna height and the same receiver.

I therefore think that an antenna that produces signals from further away may be defined as gain withing the hemisphere relative to either an isotropic point or a (however bad) reference antenna.

[Rooster]

There is really little need for building (or buying) antennae with "gain"
Aircraft fly in essentially a hemisphere over your head... so a 1/4 ground plane is the best for overall coverage IMHO - antennae with "gain" dont actually have ANY gain whatsoever... they simply redirect the radiation pattern, ALWAYS at the cost of coverage elsewhere... Imagine it as a torch bulb, visible from all angles - now add some "gain" in the form of a reflector... yes it LOOKS brighter - but only in the one direction.

[rederikus]

I would just add a kit like this and remove the switch. I had a switch completely destroy my AIS reception on one site, you never know which ones are good or bad...

The switch will not be staying. It is there because I am currently running two stations. Main, T-KCLT3 only gets known good upgrades once they are tested and proven working on my Test station T-KCLT19. Once I have the setup as good as I can get it then I will drop back to a single system with a single CAT5 cable going into one single Raspberry Pi3. The switch will then go away. My LAN is nearly all gigabit and I am fairly good with IT type stuff.

Building low-gain antennas like GPs or dipoles is easy, but most people will never be able to build anything above 3dBi gain without instruments, and even then it's hard to get it right. I used to work for a company that had one of the worlds best antenna measuring ranges, so I know...

Making antennas is fun and I got lucky with the first collinear type I built. It is still the best antenna I have. The lack of high quality measuring equipment is a major stumbling block. My oscilloscope only works up to 30Mhz so it is useless for ADS-B. I know that I must be doing sort of OK since my station T-KCLT3 is currently #2 in Charlotte NC, where I live. However I am not sure if that means I am doing really super well or, just OK-ish if you see what I mean. Many stations here have better range that me but less uptime so it is really hard to find a level.

I am an electronics engineer turned IT manager and now retired. I understand the theory pretty well and have worked in professional satellite ground stations as well as working up masts and aligning Yagis and point to point microwave dishes - A looong time ago. The problem with home built antennas is benchmarking them. I do not fully know what results a "perfect" (no such beast...) antenna would deliver at my home station. I have looked at HeyWhatsThat's, Up in the Air rings on maps and find that I seem to be getting more range than I should in some places but far less in others.

The only way to be sure I'm getting the best from my system is to buy a really good (and expensive) professionally built and tested 1090Mhz antenna. Of course, once I have this as my benchmark standard, I can check it against my home built devices but, then there is no point in doing so as I will now have a very good antenna in place.

[MrMac]

I agree with you that the extra heat is not needed. I would not mind getting rid of the switch entirely. I may ultimately drop back to one station once I have finished playing with antennas and got the absolute maximum range that I can squeeze out of all this.

I would just add a kit like this and remove the switch. I had a switch completely destroy my AIS reception on one site, you never know which ones are good or bad...

https://www.amazon.co.uk/Ethernet-Cable-Economiser-Kit/dp/B000Q6EC0C

I think I am done building antennas.

Building low-gain antennas like GPs or dipoles is easy, but most people will never be able to build anything above 3dBi gain without instruments, and even then it's hard to get it right. I used to work for a company that had one of the worlds best antenna measuring ranges, so I know...

/M

[rederikus]

My LNA + filter http://www.ebay.com/itm/1090MHz-ADSB-Filter-LNA-band-pass-filter-with-SMA-connectors-Mode-S-SAW-aviation-/122360480859?hash=item1c7d40c45b:g~AAAOSw44BYZl4~ arrived this morning so I tested it with my Franklin antenna. The range improved quite a bit but not as much as I had hoped.

I then decided to put an extra element on the end of the Franklin. 20170224_135528.jpg20170224_135545.jpg Once more range increased but it is still not to the limit defined by the HeyWhatsThat 30,000 ft Up In The Air ring.

I think I am done building antennas. I shall wait a couple of weeks and then buy a DPD Productions model.

[rederikus]

The switch was lying in one of my spares boxes. I don't remember where it came from. It had two redeeming factors in its choice. It was there and it was free. I agree with you that the extra heat is not needed. I would not mind getting rid of the switch entirely. I may ultimately drop back to one station once I have finished playing with antennas and got the absolute maximum range that I can squeeze out of all this. I am hoping to do this before the awful heat that descends upon Charlotte NC at the end of June and goes through until mid-September.

I have a Flight Aware filter ready. The last time I used it I saw a drop in range, hence the LNA. Blindly amping signals is not a good idea. It amps the noise and other unwanted signals too. I shall try a number of configurations and gains using the filter, amp, a 10dB filter and of course the Flight Aware USB stick. I also have a Jetvision USB stick so I can play with that too.

What is nice about the setup I now have is that all the connectors are contained within one meter for both receivers and antennas. All connectors are SMA (no RP-SMAs) and I have WiFi for my laptop or tablet. It really now is just plug and play.

[MrMac]

I finally finished my NEMA approved fire proof steel box to enclose both RPi3s and their power supplies, network switch and a 12volt power supply for the LNA once these emerge from the postal cloud.

Nice box. Some comments;

- I would remove the switch, and just use a pair of Cat cable splitters to get 2 separate LAN connections over your existing cable. Many of these switches have problems with interference, and it generates heat that you could do without.

- If cables now can be kept short, it seems unlikely that you will benefit from an LNA, unless it is very low-noise. Try a good filter instead!

Good luck!

/M

[rederikus]

Thank you for pointing this out.

It may and it may not. I read the specs and ordered the LNA anyway. I kind of agree with you. It may well overload the front end of the ProStick's amp. I will try it out and see what happens. You already told me that the built in LAN does not have adjustable gain and it is the receiver that has that function. It is therefore highly likely that I shall feed more level into the ProStick that it can handle. I need to plumb these limits to find just how far I can go.

I also intend trying out a longer Franklin antenna. The construction technique I have (grinding the joined ends to a D shape and soldering) allows me to easily make a Franklin with an extra two elements. I wish to see what that does for me. I'll also need at least one more LNA for this test.

I may get nowhere with this given the problems of my location but, ya gotta try.

[abcd567]

@arederikus:
You are already using a Pro Stick which has an integral 19 dB LNA. Adding another LNA may overload the receiver and worsen its performance.

Please see Pro Stick's Specs on this page:

http://flightaware.com/adsb/prostick/

[rederikus]

I finally finished my NEMA approved fire proof steel box to enclose both RPi3s and their power supplies, network switch and a 12volt power supply for the LNA once these emerge from the postal cloud.
20170220_160837.jpg20170220_160853.jpg

The two RPis (T-KCLT3 & T-KCLT19) are stacked so you need to look closely to see the two FlightAware ProSticks.

WHilst this maneuver eliminated a 21 ft RG6 downfeed, it made virtually no difference to my range. However I am now in the position where I can experiment with antennas easily using short cables and with LNA power easily to hand. I just hope that the 100 degree F + temperature in my attic doesn't cook the electronics. Time will tell.

[rederikus]

@F-EGLF1, Good advice. Antenna calculations are done assuming free air and if the installation does not reflect this then performance usually suffers. I would love to site my antenna outside but it is just not possible due to the local housing association regulations. When I lived in Reading, UK we had a nice empty loft (known as an attic over here). However in the US the attic is used to house the HVAC (Heating Ventilation Air Conditioning) unit. This is a combined ducted air furnace and a huge air-conditioner for the whole house. This device is mostly made of metal. Additionally there are air ducts that have wire wound interiors to move the air around. It is a challenge to achieve 1 metre of clear air around the antenna.

@abcd567, I built a spider 20161231_115359.jpg It did not work very well. I also built a cantenna using the large can of tomatos design. I found that the ground wire of the coax was not connected to the magnetic base of the whip antenna. Once I fixed this performance improved but was not a good as I wanted. My 8 element CoCo seems much better. I now believe that I am never going to get much better performance than I have today. I base this on a HeyWhatsThat panorama HeyWhatThat.jpg I'm near the bottom of a hole here. What HeyWhatsThat shows is pretty much what dump1090 shows dump1090.jpg. This combined with my Polar Plot stats.JPG (8 element CoCo) all seem to show that I am getting about as much range as I can hope for. Almost wherever I look, There are hills in the way AzEl.JPG

Obviously I shall try and improve things but based upon my research, I am not hopeful. My station T-KCLT3 is currently number 2 in Charlotte according to FLightRadar24's coverage. I do not expect this to last as there is F-KCLT2 station who can see far further than me.

[F-EGLF1]

@adsb567 [B]

To this end I am considering buying a DPD Productions ADS-B Vertical Outdoor Base Antenna http://www.dpdproductions.com/page_vhf_air.html#adsbout This claims 9dBi gain so it is probably better than anything I can build. Once this is installed (I cannot have an external antenna where I live) I can see if I can build one that's better.

Don't forget that these and similar antenna require a large area of free space around them, at least 3 feet (1 meter) otherwise their resonant frequency will be shifted significantly and the reception will be seriously compromised.
These are far better suited to exterior mounting, if this is not possible then an empty attic is sometimes acceptable, any nearby walls or metal structures will not only attenuate the signal but could also badly detune the antenna.

[abcd567]

@rederikus
Try these easy things to improve reception (if not yet tried)

1. IMPROVE WHIP (Click Here)
   1. Place the whip antenna (which came with DVB-T USB Stick) on a large food can or metallic plate to provide a ground plane. The tin can/plate has an added advantage that the magnetic base of whip clings to it, preventing whip from falling and keeps it upright.
   2. Cut whip to 52mm (removable part)
   
   
2. MAKE A CANTENNA (Click Here)
   
   
3. MAKE A HANDY SPIDER (Click Here)
   

[rederikus]

@adsb567 I have not failed. I've just found 10,000 ways that won't work. Thomas Edison. What you and your research has shown is what does not work as you thought and you have identified at least two ways that do work.

I have read through all 265 pages of this thread and I'm trying to take your best working efforts and apply them myself.

The problem is that the only reference antenna I have is the little whip thing that came with my first USB stick receiver. I make a new antenna and stick it up. If it gives me more range I keep it. Otherwise i bin it.

To this end I am considering buying a DPD Productions ADS-B Vertical Outdoor Base Antenna http://www.dpdproductions.com/page_vhf_air.html#adsbout This claims 9dBi gain so it is probably better than anything I can build. Once this is installed (I cannot have an external antenna where I live) I can see if I can build one that's better.