History & Research about 1090 Mhz antennae

[juangelb]

Hi people.

Once upon a time......  (hahahhha)
I dicovered the existence of ADS-B and quicly toutht ..." This is just for me "
At that time only SBS-1 was in trhe market.....
So, as I did not know anything abou this..... Contacted Kinetics and asked if here, Brazil, SBGR... I will "cath" somthing wit SBS-1 .... (trying to discover if it will worth to buy ..)
Quickly they answered that it would be better to enter to the forum to serch for this info.
I entered.... but "Brazil" did non was there at all.
Then, after some time ... asked again Kinetics, for some info on if I will be possible to catch some flights from SBGR ....
They replyed and asking me to call the local airport (SBGR) and to ask them the info :
 " How many aircraft are equiped with ADS-B Transponders"

Are they crazy ????


Ok, let this aside.....

I some mounths lather discovered a Japanese guy that came here for some days and carried your SBS-1 and reported that with some "restrictions" it worked here.

Desicion was tahek ... So Lets, buy.....


Bought, arrived.... but it catches flights not so far .... HUMMMMMMMMMMMM


Doing a lot of reserch, I fuond a very easy a cheap project to do : (link follows)
http://www.tech-software.net/1090_antenna.php

I worked on this and put the antenna trough the north window 1/2 a meter away....
Excelent reult as many as 240 NM to 45° to 48° ...

But olnly cought flights from 270 ° to 90°, as the window faces this area.....


Here was me ... unhappy again .... Hhqahhhhahhha

I discovered two more people here in the SBGR Area that have radars... and contating them, they told that ther bought an antenna from local manufacturer and it worker very well...

Well, tired on testing, building etc, why I am I working as a crazy..... Its is only necessary to cal the local nauf.
I Bought the "marvelous Antenna", from local manuf.
And when i thought that the sunny days arrived..... Indeed it was a nightmare !
The just bougt antenna performed as 30 % les than above posted link ...

So contacted the manufacturer ( probably a odd one with very large skill on doin antenas for 80 / 40 meters in early 60es ..)

No way.

So during a very tedious weekend... I took a lok on this antenna... Well it is nor working at alll .. ?
So why not to broke and open it ?
So caught a sow ... cut the radome ... and surprise :
Mesuring his internal elemants Coax Collinear, it was clkear that this antenna was "cutted" for 900 to 940 Mhz ... That was why  it performed much less than my homebrew one.

I wanted to stop in wastin tine and effort, but I think thar I have lack of luck....


hAHAHAHHHHAAAAAAAA
Then ..... already with 3 RBs, I started to do experieces with colonear coaxial antennae....
Constructed several of then...


Again, tired on doig experimets and wasting my time....


decided to buy a Wimo, Elad preamp, europenan coax cables.....



Let to continue lather.........

[OKC-Steve]

The antenna that ships with the receiver is all you need to get started.  If it doesn't work out to the horizon, then there are no airplanes squittering Mode-S in your area, and probably no Mode-S radar systems on the ground, or you need to go drive over to a hill with your laptop. Get it out of the bedroom window.  I'd say put it on the roof, but then you lose the portable nature of the device, and also attract lightning (since they are ungrounded).

The squitters all modern airplanes make is short squitters containing just their mode-s address (DF11).  More and more aircraft are squittering ADS-B with and without position (DF17). Probably 80% of commercial aircraft are now squittering DF11, and probably less than 10% are squittering DF17.  Besides squitters, there are the regular Mode-S transponders that only squawk when they are interrogated. These are the source of squawk and altitude for many aircraft.  Squawk codes are only in Mode-S DF5, and DF20, but altitude is in DF4, DF20 (Interrogated Mode-S) and DF17 (Squitter).

The way all antennas work, is that the more gain they produce, the smaller the beam pattern. 30dB gain is great, until you realize it is only in one direction.  You could buy 5 receivers and 5 30 dB gain antennas, and then network the software :-)

[juangelb]

Well, OKC-Steve

I perfecty undsrtand that antenna that ships with RB ansd SBS-1, both are good.
But both are not suited for outdorr use and if so did, and adding alot of coax even the better of the world.... The results will, o course nor be good enoug for I want.

So getting on on the story....
You can see my firts attempts (and one of the best easy and with very good results) : http://www.maquinasvoadoras.com.br/ATC-Maquinas.jpg
The so named Fundo De Panela, project from VK4TEC... worked much better that Comercial ono ar top (Electril 1090)...
The reason was that Elctril sold me a mobile antena for 840-900 Mhz and obviusly this do nor performed as well as an 1/2- - 3/4 - 34 cutted at 1090 !

Next one.... soon
 

[juangelb]

OK ...

Worked for a whole year or more in doing antennae coaxial colliner, from 8 dipoles to 21 dipoles ( 6 Dbs to 10 DBs gain)
All of them performin very well.... But again tired of cutting brass tubes, soldering, mounting, doing holes.... And everytime needing to get "autorization" from condominium to go in place and mount a new atenna...

Few mount ago decided to buy rhe better antenna that was supposedly available on the waorl + Plus an Elad Preamp + DC feeder...
All very expensive.

All arrived, got the "autorization" mounted... tested, tested.... more testing ...
GOT VERY FRUSTRATED !!!!!!!!!!!!!!1
Here, for me, in my evironment ..... Performed much, very much worst even compared with my simpleast 8 dipoles coax colinear HOMWBRIEW

[juangelb]

Supposed to have 6 Dbs gain.....

Well.... going on in my desapointig research, today I decided the same thin as I did with the antenna locally supplied (the one taht did not worked well):

caought a sow add cutted it !!!!!!!!!!!!!!!!!!!!!!1
SURPRISE !!!!!!!!!!!!!!!!!!!!!!!!!!!!1

Now I undesrtando why it performa worst than the simplest one homebrew !!!!!
It has inside a sole board with maybe 1 wavelenht antenna and somthing else...
That is very good to repace original indoor RB antenna for outdoor use, NOTHING ELSE.....
An Thisis kinda of mouting, is (in my opinion)technically  not possible to have any gain in compare with the RB kit antenna.


That´s why any of may homebrew  performed better tha comercial ones.

But alotta peolpe would be courios in undsrtand :^
Why, the hell I need a high gain atenna ????

I´ll tell You.....
1- Because the need of a long coax run
2- This cause alotta loss in the signal, and even when tring to use low loss coax.... is not enough in my case.

Ill put sone pics from the wimo inside board and at least one of a very simple homebrew coax coliner with only 8 dipoles (only 6 dbs ...on paper...)
For You to apreciate and undestand what I am talking about...


Cheers

[juangelb]

Ok Here they are 2 pictures

First one Wimo cutted and showing circiuit board that has apox the size of the inbox original RB antenna.

http://www.maquinasvoadoras.com.br/Homebriew-Wimo-1.jpg

Second picture:
http://www.maquinasvoadoras.com.br/Homebriew-Wimo-2.jpg
 Top to botton:
Homebrew radome
Homebrew coax collinear 8 X 1/2 dipoles plus 1/4 at top
Wimo radome
Wimo 26 cms long circuit board


And I dont know, but maybe for UK can be easy to catch a lotta flights...
But here it is needed to do any kinda magic to have 20 on the screen  !

hahahhha.

I just putted a screen shot on sc forun showing local converage...


Cheers.

[juangelb]

The way all antennas work, is that the more gain they produce, the smaller the beam pattern. 30dB gain is great, until you realize it is only in one direction.  You could buy 5 receivers and 5 30 dB gain antennas, and then network the software :-)

Steve, This is true in talking about Directive antennae.... Yagi, parabolic, an so on.
I´M working on Vertical Omidirectional antennae.

Cheers

[OKC-Steve]

Even with an Omni, if you get more gain, you have to squash the donut shape.  Instead of a perfect donut, you end up with a modified donut.  One of my favorite Ham antenna's had oodles (lots) of gain, but the gain was pointing up about 10 degrees.  I always wondered why it didn't work very well on a 100 foot tower, but worked so-so on a 30 foot tower.

Turns out that by mounting it upside-down the 10 degree down-tilt of the beam worked out better.

Gain is always a problem with these simple receivers.  They are really just pulse detectors. They have a Logarithmic Amplifier detector in them.  The logarithmic amp keeps adding stages of amplification until it saturates, then it drops one stage out and that's what you send to the A/D converter.

To make them work in non-optimized locations (like someones window sill) these guys put a pre-amp low noise amplifier ahead of the detector chip.  So now even a crummy installation will get a fairly good signal.  Here's the deal though, these LNA's usually have very crummy noise figures. They just amplify the noise.  So what am I getting at?

Here's what I did.  I got an SBS way back when, and sawed the digital and analog parts of the PC board into two.  Now I have a digital side, and an analog side.  Then I cut out the LNA chip (bypassed it actually but cut the power traces).  So now I have the analog board without a crummy LNA, that get's it's DC power over the coax.  Mount this in a PVC pipe and bolt it to the tower.  Run cheap coax down the tower to the receiver room. I use RG-58 I found at an auction.  This coax is only passing video, and not RF.  Also out the bottom I run the coax that came with the SBS cut down to 1 foot and tied to a transponder antenna (grounded).

The problem with the LNA is, it drives the log-amp into saturation when aircraft are close in, and the log-amp by itself can handle signals out to the horizon.

Bottom line, we need the ADS-B people (Kinetic or Airnav) to build us a system for base stations.  The current products are designed for portable use, and are very poor first generation designs.  I'm not buying another one of these contraptions until the fix the receiver designs into something that works better in a base settup.

[juangelb]

Steve,

Ok that You worked on atennae also and your interesting discovery in doing it work upside down.

Ok also to sawing to half SBS, interesting idea.
Here for saving running  10 or  12 more meters coax I am using a Ubox.
That works fine to me and also one Ubox with another RB at Buenos Aires, but
as I changed the broadband service provider... There are days that I cannot connect to it.

About the characteristics of this receivers, I undestand but i can´t figure out how this problem (saturation) could be workarouded.... Since it is receiving alotta singnals at the sime time, the weack ones the strong ones...

Well here I am still working on find a better place to put the 9Dbs (18 dipoles) because yesterday I mounted but the only place to mount was between a vertical mast of an 118-136 Mhz antenna and the support mast.

I Think that in a week or so I will mount in better position, since it needs some different hardware, is not possible to find it during Carnival.

I live in the 15 floor of a building and was allowed by condominium to pot some antnnae on top of building, but with a condition that the cables (coax) would be thinny and white...  entering trough the window.

So I put a 10 meters RGC-213 and then more 8 meters RGC-58..
And due to high loss the only way was workig on high gain atennae.

What I can do .... 

If You can tell more about the type of antenna You worked, it will be fine to know.

Also I did not undertand " ...you have to squash the donut shape .."
If you can explain, let say ... in other words , maybe... Hahhhahhha.


Chhers.

[OKC-Steve]

A perfect Omni has 0 dB gain and the beam pattern looks like a donut, with the hole in the center being the vertical antenna.



To add gain to an omni, you have to sacrifice the elevation coverage. The donut gets deformed, or even squashed flat for say 12 dB gain in the elevation pattern below.  It has very little altitude coverage.



Here's an omni antenna with 7 dB gain elevation pattern below.  Look at the elevation at 70 degrees.  How much gain exists at this 20 degrees above the horizon?  None.  It would perform rather poorly for ADS-B but be sold as high gain.  High gain is not what you want in an Omni.  High gain is what you want in a beam. 



Here's one thing to consider though: Using two antennas!  One being a 0 dB gain Omni, and another being a 9 dB gain Omni.  This would give you good close-in coverage at all altitudes, and lots of gain out on the horizon for long range targets.

The only problem you have to watch out for is phase between the two antennas.  For example, I made an antenna out of 4 beams that connected to a power-combiner (combined the 4 antennas into one output).  It didn't work very well.  I was surprised at how poorly it performed. It wasn't until an engineer asked me how I calibrated the phase, that I figured out why. A transmission from an aircraft would hit one antenna, and then a couple nanoseconds later it would hit another antenna. These would then be combined into two separate pulses coming out the combined port. Resulting in garble.

Even for two antennas, you'd need to make sure that the phases were matched, so the pulses came out of the combiner on top of each other.

[juangelb]

Steve,

First of all thanks a lot for all your time spent on explaining.
Ok perfectly understood.

But thinking about and analizing performance, I can suppose that  antenna is working fine  even with his low elevation due to when the aircraft is near  or overhead, the signal strenht of his transmission is very strong, thus is received ok.
In the other hand when aircraft is far, let´s say 50 NM, even being as high as FL4000 , his elevation from the antenna view is low... and is needed also to include the earth corvature, so I think antenna could perform good also.

Maybe the low elevation could affect very negativelly in high gain omni used for instance to receive NOAA satellites signals, since reception would start at near 0° elevation, but quickly raises and hits 90 ° ...   and it is at 800 kms away.

One big problem is in mesuring the performance, since the only way is to let polar diagram to trace .... at least for a couple of days.

Ok on the approach of putting 4 antennae and matching the feed.... yes this would get difference on the timing the signal hits one or another antenna.....
With the resulting garble does not promises good results...
But maybe this could be achieved mounting the two antennae (one of high gain and the 0 DB gain) in a single axis, I.E staked .. in a single radome and mounted far from the mast with a plate, let say 50 cms away from mast.
Mounted as if it would be  a dipole, but indeed one leg would be the 0 Db and the other leg would be the high gain
This would eliminate the time difference in the signal hitting both antennae since both are receving the sinal at the exactly same time.

But the matter is to stay studiing and testing...
And I remember that once I was doing some testing with a 1/2 - 3/4 - 3/4 simple wire and a 25 inches ground plane dish, and for some reason I let the antenna inside the window, just in a corder and upside down.
Surprisingly it caught sinals as far as 240 NM.

I think that since Ill do some testing on the 18 dipoles, only to gert some more reliable data on his performance, I will try to some kinda testing on the two stacked antennae model... Can be interesting see what happens.
I am not expecting to exten the range, since the near 240 NM line of sight phisical limit, but may be it would be possible to achieve a more steady aircraft
trackig, I.E less signal lossing and then reappearing again.

Cheers

[OKC-Steve]

Something to think about though, is the log-amp goes after the biggest signal.  For example, an aircraft on the horizon at 150 miles with 9 dB of gain will cause the log-amp to use just the last stage amplifier, and set the other stages to zero.  That means smaller pulses are deleted until the log-amp recovers after the aircraft stops transmitting.

A local target a few miles away on the ground or overhead would be deleted because it required more than one stage of amplification in the log amp.

You are correct about the poor pattern shape still being usuable, but the log-amp will always favor the targets in the gain pattern.  If you don't have that many targets it may work out fine.

A radio I used to work on had a 24 stage log-amp.  Maybe what we need are more stages, so the log-amp doesn't saturate so fast.

[Fenris]

Something to think about though, is the log-amp goes after the biggest signal.  For example, an aircraft on the horizon at 150 miles with 9 dB of gain will cause the log-amp to use just the last stage amplifier, and set the other stages to zero.  That means smaller pulses are deleted until the log-amp recovers after the aircraft stops transmitting.

A local target a few miles away on the ground or overhead would be deleted because it required more than one stage of amplification in the log amp.

You are correct about the poor pattern shape still being usuable, but the log-amp will always favor the targets in the gain pattern.  If you don't have that many targets it may work out fine.

A radio I used to work on had a 24 stage log-amp.  Maybe what we need are more stages, so the log-amp doesn't saturate so fast.

It's more to do with the AGC time constant (or its equivalent in a log amp). As soon as the signal has disappeared the log amp should immediately recover to full gain or it could miss another signal. If the signals overlap all bets are off unless there are multiple correlators available, but for that to work you need a linear receiver anyway.

[Yachtie45]

Supposed to have 6 Dbs gain.....

Well.... going on in my desapointig research, today I decided the same thin as I did with the antenna locally supplied (the one taht did not worked well):

caought a sow add cutted it !!!!!!!!!!!!!!!!!!!!!!1
SURPRISE !!!!!!!!!!!!!!!!!!!!!!!!!!!!1

Now I undesrtando why it performa worst than the simplest one homebrew !!!!!
It has inside a sole board with maybe 1 wavelenht antenna and somthing else...
That is very good to repace original indoor RB antenna for outdoor use, NOTHING ELSE.....

@ Juangelb

Bom Dia

Since I saw the pics of your homebrew and the opened up commercial one,
I am thinking of the principle the commercial antenna is following.

Viewing that circuit board
on the larger pic one can see 5 sections of equal length with the two stacked pairs of strips facing downwards
as stubs.
Now from the different colour of the board (darker rims) it seems to indicate that on its underside there might be similar stubs facing upward ( section 2 and the upmost section 5 )

Is this only my suspicious assumption or are they real,
if so how are they possibly connected.

Your additional info on that is very much appreciated

TIA
Klaus

[juangelb]

Hi Yachtie45

Well, as I cutted the radome very near to his base and the circuit board broke just one centimeter from his botton part.
Is just this botton part of circuit board that has one metallic part connected to the inner conductor of N connector, and the shield or braid connected also.
I think that inner wire was soldered to one side of circuit board and shield to the other side of circuit board.

At this time I am abroad, returning march 31 to home, and I can take a look in detail to the parts.... If the little piece of one cetimeter already was not loose.

Best Ragards. Juan