Radarspotting

Quote from: dongle on October 24, 2012, 07:32:50 PM

I've hankered after doing some ADS-B decoding for about two years, but have balked at spending anything on the idea because I have too many expensive hobbies already. I've been a radio ham for about thirty years and lately have graduated towards digital modes because of local radio noise from neighbours PLT networking devices.

About a fortnight ago, I read a website article about certain TV dongles being able to be used for ADS-B decoding, so I bought one for £25 and loaded the necessary Linux driver and software. It worked right from the start, though only with limited range with a roughly made quarter wave antenna I had lashed up and placed on a downstairs windowsill.

After some experiments with antennas and lashing up a pre-amp, I am running Virtual Radar for Linux and tapping into the linux netbook over the network with a Windows PC running a Plane Plotter trial. The results are far better than I had any right to expect.

(https://lh3.googleusercontent.com/-pepgu1pqw0s/UIgzGMtyLsI/AAAAAAAAEPs/zxilZm9uAwo/s800/plane%2520plotter%2520view.JPG)

(https://lh6.googleusercontent.com/-JLKiVn3qRjs/UIJfSMqfxEI/AAAAAAAAEOo/jk-CU2_CBTU/s800/adsb%2520pre-amp%25205.JPG)

Anyone wanting to go this really cheap way into decoding ADS-B needs to realise that THE ONLY dongles that will work like this have the following chips inside them:

RTL2832 chip to do the demodulating


E4000 tuner chip to amplify the signal, tune in to 1090MHZ and output the data at base band (Direct Conversion).

The RTL2832 is quite common in cheap TV dongles, but on its own it is not enough. The E4000 tuner chip seems to cover 64mhz to 0ver 1700 mhz, and this is unusual.

These dongles have been bought up worldwide and the E4000 chip is now nolonger in production so they may not be around for long.

The antenna I settled on in the end is a simple quarter wave with eight ground planes. It is made out of 1.5mm copper wire in lengths of 67mm built onto a cheap old fashioned coax TV plug. This is mounted on the roof on a bit of cheap fishing rod, plugged into a short coax patch lead. This goes into the loft and is connected to a simple pre-amp with about 14db of gain (more or less) and then into the dongle via another short patch lead. I take the output data down into the house via a long USB2 lead into my radio cupboard where it is decoded by an Eeepc 1000HE on Linux running GNU Radio. This decodes the data into ADS-B messages. Only the Type 17 messages are used by my system.

I either use Virtual Radar's webserver to put them on the home network, or I use Plane Plotter to listen on the Eeepc's Ip address on port 30003.

My final choice of antenna so far.
(https://lh6.googleusercontent.com/-EhULXOWjn_o/UIg3yXtUNWI/AAAAAAAAEQ0/iRD8wv8o10w/s640/arachnid%2520antenna.jpg)

An earlier experiment with four ground planes.

(https://lh4.googleusercontent.com/-Yp4KXppXduY/UIg4UrYhL8I/AAAAAAAAERI/R4mblY_hPxo/s640/adsb%2520antenna.JPG)


The setup has produced the odd few spots at about 240 miles, but more typically, I get about two hundred miles out over the North Sea and less over land where planes are obviously below the horizon in the direction of the Irish Sea where the signals have to pass over the Lake District and the Pennines. I did some looking at the terrain between my house and the Isle of Man which is my worst direction and the signals have to get over 2000 feet of Pennine Hills and 3000 feet of some Lake District mountains. It is obvious why I get the odd spot from Holland - there is nothing between us but sea.

Quote from: shakysen on October 24, 2012, 07:50:12 PM
Welcome to the Mob Dongle enjoy it .A great bunch of guys

                                                                                            Shaky

Quote from: Anmer on October 24, 2012, 07:45:21 PM
Welcome and thanks for sharing your experience.

It might encourage others to play with the inexpensive option.  ;D

Thanks Shaky and Anmer.


These are the links that got me started:


http://www.ab9il.net/software-defined-radio/rtl2832-sdr.html

http://www.hamradioscience.com/the-rtl-2832u-sdr-and-ads-b/


The system worked without a pre-amp. I could get about 180 miles without one, but it works more reliably with one and I gain about another fifty miles on the occasional spot. They are very easy to make if you know which end of a soldering iron is the hot end. You needn't spend a fortune, though I am sure it is fun to do so and I have done, many times in other aspects of the radio hobby.

You can build this pre-amp for about £5.

(http://www.lll.lu/~edward/edward/adsb/preamp/ciruit.png)

Don't use a 6.8k resistor on the base as labelled. It is too small. The text of the article warns of this and suggests 22k. The BFP420 SMD transistor can be had on ebay at a price of two for £3.

WARNING..... Please don't connect this pre-amp directly to your dongle without putting a 100p capacitor between the output of this circuit and the dongle. If you do, you may present DC power to the input of your E4000 chip in the dongle. The circuit shown doesn't explain how to power the pre-amp, you can do like I did and take +5v off the USB supply to the dongle, but do use a dc blocking capacitor to prevent current flowing into your dongle's input. It probably has a capacitor in front of the E4000 chip, but it will also have ESD protection diodes on the input and one of them won't like the 5v positive supply one little bit.


Send me a message if you want any advice.

Instructions and photos of the simple pre-amp here:
http://www.lll.lu/~edward/edward/adsb/preamp/ADSBpremap.html

Mike, maybe we need to move the other dongle posts here to keep them all together?

Don't recall a "Self-assembly" topic before?

The R820T chip in newer versions of the dongle (replacing the E4000) is slowly being included in the software for SDR radio.

If you want an E4000 version:

http://www.ebay.co.uk/itm/EzTV668-USB-DVB-T-Receiver-E4000-USA-Elonics-Tuner-Realtek-RTL2832U-EzCAP-668-/150816730652?pt=UK_Computing_Other_Computing_Networking&hash=item231d60ae1c

http://www.ebay.co.uk/itm/TV301U-DVB-T-USB-Stick-DAB-DAB-FM-RTL2832U-Elonics-E4000-Receiver-RTLSDR-SDR-/150858463554?pt=UK_Computing_Other_Computing_Networking&hash=item231fdd7942

I bought the latter version from them.

Also bought a NewSky from here:

https://www.cosycave.co.uk/category.php?id_category=56

I'll be following this thread - maybe I can learn about the hardware!

Ian

Thanks Ian,

I have a mate who has ordered a dongle with the R820T tuner chip in it. There is confusing info around about that one and in the stuff I have seen which comes from the manufacturer, it doesn't look like it will cover 1090 mhz, but other information floating around suggests it will do with he right drivers. Those dongles can be had for under £10, whereas the Cosy Cave ones are nearly £30 now. There are some on ebay that come in at under £20 from the US with the right chipset in them.

Considering the costs and the fact that the A/D convertor is 8 bit and has a low dynamic range, the one I have is surprisingly good.

One thing I've noticed since I stuck the pre-amp in front of it is that I am not picking up planes that are taking off five miles away and flying low overhead at maybe 5000 feet. It is obvious why - their signals are overwhelming the dongle's A/D convertor. Without the pre-amp on I always spotted the local traffic taking off from Newcastle Airport as soon as they were off the ground. I have more or less direct line of sight to the runway from here. Oddly enough, when planes land, I spot them all the way down to the ground even with the pre-amp, but not when they take off for some weird reason.

Quote from: IanH on October 24, 2012, 11:25:03 PM
Mike, maybe we need to move the other dongle posts here to keep them all together?

Don't recall a "Self-assembly" topic before?

I created it last night when I saw the depth of information in "Dongle's" post.

If you can point me in the direction of the posts I'll see if I can easily move them.

Thanks for a very informative description.

One question that I get asked a lot is what is used to decode the ADS-B messages and output onto port 30003?

Is it gr-air-modes (https://github.com/bistromath/gr-air-modes)?

What seems to be missing is a layman's Guide to creating the whole setup.  Clearly this isn't an out-of-the-box PC install and use option.  But maybe with a good Instruction Manual it could be?

Hi All .The problem is boss there's that many folks Latched on to it  it's getting swamped at the moment. the nearest thing I've found to a user manual is on
www.atouk.com/sdrsharpQuickstart I'll keep looking



                                                                                  Billko

That's the opportunity.  I'm on the case.

Hi Anmer,

I t certainly isn't an out of the box thing if you have no prior experience of using linux, which I really haven't although I did have a dual boot install on a netbook which I'd done just to look at what I could do with linux. However - that said, it is not really hard or anything, but it is REALLY cheap. My whole outfit, including antenna on the roof, a ten meter USB cable to the loft, software and hardware cost about forty pounds.

All I can tell you about the gr-air modes question is that I think that is a script which comes already as a part of GNU Radio which is a free download on linux. Once you have installed Ubuntu 12.04, GNU Radio, and Virtual Radar, all you need then do is plug in your dongle, connect an antenna and run an already installed script from terminal windows in UBUNTU.

[EDIT: I missed a step here. you also need to install
gr-air-modes written by Nick Foster. It is all covered in the hamradioscience link I posted. Sorry about the omission.]

I opened a terminal and typed the following:

uhd_modes.py -d -P -g 43

and within a second I had ads-b messages cascading down the screen. This was taken in the early days before I made and connected the  pre-amp. It was done with a simple little antenna - the one shown further up the thread with four ground planes. That was built on a £0.80 TV coax plug out of the inner wire from some satellite TV coax. Any self supporting wire will do of about 1.5mm, so if you don't have coax lying around, the earth wire out of some electrical cable will do. The elements should be made 68mm long if the wire is bare and 65mm long if it is covered with insulation. Just solder the ground planes to the inner cable grip and make sure there is no short between the vertical wire (which is connected to the centre of the coax plug) and the ground planes. A little bit of insulator needs to be fitted in there at the base where the cable grip will contract over the wire as you screw up the plug.



When I opened a new terminal and changed directory into the place where I had installed Virtual Radar Server for linux and typed:

mono VirtualRadar.exe

a window opened on the linux netbook which gave me details of the ip address where the server was making the Virtual Radar Server web page.

(https://lh3.googleusercontent.com/-LR2VLwXMfiQ/UIj7AvoYZCI/AAAAAAAAERk/pIinHtXv4z0/s1024/adsb%2520map%2520planes%2520too%2520big.JPG)

The above screen dump was snatched this morning and benefits from a small simple pre-amp I lashed up.


Since the Linux version of Virtual Radar Server tells you the network address of the web page, when in the house on the same network, I can open that on a different laptop and that way it is far more convenient since I am not tethered to the long usb lead up to the  loft where the dongle now lives with its pre-amp.

By the way - when I first set this up, I connected the dongle to the ordinary TV antenna and plugged the dongle in downstairs at the edn of a ten meter TV coax. I could see planes about thirty miles around with a horizontally polarised TV aerial set up for 800 mhz. That proved it was worth pursuing further.

This link gives as near a blow by blow set of instructions as anyone would likely need on getting the software set up and installed. It is a really good resource for anyone wanting to try this:

http://www.hamradioscience.com/the-rtl-2832u-sdr-and-ads-b/

The part underneath the heading 'Linux for Newbies' is the bit I used. It takes a while for the installs to happen, but mine worked faultlessly even if it did take a while. bear in mind, I was installing on an N240 netbook so it wasn't a power machine.

Thanks.

As I mentioned earlier I'm getting more and more enquiries about this option, some from less technically experienced individuals.  But as you say, it's a cheap option and if it gets someone into the hobby that's a good start.

Has anyone tried feeding dongle data to Flightradra24.com or Planefinder.net?

Ah - Anmer - yes you were right. It is gr-air-modes written by Nick Foster that  decodes and makes available the data on port 30003. Apparently, it emulates the decoding behaviour of the SBS1. I completely forgot to mention that, but it is all explained in that link I posted

Quote from: Anmer on October 25, 2012, 11:38:55 AM
Thanks.

As I mentioned earlier I'm getting more and more enquiries about this option, some from less technically experienced individuals.  But as you say, it's a cheap option and if it gets someone into the hobby that's a good start.

Has anyone tried feeding dongle data to Flightradra24.com or Planefinder.net?

I think you will need to download and pay for Plane Plotter to be able to share your data. The dongle works with Plane Plotter, of course. You just pretend it is an SBS1 and point the program at the ip address of the Linux machine.


ShakeySen mentions SDR Sharp in the link he refers to. I tried that because there was a copy sent with my dongle. It didn't seem that great. I think there are issues about the Windows driver. Also, I am unsure how you would decode the ADS-B data that you managed to receive with SDR Sharp so you might have problems sending it to an ADS-B displaying program. Obviously, receiving bursts of ADS-B is one thing, decoding them into Type 17 messages is another. That is what gr-air-modes written by Nick Foster does for you when you type that command I mention up above:

uhd_modes.py -d -P -g 43

To me, linux is a bit of a pain, because I have never really got into it, and I can't easily remember terminal commands, but it sure as hell does this job on the cheap.

Quote from: dongle on October 25, 2012, 11:44:50 AM
I think you will need to download and pay for Plane Plotter to be able to share your data. The dongle works with Plane Plotter, of course. You just pretend it is an SBS1 and point the program at the ip address of the Linux machine.

I don't think so but it needs to be tested.

If you can get decoded data to port 30003, then the Flightradar24.com feeder software should work:

http://www.flightradar24.com/software

Quote from: Anmer on October 25, 2012, 11:48:29 AM

Quote from: dongle on October 25, 2012, 11:44:50 AM
I think you will need to download and pay for Plane Plotter to be able to share your data. The dongle works with Plane Plotter, of course. You just pretend it is an SBS1 and point the program at the ip address of the Linux machine.

I don't think so but it needs to be tested.

If you can get decoded data to port 30003, then the Flightradar24.com feeder software should work:

http://www.flightradar24.com/software

Ah - well - that's good then. You can definitely do that. That is how I am running Plane Plotter. I know nothing of the Flightradar feeder software, but have data at port 30003 on the linux machine. It may be they have linux software to run on that machine, or their windows version may allow you to point at a linux machine on your network through the wifi. I have to go out now, but I will try and do that later on or tomorrow.

Thanks.

There are linux feeders available:

http://forum.flightradar24.com/threads/4270-Linux-feeder-software-for-Flightradar24

Hi Boss wading thru the pile's of  stuff on The Dongle this site may serve  http://superkuh.com/rtlsdr.html

Quote from: shakysen on October 25, 2012, 12:53:56 PM
Hi Boss wading thru the pile's of  stuff on The Dongle this site may serve  http://superkuh.com/rtlsdr.html

There is some good stuff on there Sir.

I notice that they are saying that the more widely available tuner chip (R820T) can work on frequencies that the manufacturer does not document as being possible. If the gr-airmodes can initialise it and tune it in like it does the E4000 tuner, there will be no shortage of cheap dongles that can be used for ADS-B into the future when the E4000 ones run out.

Dongle, what "dongle" hardware did you buy?

Mike - All the previous dongle stuff in is in OFF TOPIC section under the single thread "My new receiver".

In response to some of Dongle's comments:

For the ADS-B signal from the DVB-T stick, I chose to run Ubuntu under Virtualbox on a Win7 PC. I did note all the detail so I'll put that together in a document. It is unlikely to run on a Netbook though. My reception wasn't too good but that was likely to be an antenna problem. And since I have an SBS-1e, I haven't followed up since. Just proved it worked  ;)

SDRSharp is very much a front end for radio reception. It gets updated frequently and I use it to listen to airband radio. So the latest version probably works a lot better than the version with the dongle. I agree that without a decoder it isn't intended for ADS-B. But you can feed ACARS audio into acarsd (http://www.acarsd.org/). If the scanner function is added it could poll through the frequencies.

Ian

Quote from: Anmer on October 25, 2012, 02:33:45 PM
Dongle, what "dongle" hardware did you buy?

I got one of these, but this guy has put his prices up a lot since then. He knows what he has got, I think and realises it has much more value as an SDR radio than it ever had as a TV dongle. It is the Newsky TV28T.

(http://thmb.inkfrog.com/thumbn/noodlehed/tv28t_7.jpg=596)

Mine came without an antenna but with some software on a home burned CD.

http://www.ebay.co.uk/itm/120994408433?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

The same board is available in other dongles. There are American ones that are on sale for far less and some from HK for about £12

see lower section where International Sellers are offering items.


http://www.ebay.co.uk/sch/i.html?_nkw=E4000+%2B+Rtl2832u&_sacat=0&_odkw=E4000+%2B+Rtl2832&_osacat=0&_from=R40

ALWAYS CHECK THE CHIP LINE UP. (RTL2832U + E4000) No guarantees if other chips are used instead of those.

Excellent, thanks Dongle.

Having bought from eBay seller "nooelec" (1st 4 items in your eBay list are from him), I would trust him to know what he was selling.

And just about to post what shaky just has.

Trouble is identifying what is on eBay from the list!

Ian

I'll try Cosy Cove again tomorrow and failing that I'll get one from the eBay seller.

Then the fun begins.  :)

CosyCave has put his prices up a big amount, going by that last auction. On the other hand, he has soldered Electro Static Protection diodes into my dongle. They only cost pennies, and ought to be fitted at the factory, but weren't. You really do need them or your dongle might go very deaf all of a sudden during a hail storm when charged up specs of ice start hitting your antenna. Of course, if you made an antenna which is a DC short, such as a Slim Jim, or a J-pole, you wouldn't need to worry about that. Neither would you if you had a home made pre-amp in front of it, because that would take the hit if there was one and the transistor in the design I posted costs buttons.

Here is a neat antenna designing site for antennas that are a dead short for static.

http://www.m0ukd.com/Calculators/Slim_Jim/index.php


Ian -

Thanks for the info on using the dongle for ATC listening. I have an all modes tranceiver which can do this, but I had not realised there were better versions of the HDSDR software and perhaps drivers available for it. I did start off with Windows and HDSDR because I am not any sort of a Linux fan (only because I don't really know it well) but my impression was that it was awkward to use and there was a lot of distortion on it when I tried to use it for FM wideband programme listening. The quality was awful, actually, but this is not a hardware issue, only one of maybe drivers and the software which didn't really have the scope for Wide FM (ie broadcast station FM).

I will look about for an update.

SDRSharp is a Windows program. You have to install the Zadig drivers first which replace the standard Windows drivers for the DVB-T stick. Looks like you have the same one as me from CosyCave.

If you look at the downloads page on SDRSharp.com, the current Dev downloads are version 977. I was using version 838 at the beginning of the month! You also need to update the the pre-built Windows RTLSDR binaries and libraries from Osmocom (details here in SDR# section of http://rtlsdr.org/softwarewindows ) since that has been separated out but also is being updated.

For me, this provides sufficient ATC monitoring at a bargain price.

Ian

Thanks Ian.

That's very helpful. I'll have a go later and see what happens. It will be a touch awkward to try the stick down on VHF since it is now plumbed into the ADS-B antenna and pre-amp and is up in the loft. I have a ten meter USB cable coming down into my radio cupboard -a  sort of walk in small room about 5' by 5' on the landing. If the R820T tuner chips prove functional for this, I wills end for one. They are available on ebay for less than £7.

EDIT:

It looks from this link that not only can the R820 stick work with SDR Sharp, but also with gr_modes, so it should do ADS-B too. For something like £6.80 delivered from China, this would be a spectacular bargain!    :)

https://groups.google.com/forum/#!topic/ultra-cheap-sdr/KDcd40590ys

SDR Sharp problem

SORTED NOW - ignore

It was a net framework problem.

Got SDR sharp running and stable on the loft mounted dongle via the long usb cable.

I didn't change the antenna or pre-amp so I had limited listening potential, but I could hear weak two meter activity and the tower at the local airport. When I put the dongle onto 1090 mhz, as you would expect, I could see red streaks and lots of them either side of the centre frequency. There would seem to be some slight error in the frequency declared by the dongle. I'll make a note of it next time I run it. It seemed less down on VHF and a good bit more up on 1090mhz.

Thanks for the instructions Ian.

Found this interesting pile of information about gr-air-modes. Scroll down to the README file if interested. It seems that gr-air-modes will do a lot more than I expected.

https://github.com/bistromath/gr-air-modes

Well worth a look if anyone is interested in using the program with a dongle.

Things seems to be moving with gr-air-modes.

The final instruction in http://www.hamradioscience.com/the-rtl-2832u-sdr-and-ads-b/  no longer works:

uhd_modes.py -d –P

gives an error that it has been deprecated.

New command for new installations is:

modes_rx –d –P

For various reasons I tried two installations today. First one worked with this new command line, second one failed with an error I don't yet understand. Perhaps some code being changed behind the scenes? I'll try again tomorrow.

Ian

Well spotted there Ian. I wondered why I could see no reference to uhd_modes in the ReadMe file, but I saw the one you mentioned. I wonder if it works better in some way, and if so, how I should upgrade.

Vile weather here. Just had to pick up the wife from the hospital - her mother was taken ill today and she went in with her in the ambulance. It is snowing like crazy and the roads are an inch or more deep. Drove all the way there and back at 20 - 25 miles an hour.


I ordered a new dongle with the R820T tuner chip. Cost a touch less than £7 including postage from HK. Should take about three weeks or so. I'll play about with it on VHF connected to a new 300 ohm loop aerial I will make for Freeview and VHF. I have a good high location here so I can get away with bizarre aerials on Freeview. A vertical VHF loop will be broadband and will tolerate a lot of liberties while still performing. I'll connect to it with the dongle witha  4:1 balun to bring the impedance down to nearer 75 ohm. Just had a thought - if I make a uhf loop for the TV and connect it to a vhf one for the dongle and connect with a 2:1 balun to the pair of them, I'll be able to use the same downlead for monitoring air band and watching TV.  It'll cost pennies to try this. I've got enough wires going up the house for my other activities so if I can use one for two purposes, so much the better.

Just in-case I lose it http://www.techthefuture.com/technology/hackrf-lets-you-explore-the-radio-waves/

Dongle sir,

When you refer to balun and put up circuit diagrams for pre-amps I have very little idea what you are on about.

I do know the hot end of a soldering iron but your knowledge (and I suspect several others here based on discussions that have gone straight over my head)  is way beyond my understanding  ;)

I can deal with software, PC hardware but electronics is a vague memory - I think they were just inventing the integrated circuit when I studied any electronics at college - most of which I have forgotten over the decades since I had no use for it.

So any help in that hardware aspect of things would help me. I'm not daft, just no experience of those things!

Ian

Hi Ian,

Well first off, I'm just an amateur dabbler, but anything I can assist you with, I will do my best to do so.

If you let me know what you want to do, I will try and advise.

You mention baluns. These are often used as impedance transformers to adapt the typical 50 or 75 ohm impedance of a radio to antennas that have a different impedance.

A dipole has a natural impedance of about 75 ohms. it will easily match to 75 or 50 0hm coaxial cable and the 50 or 75 ohm input of a radio or TV system. TVs are usually 75 ohm as is TV and satellite TV coax. By matching the impedance of the whole system, you enable the maximum efficiency of the system to detect the signals that arrive at the antenna. In the context of say ADS-B reception, by matching the antenna and the coax properly, you will increase the ability of the system to receive weak signals from far away aircraft. The problem is a little more complicated in that an antenna is only going to present this efficient transfer condition ifit is resonant at the frequency you are trying to receive. You achieve this by cutting the element lengths to exactly the right length for the particular frequency. For ADS-B reception, a dipole will have elements made of bare wire of 68mm, or covered wire of about 65mm.

I mentioned dipoles above. They are not that much used for omni-directional, vertical antennas, because they can have a disturbance to their radiation (or their reception) pattern caused by the coax feeder coming close to the active elements of the aerial, and shadowing in one direction.  A more usual antenna for simple omni directional performance is the Ground Plane type. It consists of a vertical radiator element and usually, about four ground planes - elements which come out at 90 degrees at the base of the radiator. These are connected to the coax shield and provide a sort of artificial ground for the radiator to work against. The natural impedance of a ground plane with horizontal ground planes is about 36 ohms. If they are sloped downwards at about 45 degrees the impedance is more likely about 50 ohms, which for say a transmitting ham radio antenna would be ideal since it matches the output of both the transceiver and the usual 50 ohm coaxial cable used in ham band equipment. If you brought the radials down vertically, the impedance would rise to about 75 ohms, mainly because the system has become more like a dipole - two elements in the same plane, fed in the middle. 

This image shows a small home made Ground Plane antenna. It has been built for a higher frequency than ADSB, but the constructional detail is obvious enough. remember that for ADS-B you need 65mm long elements.

(http://www.vias.org/wirelessnetw/img/wndw-print_img_44.jpg)


All these points about impedance of different antennas assume that the elements have been cut to the exact length of the quarter wave length of the frequency of interest. If they are longer or shorter by any appreciable amount the impedance will change a great deal and the efficiency of the antenna for receiving or transmitting radio signals will alter severely. This stuff is much more important for a transmitter than for a receiver because a transmitter will be seriously damaged by transmitting into a badly matched antenna. A receiver will only suffer some loss of efficiency. It won't come to any harm.

Most TV antennas for terrestrial signal reception of the traditional sort, have a folded dipole element which is the main component connected to the coax. These are usually fashioned into a sort of squashed oval shape. They have some gain over an ordinary two element dipole and they are safe for the front end of the receiver because they can protect against the high static voltages that can build up between two separate dipole or ground plane type elements in certain weather conditions like snow and hail, or dry winds which can charge up a dipole or a ground plane so that they have thousands of volts of static across the two elements. Static like this will destroy tiny delicate transistors and the complex static sensitive circuits such as the E4000 tuner in a dongle. Snow flakes are very often  highly charged because they have been rubbing against one another in a cloud for quite long periods. It is rapidly moving ice crystals high up in thunder clouds that create lightening as they blew about. The  charges they carry can be very harmful to your radio front end or your dongle. I have been a ham radio fan for many years and like many other hams I have actually seen quite large sparks jumping across atu coils during snow and hail storms. I remember one night hearing my atu crackling with electric discharges during snow.

FOLDED DIPOLE IMAGES FOR VARIOUS FREQUENCIES:
http://www.google.co.uk/search?aq=f&q=folded+dipole&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=dRONUKPxEKKV0QXzqYD4Cw&biw=1066&bih=590&sei=exONULfOIqbG0QWtrYGABQ

In another post, I mentioned that a folded dipole, or a slim jim type antenna, or a J-POLE type are naturally protective against static build up, for the simple reason that the inner and outer of the coax are at the same dc potential. This is because they are made of one continual piece of wire. While they are a DC short circuit and naturally dissipate static, they are not a short to radio waves which are very high frequency AC voltages and currents. These see a properly formed folded dipole or a j-pole or a slim jim type antenna as a tuned circuit. Whether they are 'proper'or not for the particular frequency of interest, depends mostly on the length of the elements being correct.


Slim Jim type antenna. NOTE! The dimensions on this diagram are not for ADS-B. There is a calculator link below that will allow you to work out proper measurements for a slim Jim.

http://www.m0ukd.com/Calculators/Slim_Jim/index.php

(http://www.picaxe.orconhosting.net.nz/433slimjimfox.jpg)


To calculate the measurements of a  half wave length of insulated wire the following formula is used:

143/f         where f is given in MHZ and the resulting number is the length of the half wave length in meters.

Take an ADSB antenna.

143/1090 = 0.131

This means that a half wave at 1090 mhz is 131mm long. For a dipole this means you have two elements of half that length each, since a dipole is usually made of two quarter wave sections. The same is true of a ground plane as far as length is concerned; so you have elements that are half of 131mm or more or less 65mm each.

Some antennas such as collinear types have half wave long elements stacked above one another, typically three of them, but to bring the impedance down to an acceptable level they have quarter wave phasing loops which act as impedance transformers.

Antennas can get pretty technical and complicated because as well as being made up of wires which provide inductance, they also have capacitance, but the simple description I have given pretty much covers basic construction of simple dipoles and ground planes.

I mentioned folded dipoles earlier. These have a much higher impedance than ordinary dipoles. A folded dipole will have an impedance around 300 ohms if it is cut right for length. It is usually a full wavelength long at the frequency of interest, so its formula would be not 143/F but 286/F.  The advantage of the folded dipole is threefold. It has gain and low angle radiation. It is also immune to static voltages because they simply run to ground. It is also more broad banded than the ordinary dipole or ground plane antenna and will work well a frequencies either side of its ideal one which is not so true of the other kinds of antenna mentioned.

To match a 300 ohm folded dipole to a 75 ohm TV coax, you would need to divide its impedance by four (300/4 = 75). This can easily be done by a 4:1 transformer or a 4:1 balun. A 4:1 transformer might be made on a small ferrite ring, having a few turns (maybe about four) with two wires connected like this:

(http://www.rason.org/Projects/balun/IMG00001.GIF)


There is a wide variety of balun types that you can look up. I find them quite hard to understand when trying to make them.

You can actually buy quite cheap 4:1  (300 ohm to 75 ohm) baluns for TV that would probably be suitable for ADS-B frequencies if you wanted to mess about with a folded dipole turned vertical.

(http://i.ebayimg.com/t/BALUN-300-75-OHMS-TV-FM-AERIAL-SIGNAL-ADAPTOR-COAX-PLUG-/00/$(KGrHqR,!l!E3HZ+N)DfBN5JNy7qYg~~0_12.JPG)

http://www.ebay.co.uk/itm/BALUN-300-75-OHMS-TV-FM-AERIAL-SIGNAL-ADAPTOR-COAX-PLUG-/200607601215?pt=UK_Computing_Sound_Vision_Video_Cables_Adapters&hash=item2eb525123f&_uhb=1


Here is a vertical folded dipole so you can see how it should be mounted.

(http://www.atcs-bf.com/image/antennes/11-Half-wave_Folded_Dipole_Ant.jpg)

Sorry if this is rambling - I have been out for a curry and some beer. :)



This post has been edited to make things clearer.





http://en.wikipedia.org/wiki/Dipole_antenna

Hi Ian After nearly 50 years Of Playing around with Antenna related projects from Homebrew atu's to 11mtrs yagi's quad's an all manner of stuff if you just want to use a balun the best thing to put in line is RF choke 6 to8 turns wrapped round a piece of 40mm wastepipe. With pre-amps dont forget it pulls in unwanted noise also

Well that is going to take some reading and digesting  :)
The Pictures should help  ;)

Thank you

Ian

Hi friends. Is it possible to use dongles for MLAT in Planeplotter? Or just 30003 listening mode?

Welcome

I suspect a DVB-T dongle isn't good enough for Mlat but I really don't know.

Maybe Satcom from PlanePlotter Support can advise?

Hi May help.  http://www.youtube.com/playlist?list=PL618122BD66C8B3C4

Hi guys !   :)


Brand new to the forum & the subject of radar-spotting
Im still awaiting my dongle, but thought I'll build up a Linux box [size=78%]and get started[/size]


If there's a different thread for "troubleshooting" then I apologize in advance
but I read through a lot of stuff on this forum regarding my problem,
but it either does not exist - or this idiot has missed it


On a clean install of Linux 12.10 32bit, dual core, 3GB, I ran the command as per instruction
"wget http://www.sbrac.org/files/build-gnuradio (http://www.sbrac.org/files/build-gnuradio) && chmod a+x ./build-gnuradio && ./build-gnuradio"
all goes well, but after a long, very-very, long time of sitting still on
"Done Fetching Gnu Radio via GIT..."
it return an error
"Could not find gnuradio/gnuradio-core after GIT checkout GIT checkout of Gnu Radio failed!"


Did I miss something critical or maybe the link is temp out of service, or changed ?


Would really appreciate any help


p.s. txt file attached of procedure from start to error




[Attachment deleted by Admin to save file space]

Welcome.

Are you running Linux on a dedicated hardware platform?

I've installed Ubuntu on XP using Oracle VM Virtual Box.  Installing GNURadio was a bit painful and took a couple of attempts.  That was on Thursday just before I left for Bristol.  Just got back this morning and will check if it's all OK later.

If I've posted before Boss sorry about it.http://spench.net/

Quote from: Anmer on November 12, 2012, 01:08:27 PM
Welcome.

Are you running Linux on a dedicated hardware platform?

Yes, clean fresh Ubuntu 12.10 install on a blank disk, all updates etc done
as far as Im aware of :-X

Not tried installing on Ubuntu 12.10, only 12.04. And also only as a virtual machine.

I've just run the command "git clone --progress http://gnuradio.org/git/gnuradio.git" which is part of the build-gnuradio script and it worked ok.

Try running that command in your home directory (I assume that is where you are running the build-gnuradio script). it should return to the command line after a while - depends on speed of PC.

If that works, try running the build-gnuradio script script again - from my basic understanding of the script it will try to pull the files from the git repository again but even it it fails during the script, it looks for the presence of folder "gnuradio-core" which will be there if the standalone download worked.

If none of that works, I'll load up 12.10 on a PC possibly tonight.

Ian

Thanks Ian !


Sry, I should have reported back sooner,
I kept on trying without success, then I found all the files on the system & deleted them ( did I mention I know ZILTZ about Linux ? )


I then followed another script that requires the creation of a folder, before the download .... that worked !
( If actually due to that or the fact that I changed my internet connection to another medium & fiddled with it bit, I wont know)


The next step was the gr-air-modes, if that finished successfully, I wont know until I can connect a dongle.


Q: Is there anything I can run until such time as I have my dongle to check if all installed OK ?

p.s. I used this link and performed steps 4 & 5
http://www.irrational.net/2012/08/06/tracking-planes-for-20-or-less/


Regards

You can try typing rtl_test -t at the command line.

You should get back a simple "No supported devices found."

And also modes_rx --help will show the help screen. Important to note that "modes_rx" replaces the command "uhd_modes.py".

And something I found last night:

Try typing modes_gui - that should indicate software installed ok.

Ian

Thanks Ian    8)


everything responded as u said ... so looks like I'm in  business for now

What are you going to display the dongle output on?

I didn't think that far ahead yet ...  ???


Maybe Google Earth, or get suggestion from the forum about other packages available

I can offer a trial with a dedicated Windows hardware.

If you have a dongle with E4000 and RTL2832U AND it does cover 1090 MHz (you can find out by using rtl_test you may want to send me a PM and I will direct you to the downlink and a dedicated Yahoo group.

But be warned. Without a proper antenna (75 Ohms!) the dongle is deaf and due to its slow clock it will receive much more less than a dedicated device.

Andy

Thanks Andy.

What's a "proper antenna"?  Would my GP-1090 be any good?

Andy,


I will PM u later tonight


Antenna ... Im getting from a llocal guy that specializes in these types
and he also supplies to all the radar box guys


I will consider a pre-amp when i get to it


I'm going to use 1inch thick coax cable ... just to be sure  :) :) :)

It is a TV dongle, so my guess would be that 50 Ohms antennas, connectors and splitters pay their tribute to a lousy sensitivity. Also at 1090 MHz in my case the dongle tuner is only 12 MHz away from its tuning gap and I am afraid that it is quite deaf in that area.

On the other hand the effective rsolution of the A/D converter is only 7 bit (!) and the dynamic range is less what we are used to.

Only experiments will show.

On my window sill and side by side with other receivers the dongle is half in range and 10% in detection rate (stock antennas).

Andy

But £20 allows people to try out receiving ADS-B for themselves even with all the limitations - maybe they move on to better things.

I've got 2 dongles - the gaps start at 1109 and 1117 so not quite as close to 1090 as yours.

Ian

Am I reading you guys correctly ... When I receive my "package"
I might end up with a receiver that's "dead" on  1090MHz ?  ???

In total agreement with you Ian if folks  can get on it for a small fee. I'm More than Happy with these Dongles.

Quote from: shakysen on November 13, 2012, 05:44:31 PM
In total agreement with you Ian if folks  can get on it for a small fee. I'm More than Happy with these Dongles.

But are you trying to track ModeS/ADS-B aircraft or just listening to the radio?

Smokey don't know if this is the type your getting  http://www.hamradioscience.com/10-ads-b-receiver-rtl2832u-r820t/ 

Smokey

First thing to do when you get the dongle is to run rtl_test -t

That will tell you the available tuning range (52-2216, 52-2232 MHz on mine), and the non-available gap (1117-1238, 1109-1260 MHz for mine).

Yes some do seem to have that gap overlapping the 1090MhZ frequency but don't panic until it arrives.

Ian

[Attachment deleted by Admin to save file space]

Quote from: shakysen on November 13, 2012, 06:27:34 PM
Smokey don't know if this is the type your getting  http://www.hamradioscience.com/10-ads-b-receiver-rtl2832u-r820t/

A mate of mine already got his and its the Realtek RTL2832U Elonics E4000

I just emailed him & shared the thought that maybe I should actually get the /R820T as per your link
BUT, between me & him, we are TOTAL Linux IDIOTS  :-\ so if its going to require any serious Linux fiddling
we wont be able to do it - we rely on the clever guys to write the software that we can just download & run
... unless its irrelevant if its the 4000 or the R820

Quote from: Anmer on November 13, 2012, 05:45:23 PM

Quote from: shakysen on November 13, 2012, 05:44:31 PM
In total agreement with you Ian if folks  can get on it for a small fee. I'm More than Happy with these Dongles.

But are you trying to track ModeS/ADS-B aircraft or just listening to the radio?

In my case it would be to track the AC, already have the coms radio in place


Just another question on the installation if I may
with reference to http://www.irrational.net/2012/08/06/tracking-planes-for-20-or-less/
step 5

cd - OK
git clone https://github.com/bistromath/gr-air-modes.git - OK
cd gr-air-modes - OK
cmake . - OK
make - OK
sudo make install - OK, now it works ??? EDITED
sudo ldconfig - see no action, just returns to prompt

The E4000/2832U combination was the system that was first identified as being more than just a DVB-T dongle. People wrote software to utilise its capabilities.

The E4000 is no longer being made (and hence was becoming expensive) so the DVB-T manufacturers look to have chosen the R820T instead. And the SDR guys have written drivers for that chip. So it probably no longer matters which of the chipsets you have. I suspect that the R820T's availability compared to the E4000 is reflected in its lower price.

Not seen many comments on the R820T performance - another member here "Dongle" was buying one but not heard the outcome.

Bottom line, if you've got one on order, try it out when it arrives.

Ian

The R820T is many times more sensitive than the E4000 at 1090 MHz.

Also it seems to be guaranteed that it covers 1090 MHz, while I have a few E4000 dongles that end just before 1090 MHz  ???

Please see the other thread on RTL1090 software or

http://tech.groups.yahoo.com/group/rtl1090_english/

Andy