Dongle

[shakysen]

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

[IanH]

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

[dongle]

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.




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




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:




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://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.



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

[shakysen]

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

[IanH]

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

Thank you

Ian

[nakos]

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

[Anmer]

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?

[shakysen]

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

[Smokey]

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 && 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]

[Anmer]

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.

[shakysen]

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

[Smokey]

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

[IanH]

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

[Smokey]

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

[IanH]

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