AirNav Systems Forum
AirNav RadarBox and RadarBox24.com => AirNav RadarBox and RadarBox24.com Discussion => Topic started by: typist on August 25, 2010, 07:19:15 AM
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I had this stupid idea last night, mounting a high gain parabolic reflector on an old ceiling fan (mounted upside down, possibly with some gearbox), and let it rotate continuously.
A long mode S squitter is 8+112 bits if I am not mistaken, thus 120us (microseconds). Am I wrong if I assume I could pick up most squitters if I rotate the antenna fast enough?
Good coax rotary joints are expensive, so I would just mount the entire radarbox and a netbook on the ceiling fan contraption. USB is relayed over a local wifi loop to the workstation were the radarbox software runs (usb over wifi works perfectly and amazingly reliably for me already). To test it the idea, netbook battery power is more than enough. For a more permanent installation, power could be supplied to the netbook via electrical slip rings (the kind which is used in windmills, 30-40$). The whole contraption would then ideally be weatherproofed with a fibreglass dome (or a pvc bucket...).
I was thinking about sth like this antenna:
http://www.moonraker.eu/Scanning-Receiving-and-Avionics/Avionics/Avionic-Antennas-And-Accessories/RADAR-SKYSEARCHER-1090MHz-DIRECTIONAL-ANTENNA
Yes, I know, this is a particularly clumsy and useless setup...one of the advantages of a ADS-B is that it doesn't need expensive rotary constructions like primary radar, so making it rotate is a bit of a joke. Still... I'm wondering if anyone with more experience than me can tell me if a setup like this could possibly ever catch most squitters? what kind of rpm should I be aiming for?
thank you in advance for your thoughts :)
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I think you're missing the point.
A rotating primary radar only detects aircraft because it's transmitting and receiving all the time, i.e. any time it's pointing at an aircraft it knows it's always going to get a reflected signal.
OTOH a rotating Mode S receive-only antenna, assuming it's directional, will by definition have a limited beam width and will only pick up signals if an aircraft happens to be transmitting a squitter or interrogation response during the period that the beam is pointing at the aircraft.
Say, for example, your antenna has a 20º beam width - that only gives you a 1 in 18 (about 6%) chance of picking up any given aircraft transmission, with the remaining 94% of transmissons happening while the antenna is pointing in the wrong direction. And that ratio will hold whatever rate you rotate the antenna at.
The answer, of course, is to have a much wider beam so that you can pick up most, if not all transmissions - 360º would be good :-)
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thanks :) this is kind of what I assumed was halfbaked...with regards to my idea. the standard antenna which comes with radarbox seems to receive roughly 2-3 messages per second (or less) per aircraft. so...with 20 deg useful beamwidth, could I theoretically cover every sector for roughly a second, if I let the antenna rotate the entire 360 deg in 18 seconds (roughly 3 rpm), and adjust software timeouts to say 1 minute? yes, this way I would miss most of the transmissions...and a plane at 900 kmh will have travelled 7.5 kilometers already if I am lucky enough to pick it up twice per minute...and I probably dont need high gain anymore because it will either be closer already, or below the horizon.
yes...I do realize a better omni antenna is the solution, and a lot less hassle :)
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Very interesting topic. Even if limited to receive on a few degrees, as anyone tested this antenna in comparison with common Mode-s antennas?
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Very interesting topic. Even if limited to receive on a few degrees, as anyone tested this antenna in comparison with common Mode-s antennas?
As it happens, I've had a (non-rotating) Skysearcher antenna hooked up to my Brand X Mode S receiver for the last 3 months, pointing at Heathrow. Reception is, as you would expect, better than the omnidirectional magmount in the direction it's pointing, and still not too bad in other directions.
I haven't tried it with RadarBox, but that's only because the Skysearcher came with a downlead that terminates in a BNC.
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>Reception is, as you would expect, better than the omnidirectional magmount in the direction it's pointing
How better is it? How do you measure it? Range?
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if the openings angle of this antenna is about 90 degrees or more, you can put up 4 antennas in each direction (N,S,E,W) en connect them via 1/4 wave coupler to the main coax.
So you have an omnidirectional antenna with more gain.
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How better is it? How do you measure it? Range?
No, I'm not interested in range. It may well be better than the omni in the direction that it's pointing, I haven't measured that.
Where I wanted (and got) an improvment is the ability to track aircraft further down the glideslope on approach, and catch them earlier on climbout, both of which add value to my EGLL movements website.
Incidentally, the arrival algorithm also now identifies inbound aircraft while they are still in the holding stacks, so users get more warning of anything interesting that's coming in.
www.civilaircraftregisters.org/Mode_S_Resources/LogReport/EGLLADSB.asp
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Very interesting topic. Even if limited to receive on a few degrees, as anyone tested this antenna in comparison with common Mode-s antennas?
As it happens, I've had a (non-rotating) Skysearcher antenna hooked up to my Brand X Mode S receiver for the last 3 months, pointing at Heathrow. Reception is, as you would expect, better than the omnidirectional magmount in the direction it's pointing, and still not too bad in other directions.
I haven't tried it with RadarBox, but that's only because the Skysearcher came with a downlead that terminates in a BNC.
Morning Dave - I'm very interested in the Skysearcher and as you are the only guy who seems to have one I wonder if I could ask you a couple of questions?
Firstly the beam width - the traffic I'm interested in would be contained comfortably in a 45 degree angle. Am I right in assuming there's a narrow angle "hotspot" of X degrees which reduces in effectiveness as the angle widens?
Range we don't know but would you have any reason to suppose that the range in the preferred direction would be less than that of a "standard" aerial?
And finally, have you any knowledge of a radio controlled low-loss switch that could be used to run the Skysearcher and my existing aerial jointly into the one box, thus allowing switching between them as the occasion demanded?
Thanks John.
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Morning Dave - I'm very interested in the Skysearcher and as you are the only guy who seems to have one I wonder if I could ask you a couple of questions?
Firstly the beam width - the traffic I'm interested in would be contained comfortably in a 45 degree angle. Am I right in assuming there's a narrow angle "hotspot" of X degrees which reduces in effectiveness as the angle widens?
I would assume so - I did in fact ask Moonraker if they could provide a a polar diagram, but they said no.
Range we don't know but would you have any reason to suppose that the range in the preferred direction would be less than that of a "standard" aerial?
If the range in the direction it's pointing was less than the omni then there wouldn't be much point in having it :-) But, as I said, I haven't done any range measurements.
And finally, have you any knowledge of a radio controlled low-loss switch that could be used to run the Skysearcher and my existing aerial jointly into the one box, thus allowing switching between them as the occasion demanded?
Nope, that's definitely out of my comfort zone :-)
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Thanks Dave - the idea of "homing in" to stuff coming into my local airport appeals. Although only crowflight 14 miles distant, reception from that direction is not the best.
RB tucked up in the loft means any aerial switch mechanism will have to be radio controlled, which should be a nice little challenge.
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And finally, have you any knowledge of a radio controlled low-loss switch that could be used to run the Skysearcher and my existing aerial jointly into the one box, thus allowing switching between them as the occasion demanded?
this looks like an ok switch:
http://www.ssejim.co.uk/44-remotecontrolledantennaswitch.new.20.htm
not radio controlled though, you can at something like this, possibly something with a better range:
http://bestofferbuy.com/Wireless-Digital-Remote-Control-Switch-for-Home-Appliance-(Model:T-923B)-White-p-25305.html?currency=GBP&utm_source=gbase&utm_medium=cse&utm_campaign=gbase
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Dave why don't you add departure airport information to the EGLL arrivals page?
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Dave why don't you add departure airport information to the EGLL arrivals page?
Because it's an arrivals page :-)
Actually it's on my to-do list, thanks for the reminder. Departures are already on the search page, in fact.
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Tks. The addition of the origin airport will be something very interesting. When do you plan to implement it? Also where is the search page you mention?
Also and browsing other files on the same folder, which applications are these?
http://www.civilaircraftregisters.org/Mode_S_Resources/AirNav%20NavData%20Update%201.jpg
http://www.civilaircraftregisters.org/Mode_S_Resources/AirNav%20NavData%20Update%202.jpg
Have you developed some addons for RadarBox? Would it be possible to share them with other users?
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Tks. The addition of the origin airport will be something very interesting. When do you plan to implement it? Also where is the search page you mention?
I think we're at cross-purposes here, I thought you were referring to departures from EGLL. Heathrow is the only airport close enough for me to be able to pick up aircraft taking off with my own box.
Having said that, I do have a routine that detects takeoffs and landings at nearly 100 of the world's major airports, using data from the PlanePlotter network (with their permission). For obvious reasons I can't host that data on my own website.
Also and browsing other files on the same folder, which applications are these?
http://www.civilaircraftregisters.org/Mode_S_Resources/AirNav%20NavData%20Update%201.jpg
http://www.civilaircraftregisters.org/Mode_S_Resources/AirNav%20NavData%20Update%202.jpg
Have you developed some addons for RadarBox? Would it be possible to share them with other users?
See www.airnavsystems.com/forum/index.php?topic=4562.msg45833#msg45833
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Tks Dave. 3 questions:
1- When do you plan to add the origin airport to the arrivals page and destination airport to the departures page?
2- Whay is the URL for the EGLL departures page?
3- how do you on your script know that a plane without GPS (with a position shift) is landing on 27L or 27R?
Tks.
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So many questions ! I thought you had developed your own solution for all this stuff :-) Still, as you asked nicely ...
1- When do you plan to add the origin airport to the arrivals page and destination airport to the departures page?
To be honest, it's not a priority I could do it any time, as the database already has the LHR flight schedules, but in all the feedback I get regarding the website, nobody has ever asked for it before.
2- What is the URL for the EGLL departures page?
If you visit the search page at http://www.civilaircraftregisters.org/Mode_S_Resources/LogReport/EGLLADSBsearch.asp you will be able to view both arrivals and departures.
3- how do you on your script know that a plane without GPS (with a position shift) is landing on 27L or 27R?
That's something you will have to work out for yourselves :-) In fact, there is no single solution to this, but there are several things you can usefully do. One is to monitor what runway is being used by other landing and departing traffic, which often will tell you the runway that must have been used. Another strategy, which works if an arriving aircraft is held at any of the 4 stacks, is to work out the position offset by detecting the start of the outbound turn (i.e. overhead the VOR).
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Tks for your reply.
1- It is strange as it would be a very interesting addition. We understand that you aren't too much interested in it maybe because of technical reasons but if you want we help you with our own flight number database experience.
2- Tks. Is there a departure only page (like the arrivals page)?
3- "One is to monitor what runway is being used by other landing and departing traffic, which often will tell you the runway that must have been used."
Wouldn't work as sometimes the T/O runway could be used for landings, as an expcetion due to traffic.
"Another strategy, which works if an arriving aircraft is held at any of the 4 stacks, is to work out the position offset by detecting the start of the outbound turn (i.e. overhead the VOR)."
Couldn't work too as flight could be vectored without flying over the VOR...
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1- It is strange as it would be a very interesting addition. We understand that you aren't too much interested in it maybe because of technical reasons but if you want we help you with our own flight number database experience.
Thanks for the offer, but I don't need any help with flight routings :-)
2- Tks. Is there a departure only page (like the arrivals page)?
Not at present.
The database certainly does log departures in real time - in fact it's currently configured to send selected users an SMS/text message as soon as an interesting aircraft gets airborne. But the main flights table (which currently has just under 8.9 million records) has a default index on last transmission time, which is great for getting arrivals in order but not so good for sequencing departures. One day I'll get around to adding the required extra index.
3- "One is to monitor what runway is being used by other landing and departing traffic, which often will tell you the runway that must have been used."
Wouldn't work as sometimes the T/O runway could be used for landings, as an exception due to traffic.
Now you really should know better than to tell me what does and doesn't work :-)
I'm well aware of how TEAM (Tactically Enhanced Arrivals Mode) works at Heathrow, where the designated departure runway is sometimes used for arrivals. But:
a) this only happens at certain, strictly limited times of day (full "mixed-mode" is prohibited at Heathrow)
b) an aircraft won't be landing on the same runway as another is taking off from at the same time :-)
c) landings on the two runways are never simultaneous, for separation reasons - they are always staggered
"Another strategy, which works if an arriving aircraft is held at any of the 4 stacks, is to work out the position offset by detecting the start of the outbound turn (i.e. overhead the VOR)."
Couldn't work too as flight could be vectored without flying over the VOR...
There you go again :-) I didn't say it works for all flights, only those that actually fly the holding pattern.
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>Thanks for the offer, but I don't need any help with flight routings :-)
Are you going to implement them or not? When?
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Are you going to implement them or not? When?
I don't understand why you keep asking me the same question.
The feedback I get from users of the EGLL website suggests that they couldn't care less about where a flight has come from or is going to, so adding this data isn't a high priority.
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>that they couldn't care less about where a flight has come from or is going to
I know many users of your site that have exactly the opposite opinion. I really think it could be very interesting and if you need our know-how we are here to help you.
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I know many users of your site that have exactly the opposite opinion. I really think it could be very interesting and if you need our know-how we are here to help you.
Correction, you know nothing about the users of my website.
But as you are so insistent in wanting to help me, it would be churlish of me to refuse :-)
What routing do you have in your database for AIC188, please ?
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What routing do you have in your database for AIC188, please ?
Why do you need to ask? You know full well that you can answer that question yourself using:
http://www.airnavsystems.com/cgi-bin/ANLV_SV/ANLV_SV_user.exe?usgetorgdst=0&usemail=PGANRBxxxxxx&usversion=ANRB301&fnumber=AIC188
AIC188,CYYZ,EGLL,VIDP,
And what has any of this got to do with a continuous rotation high gain antenna? Can we keep on topic.
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And what has any of this got to do with a continuous rotation high gain antenna? Can we keep on topic.
Hey, don't blame me for the thread drift, I didn't start it !
www.airnavsystems.com/forum/index.php?topic=5356.msg53821#msg53821
And if AirNav want to start a new thread for their repeated offers to help me, that's entirely up to them :-)
I'm simply trying to establish if their offer is of any value, so I'd suggest we let them answer, besides they may not agree with your routing (I don't).
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Let's keep on topic and Dave, you're the best! :-)
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Let's keep on topic
I guess that means you're not going to answer my question, then ?
Your offer of help didn't last long ... :-)
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Lets keep that to PMs please. So we can keep the thread on the antenna topic.
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Quote from first topic post "Good coax rotary joints are expensive, so I would just mount the entire radarbox and a netbook on the ceiling fan contraption"
would this void the warranty??? :)
Ground base VOR station use a rotating type system but instead of rotating the antenna they have a series of antennas mounted in a circle and rotate it eletricaly I.E Via high speed swicthing.
I agree with a previous post , to get any decent gain advantage its beam width would be too narrow. just go higher with what you got if you can.
My nabors would have a major hissy if i put something like that up , whering away all night.
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hallo,i have a skysearcher that i bought from moonraker. i was puzzled by the fact that the whole of the aerial seems to be one big short circuit.top and bottom of the dipole along with the reflector all bell out just like it was made from one piece. how can this be? i have made lots of aerials up in my workshop and i know a bit about them but the skysearcher has me stumped. ok i said, maybe its some new design but i wanted to understand it so i emailed moonraker and all i got was some silly reply from a guy called justin. when i emailed again he said he would contact the makers in japan and get back to me. needless to say thats the last i heard from him.anyway, i put the aerial up and pointed it south with much expectation and was dissapointed that the planes were lost at about 100 miles!.with my home made whip i can get down to lasno which is about 185 miles from my location in cork.so, is the skysearcher faulty or is the design not that good. im not getting the gain that moonraker advertise. however, i might be doing something wrong, though what, i dont know.one other point, a friend of mine who is a radar technician,a licenced ham and who has a vhf business licence does not understand this aerial either. i would welcome any views
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I have never heard of this kind of antenna , drop me a line at the email address below and ill send you some plans for a good 9 Db colinear vertical ,I have made 3 of these and they work very well and easy to make if you have basic soldering skills.
Geoff.
[email protected]