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Aircraft Data Decoding A forum to discuss decoding the various data transmissions such as ACARS, Mode-S, ADS-B, etc.

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  #21 (permalink)  
Old 06-04-2014, 11:38 AM
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I think people are confusing radar with "virtual radar." Hobbyists who track aircraft are not seeing actual radar returns. We are decoding and displaying positional data transmitted from suitably equipped aircraft.

ATC uses actual radar and can see just about everybody, military or civilian.
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Old 06-04-2014, 2:49 PM
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so is it anyway a regular civilian can setup his own radar setup for a reasonable price?im guessing not but i have to ask lol
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Old 06-06-2014, 1:20 PM
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Radars are high-powered radio transmitters. They have to be licensed and coordinated. The emitters themselves have to be tested and approved, which means purchased from a reputable manufacturer. Depending on the frequency ranges and power levels used, they can also be extremely dangerous.

Radar is not a feasible hobby.
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Old 06-10-2014, 7:56 AM
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I know that ATC have their own radar, but radar isn't an IFF kind of thing, it just shows a blip that something is there. How do you differentiate between military and civilian aircraft with just a blip? Do Military aircraft even show up on a TCAS? If they aren't using ADS-B then I think that answer would be no. Actually, NEXTGEN shares data with TCAS so a blip from a radar could be shared with civilian aircraft I guess.
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Old 06-10-2014, 12:51 PM
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I don't really care enough to do your research for you. Perhaps you should read up on how ATC, TCAS, etc. actually work. Then you wouldn't have to make so many guesses.
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Old 06-10-2014, 4:53 PM
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I realize you are talking about things like ATC radar, and not just any old radar, but a couple of comments. For ATC specific gear, and as generally applied to this discussion, your comments are right on the money. But there are exceptions.

Quote:
Originally Posted by DaveNF2G View Post
Radars are high-powered radio transmitters.
Note necessarily, remember average power is what counts. I have seen radars with average powers of well under 100 Watts with some pretty impressive ranges. I have seen FMCW radars with peak (and average, since it is CW) powers of under 2 Watts that were pretty darned good also.

Even a big old 6 foot antenna Raymarine 12 kW peak power Super HD radar that can see up to 72 nm is not that bad. Sure, it is 12 kW, or 12000 Watts peak power. But in its worst case mode (1 microsec PW and 820 Hz PRF) the duty cycle is only about .00082, so the average power from the transmitter is just under 10 Watts. The Radhaz zone exist, but is pretty short. 4 kW radars can have average transmitter power of under a Watt.

Of course, many radars are real power, I have worked on systems with peak transmitter powers measured in MW. And that is not even the ERP, just the transmitter power. Take a MW power level radar transmitter and hammer it into a 40+ dBi antenna gain and the power level gets real, real quick.

Quote:
Originally Posted by DaveNF2G View Post
They have to be licensed and coordinated.
Not necessarily true. The majority of radars in the US are not coordinated and only fall under the category of licensed by rule. Just like CB and VHF marine radio you can put a radar on your boat with no licensing or coordination effort on your end. There are probably more marine radars that do not require licensing (on “voluntary” ships or vessels) in the hands of Americans than all other kinds of radar combined. In any decent size harbor you can see hundreds at a time.

I have picked up used Raymarine units for well under $500, and some new radars are only in the $1000 range.

Are such radars meant to paint or track aircraft? No, and they have a limited look up angle. However I have, many times, tracked fixed wing aircraft and helicopters on marine radars.

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Originally Posted by DaveNF2G View Post
Radar is not a feasible hobby.
In general I agree, it is not a hobby for the masses. However, I know of one or two people who have made them hobbies. I have looked at and processed the echos of my own transmissions on VHF and UHF ham gear. I know an individual that has a UHF CW beacon that includes radar functionality. It is a propagation beacon with full ID. It also sends pulses distributed among the IDs, and he has processed and displayed the resultant returns often.

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Old 06-11-2014, 1:37 PM
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Quote:
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Quote:
Originally Posted by DaveNF2G View Post
Radar is not a feasible hobby.
In general I agree, it is not a hobby for the masses. However, I know of one or two people who have made them hobbies.
Don’t know why I didn’t think of this aspect when I wrote my original response, but one area that is gaining popularity concerning radars and the hobby aspect is passive bistatic radar.

You can use the energy of non-cooperative transmitters to track aircraft. Such transmitters might include FM radio stations, digital TV stations, cell tower signals, etc. You then look at and process in various ways the reflections of these sources off the aircraft / targets. A growing number of hobbyist are using the inexpensive RTL Dongle SDRs as the core of such systems. There are a few web pages and YouTube videos up with results.

At a much more simple level you can detect and display the Doppler shift of aircraft in flight with very simple equipment. True, this is not “tracking” as you derive no positional data, but you can still detect the aircraft. I have often used the ATSC pilot from Channel 7 in Los Angeles for this purpose. There are several ways to do this, the most simple is to use an SSB capable receiver and display the detected audio. I point the antenna down south (LA and LAX are south of me, over 120 air miles away) tune the receiver to 174.309 MHz and in USB mode. This results in a 1 kHz audio tone from the pilot. Channel the audio into an audio spectrogram program (something like Argo or SpectraVue works just fine) and set the levels, widths, and update rates appropriately. In busy air space it won’t take long for Doppler shifted reflections to show up.

This is aircraft departing LAX:


This is aircraft on approach to LAX:


Remember these images do NOT show “tracks” as such, no positional data is present. They show only radial velocity referenced to the transmitter source.

T!
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Old 06-12-2014, 2:58 PM
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Quote:
Originally Posted by poltergeisty View Post
I know that ATC have their own radar, but radar isn't an IFF kind of thing, it just shows a blip that something is there. How do you differentiate between military and civilian aircraft with just a blip? Do Military aircraft even show up on a TCAS? If they aren't using ADS-B then I think that answer would be no. Actually, NEXTGEN shares data with TCAS so a blip from a radar could be shared with civilian aircraft I guess.
ATC has basically 4 types of radar, long range, terminal (at an airport), ASDE and secondary radar, commonly known as the beacon radar or IFF or ATCRB if you want to call it that. The ATCRB is a type of radar operating on 1030 and 1090 MHz. The aircraft has to interrogate this radar. This radar on the ground includes Mode-S. All this Mode-S essentially does is provides more info about the aircraft like the type of aircraft. Each aircraft that has Mode-S has a unique Mode-S identifier which is programmed into the Mode-S transponder.

I think ADS-B is an entirely separate system but I'm not sure since it came out after I left Flight Inspection Ops and avionics maintenance and I don't handle any mobile/aircraft ADS-B systems in my job now with the FAA.

TCAS operates on the same 1030 and 1090 MHz frequencies but is mainly aircraft to aircraft. It operates separately from the ATCRB radar. To accomplish this there is a data buss on the aircraft referred to ARINC 429. There are 2 types of ARINC 429 busses, fast and slow. On this buss when the transponder/ATCRB transmits it sends a word telling the other 1030/1090 MHz systems not to transmit. The TCAS does the same thing.

The primary radar indeed just basically sends a pulse out and receives a reflection from anything it hits. This reflection could be aircraft, cars, big birds or weather. If you were to look at a controls radar screen for each aircraft at the radar facility you would see those marks, the skin paint from the primary radar and just a bit farther out the ATCRB return. By the way the primary radar return isn't a "blip" but a line on the screen.

Once the primary radar and the ATCRB receive it's return the info goes into a computer, at 1 time called the common digitizer, which turns this analogue info into digital info so it can be sent to the ATC radar room. At that point more computer magic happens and the data tags, which contain the call sign, speed ATCRB setting (squawk code) altitude and more are added to the "blips" and then out to the controllers screen. I'm not sure if ATC can add a data tag to an aircraft that isn't using an ATCRB. But now it is almost impossible to even get close to a major airport without a ATCRB in the aircraft. I guess if the aircraft were out in the middle of no where, like the west, you can have very few problems flying around with a ATCRB transponder.

At one time if a controller didn't see the primary return and just the ATCRB return they could not provide radar info to the aircraft. I do know of at least 1 FAA facility that has a waiver for this requirement.

As for your question about how different military "blips" differ from civilian "blips" they don't. Both the primary radar and the ATCRB returns look exactly the same. The only difference is in the computerized tags added by the system at the radar control facility. AND the tags for all aircraft are identical in the fact that they have the exact same type info on the tags. The only difference is the info shown in the radar tag.

And yes both military and higher end civilian aircraft have TCAS. I don't know if every military aircraft have TCAS BUT with just the ATCRB return to the TCAS system will create a target on the TCAS indicator.

I remember when I was still flying with FAA Flight Inspection myself and 2 pilots went to Atlanta to pickup a new aircraft. It had 1 of the 1st TCAS systems installed in FAA aircraft. Just to see it work is pretty cool.

Hope this explains a bit about FAA radar.
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Old 06-16-2014, 12:38 AM
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So military aircraft don't transmit position reporting data, okay. But how do you track them? LOL! That's all I want to know. For example, there was a TU some BS or other Russian Bear come within 50 miles off the California coast. What differentiated them from us? I mean military jets don't even transmit tracking data. So do military aircraft just use Mode S?
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Old 06-16-2014, 11:47 AM
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Quote:
Originally Posted by poltergeisty View Post
So military aircraft don't transmit position reporting data, okay. But how do you track them? LOL! That's all I want to know. For example, there was a TU some BS or other Russian Bear come within 50 miles off the California coast. What differentiated them from us? I mean military jets don't even transmit tracking data. So do military aircraft just use Mode S?
Google "IFF" - Identification Friend or Foe - That should help you answer your question
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Old 06-16-2014, 11:47 AM
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ADS-B is the basis of the NextGen system in the United States. It is not radar.

BTW, to say something is "licensed by rule" is to agree with my assertion that a license is required. A transmitter in a LBR service is only licensed if it is being operated in compliance with the pertinent rules. Otherwise, it does not enjoy "licensed" status.
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Old 06-16-2014, 12:56 PM
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The TCAS for the LAX airport area the other day. Screenshot from the planeplotter software.
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Old 06-16-2014, 5:04 PM
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They really need to get rid of those obsolete IBM/360 systems.
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Old 06-17-2014, 11:28 AM
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The map would probably be more meaningful with less info displayed. Maybe just the reg and/or flight number and/or aircraft type?
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Old 06-17-2014, 2:21 PM
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Quote:
Originally Posted by DaveNF2G View Post
BTW, to say something is "licensed by rule" is to agree with my assertion that a license is required. A transmitter in a LBR service is only licensed if it is being operated in compliance with the pertinent rules. Otherwise, it does not enjoy "licensed" status.
Which is why I said "no licensing or coordination effort on your end". On a “voluntary vessel” (one not required by law to be equipped with a radar) you do not have to do anything but be in compliance. Take the radar out of the box, install it as you safely see fit on vessel, make sure that vessel is in the water (can't use them on shore). No effort or paperwork on your end are required to license or coordinate the radar. It is just like a marine VHF radio or a CB radio in regards to licensing, and just as difficult to "get" the license.

Of course essentially everything in the US is licensed if it legally transmits. It may be a service specific license or it may be license by rule, but off the top of my head I can't think of a single thing that intentionally transmits that is not in some way licensed.

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Old 06-17-2014, 2:42 PM
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Radios are not licensed. Radio operators are licensed. No operator license is required for intentional radiators operating under Parts 15 or 18 of the FCC Rules.
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Old 06-17-2014, 4:56 PM
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Quote:
Originally Posted by DaveNF2G View Post
Radio s are not licensed. Radio operators are licensed. No operator license is required for intentional radiators operating under Parts 15 or 18 of the FCC Rules.
Yes, radios are not licensed (that falls more in the realm of certification and type acceptance), the operator is licensed. But without the radio the operator has no need of a license and the radio service determines the operators licensing requirement. Perhaps I should have said “Of course essentially everyONE in the US is licensed if THEY legally transmit”. The general point I was making is that in order to operate certain types of radar (of a type that is common and relatively inexpensive in the US) you do not need to do anything to license (not even any paperwork to file or fees to pay) the operator or coordinate the radar with anyone, I did not say they did not need to comply with regulations, in fact I very much said they did need to comply to be legal.

These are questions below, not statements, I do not know myself (not my gig man - Zonker) but it seems to me the regulations imply several things.

We are rather far afield from the thread here, but wouldn't Part 15 and 18 still be "license by rule" even if they do not use that specific term? As long as whatever the device is conforms to the rules they are legal to use, when they step outside those boundaries they are no longer legal, and thus “unlicensed”. I don’t really see a difference there from services that use the specific description of “license by rule”.

Of course some “transmitters” are Part 15 devices, such as low power FM transmitters, Baby Monitors, Wireless Microphones, etc. If you violated the rules and added an amplifier / antenna to make those transmitters perform outside Part 15 parameters wouldn’t you still be liable to receive an NOUO? Just exactly like a CBer running an amplifier? If the Part 15 / 18 equipment is illegal it is “unlicensed operation”, at least that is the way the FCC Enforcement folks seem to like to write up illegal FM transmitters, as Part 15 violations. That would seem to imply that legal operation is the opposite of unlicensed.

I gather, based on reading the Enforcement Bureaus releases, that the FCC itself differentiates radio transmitters from intentional radiators, despite them both potentially or originally falling under Part 15. In the event that issues are not resolved at the NAL / Citation level and escalate it seems like most “noise” and leakage type issues are given Notice of Violation, while most radio transmitter (lets generalize transmitter to something connected to an antenna with the intent to distribute a signal) type operations are given Notice of Unlicensed Operation. If your plasma TV or electric fence is the issue you seem to get an NOV, but if you put a bigger antenna on your Baby Monitor or FM Wireless microphone you seem to get an NOUO.

T!
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Old 06-17-2014, 5:45 PM
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Wink you can find out hoew to track some of them here

Military Comms Monitoring MilAir Frequencies HF VHF UHF
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Old 06-18-2014, 8:42 AM
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That screenshot is just showing a ton of TIS-B messages (the lowercase-starting hex code and the .NO-REG are clues). Can sure make a mess of a screen...
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Old 06-18-2014, 9:30 AM
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The regulatory discussion has indeed parted company with the topic of this thread. I can't think of any specifically regulatory forums on RR (except for the service-specific forums), but if this conversation needs to be continued, then a topical thread should be initiated somewhere more appropriate.
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