Finding info and frequency of radar?

[MUTNAV]

I was stationed at a military/civilian airport on the DEW Line for awhile. The living accommodations were basically co-located with the radar site. I could hear those radar chirps with each sweep while listening to my Sony Walkman, which was just a cassette tape player (no radio in it). I often wonder how dangerous to ones health the RF radiation was from that ?

my guess is not much danger.... It should have been evaluated anyway (depending on what year / era it was), of course microwave ovens were considered something to make and market after a Radar tech found that his hershey bar melted when working on an exposed antenna, so......

With the older cell phones if you left one near your computers speakers, they would let you know about a phone call before the phone did (and in my case, every time the phone checked in with the cell tower).

Thanks
Joel

 

[ArloG]

my guess is not much danger.... It should have been evaluated anyway (depending on what year / era it was), of course microwave ovens were considered something to make and market after a Radar tech found that his hershey bar melted when working on an exposed antenna, so......

With the older cell phones if you left one near your computers speakers, they would let you know about a phone call before the phone did (and in my case, every time the phone checked in with the cell tower).

Thanks
Joel

Don't want to get off on a tangent here. 2 stories come to mind.
A brief wiki on military airfield surveillance radar tells of 2.3-2.9 GHz and a Klystron output of 1.3 MW, pulsed at 1 microsecond.
That's a lot! RF exposure a distance away with the rotating antenna? Who knows. If you rode the transponder boom or were close if the drive motor stalled. Toast? Literally?

But one buddy in the Army stationed in Germany in the 80's mentioned the field radar shack he was in during exercises got frigid. They would occasionally go out and stand in front of the stationary dish "to warm up". I dunno. I call bs. But then again who knows. He came back after discharge and carried a 1/2 keg up a flight of steps on his shoulder. Because he was a tough Army guy. Cleared the top step and dropped the full keg on his big toe. It still looks like a nasty flattered burrito today.

But my dad was in the Aleutians in the late 50's, early 60's. When the russkies were testing ballisitc missiles and MIRV's.
He was in the hush-hush Nancy Raye group. Rivet Ball, Cobra Ball RC-135's. Wiki that and go as far as you wish.
He told me once that one of the KC-135 variants had cameras on one side on the plane and a fiberglass fuselage on the other with megawatt radars.
They would fly up and down the Aleutian peninsula and photograph missiles going up and radar track them coming back down.
During ground tests of the radar system before a mission they would crank up the power over an empty field.
Any arctic foxes (he said there were tons of them, like prairie dogs) close by got fried when they turned on the microwaves.
I can't call bs on that because I used to overhear them talking over beer and pinochle.

You probably shouldn't cut a peep hole in the screen sammaged between the door of the microwave to better see when your Hot Pockets are done. Right?

 

[dkcorlfla]

Interesting results on UHF using small 3 element Yagi pointing straight up. See the signal flutter at 451.5? It would show up each time an aircraft was overhead. I was using my stand alone ADS-B tracker to keep tabs on the aircraft. They were landing to the south this morning and are about 2600 to 3000 feet up. I believe what I'm seeing and hearing is a commercial digital station that is out of range skipping off the bottom of the aircraft. My best guess as to the on and off signal is it's reflecting off different parts of the aircraft. I think with a better higher gain antenna and using a higher frequency I could pick up a lot more. Still want to try and pickup radar but I need to come up with a dish and feed that could receive the high stuff. It was a fun and good learning experience.

BTW - I have a .wav sound recording but did not see an option to upload it.

 

[Token]

Hi all, I live under the ILS to a major airport and another to the north about 15 miles.

I'm curious if it might be possible to hear reflected radar pulses when the aircraft fly overhead.

Tried to run some searches but so far I have not found anything on the radar just other stuff like weather radar and Flightaware.

Any ideas on how to find more info on the aircraft radar and not weather?

Yes, you absolutely can hear / detect the reflections of radar pulses, or any other RF, off of aircraft. Research "bistatic radar" and "passive coherent location".

I recommend you do not initially try to look for specific radar signals, but rather pick more common RF sources to look at. It is tempting to use FM radio signals as a source, and this is absolutely doable, however the Doppler shift imparted on a CW (by this I mean CW, continuous wave, not CW, Morse code) signal is far easier to hear and detect. There are a number of signals that are handy for this, but I like the ATSC pilot tone on TV channels.

Frequencies below are approximate, I have noted not all stations are dead on the money with regards to frequency.

Lets say you have a local RF channel 7 TV station. Not one that identifies as channel 7, but one that transmits on channel 7 regardless of the identified TV channel. There will be an ATSC pilot tone associated with this transmission on 174.310 MHz. Tune a stable receiver to 174.309 MHz, in USB mode, and you will hear (and be able to plot) a 1 kHz tone from this transmission. Point an antenna at the area you think aircraft will transit.

You should see the Doppler shift that aircraft put on that pilot as they transit that area. You will also see the pilot tone, but the Doppler shift can be clearly seen (and heard) if you put the audio into something like a waterfall spectrogram.

Here is an example of what I mean. I am tuned to 174.309 MHz, in USB mode, with my antenna turned in such a direction that I am looking at the approach to LAX. You can clearly see the strong 1 kHz tone of the ATSC pilot, but you can also see the targets reflecting RF.

A different time of the same day, when there are more departures than landings, and the antenna more oriented towards the departure end.

T!

 

[Token]

Don't want to get off on a tangent here. 2 stories come to mind.
A brief wiki on military airfield surveillance radar tells of 2.3-2.9 GHz and a Klystron output of 1.3 MW, pulsed at 1 microsecond.
That's a lot! RF exposure a distance away with the rotating antenna? Who knows. If you rode the transponder boom or were close if the drive motor stalled. Toast? Literally?

But one buddy in the Army stationed in Germany in the 80's mentioned the field radar shack he was in during exercises got frigid. They would occasionally go out and stand in front of the stationary dish "to warm up". I dunno. I call bs. But then again who knows. He came back after discharge and carried a 1/2 keg up a flight of steps on his shoulder. Because he was a tough Army guy. Cleared the top step and dropped the full keg on his big toe. It still looks like a nasty flattered burrito today.

These kinds of stories (warming up with RF) have been around as long as radar has. I have been hearing them since at least the 1970's (when I worked on my first radar professionally), and I have been told (by old timers then) that they had been around forever. And every one of those stories I have followed up on was BS.

Lets talk power. 1 MW sounds big, but what is the duty cycle? A fairly typical radar duty cycle is below -30 dB DC, or 1/1000 (or less) the peak power. So the 1 MW becomes more like 1 kW of average power. Sure, I have worked on radars with DC's more like 20-30%, but those are the exceptions, not the rule. Now push that 1 kW into an antenna, get some antenna gain, and the numbers get big again. But, space loss adds up.

A modern ASR-11 Airport Surveillance Radar has an average power of 2.1 kW. The RADHAZ limit for MPE (Maximum Permissible Exposure) is 43 feet. That level is 5 mW/cm^2, 5 millWatts per square centimeter 5 mW is not going to warm up anything. Sure, as you get closer the power density goes up, but realistically even if you hang a pack of hotdogs right on the feed assembly you are not going to warm much up. Been there, done that, and most of the times it was pretty disappointing. Most of the time.....

T!

 

[littona]

my guess is not much danger.... It should have been evaluated anyway (depending on what year / era it was), of course microwave ovens were considered something to make and market after a Radar tech found that his hershey bar melted when working on an exposed antenna, so......

With the older cell phones if you left one near your computers speakers, they would let you know about a phone call before the phone did (and in my case, every time the phone checked in with the cell tower).

Thanks
Joel

We had the same noise on cordless phones and stuff when I was stationed at a Scope Signal III site in Nebraska. We had a 10kW omnidirectional HF weather fax antenna a few thousand feet from the dorm.

Then there's that one time I was working on an antenna near a radar and felt my metal rimmed glasses buzz. The radar guys told me that they blanked it out in my direction...

The radar guys would occasionally do silly things like hang a bratwurst in front of the radar sail. (hint: poof)

On exercise deployments, they'd sometimes put a fluorescent tube on a camo pole so they could see it light up and know the radar was still working from a distance.

Then we had other radar guys that learned that you can't put up radar scattering camouflage netting near a radar. It has little metal rings woven into it. They get all sparky when the radar sweeps by.

RF is fun!

 

[MUTNAV]

These kinds of stories (warming up with RF) have been around as long as radar has. I have been hearing them since at least the 1970's (when I worked on my first radar professionally), and I have been told (by old timers then) that they had been around forever. And every one of those stories I have followed up on was BS.

Lets talk power. 1 MW sounds big, but what is the duty cycle? A fairly typical radar duty cycle is below -30 dB DC, or 1/1000 (or less) the peak power. So the 1 MW becomes more like 1 kW of average power. Sure, I have worked on radars with DC's more like 20-30%, but those are the exceptions, not the rule. Now push that 1 kW into an antenna, get some antenna gain, and the numbers get big again. But, space loss adds up.

A modern ASR-11 Airport Surveillance Radar has an average power of 2.1 kW. The RADHAZ limit for MPE (Maximum Permissible Exposure) is 43 feet. That level is 5 mW/cm^2, 5 millWatts per square centimeter 5 mW is not going to warm up anything. Sure, as you get closer the power density goes up, but realistically even if you hang a pack of hotdogs right on the feed assembly you are not going to warm much up. Been there, done that, and most of the times it was pretty disappointing. Most of the time.....

T!

and of course when you "push it into an antenna" that also is usually over a pretty good aperture.


Thanks
Joel

 

[MUTNAV]

Yes, you absolutely can hear / detect the reflections of radar pulses, or any other RF, off of aircraft. Research "bistatic radar" and "passive coherent location".

I recommend you do not initially try to look for specific radar signals, but rather pick more common RF sources to look at. It is tempting to use FM radio signals as a source, and this is absolutely doable, however the Doppler shift imparted on a CW (by this I mean CW, continuous wave, not CW, Morse code) signal is far easier to hear and detect. There are a number of signals that are handy for this, but I like the ATSC pilot tone on TV channels.

Frequencies below are approximate, I have noted not all stations are dead on the money with regards to frequency.

Lets say you have a local RF channel 7 TV station. Not one that identifies as channel 7, but one that transmits on channel 7 regardless of the identified TV channel. There will be an ATSC pilot tone associated with this transmission on 174.310 MHz. Tune a stable receiver to 174.309 MHz, in USB mode, and you will hear (and be able to plot) a 1 kHz tone from this transmission. Point an antenna at the area you think aircraft will transit.

You should see the Doppler shift that aircraft put on that pilot as they transit that area. You will also see the pilot tone, but the Doppler shift can be clearly seen (and heard) if you put the audio into something like a waterfall spectrogram.

Here is an example of what I mean. I am tuned to 174.309 MHz, in USB mode, with my antenna turned in such a direction that I am looking at the approach to LAX. You can clearly see the strong 1 kHz tone of the ATSC pilot, but you can also see the targets reflecting RF.

A different time of the same day, when there are more departures than landings, and the antenna more oriented towards the departure end.

T!

Maybe you could hear the Doppler shift if your receiver is in FM mode? Haven't tried it but might be worth a shot...


Thanks
Joel

 

[MUTNAV]

That's what I was trying to do; however, the station I was monitoring came back with a call sign that did not match the station I thought I had so I do not know. BTW - I just found a solid steady trunking control channel on 455 Mhz and I already have a yagi beam for that frequency so that will be the next thing to try. Point it near straight up and the next time the aircraft are landing to the south I just might see and or hear something. If nothing else it was fun trying.

I just watched a video (from Rhode and Schwarz about bistatic radar, and one of the interesting things about it was that if the aircraft is between you and the transmitter, the doppler effect turns out to be zero

So what we need to do is either look at the backscatter from emitters (like a normal radar but with transmitter and receiver seperated), or the magnitude of the reflections from the aircraft, which are much larger when between the source and yourself.

The Rhode and Schwarz webinar (they sell test equipment and were saying how to do the tests for passive radars) says that the reflections are much larger this way, to the point of suggesting satellites for low RCS aircraft are a good idea.

Thanks
Joel

 

[Token]

Maybe you could hear the Doppler shift if your receiver is in FM mode? Haven't tried it but might be worth a shot...


Thanks
Joel

Or use USB, 1 kHz offset (or any specific offset within the audio passband), and put a notch filter on the 1 kHz tone. Then you will only hear signals that are not the source tone.

T!

 

[dkcorlfla]

Yes, you absolutely can hear / detect the reflections of radar pulses, or any other RF, off of aircraft. Research "bistatic radar" and "passive coherent location".

I recommend you do not initially try to look for specific radar signals, but rather pick more common RF sources to look at. It is tempting to use FM radio signals as a source, and this is absolutely doable, however the Doppler shift imparted on a CW (by this I mean CW, continuous wave, not CW, Morse code) signal is far easier to hear and detect. There are a number of signals that are handy for this, but I like the ATSC pilot tone on TV channels.

Frequencies below are approximate, I have noted not all stations are dead on the money with regards to frequency.

Lets say you have a local RF channel 7 TV station. Not one that identifies as channel 7, but one that transmits on channel 7 regardless of the identified TV channel. There will be an ATSC pilot tone associated with this transmission on 174.310 MHz. Tune a stable receiver to 174.309 MHz, in USB mode, and you will hear (and be able to plot) a 1 kHz tone from this transmission. Point an antenna at the area you think aircraft will transit.

You should see the Doppler shift that aircraft put on that pilot as they transit that area. You will also see the pilot tone, but the Doppler shift can be clearly seen (and heard) if you put the audio into something like a waterfall spectrogram.

Here is an example of what I mean. I am tuned to 174.309 MHz, in USB mode, with my antenna turned in such a direction that I am looking at the approach to LAX. You can clearly see the strong 1 kHz tone of the ATSC pilot, but you can also see the targets reflecting RF.

A different time of the same day, when there are more departures than landings, and the antenna more oriented towards the departure end.

T!

Thanks for the info and screen shots. I just have to look into this in more detail. I will do some research on the "ATSC pilot tone on TV" and the QRSS Viewer program.

 

[Token]

Thanks for the info and screen shots. I just have to look into this in more detail. I will do some research on the "ATSC pilot tone on TV" and the QRSS Viewer program.

ATSC (Advanced Television System Committee) is the standard for digital TV in the US. It is basically a digital standard that allows multiple channels of data in a single transmission, and occupies the same bandwidth as the old NTSC channels did, about 6 MHz. This allowed the transition from the old analog TV system to the current HD digital system without completely reorganizing the way the TV RF spectrum, and channelization, worked.

Each TV channel in the US is 6 Mhz wide. The TV spectrum is in 3 parts, VHF-Lo, VHF-Hi, and UHF. Part of each channels transmission is a “Pilot Carrier”. This looks like a carrier in the signal, a steady, unmodulated tone. It is positioned about 309.44 kHz from the lower frequency edge of each channel allocation. So TV channel 2 would be the frequency range from 54.0 to 60.0 MHz, and the ATSC pilot would be at about 54.30944 MHz. Channel 7 is from 174 to 180 MHz, and the pilot is at about 174.30944 MHz. And channel 14 is form 470 to 476 MHz, with the pilot at about 470.30944 MHz.

You can find the channelization for TV in the US here:

Pan-American television frequencies - Wikipedia

en.wikipedia.org

While I used QRSS Viewer in that picture example, done 13 years ago, I am not sure I would recommend it today. That program works well, but it is quite old and might be hard to find. You can use any program that will show a spectrogram of the audio. Something like the audio program Audacity should work fine. And many SDR software packages have the ability to zoom in enough and slow the waterfall down enough to do it in the software controlling an SDR.

Here is another example done in a different software, in this case SpectraVue. In this case, an RFSpace SDR-IQ SDR was used with an Icom R8500. The R8500 was tuned to 174.310 MHz and the SDR-IQ was sampling the 10.7 MHz IF. So no audio involved here, just direct sampling (and recording, this image is actually taken form the recording) of the IF. However, I could have used this same program and the sound card in the computer to do this all at audio, if I wanted to.

I prefer working with IQ recordings because you have the option to process the data differently at a later date. As you learn or think of new techniques you can go back and apply them over and over to a historic signal, instead of having to capture it again, or under differing conditions.

Stepping away from this specific signal source, you can pretty easily detect Doppler shift, and other reflections, on many different signals. I have seen Doppler shift, be it aircraft, meteor, or atmospheric induced, on shortwave signals, VHF signals, UHF signals, etc. And, if you know the source frequency (such as being able to see the ATSC tone and the reflection at the same time) you can calculate the target radial velocity.

T!

 

[dkcorlfla]

Aluminum overcast? The info from Token about using broadcast TV and their ATSC pilot tone really opened my eyes and mind to what can be done. One thing led to another and I have come across lots of additional info and resources.

Found a web site (Over the Air Digital TV and How to Get It) that has a ton of info on TV stations and has calculators to help find the location of the TV broadcast towers. I found one near Tampa that is just below the horizon so I only see a very faint trace of the ATSC pilot tone until the aircraft get between my receiver and the transmitter. Well, there are a heck of a lot of aircraft in the air between Orlando and Tampa and the tone comes alive with all kinds of flutter on the signal depending on the direction. When I took the snap shot below the tone was steady on from all the reflections.

Here are some more keywords that will pull up lots more if anyone is interested.

"AirScout" software used to predict "Aircraft Scatter Propagation" Make sure to take a look at the Doc for AirScout as it has a ton of info.

 

[dlwtrunked]

I was stationed at a military/civilian airport on the DEW Line for awhile. The living accommodations were basically co-located with the radar site. I could hear those radar chirps with each sweep while listening to my Sony Walkman, which was just a cassette tape player (no radio in it). I often wonder how dangerous to ones health the RF radiation was from that ?

That was receiver overload from it on another frequency.

 

[MUTNAV]

Aluminum overcast? The info from Token about using broadcast TV and their ATSC pilot tone really opened my eyes and mind to what can be done. One thing led to another and I have come across lots of additional info and resources.

Found a web site (Over the Air Digital TV and How to Get It) that has a ton of info on TV stations and has calculators to help find the location of the TV broadcast towers. I found one near Tampa that is just below the horizon so I only see a very faint trace of the ATSC pilot tone until the aircraft get between my receiver and the transmitter. Well, there are a heck of a lot of aircraft in the air between Orlando and Tampa and the tone comes alive with all kinds of flutter on the signal depending on the direction. When I took the snap shot below the tone was steady on from all the reflections.

Here are some more keywords that will pull up lots more if anyone is interested.

"AirScout" software used to predict "Aircraft Scatter Propagation" Make sure to take a look at the Doc for AirScout as it has a ton of info.

Just remember that if the aircraft is between you and the transmitter, the Doppler effect will be minimal, if any...

(the doppler shift from a reflection as the aircraft is moving away from the transmitter is canceled by the Doppler effect of it approaching you IAW the Rhode and Schwarz bistatic radar webinar).

You should be able to pick up the scatter though.

https://tvfool.com/ and FM Fool - Home are also good sites


Thanks
Joel

 

[Token]

Just remember that if the aircraft is between you and the transmitter, the Doppler effect will be minimal, if any...

(the doppler shift from a reflection as the aircraft is moving away from the transmitter is canceled by the Doppler effect of it approaching you IAW the Rhode and Schwarz bistatic radar webinar).

You should be able to pick up the scatter though.

In the bistatic model and with a non-cooperative illuminator, I think there are 2 conditions (not counting a non-moving target) when there is no Doppler shift detectable. Plot the two points on a map, the location of the transmitter and the location of the receiver. Draw a line from one to the other, terminating at the two points. Anytime a target is on that line, there will be no detectable Doppler shift, regardless of target motion. The second condition that will show no Doppler is anytime a target is between the end points defined by the two locations and moving parallel to that line. Movement not parallel to the line, and not on the line, will show Doppler shift.

T!