9 ms·

6 GHz frequency modulated radar

261 points by paulgerhardt 12y ago

ChuckMcM 12y ago
I really love that you can get a power amplifier for the 5Ghz RF for about $2.
- a1k0n 12y ago
  The VCO (HMC431LP4) seems to be more like $20, though. edit: should have read the rest of the article after the schematic where he says as much
- VLM 12y ago
  Its about the right price for +20dBmW at 6cm. minicircuits.com has several MMIC in that freq range at that output power. Transcom sells a nice well over 30 dBmW MMIC for that same freq band... you can buy a kit from minikits in australia, the EME141-5800, the bare chip is like $20. Some ham radio work shows you don't need the fancy 4 layer weird oshpark material for workable stuff in that general freq range. http://www.w1ghz.org/MBT/multiband.htm http://www.w1ghz.org/MBT/multiband.htm As an interesting extreme opposite comparison, there was a B-29-ish era chirp radar altimeter for aircraft landing which was almost entirely mechanical. A little buzzer/motor thing varied the size of a resonant cavity by a little bit, and the resulting audio signal was turned into a voltage / altitude using something like a capacitor/resistor bridge. So one vacuum tube, a resistor, a capacitor, a diode mixer, and a meter (and a lot of plumbing) If you'd like better antennas around that range, yet again, just ask a ham radio guy. Its a very awkward freq band where dishes, and most importantly dish feeds, are huge compared to 10 or 24 GHz band, but a loop yagi like you'd use at 2 GHz or lower would be ridiculously small. The microwave ham radio contester guys seem to like horn antennas at that band so couple it into a moderately large waveguide and attach the (homemade) waveguide to a (homemade) horn antenna.
- mng2 12y ago
  What costs money is the spectrum analyzer, network analyzer, and Microwave Studio license.
  - bsder 12y ago
    Exactly. Testing RF is a PITA because the test equipment is so stupidly expensive.
    - Animats 12y ago
      Yes. Back in the 1990s I built a little LIDAR system using much the same principle as this system - modulate the output beam with a 20MHz carrier, down-convert at the receive end using the same local oscillator like an FM receiver, and measure the phase shift between the down-converted output and input. That transformation is phase-preserving, and the phase shift at the lower frequency represents the range. It wasn't hard to build. But I didn't have the test equipment to adjust it.
aidenn0 12y ago
The best antenna upgrade for least work would probably be to build a Yagi
- Florin_Andrei 12y ago
  That would be a pretty tiny Yagi, too. :)
- hwillis 12y ago
  Actually no, a yagi would be very bad. The Radar has a 700MHz bandwidth, almost 12% of the center frequency, and yagis work for a fraction of that. A horn is pretty simple to make.
  - aidenn0 12y ago
    Oh! I didn't see the bandwidth was so wide. You are correct. Wouldn't the resolution still be decent with a narrower bandwidth (i.e. the 10s of MHz that a yagi could manage)? Also, as an alternative to a horn antenna, a parabolic reflector should work well in this band without being too large, right?
    - madengr 12y ago
      No, FMCW radar range resolution is proportional to RF bandwidth. You would still need the horn as a feed for the dish, but yes, you would get more gain.
    - hwillis 12y ago
      The range resolution would go from 8.5" to five yards if you changed the bandwidth to 30 MHz. Currently the radar could figure out the direction a person is facing to about 45 degrees. 5 yards would be good to find the orientation of a house. Parabolic antennas are just horns with lenses. The bigger the parabola, the better the focus and the wider the bandwidth. A horn would be a few inches across, but a 700 MHz reflector would be a couple feet.
jwr 12y ago
Very impressive. I would have thought that this sort of RF work is outside the hobbyist realm. The rest of the blog is equally impressive — 217-ball BGA soldered in a home-made reflow oven?
- sliverstorm 12y ago
  He's an EE student and clearly a pretty good one, so IMO he is beyond the typical hobbyist realm. The nebulous space of the professionally trained tinkerer. bunnie huang comes to mind as another example of this sort. When he cracked the Xbox, he had training & equipment that hobbyists don't have- but he did it in the hobbyist spirit.
  - rasz_pl 12y ago
    Today you can get access to equipment thru hackerspaces, so its not even all that expensive.
    - sliverstorm 12y ago
      It still depends on what you want to do- sniffing high speed memory busses and work in reflow ovens are still out of reach of most hackerspaces I have seen.
      - VLM 12y ago
        You can use a rework station (basically a low air speed hot air gun) and wave it around. You'll need one anyway. Maybe $100 minimum. The biggest problem with building your own reflow oven is the conversion kit mfgrs want their profit off repacking and marking up retail parts (arduinos, SSRs, thermocouples, etc) and of course you need a donor oven (maybe $50 at walmart?) so you end up paying like $150 to bodge something together.... while over on ebay, you can get a brand new professional reflow oven shipped to you for a bit over $200 from the usual gray market sellers. Supposedly they work pretty well and I'll eventually buy one. Or maybe they're junk. If I get closer to buying one I'll research it in detail. I've done the skillet / hot plate + pan thing. Make a sling of kapton tape (you do have kapton, right?) because otherwise you're going to melt the solder and then stand there thinking "um, ok, so now how do I remove a PCB thats too hot to pick up, and leaving it on the hot plate for 30 minutes while it cools down exceeds all sanity" Even with lead free solder paste I think its unacceptable to share hot plate with kitchen and lab. You can put the PCB on a steel spatula and the whole works on the hot plate and that works pretty well if you don't do kapton. (edited to add and you can easily spend more than the cost of a reflow oven by trying to avoid buying a reflow oven, because a non-contact IR temp meter is a handy accessory to the hot plate technique, but if you need to "charge" the cost of a IR thermometer to the hot plate project, suddenly its cheaper to just buy an oven...) Hand soldering SMD is very easy but slow. Faster than hand soldered thru-hole, but still pretty slow. I have done 0201 RF parts but it was not really any fun at all, the bigger stuff is much easier to hand solder. And no caffeine allowed.
lowglow 12y ago
This really makes me wish I took Antennas as an elective in EE. Are there any good books/resources to get up to speed on things like this?
- w8rbt 12y ago
  The ARRL Antenna Book is pretty good: http://www.amazon.com/ARRL-Antenna-Book-22nd-Softcover/dp/087259694X http://www.amazon.com/ARRL-Antenna-Book-22nd-Softcover/dp/08...
- hwillis 12y ago
  http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/ http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-... http://www.amazon.com/Short-Range-Practical-Approaches-Electrical-Engineering/dp/143986599X http://www.amazon.com/Short-Range-Practical-Approaches-Elect... http://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/0133957241 http://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/...
- Jach 12y ago
  The lecture notes on the MIT site these projects are inspired from has some useful PDFs: http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/lecture-notes/ http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-... When I was building my own version, Kai Chang's RF and Microwave Wireless Systems was a really great resource for the basics. Beyond that, you'll want to have a good foundation in signal processing to make use of the data from the device. The author doesn't mention it, but the radar he has is capable of creating SAR images. I'd love to see the results of a 6 GHz radar -- Dr. Greg Charvat (one of the MIT guys) has a demo on his website of a 10 GHz version that's pretty impressive. His thesis can help with some signal processing details, but the book Spotlight Synthetic Aperture Radar: Signal Processing Algorithms by Carrara, Goodman, and Majewski is even better.
darkarmani 12y ago
I'm not sure this is legal in the US w/r/t FCC. I know the author isn't in the US, but pointing this out for US hackers.
- Florin_Andrei 12y ago
  > I'm not sure this is legal in the US w/r/t FCC. What is the rationale for not allowing these?
  - ne0n 12y ago
    It's not specifically not allowing these devices, it's broadcasting on a restricted frequency without the proper license. The FCC regulates who can broadcast on which frequencies. Getting a ham license can open it up a bit, but there are still regulations to follow.
    - lettergram 12y ago
      I wish they would open up 214-400 THz range. Then instead of charging everyone $99/month for poor cell phone service, we can charge $99/month just for living.
      - triangleman 12y ago
        Infrared?
        kbaker 12y ago
        I think parent might have meant the Black-body radiation of a human [1], but was off by an order of magnitude... should be 14 um to 7.5 um wavelength = 21.4 THz to 40.0 THz. [1] http://en.wikipedia.org/wiki/Black-body_radiation#Human_body_emission http://en.wikipedia.org/wiki/Black-body_radiation#Human_body...
    - bravo22 12y ago
      He is not offering the product for sale. It is experimental and therefore allowed.
lettergram 12y ago
I'm impressed! Since, I'm not an EE, is there a better antenna which could reduce the noise in the signal? It looks as if the noise comes in a pattern and I was curious if that is because of the ripples in the antennas (i.e. cans)?
- gcb0 12y ago
  Most highly accomplished EEs can't answer most questions about fields, let alone antennae design detail.
  - hwillis 12y ago
    Good engineers can do dipole approximations in their heads. This would require a computer- there are just too many internal reflections.
- hwillis 12y ago
  No, the ripples show up for very simple reasons. Each bar is a reflection at a distance, the wider bars represent wider objects(which will reflect over a larger range of distances, since the radar beam is not very straight). He guesses what a few of the reflections are and some of it is probably the ground. The best antenna for radar is almost always a very directional one. Most radars use dish antennas of various designs. The very large majority of DIY microwave radios(more than you'd think) have horn antennas, which are desirable for their large bandwidth. You wouldn't use a yagi on a radar because its bandwidth is very limited, and bandwidth is directly related to resolution.
jkaunisv1 12y ago
I don't really see how the radar images at the bottom reflect the scene he showed. Any tips on reading those?
- hwillis 12y ago
  The radio waves are collected at points and don't have any x or y data, so making an image out of it is pretty challenging and usually requires moving the radar beam. He just kept the beam still, so the only things you can really see are things that move. In the image, the bottom axis is distance(calculated from the time the reflection took/the frequency output by the mixer), the color is the strength of the reflection, and the left axis is the time. He walked away from the setup and then back, visible as the two lines, which fade out almost completely as he changes direction, because he is far away and therefore looks smaller to the radar. http://hforsten.com/static/img/fmcw/football_field_range.png http://hforsten.com/static/img/fmcw/football_field_range.png From this data you could theoretically build an image of his upper torso and head, but it would be very blurry. His arms and legs were not static, and the radar doesn't know how they were moving, so they would just show up as blurs.
  - jkaunisv1 12y ago
    Cool, thanks! That helps a lot. Even though I knew what the axes were my intuition struggled a bit, I think partly because I'm so used to the bottom/X axis being used for time.
lifeisstillgood 12y ago
There is too much interesting cool stuff in the world - I will never get to try out half of it ! It's like realising that willy wonka's chocolate factory is bigger than you can walk around in one lifetime. Darn it.
- JabavuAdams 12y ago
  Step 1: Life-extension
madengr 12y ago
Nice work. Could ditch the Wilkinson though since your coupling to the mixer is -10 dB, so just use a resistive tap instead of 3 dB splitter and 7 dB attenuator.
fegu 12y ago
Very impressed. Solid knowledge demonstrated. The blog makes it seem so easy, but imagine the years of trial and error needed to produce this knowledge (which of course the author gets "for free")
ck2 12y ago
This makes me wonder if you could map a building using existing 5ghz wifi n/ac signals.

261 points by paulgerhardt 12y ago

ChuckMcM 12y ago

I really love that you can get a power amplifier for the 5Ghz RF for about $2.

a1k0n 12y ago
The VCO (HMC431LP4) seems to be more like $20, though. edit: should have read the rest of the article after the schematic where he says as much
VLM 12y ago
Its about the right price for +20dBmW at 6cm. minicircuits.com has several MMIC in that freq range at that output power. Transcom sells a nice well over 30 dBmW MMIC for that same freq band... you can buy a kit from minikits in australia, the EME141-5800, the bare chip is like $20. Some ham radio work shows you don't need the fancy 4 layer weird oshpark material for workable stuff in that general freq range. http://www.w1ghz.org/MBT/multiband.htm http://www.w1ghz.org/MBT/multiband.htm As an interesting extreme opposite comparison, there was a B-29-ish era chirp radar altimeter for aircraft landing which was almost entirely mechanical. A little buzzer/motor thing varied the size of a resonant cavity by a little bit, and the resulting audio signal was turned into a voltage / altitude using something like a capacitor/resistor bridge. So one vacuum tube, a resistor, a capacitor, a diode mixer, and a meter (and a lot of plumbing) If you'd like better antennas around that range, yet again, just ask a ham radio guy. Its a very awkward freq band where dishes, and most importantly dish feeds, are huge compared to 10 or 24 GHz band, but a loop yagi like you'd use at 2 GHz or lower would be ridiculously small. The microwave ham radio contester guys seem to like horn antennas at that band so couple it into a moderately large waveguide and attach the (homemade) waveguide to a (homemade) horn antenna.
mng2 12y ago
What costs money is the spectrum analyzer, network analyzer, and Microwave Studio license.
- bsder 12y ago
  Exactly. Testing RF is a PITA because the test equipment is so stupidly expensive.
  - Animats 12y ago
    Yes. Back in the 1990s I built a little LIDAR system using much the same principle as this system - modulate the output beam with a 20MHz carrier, down-convert at the receive end using the same local oscillator like an FM receiver, and measure the phase shift between the down-converted output and input. That transformation is phase-preserving, and the phase shift at the lower frequency represents the range. It wasn't hard to build. But I didn't have the test equipment to adjust it.

aidenn0 12y ago

The best antenna upgrade for least work would probably be to build a Yagi

Florin_Andrei 12y ago
That would be a pretty tiny Yagi, too. :)
hwillis 12y ago
Actually no, a yagi would be very bad. The Radar has a 700MHz bandwidth, almost 12% of the center frequency, and yagis work for a fraction of that. A horn is pretty simple to make.
- aidenn0 12y ago
  Oh! I didn't see the bandwidth was so wide. You are correct. Wouldn't the resolution still be decent with a narrower bandwidth (i.e. the 10s of MHz that a yagi could manage)? Also, as an alternative to a horn antenna, a parabolic reflector should work well in this band without being too large, right?
  - madengr 12y ago
    No, FMCW radar range resolution is proportional to RF bandwidth. You would still need the horn as a feed for the dish, but yes, you would get more gain.
  - hwillis 12y ago
    The range resolution would go from 8.5" to five yards if you changed the bandwidth to 30 MHz. Currently the radar could figure out the direction a person is facing to about 45 degrees. 5 yards would be good to find the orientation of a house. Parabolic antennas are just horns with lenses. The bigger the parabola, the better the focus and the wider the bandwidth. A horn would be a few inches across, but a 700 MHz reflector would be a couple feet.

jwr 12y ago

Very impressive. I would have thought that this sort of RF work is outside the hobbyist realm. The rest of the blog is equally impressive — 217-ball BGA soldered in a home-made reflow oven?

sliverstorm 12y ago
He's an EE student and clearly a pretty good one, so IMO he is beyond the typical hobbyist realm. The nebulous space of the professionally trained tinkerer. bunnie huang comes to mind as another example of this sort. When he cracked the Xbox, he had training & equipment that hobbyists don't have- but he did it in the hobbyist spirit.
- rasz_pl 12y ago
  Today you can get access to equipment thru hackerspaces, so its not even all that expensive.
  - sliverstorm 12y ago
    It still depends on what you want to do- sniffing high speed memory busses and work in reflow ovens are still out of reach of most hackerspaces I have seen.
    - VLM 12y ago
      You can use a rework station (basically a low air speed hot air gun) and wave it around. You'll need one anyway. Maybe $100 minimum. The biggest problem with building your own reflow oven is the conversion kit mfgrs want their profit off repacking and marking up retail parts (arduinos, SSRs, thermocouples, etc) and of course you need a donor oven (maybe $50 at walmart?) so you end up paying like $150 to bodge something together.... while over on ebay, you can get a brand new professional reflow oven shipped to you for a bit over $200 from the usual gray market sellers. Supposedly they work pretty well and I'll eventually buy one. Or maybe they're junk. If I get closer to buying one I'll research it in detail. I've done the skillet / hot plate + pan thing. Make a sling of kapton tape (you do have kapton, right?) because otherwise you're going to melt the solder and then stand there thinking "um, ok, so now how do I remove a PCB thats too hot to pick up, and leaving it on the hot plate for 30 minutes while it cools down exceeds all sanity" Even with lead free solder paste I think its unacceptable to share hot plate with kitchen and lab. You can put the PCB on a steel spatula and the whole works on the hot plate and that works pretty well if you don't do kapton. (edited to add and you can easily spend more than the cost of a reflow oven by trying to avoid buying a reflow oven, because a non-contact IR temp meter is a handy accessory to the hot plate technique, but if you need to "charge" the cost of a IR thermometer to the hot plate project, suddenly its cheaper to just buy an oven...) Hand soldering SMD is very easy but slow. Faster than hand soldered thru-hole, but still pretty slow. I have done 0201 RF parts but it was not really any fun at all, the bigger stuff is much easier to hand solder. And no caffeine allowed.

lowglow 12y ago

This really makes me wish I took Antennas as an elective in EE. Are there any good books/resources to get up to speed on things like this?

w8rbt 12y ago
The ARRL Antenna Book is pretty good: http://www.amazon.com/ARRL-Antenna-Book-22nd-Softcover/dp/087259694X http://www.amazon.com/ARRL-Antenna-Book-22nd-Softcover/dp/08...
hwillis 12y ago
http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/ http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-... http://www.amazon.com/Short-Range-Practical-Approaches-Electrical-Engineering/dp/143986599X http://www.amazon.com/Short-Range-Practical-Approaches-Elect... http://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/0133957241 http://www.amazon.com/High-Speed-Digital-Design-Handbook/dp/...
Jach 12y ago
The lecture notes on the MIT site these projects are inspired from has some useful PDFs: http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/lecture-notes/ http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-... When I was building my own version, Kai Chang's RF and Microwave Wireless Systems was a really great resource for the basics. Beyond that, you'll want to have a good foundation in signal processing to make use of the data from the device. The author doesn't mention it, but the radar he has is capable of creating SAR images. I'd love to see the results of a 6 GHz radar -- Dr. Greg Charvat (one of the MIT guys) has a demo on his website of a 10 GHz version that's pretty impressive. His thesis can help with some signal processing details, but the book Spotlight Synthetic Aperture Radar: Signal Processing Algorithms by Carrara, Goodman, and Majewski is even better.

darkarmani 12y ago

I'm not sure this is legal in the US w/r/t FCC. I know the author isn't in the US, but pointing this out for US hackers.

Florin_Andrei 12y ago
> I'm not sure this is legal in the US w/r/t FCC. What is the rationale for not allowing these?
- ne0n 12y ago
  It's not specifically not allowing these devices, it's broadcasting on a restricted frequency without the proper license. The FCC regulates who can broadcast on which frequencies. Getting a ham license can open it up a bit, but there are still regulations to follow.
  - lettergram 12y ago
    I wish they would open up 214-400 THz range. Then instead of charging everyone $99/month for poor cell phone service, we can charge $99/month just for living.
    - triangleman 12y ago
      Infrared?
      - kbaker 12y ago
        I think parent might have meant the Black-body radiation of a human [1], but was off by an order of magnitude... should be 14 um to 7.5 um wavelength = 21.4 THz to 40.0 THz. [1] http://en.wikipedia.org/wiki/Black-body_radiation#Human_body_emission http://en.wikipedia.org/wiki/Black-body_radiation#Human_body...
  - bravo22 12y ago
    He is not offering the product for sale. It is experimental and therefore allowed.

lettergram 12y ago

I'm impressed! Since, I'm not an EE, is there a better antenna which could reduce the noise in the signal? It looks as if the noise comes in a pattern and I was curious if that is because of the ripples in the antennas (i.e. cans)?

gcb0 12y ago
Most highly accomplished EEs can't answer most questions about fields, let alone antennae design detail.
- hwillis 12y ago
  Good engineers can do dipole approximations in their heads. This would require a computer- there are just too many internal reflections.
hwillis 12y ago
No, the ripples show up for very simple reasons. Each bar is a reflection at a distance, the wider bars represent wider objects(which will reflect over a larger range of distances, since the radar beam is not very straight). He guesses what a few of the reflections are and some of it is probably the ground. The best antenna for radar is almost always a very directional one. Most radars use dish antennas of various designs. The very large majority of DIY microwave radios(more than you'd think) have horn antennas, which are desirable for their large bandwidth. You wouldn't use a yagi on a radar because its bandwidth is very limited, and bandwidth is directly related to resolution.

jkaunisv1 12y ago

I don't really see how the radar images at the bottom reflect the scene he showed. Any tips on reading those?

hwillis 12y ago
The radio waves are collected at points and don't have any x or y data, so making an image out of it is pretty challenging and usually requires moving the radar beam. He just kept the beam still, so the only things you can really see are things that move. In the image, the bottom axis is distance(calculated from the time the reflection took/the frequency output by the mixer), the color is the strength of the reflection, and the left axis is the time. He walked away from the setup and then back, visible as the two lines, which fade out almost completely as he changes direction, because he is far away and therefore looks smaller to the radar. http://hforsten.com/static/img/fmcw/football_field_range.png http://hforsten.com/static/img/fmcw/football_field_range.png From this data you could theoretically build an image of his upper torso and head, but it would be very blurry. His arms and legs were not static, and the radar doesn't know how they were moving, so they would just show up as blurs.
- jkaunisv1 12y ago
  Cool, thanks! That helps a lot. Even though I knew what the axes were my intuition struggled a bit, I think partly because I'm so used to the bottom/X axis being used for time.

lifeisstillgood 12y ago

There is too much interesting cool stuff in the world - I will never get to try out half of it ! It's like realising that willy wonka's chocolate factory is bigger than you can walk around in one lifetime. Darn it.

JabavuAdams 12y ago
Step 1: Life-extension

madengr 12y ago

Nice work. Could ditch the Wilkinson though since your coupling to the mixer is -10 dB, so just use a resistive tap instead of 3 dB splitter and 7 dB attenuator.

fegu 12y ago

Very impressed. Solid knowledge demonstrated. The blog makes it seem so easy, but imagine the years of trial and error needed to produce this knowledge (which of course the author gets "for free")

ck2 12y ago

This makes me wonder if you could map a building using existing 5ghz wifi n/ac signals.