Homemade 6 GHz pulse compression radar • Hacker News Board

Re: Homemade 6 GHz pulse compression radar

#41

Post by topynate » Thu, Apr 04, 2024, 6:49 PM UTC

gertrunde wrote: post #6

throwup238 wrote: post #2

This is great. It’s the last piece I needed for my suburban missile guidance system! This will be the last year the Joneses survive the annual block party. Can you do phased array radars next? I need the extra precision. There’s a few neighbors who don’t clean up after their dogs…

There is this: https://www.crowdsupply.com/krakenrf/krakensdr (Although they had to take the radar elements out of the firmware/software, most likely due to ITAR - ref link: https://forum.krakenrf.com/t/where-has-the-passive-radar-cod... )

A similar ITAR restriction on controlled reception pattern antennas means that GPS jamming is still much more of a problem than it needs to be. Three antenna elements are all you get, according to this: https://www.gpsworld.com/toughen-gps-to-resist-jamming-and-s...

Re: Homemade 6 GHz pulse compression radar

#42

Post by amanda99 » Thu, Apr 04, 2024, 6:58 PM UTC

The Finns strike again. Just the depth and number of different areas of expertise is insane to me. It seems he planned it all out, had it printed in China, and then 1/2 of the boards actually worked. That's like building a whole backend+frontend app and hoping it works after a month of coding on startup.

Re: Homemade 6 GHz pulse compression radar

#43

Post by _Microft » Thu, Apr 04, 2024, 7:07 PM UTC

pythonguython wrote: post #36

Can someone explain why those differential pairs are routed with so many curves instead of straight paths? (E.g. see the photo under the “ADC and DAC rotting” section)

"The traces are length-matched with squiggly lines[...]. The trace matching requirement is ±10 ps according to the Zynq PCB design guide, which is approximately ±2mm in trace length. [...] There is also some delay difference inside the FPGA package which should be considered in the length matching."

This is a shortened excerpt from the article. It can be found below the image with six colorful images of PCB layers. I'm curious how the delays inside the FPGA package are known. Is there a table which pin adds how much delay to a signal or something like that?

Re: Homemade 6 GHz pulse compression radar

#44

Post by henrikf » Thu, Apr 04, 2024, 7:08 PM UTC

georgeburdell wrote: post #38

davekeck wrote: post #5

Earlier quoted context omitted.

> Cost was 330 USD for PCB manufacturing and assembly of two PCBs and additional 225 EUR (240 USD) for components from Digikey that I soldered myself. This is including 24% VAT and shipping costs.

Plus the test and validation equipment which are $$$

I actually didn't use any expensive test equipment, only oscilloscope and multimeter. Even design and simulation software was all open source.

Expensive signal analyzer or spectrum analyzer would have been useful, but they aren't absolutely necessary. It's possible to use the radar itself for many tests and debugging.

I have tried to limit the projects I do on my own to only the equipment that I have home and open source software.

Re: Homemade 6 GHz pulse compression radar

#45

Post by henrikf » Thu, Apr 04, 2024, 7:20 PM UTC

_Microft wrote: post #43

pythonguython wrote: post #36

Can someone explain why those differential pairs are routed with so many curves instead of straight paths? (E.g. see the photo under the “ADC and DAC rotting” section)

"The traces are length-matched with squiggly lines[...]. The trace matching requirement is ±10 ps according to the Zynq PCB design guide, which is approximately ±2mm in trace length. [...] There is also some delay difference inside the FPGA package which should be considered in the length matching." This is a shortened excerpt from the article. It can be found below the image with six colorful images of PCB layers. I…

The FPGA manufacturer has characterized all their package pin delays. It's possible to export a csv file with internal delays of the package for each pin from the FPGA design tool. With Xilinx Vivado it's just File -> Export I/O Ports.

Re: Homemade 6 GHz pulse compression radar

#46

Post by gambiting » Thu, Apr 04, 2024, 7:25 PM UTC

maestroia wrote: post #37

throwway120385 wrote: post #35

Earlier quoted context omitted.

Wouldn't the FAA or FCC in the US have some jurisdiction over such a setup?

The "6 GHz" band is an unlicensed frequency for very-low power (VLP) devices in the US. Specific bands are: "U–NII–5 (5.925–6.425 MHz) and U–NII–7 (6.525–6.875 MHz)". VLP is defined as those devices which "operate at up to −5 dBm/MHz power spectral density (PSD) and 14 dBm EIRP". https://www.federalregister.gov/documents/2024/01/08/2023-28... .

In fact you can get WiFi routers that use 6Ghz as the third band after 2.4Ghz and 5Ghz.

Re: Homemade 6 GHz pulse compression radar

#47

Post by beeeeerp » Thu, Apr 04, 2024, 7:26 PM UTC

itishappy wrote: post #26

user_7832 wrote: post #11

Earlier quoted context omitted.

So would this mean that with a few more transmitting and receiving antennas it could have comparable resolution to lidar?

In theory, though it sounds like to compete with LIDAR it will need about 1000x more antennas, with a related increase in electronics.

Cutting-edge AESA radar like on the F-35 is incredible. It actually looks like a black and white photograph. I think your guess on antennas is roughly correct based on what we know about modern AESA.

Re: Homemade 6 GHz pulse compression radar

#48

Post by AnarchismIsCool » Thu, Apr 04, 2024, 7:27 PM UTC

henrikf wrote: post #25

AlwaysNewb23 wrote: post #18

This is really impressive. Do you plan to use it for anything or another project?

I built it to see if I could. I didn't have any particular use case in mind.

Would this be useful for another SAR setup?

Re: Homemade 6 GHz pulse compression radar

#49

Post by _Microft » Thu, Apr 04, 2024, 7:36 PM UTC

henrikf wrote: post #45

_Microft wrote: post #43

Earlier quoted context omitted.

"The traces are length-matched with squiggly lines[...]. The trace matching requirement is ±10 ps according to the Zynq PCB design guide, which is approximately ±2mm in trace length. [...] There is also some delay difference inside the FPGA package which should be considered in the length matching." This is a shortened excerpt from the article. It can be found below the image with six colorful images of PCB layers. I…

The FPGA manufacturer has characterized all their package pin delays. It's possible to export a csv file with internal delays of the package for each pin from the FPGA design tool. With Xilinx Vivado it's just File -> Export I/O Ports.

Does KiCad allow to take these delays for each pin into account automatically or do you need to do all that manually?

Edit: it's using the pad property of "pad-to-die-length" if doing it manually, right?

Re: Homemade 6 GHz pulse compression radar

#50

Post by aidenn0 » Thu, Apr 04, 2024, 7:38 PM UTC

auspiv wrote: post #15

Incredible work. Crazy that this could be done by a single person. Stick it on a rotating pedestal and you've got a planar radar detector. Add some tilt and then it's not much different than aircraft/weather radar I suppose. The cost (in $LOCAL_CURRENCY, or $570 according to another comment) isn't great but I can only imagine how many hours this took. Given a proper budget, the sky is the limit. Anyone know how .mil…

> Anyone know how .mil aircraft would interpret being tracked by a 6 GHz radar build by a civilian(yes I am aware that his estimated max distance is 1200m, assume he increased that by a factor of 10 with larger antennas or something)?

Regulations for signal strength are ERP, so a more directional antenna could make it no longer legal to use the 6GHz band.