The rest of the blog is equally impressive — 217-ball BGA soldered in a home-made reflow oven?
"This work is sponsored by the Department of the Air Force under Air Force Contract #FA8721-05-C-0002."
well, you can build high-quality un-locked GPS receiver as a DIY too :)
I've always thought star trackers would make wonderful backups to GPS for high-altitude aircraft (they work even during daylight hours depending on atmospheric conditions).
A USAF U-2 on a high altitude polar air sampling mission accidentally wandered into Soviet airspace at the height of the Cuban missile crisis because auroras blocked the pilot's stellar fixes.
We had the BGGM, a model of the Earth's magnetic field, that gives us magnetic field strength and direction, given lat/long, altitude, and date. Accuracy was around 0.5deg in direction and I think 0.5% in strength. I'm not sure about the validity of it at more exotic locations and high altitudes, though. We used it as an accuracy check when taking field measurements to determine direction. I can elaborate if anybody's interested.
As for using the data to check aircraft location, if the model is reasonable valid in those conditions, it might work as a sanity check. I doubt it would be practical to reverse it and get location from field information, though. It's already tough to get really good field data in an environment filled with metal objects and electric currents, though.
https://upload.wikimedia.org/wikipedia/commons/2/28/Mv-world... from https://en.wikipedia.org/wiki/Magnetic_declination
Well, that implies they have the expertise to do so. Using a GPS is orders of magnitude easier.
Disclaimer: I am a geo/navi/celestial positioning nerd.
illegal where? for sale in US? I'd not be surprised that GPS gadgets produced in China for US market are just loaded with different version of firmware containing those limits while the same gadgets going somewhere else - with no limits firmware, or may be with even stronger limits (until pretty recently many "US legal" consumer GPS gadgets were illegal in Russia for being "too precise" :)
Goodbye export controls. Its PGP all over again, just with atoms instead of bits.
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.
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.
I still remember trying to do 0201 with the reflow station, accidentally blowing caps right off the board :)
The PDF has the full story, the first link has some neat photos including die shots.
smallerr one $16 free shipping
programming dongle ~$5
We live in amazing times for hardware developers. Stuff that was out of reach 10 years ago is peanuts right now.
Contrary to popular belief soldering SMD in general is way easier than dip, all you need is an oven/hot plate/hotair gun and solder paste/flux. Magic happens due to molecular surface tension instead of your manual dexterity.
BGA is outside my abilities, however.
I think most people under-estimate the degree to which you can click a button on your computer and get manufactured goods in the mail. Even for small runs like ten boards I can cost-effectively get the boards fabricated and stuffed and delivered to my desk in a day or a few days depending on how much I'm willing to pay.
It's like realising that willy wonka's chocolate factory is bigger than you can walk around in one lifetime.
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
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.
Testing RF is a PITA because the test equipment is so stupidly expensive.
It wasn't hard to build. But I didn't have the test equipment to adjust it.
edit: should have read the rest of the article after the schematic where he says as much
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.
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.
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)?
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.
Are there any good books/resources to get up to speed on things like this?
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.
Good practice is to stick to the open bands: http://en.wikipedia.org/wiki/Amateur_radio_frequency_allocat...
Also, he says he's aiming for a radar band: "The reason I chose to use 5 – 6 GHz band was because there is a band reserved for radars around 5.8 GHz and this range overlaps with 5 GHz WLAN."
Even on the ISM bands (http://en.wikipedia.org/wiki/ISM_band) any transmitter must still be submitted for Type Approval Testing.
The only exception to Type Approval is on the Amateur bands where "homebrew" is permitted (and encouraged). However the Amateur Regs specifically rule out any commercial use.
The only way this could legally be operated is in a professional quality screened room, or if the University has an "Experimental" class radio license.
What is the rationale for not allowing these?
Then instead of charging everyone $99/month for poor cell phone service, we can charge $99/month just for living.
Any experimental device must be covered by the appropriate experimental class license.
Think about it. Any dumb CBer could claim that his homebrew Linear is "Experimental".
FCC gives you exemption for up to five units . You are also exempted during development; how else could you even build the thing. FCC of course reserves the right to come in and tell you that your device is messing up the neighborhood and to cut it out.  Your device can't be used explicitly for the purpose of broadcast or jamming.
The experimental license is for those who actually want to broadcast/communicate on those restricted frequencies.
And yes, you are exempted for ownership while under development, but your organisation needs a written license or permit, plus you cannot transmit outside a screened room.
The Experimental License is for those who wish to Transmit outside a screened room.
Note that the O.P. is in Finland, not USA and the licensing details vary with each country.
Source: Half a lifetime as a Government Radio Inspector.
You are right. Broadcasting was the wrong word.
Given your extensive experience, then perhaps you can help clarify something for me: How do you reconcile the experimental license requirement with the FCC part 15 exemption I linked to?
For reference, my background is hardware development and I have done a fair bit of RF but they've all been in ISM band and we never had to get FCC approval until we intended to make/market the product and don't know of anyone who has ever obtained an experimental license, or a license of any kind.
Was this because of the ISM band or are people technically doing it wrong, but getting away with it because the device isn't radiating so high that it actually interferes with a neighbour and leading to an FCC complaint?
The sources you link to refer to radiated emissions from non-transmit devices. All electronic equipment which is marketed requires a whole slew of Compliance testing.
This covers things like standards for connections to Power or Telephone, as well as Radiated and Conducted Emissions and RF Immunity. Various classes of equipment (eg Commercial, Industrial, Military, etc) have different standards to meet.
Part 15 makes some exemptions for low power Domestic devices. But you still require Type Approval even under Type 15, it's just that the requirements are somewhat relaxed.
If you are an approved developer, you are covered for Possession of non-approved equipment during development.
But this has nothing to do with equipment which can transmit. Transmitters require all of the above testing, but also a further round of testing to do with harmonics, stability, bandwidth, power levels, etc.
If you wish to test a non-approved Transmitter you must do so in a professional-grade screened room, or apply for an Experimental License to cover specific Frequencies and Locations.
Years ago an organisation could apply for a blanket Experimental License which basically covered any testing in the organisation. It's main function was to ensure that a nominated individual understood (and was responsible for) all of the relevant regulations. Typically the nominated individual would hold a First Class Broadcast or Marine ticket. More recently these Licenses have been supplanted by limited permits for specific frequencies and locations.
People think that it is fine to transmit on "unused frequencies". The problem is that there are virtually no frequencies which are not allocated to some organisation.
And people often don't realise how an incredibly low power transmission (or harmonic) can block a sensitive Emergency receiver on the other side of town.
I could tell you dozens of stories of clever people who thought they were using "unused" frequencies. Typically they were inadvertently transmitting on the input frequency of an Emergency Repeater and hundreds of users were slowly getting angrier and angrier until the Authorities managed to track them down. When convicted they not only paid large fines, but also the Investigator's costs and the downtime for the company affected.
The reason for the specific permits is that if things do go wrong, the authorities can quickly get in touch and fix the problem.
Thank you for that information.
Also, as an alternative to a horn antenna, a parabolic reflector should work well in this band without being too large, right?
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.
You would still need the horn as a feed for the dish, but yes, you would get more gain.