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Comment: Re:Why is it so cheap? (Score 2) 155

by wramsdel (#46082933) Attached to: $499 3-D Printer Drew Plenty of Attention at CES (Video)

I was at CES, and I specifically asked to see one of the filament cartridges. Assuming the ones on the show floor are the same design that will ship with the printer, there are no electrical contacts on the cartridge, so likely no "chip" as is the case with ink cartridges. It looked to me like it would be fairly straightforward to reload one of the cartridges with commodity filament.

Comment: Re:Lame (Score 1) 140

And speaking of front-ends, there's some funky stuff going on in the bladeRF's:
http://nuand.com/bladerf.pdf
C331, the receive switch blocking cap, is 6.8pF. At 300 MHz, it has a capacitive reactance of 78 ohms. Unless there's a good reason for that (e.g. RF tuning), that's pretty irregular. Typically switch blocking caps are chosen to have very low reactance at the frequency of interest, so as to minimally perturb the 50 ohm environment of the switch port. The reference curves in the switch datasheet were taken with 47pF caps.

Another oddity: the switch control lines are bypassed at the switches with 8.2pF. The bypassing itself is good practice, but again, I question the value. At 300 MHz that's not a very effective bypass. Bumping up the cap values and adding a series element, a ferrite bead or even a resistor, would provide better rejection of environmental RF. My guess is that those traces are run on the surface layer, unshielded, as well.

Comment: Re:Lame (Score 1) 140

Okay, so most significantly what I'm hearing is superior weak-signal performance by virtue of good DSP. I'll buy that. Your point about front-ends and the "stick" SDRs is well taken. I've never taken these things seriously because I take a look at most of the front-ends and there's...nothing. No filtering, no shielding, no preselection. And to think that some of them are 8-10 bits and depend heavily on pre-converter gain management, with nothing more than a silicon VGA with a few hundred microamps at best of bias...wow. It's damn scary. I can't imagine taking any of them to a mountaintop somewhere that has 25 transmitters going full-bore on a dozen bands and having a good experience with it. Maybe I'm just an RF design bigot. Anyway, I'll look into the SDR-IQ, sounds like an interesting piece of gear.

Comment: Re:Lame (Score 1) 140

Can you define what you mean by "performance" above? Nothing I've read about amateur SDRs has shown them to "wildly" outperform analog radios in:
MDS
Noise figure
Blocking dynamic range
Intermod
Desense
Third-order intercept
Power consumption
In fact, certain SDR architectures may include things like spurious-free dynamic range impairments that are significantly *inferior* to analog radios. I don't deny that there are many things an SDR can do that an analog radio simply can't, chief among them being accommodate new modulation schemes without hardware modification, but I think they're far from a complete replacement for analog.

Comment: Re:Why can't they put a simple FET in there (Score 1) 111

by wramsdel (#34510166) Attached to: Video Shows Why Recharging Kills Batteries

Oh, they certainly exist. I design small consumer electronics devices, some of which have lithium-chemistry batteries. Many of the sub-amp battery charger ICs that I've used (case in point, the Intersil ISL6292) will drop to zero charge current at the end of the charge, when current into the cell drops below a certain threshold for a given voltage. I can't speak to current design practices for laptops, but I'd guess that they do the same. Of course, charging a device that's operating is an entirely different scenario and can be a real can of worms from a design standpoint.

Comment: Re:$800 ?! (Score 1) 114

by wramsdel (#34285664) Attached to: Arduino-Based, High Powered LED Lighting Over Wi-Fi

Unfortunately you left out 4) amortized development costs, 5) what the market will bear, and potentially 6) licensing costs. Consider the engineering work that goes into something like this...easily a few hundred engineer-hours. Now consider that the fully-burdened cost for a junior engineer is close to $100/hr. It goes up from there. So now we're talking in the mid-five figures before you sell unit 1. That's *just* labor. Care to add in ancillary costs? As for what the market will bear, there are LED luminaries on the market ranging in price from $500-ish to well over $1000. $800's not unreasonable there, assuming this is a comparable fixture. Finally, they may well be paying a stiff royalty to Color Kinetics. If you want to have anything to do with intensity-controlled LED lighting, chances are you're infringing on a Color Kinetics patent. They've locked up all the approaches that a reasonable engineer would consider trivial, and they defend their patents zealously. If I were these guys, there's no way I'd go near this without either paying the piper or spending considerable time with a patent lawyer (mo' money) to make sure I didn't get shut down after the first unit sold.

But you're right, it sure does look bomb-proof.

Comment: Re:Why? (Score 1) 313

by wramsdel (#33887832) Attached to: Casio Unveils New Color Screen Graphing Calculator

In my experience it's the other way around. I used a calculator *way* more in school (electrical engineering) than I ever have in industry in the last ten years. Why? Well, mostly because the math's much easier now...I don't routinely deal with complex or matrix math, which means a laptop with Excel is sufficient for 80% of what I do, and the remainder can pretty much be done in my head (nb: remember common logarithms and exponentials). Since my laptop is pretty much always within arm's reach, I just keep an Excel scratchpad open at all times. It's also nice to have room to spread out, or adjust various parts of the equation real-time, without having to use an antiquated and constrained interface.

Comment: Not quite out of the woods yet (Score 1) 135

by wramsdel (#33693284) Attached to: FCC White Space Rules Favor Tech Industry

Note specifically the part about "the rules will require devices to be capable of knowing their location and using an online database to find out which channels are active in their area". Seems that presupposes that whitespace devices for all time, or at least until the rules are changed, will need both geolocation ability and WAN connectivity. I seriously doubt that users will ever be allowed to simply plug in the operating location to the device, as that would allow the whole system to be easily circumvented. Requiring geolocation and connectivity is fine for applications embedded in a cell phone or a laptop (which already has these facilities), but standalone devices will have a pretty steep cost burden. Even in the embedded scenario, now we need some way of ensuring that the device gets a GPS fix (how frequently?) and communicates that in some standard way to the whitespace system. Hopefully client devices will be relieved of this burden by virtue of their connection to a known base, but will that restrict the usable range of the system, given that you don't want a client to wander too far from the base? Be interesting to see how all this plays out.

Comment: Re:Cell phone GPS not the same... (Score 2, Informative) 328

by wramsdel (#33248670) Attached to: Recycling an Android Phone As a Handheld GPS?

That's because he's looking at LNA gain on an active antenna. Oops.

I can pretty much guarantee you that those helical and ceramic patch antennas won't be much more than +3 or +4 dBi. There are only two ways to improve antenna gain: directionality and physical size. Directionality (aside from "up") is exactly what you *don't* want in a GPS antenna. You ideally need 360 degree azimuthal and 180 degree elevational coverage, and that's only if you don't plan on ever tilting the device from the horizontal plane. As for physical size, well, all of those antennas are within the same order of magnitude of compactness, so I don't expect much variation there. Yes, structural design matters, but it's a few dB of matters, not tens.

Comment: Re:Cases (Score 4, Insightful) 427

by wramsdel (#32697420) Attached to: Experts Explain iPhone 4 Antenna Problem

It'll insulate the metallic ring that's "part of the antenna system", which might mean "the antenna" or might mean "some other element that helps the antenna do its work" (i.e. a resonant grounding piece). Antennas are tuned, resonant, structures...think of a tuning fork that needs to oscillate at a certain frequency. Bridging the gap between the two exposed elements changes the electrical characteristics of it such that the antenna becomes detuned and reception is impaired. By applying a case, your hand can no longer come in contact with the ring, so the antenna isn't as severely detuned and the cell phone signal isn't as attenuated. I say "as severely" because there will always be some impact when your hand is in reasonable proximity to the device, but it won't be of the magnitude that direct contact would be.

Comment: Re:maturity? (Score 2, Insightful) 425

by wramsdel (#31189774) Attached to: New Plan Lets Top HS Students Graduate 2 Years Early

I absolutely agree. It's probably going to sound curmudgeonly, but there's been a huge shift in the U.S. from guiding behavior to controlling environment. This is great...until the environment is no longer controlled. As soon as that happens, a child whose environment has been meticulously managed from birth suddenly finds her/himself completely unable to cope. Blech. My kid's only one, but my philosophy even now is to help him understand himself, characterize his environment, and act accordingly. It means letting him fail sometimes, because he chose wrongly, but it also means that he's much more in control when confronted with a new situation. I find it far less stressful for both of us.

Comment: Re:That is positively asinine. (Score 2, Insightful) 285

by wramsdel (#30727616) Attached to: CES Vendors Kicked Out of Hotels For Showcasing Wares in Room

Everything you've said is true. You've also made largely ethical arguments, and ethics in business is dead. Yes, the parasites in the suites are costing the big guys money and face time. The big guys are also doing everything within their power to put the little guys at a competitive disadvantage. That's how business is done. That's not a justification, it's not an excuse, it's a statement of fact. The companies exhibiting in suites are, at worst, in breach of contract with the hotel, and it's quite likely that that breach is with the tacit consent of the hotel. You cannot convince me that an entity which spends tens of millions of dollars deploying surveillance hardware to catch people cheating or counting cards doesn't know exactly what's happening in each and every one of their rooms and suites. This time, the CEA got pissed and told the hotels to play ball, and they did. Individuals go to Vegas to gamble, it's not surprising that companies would do the same.

I bet the human brain is a kludge. -- Marvin Minsky

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