Dan's Data letters #103
(page 2)
Publication date: 8 May 2004.Last modified 03-Dec-2011.
Wireless + trains = ?
Will the fact that I live next to a very busy electrified train line cause major problems with interference if I was to set up a wireless network at home? Also, in spite of the hype and promised speeds that the hardware vendors come up with, is a wireless network (either 802.11a, b or g) fast enough, and will it give good enough ping times, for online gaming?
Mike
Answer:
You might have interference problems, but probably not. Electric train arcs, like any arcs, produce wideband
RF noise, but the inverse square law eats up their power pretty quickly with distance. If you can listen to the radio
and watch broadcast TV, you should be able to use wireless networking as well without noticing any horrible bandwidth
or latency problems.
Wireless is more than fast enough for games. Games don't need much bandwidth; hosting servers is another matter, but just playing most games only requires a few times the bandwidth of a dial-up connection, at most, for a pretty much optimal experience. So 802.11b is fine for gaming. The faster wireless protocols are overkill for that application, but not for shifting files around your WLAN.
Latency shouldn't be a problem either. Wireless networking will add a few milliseconds to your ping times, but you won't notice that.
Non-mobile entertainment
I am interested in hooking up a Kenwood MPC-222 car stereo in my living room. Most likely I will fashion some kind of wooden box with a hole in the front. How should I power this project? It will end up in the basement/workbench area hooked into an old receiver/amplifier with speakers.
Tim
Answer:
No big deal; a 12/13.8V DC power supply with an adequate current rating will do it. There are lots of 13.8V power
supplies in every decent electronics store; they're generally intended to power automotive CB radio gear from the
mains, but they'll also run car stereos just fine, as long as you don't want to power some thousand watt amp or something.
If you're just powering a head unit that's using a separate amp to drive the speakers, then a quite low powered adapter should be adequate. A one amp 12 or 13.8V wall wart may well do the job.
Make sure you get a regulated adapter, though. A 12V unregulated adapter will deliver almost 17 volts when it's unloaded, and not make it down to 12V unless it's fully loaded.
Certified silence
I'm looking for a quiet PC case, rather like the excellent Antec Sonata but critically, with a CE Mark. Its to make up computers for my company, and we need to have CE marked cases. Any ideas? Or any recommendations for quiet cases that might be CE Marked? My base line is a 120 mm case fan, and a quiet PSU.
Luke
Answer:
I'm not sure what the deal actually is with bare cases and the CE Mark. I know I've reviewed
them upon occasion, but after trying to find information on the subject and, immediately, developing the strong
desire to eat my own head that always arises whenever I try to decipher the
stuff that comes out of Brussels,
I have given up. Perhaps some reader can tell me where I can find some relatively concise description of what CE Mark
testing for computer gear actually entails; every link I followed dead-ended rapidly with helpful information about
how and when to display the cursed Mark, not what the heck it actually meant.
Obviously, a case that doesn't come with a PSU can't be tested for the electro-magnetic radiation portion of CE Mark compliance, but if it does come with a variously Ticked and Marked PSU, then the CE Mark only covers the PSU. Perhaps enclosures just get tested for all the other CE Mark stuff, which I imaging any normal case would pass easily, though who knows; once again, life's too short for me to spend all freakin' day banging my head against EC bureaucratese.
If you need CE-Mark-tested PCs, then you're going to need to test them after they're constructed, I presume; that'll cost fortunes. Or you can just buy brand name boxes, which should all be fully certified, unless of course you're not actually in Europe - in which case you shouldn't need CE Mark certification in the first place.
Or, in flagrant violation of at least a million EU ordinances, you could always buy any old case that meets your noise requirements, then print your own CE stickers and put them on them to keep your PHBs happy.
Phone panic
There has recently been what I thought was some appallingly stupid anger in my suburb of Oatley, spouting from a community group about a 3G tower that Hutchison Telecoms erected in the local park. Apart from their determination to destroy such a blatant phallic symbol, the main concern the protesters had was that the radiation would damage the health of their children.
Of course, there's been the typical hypocrisy, such as mothers who are wearing "No 3G" T-shirts smoking cigarettes when their kids are huddled at their feet. I just know they're thinking of the children.
Anyway, I've been sceptical of their claims, but the recent Dutch study, which is being loudly trumpeted by the activists as being proof that 3G towers cause health problems, has me a little worried.
I know that you talked about radiation here, but I'd like to know whether you think the Dutch study is enough to challenge the safety of 3G towers. Could there actually be something to all the outrage? Or is there still insufficient data to draw such a conclusion? I feel like a Luddite for saying so, but perhaps it should be the responsibility of the telcos to prove that their products don't harm the public before they release them, just as food producers have to show that their additives aren't poisonous.
Please, give a warning before you call me a Luddite, so that I can cover my face in shame.
Chris
Answer:
Well, the risk to the kids from second-hand smoke in outdoor
areas closely approaches zero, and is certainly swamped by the pollution they're subjected to by merely living in
the suburbs - but raising the subject of relative risk with the protesters (or the
unimpeachably ethical broadcasters who're
paid to agree with them) is unlikely to win you friends anyway.
Until it's replicated, the TNO study you refer to (which you can download in PDF format here) is just another of those single studies that can be found to support any idea you care to name. The authors of the TNO study have (presumably under pressure from the Giant Telecomms Company Conspiracy) emphasised this themselves.
In any case, even if the TNO study is right on the money, the notion that some people develop headaches and nausea and whatnot when subjected to some kind of radiation does not tell us that the radiation is a serious health risk. Lots of things that do no long term damage cause headaches and/or nausea. Some people get headaches and nausea when they ride public transport. Big deal.
I, and every other sane person, agree that people who create new products should take reasonable precautions to make sure those new products won't kill the people who use them, but it should be noted that proving beyond all doubt that a new product is harmless is impossible. You can't tell, authoritatively, whether something will harm the public without exposing the public to it.
Just proving beyond reasonable doubt that a product is harmless can be very difficult, if the word "reasonable" is defined broadly enough by people who don't know anything about the field they're busy having doubts about. Their doubts don't have to be all that unreasonable, anyway; most products can be harmful in some way, after all, and we face such risks every day.
Fill your car up at a petrol station and you breathe a low concentration of poisonous petrol vapour. Buy a crappy $49 telescope and it may or may not have a label warning you not to look through it at the sun (this one had such a label!). The bottle of gin in my cupboard tells me on the label how many standard drinks it contains, but the label doesn't tell me how much I should drink for optimum health (probable answer: None).
Instead of holding companies to an unattainable product testing ideal, and losing sight of the risks we run every day without thinking about it, we should simply make sure they're not being negligent or misleading - failing to do reasonable tests of their products, or covering up unfavourable findings. The telecomms companies have definitely covered up unfavourable research; that deserves to be investigated. We shouldn't, however, automatically conclude that this means they must be just like the tobacco companies, trying to hide a Terrible Secret. After all, the tobacco companies didn't manage to hide the basic epidemiological fact that smokers weren't healthy. No such evidence supports the idea that mobile phones are risky.
Quite a lot of research about mobile phones has made it to light, some of it independent, and all that's come of it all is tenuous evidence that phone radiation may have some minor effects on humans. This, despite cellphones having been in wide use now for decades. We keep changing phone standards, but each new standard uses less RF energy, so unless the frequency increases and pulsed RF make a big difference, it seems unlikely that there's any extra risk from newer kinds of mobile phone, or their base stations.
Invisible battery
I'm having a problem with a NiMH battery pack that I put together for my digital camera. The camera is an Olympus C-4000 that wants 6V through its DC input. The pack consists of five sub-C 1.2V 3300mAh batteries.
To charge this pack, I've been using a charger that I picked up from a local hobby racing store. I've been using a spare 250W ATX power supply as the charger's input. I've drained the pack twice before, and have successfully charged it back up with this combination.
I recently went through a photographic dry spell where I didn't use my digital camera for about four months. I figured that the battery pack would discharge itself, and when I wanted to use it again, I could just hook it up to the charger for a couple of hours.
It's springtime here in Wisconsin, so I'd like to take some pictures now. But when I hook up the battery pack to the powered charger and hit the "START CHARGING" button, the charger just blinks its little light at me - as though there were no batteries at all hooked up to it. I've used my multimeter to verify that the PSU is sending voltage to the charger - the charger just isn't passing any voltage out to the battery pack.
I went back and re-read your quick guide to memory effect, and noticed that you mentioned the possibility of stronger cells in a pack "reversing" weaker cells during discharge. At the time I built the pack, I didn't realize this was an issue, so I kept the batteries in the pack connected together all the time, even during the dry spells when I didn't use the pack much. Do you think that doing so might have killed the pack by "reversal" during discharge? What sort of testing can I do to see if the pack or the charger is at fault here?
Matt
Answer:
Yes, your pack would have gone flat on the shelf over the months you didn't use it. Different NiMH cells have different
levels of self-discharge, but they're all quite bad. Some will still have a better-than-nothing amount of juice left
after four months; many won't.
Your charger problem is probably happening because the pack's gone dead flat. Some chargers can only detect a battery if it's still got some terminal voltage left; they won't start charging if the pack's dead flat. The solution is to charge the battery a little bit by some other means, so it shows some terminal voltage and convinces the charger that it's really there.
If you can put the charger in trickle mode and leave the battery for a few minutes, that ought to do it. Alternatively, you can just connect the battery directly to the five volt output of the PC PSU you're using to power the charger (red wire to red wire, black wire to black wire, in case you're wondering). That'd slap a fair few milliamp-hours into the pack quite safely, since that charge voltage you'll be using is well below the full voltage of the pack, and the cells you're using are high-current models that won't be fazed at all by a jolt of high charge current. You could leave the pack connected to 5V all day if you wanted, but you'd never get more than a small amount of charge into it. That small amount should be more than enough to make the pack visible to the charger, though.
Cell reversal is definitely not the problem; it can't happen during self-discharge. In self-discharge, each individual cell is discharging internally, not supplying current to anything outside it. People who plug resistors into the output wires of their battery packs to flatten them will reverse cells, but people who just leave the packs lying around won't.
(Matt got back to me after a couple of days. Yep, trickle charging the pack for a few minutes did the trick!)
And now, a word from some scum
[Presented as received.]
My name is David Scott I am a media buyer for Mindset Interactive. We are a full service-advertising agency, based in Irvine, California.
After reviewing your site I have become very interested in purchasing ad-space on your site. If you could make $500.00 a day in advertising, would you consider testing our pop for one day? We have live login to view stats so you will know what you are making in real-time.
We pay some sites to bundle our exe and they make an average of $1000.00 a day.
Sites like www.imbum.com and www.originalicons.com have more than tripled there advertising revenue just from running or advertisements.
AT-games now sits on over 300 sites we are spending over $350,000.00 a month in advertising.
Test our POP for two hours if we do not at least double your advertising revenue take it down.
There is no risk, and no binding contract. We are confident that after you test you will see that there is no other company that pays more than Mindset.
Take care,
David Scott
Media Buyer Mindset Interactive
5 Corporate Park #160
Irvine, Ca 92606
davidscott007@adelphia.net
Answer:
No, my ungrammatical friend, your company is not "a full service-advertising agency". You are
spyware
pushers, and have been
for years.
I hope you contract a debilitating disease.
The fun continues
I've visited your site and think that the content about Reiki would be of interest to the visitors to my Web site.
It's a site similar to yours but it doesn't compete with your web site. I was wondering if you would like to trade links with me?
Juan
Answer:
I was one of 95 people in the To: field of this e-mail, so I suppose Juan didn't have time to thoroughly examine my
opinions about Reiki. The only place I mention it at all is in passing on my old page
here, where I'm not exactly complimentary about it.
To reiterate: Reiki is a friggin' scam. It achieves nothing a placebo wouldn't. It is often surprisingly expensive. Its practitioners are either deluded, or rip-off artists. Juan would appear to be in the first category.
And, in conclusion: Bah, humbug.
