- Selectivity vs. sensitivity - 8 Updates
- Saving LCD screens that were under water - 8 Updates
- PC desktop main fan won't turn on after rooting around inside with cabling - 1 Update
| micky <NONONOmisc07@bigfoot.com>: Jun 07 08:32PM -0400 I've known the basics of sensitivity and selectivity for a long time, and I read more abou them on the web this week, but it hasn't helped. I want a newer car radio for my 2005 Toyota Solara, and I live in Baltimore and want to be able to receive WAMU, 88.5 and WCSP (c-span)90.1, from DC. Which value matters in predicting whether I'll be able to do so, selectivity or sensitivity? My current radio gets both stations, but there have been radios that don't get stations I know exist and in that situation, there is a general low level noise something like the wind blowing. I suppose you have all heard it. Alternatively, limiting what I pay to $300, maybe 400 and 500 at the very most, what brands are "certain" to get any station my Toyota radio gets and my Chrylser radio got in the previous 3 cars. I'll probably buy from Crutchfield becasue they have kits to connect to the steering wheel controls. Mostly I want the new radio to have a USB and AUX input, and maybe buttons instead of a touch screen. It would be nice if it played CD's and I guess no such radio will play cassettes. Buttons are easier to use while keeping ones eyes on the road. OTOH, though I have very little use for GPS, the current car has it (uses a CD for the maps) and there is no monthly charge. If on the new radio it was a one time charge included in the price of the radio, it might be nice to have once in a great while. Thanks in advance. |
| jurb6006@gmail.com: Jun 07 06:20PM -0700 You want these stations in your car ? Well, a buddy has a Ford Taurus with a radio with extreme sensitivity and doesn't exhibit that noise like older tuner due to the digital signals etc. on the carrier. Some tuners vary the IF bandwidth with signal strength or even multipath reception. (Shotz ?) this gives you the low distortion of the wide bandwidth on better signals and limits distortion on weaker or much reflected signals. A quite good design I say. When you are dealing with a weak signal, narrow bandwidth is almost always the choice as noise goes up with bandwidth, and it of course affects selectivity. It affects THD especially in stereo because the sidebands are blocked. Sure, you can get by with a +/- 75 KHz bandwidth but it sounds like shit. How picky are you ? So you have questions that sales is not going to be able to answer here, I don't know what to tell you. Look at audiophile specs on these tuners if you can get them. the quieting curve, THD vs. signal level. No way can they quantify how it handles multipath, but that is usually less of an issue with a signal originating farther away. (unless you are in NYC itself) So in the end, both parameters you ask are important. I tighter bandwidth will shield out local stations that are stronger. If you have them 200 KHz away you definitely need the utmost in selectivity. Sensitivity is related but shorter bandwidth will result in better quieting. Thus a tuner with shorter bandwidth will measure better in selectivity with all other things equal. I used to custom align IF strips on old tuners for that. Another factor is that the frequencies you mentioned are at the low end of the band. that means the varactors are operating at higher capacitance and inaccuracy and drift are worse. this is almost impossible to tweak, I would not attempt it and lack the equipment to do it anyway. As such, an in person audition ight be necessary. Go to the store whether you buy there or not and search the lower end of the FM band on various units. if you find one with really superior performance buy it, and insist on getting THAT ONE, not another one in the box. that may be the only way to do it. Anyway, that is my take on it, take it or leave it. |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 07 11:23PM -0700 On Thu, 07 Jun 2018 20:32:03 -0400, micky <NONONOmisc07@bigfoot.com> wrote: >(c-span)90.1, from DC. >Which value matters in predicting whether I'll be able to do so, >selectivity or sensitivity? Both, and both have complications. For selectivity, if your FM radio can hear HD Radio (IBOC), it needs to have an IF bandwidth of at least 400 KHz. Here's what it looks like on a spectrum analyzer: <http://www.learnbydestroying.com/jeffl/crud/KBRG-100_3.jpg> <http://www.learnbydestroying.com/jeffl/crud/KCSM.jpg> It won't work if the IF bandwidth (-3dB down) were exactly 400 KHz as it would be clipping the corners of the IF bandpass and probably have horrible group delay. It has to be wider, typically about 500 to 600 KHz IF bandwidth. However, even if it was 400 KHz wide, you would still have an adjacent channel problem. In the US, FM channels are on 200 KHz intervals. That means the digital part of the spectra overlaps the conventional analog FM part of the spectrum in the adjacent channel. If you were listening to a conventional FM station, and there were an HD Radio digital station on the adjacent 200 KHz slot, its digital signal would slop into your IF bandpass and all you would hear is digital garbage. The closest approximation to a solution are the digital FM receiver and demodulator chips by SiLabs. <https://www.silabs.com/products/audio-and-radio/multi-band-radios> The IF bandwidth is programmable and very much a brick wall. The designers can narrow up the IF bandwidth to exactly 200 KHz which will remove most, but not all, of the HD Radio garbage in the adjacent channel. You'll find these chips in radios by Tecsun and Meloson. Not sure about car radios. So the importance of selectivity depends on what you're listening to (conventional FM, or HD Radio) and what's on the adjacent channel. It's almost midnight and I'm beat. I'll dive into the sensitivity part later, when I'm more awake. Incidentally, FM receiver sensitivity is rather oddly measured in dBf (dB above 1 femtowatt). -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 07 11:29PM -0700 On Thu, 07 Jun 2018 20:32:03 -0400, micky <NONONOmisc07@bigfoot.com> wrote: >Which value matters in predicting whether I'll be able to do so, >selectivity or sensitivity? This looks like a tolerable explanation of what the numbers mean: "How to select an FM tuner for 88-108 Mhz DX" <http://home.iprimus.com.au/toddemslie/howtoselectatunerforfmdx.html> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Look165 <look165@numericable.fr>: Jun 08 04:08PM +0200 selectivity is the opposite to sensivity. |
| John-Del <ohger1s@gmail.com>: Jun 08 07:56AM -0700 > You want these stations in your car ? Well, a buddy has a Ford Taurus with a radio with extreme sensitivity and doesn't exhibit that noise like older tuner due to the digital signals etc. on the carrier. I had more than a couple of people complain that their factory Ford radio had better AM DXing range than their aftermarket radio. I don't know about the new Fords, but Fords through the early 2000s had very sensitive and reliable factory radios. The last Ford I had was a 2000 Explorer, and that radio could pick up WFAN and WCBS (New York AM stations) almost like they were locals. I could listen to ballgame from New York when others couldn't. Too bad Ford didn't know as much about automatic transmissions as they do about building radios. |
| root <NoEMail@home.org>: Jun 08 03:21PM >WCBS (New York AM stations) almost like they were locals. I could listen to >ballgame from New York when others couldn't. Too bad Ford didn't know as much >about automatic transmissions as they do about building radios. Where were you when you listened to WFAN and WCBS? I had a 1946 Studebaker which could pick up Los Angeles radio stations when I was in Twin Falls, Idaho. |
| John-Del <ohger1s@gmail.com>: Jun 08 08:35AM -0700 On Friday, June 8, 2018 at 11:21:55 AM UTC-4, root wrote: > Where were you when you listened to WFAN and WCBS? > I had a 1946 Studebaker which could pick up Los Angeles radio stations > when I was in Twin Falls, Idaho. Wolcott, CT (near Waterbury) - certainly in range for a decent radio, but a lot of AM radios don't get them around here. I drove my brother's 2012 BMW couple of weeks ago and couldn't listen to the Yankee game on FAN. Picked up every other word drowned in mostly static. When I'm sitting on my back deck listening to a ballgame, I use an Emerson 911 transistor radio - circa early 1960s. Picks it up nice and clear. https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjm6q_mqmU0dl73xvI5xrvNNbc-4rheIKflJhlcYBZ6Tqw7sIx5S3jobpWuBz-ufr0IJvf1yxFOdy-i5FCZH5rfnPuLk48jIgma3zet0bVkGTkHuqyUjzIyb72fncKT4uLEgJI62uu592ht/s1600/%2524%2528KGrHqV%252C%2521jkE66tt%252BVPkBOvs91HOEQ%257E%257E60_3.jpg |
| oldschool@tubes.com: Jun 07 02:31PM -0500 On Thu, 7 Jun 2018 09:38:48 -0400, Phil Hobbs >Cheers >Phil Hobbs >(Who has a deep affection for his storm drain) It was not the roof, a water pipe broke the main brass valve. The water was shut off at that valve and there was heat tape on the valve and the pipe below that valve, but that heat tape must have failed. Water was pouring out of the building. It's hard to tell how deep it got. I guess the weather stripping was pretty good to allow the water to build up. I'm still trying to decide whether to destroy the building or to gut it. One wall actually is pushed off the floor, but the porch is holding it tight. Little by little I have been salvaging stuff. All clothing and any cloth is trash. All books are trash, all furniture is trash. But I have been saving CDs and DVDs. They need to be washed is all. And saving all tools and metal stuff. I decided to see what I could do with the electronics. Several transistorized radios work fine, except for the speakers. But it appears the LCD stuff is trash. That GPS screen is touch screen and the touch part no longer works, plus the longer it's been plugged in, the more of the screen is turning black. That GPS was never worthwhile anyhow, so I I dont much care. That scanner was nice though. I guess I'll just have to go on ebay and find a replacement. There are a few pices of tube gear. I have not plugged them in, because I fear water in the transformers. I'll probably pop the tops off them transformers and see how they look inside. There were also some computers in there. Old ones that I really wont miss. But I found that all computer motherboards and cards do survive floods. But the drives are all trash. But I am not gonna waste time on them computers. I may salvege a few of the cards and the RAM, and send the rest of them to the recycler. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jun 07 12:58PM -0700 We have a summer house that flooded some time ago (we are 8' up now), and in it were a number of electronic pieces including: Soundcraftsman Tuner, with Backlit LCD screen Dynaco PAT4 Dynaco ST120 Sony CD Player Sony VCR The speakers were above the flood waters. All of the above traveled through our Bosch dishwasher with exactly 1/2 the normal amount of detergent. From there they went into a 150F gas-fired oven for four (4) hours. Tops off, guts exposed, but upside down. Moving parts, slide-rails and so forth were lubricated before returning to service. Some belts were also replaced (with O-rings). All are fine. If the alternative is landfill, heroic measures are entirely appropriate. Peter Wieck Melrose Park, PA |
| mike <ham789@netzero.net>: Jun 07 01:15PM -0700 On 6/7/2018 9:24 AM, Jeff Liebermann wrote: > pressure and thus push the water out of the panel. That didn't work. > I also tried using a vacuum pump on the outside to help suck out the > water, but that also failed. I'm surprised that the vacuum failed. Should pump down to the vapor pressure of water and hang there until the water is gone before continuing the pressure descent. That's as dry as you're ever gonna get it. Even if it did get the water out, the LCD still might not work. Best results were to attach something |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 07 04:32PM -0700 >I'm surprised that the vacuum failed. Should pump down to the vapor >pressure of water and hang there until the water is gone before continuing >the pressure descent. That's as dry as you're ever gonna get it. I agree. It should have worked. I still have all the equipment (except the fish tank) and could probably try again. I see water and chemical cleaner damaged laptop displays all the time. They usually have a jagged area near the bottom of the screen that has turned dark black and shows no image. Most of the damage comes from spray cleaners used to clean the LCD display, where the cleaner or water was allowed to run down the screen, under the bezel, and into the display. I was using an Edwards E2M-1.0 2 stage rotary vacuum pump: <https://shop.edwardsvacuum.com/products/r1/list.aspx> It's been run well past its 30,000(?) hr major overhaul point and is probably leaking around all the rubber vanes and seals. As I recall, it went down to about 200 milliTorr and refused to go lower, probably because of leaks in the reinforced fish aquarium I was using for a test chamber. Water has a vapor pressure of 25 Torr (0.5 PSI), so that should have easily sucked all the gas and water vapor out even with all the leaks. I had hoped to see some boiling near the hole, but didn't see any. What I think might have happened is the air pressure equalization hole got plugged up with a RTV used to seal the glass panel. The pressure on the parallel glass plates might have compressed the RTV seal, which then expanded sideways and closed the hole. Just a guess(tm). >Even if it did get the water out, the LCD still might not work. Yes, but it was worth the risk. At the time, large LCD panels were rather expensive. However, when I put everything back together, I still had a 1/4" wide jagged black smear at the bottom of the screen near both corners. Incidentally, my "fix" for this customer was rather creative. I flipped the monitor over by reversing the position on the VESA mount and inverted the display using the Nvidia display control application. It then had black areas near the top of the display, where there's very little worth seeing. However, the customer could now see the bottom of the screen, where the task bar and Start button reside. Moving just the task bar to the top of the screen didn't work, because the Start button was under the black blob and couldn't be seen. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| "Carl Ijames" <carl.ijamesXX@YYverizonZZ.net>: Jun 07 08:47PM -0400 "Jeff Liebermann" wrote in message news:6pdjhd18c3l7e90f7e4fddoasv0j1t6i6g@4ax.com... >I'm surprised that the vacuum failed. Should pump down to the vapor >pressure of water and hang there until the water is gone before continuing >the pressure descent. That's as dry as you're ever gonna get it. I agree. It should have worked. I still have all the equipment (except the fish tank) and could probably try again. I see water and chemical cleaner damaged laptop displays all the time. They usually have a jagged area near the bottom of the screen that has turned dark black and shows no image. Most of the damage comes from spray cleaners used to clean the LCD display, where the cleaner or water was allowed to run down the screen, under the bezel, and into the display. I was using an Edwards E2M-1.0 2 stage rotary vacuum pump: <https://shop.edwardsvacuum.com/products/r1/list.aspx> It's been run well past its 30,000(?) hr major overhaul point and is probably leaking around all the rubber vanes and seals. As I recall, it went down to about 200 milliTorr and refused to go lower, probably because of leaks in the reinforced fish aquarium I was using for a test chamber. Water has a vapor pressure of 25 Torr (0.5 PSI), so that should have easily sucked all the gas and water vapor out even with all the leaks. I had hoped to see some boiling near the hole, but didn't see any. What I think might have happened is the air pressure equalization hole got plugged up with a RTV used to seal the glass panel. The pressure on the parallel glass plates might have compressed the RTV seal, which then expanded sideways and closed the hole. Just a guess(tm). >Even if it did get the water out, the LCD still might not work. Yes, but it was worth the risk. At the time, large LCD panels were rather expensive. However, when I put everything back together, I still had a 1/4" wide jagged black smear at the bottom of the screen near both corners. Incidentally, my "fix" for this customer was rather creative. I flipped the monitor over by reversing the position on the VESA mount and inverted the display using the Nvidia display control application. It then had black areas near the top of the display, where there's very little worth seeing. However, the customer could now see the bottom of the screen, where the task bar and Start button reside. Moving just the task bar to the top of the screen didn't work, because the Start button was under the black blob and couldn't be seen. Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 ======================================================= First, the water ran in the hole as liquid but you are trying to get it back out as vapor which is going to be a much slower process. There is about a 1000 fold expansion in volume going from liquid to vapor, and the flow conductance of the hole will be 2-10 times lower for vapor depending on the pressure (for this case, using a pump with the liquid would be cheating :-)). Second, depending on the size of the hole and the mass of the glass at the hole and how much water there is and where the boiling and thus evaporative cooling is occurring and lots of other things it is entirely possible for the water to freeze as it boils inside the hole so the ice can plug the hole. This stops the drying and the evaporative cooling as the ice slowly warms back up by conduction from the mass of the LCD, melting the ice, so it can boil again, then freeze and plug the hole, and round and round it goes. The vacuum is also an insulator so the LCD will slowly cool down and each melting cycle will be slower - venting to atmosphere every so often can actually speed things up sometimes. With one tiny pinhole this probably isn't an issue but if you are trying to dry something bulky like a book a heat lamp and venting to melt the ice block occasionally really helps. Of course, that assumes you aren't freeze drying something fragile like a drug where you need the frozen matrix to prevent chemical damage. Anyway, I think vacuum would work but it will be very slow. The descriptions I've heard using dry rice talk to dry a wet cell phone talk about a few days, and I bet the vacuum wouldn't be much faster to dry an LCD. -- Regards, Carl Ijames |
| mike <ham789@netzero.net>: Jun 07 10:13PM -0700 On 6/7/2018 4:32 PM, Jeff Liebermann wrote: > black and shows no image. Most of the damage comes from spray > cleaners used to clean the LCD display, where the cleaner or water was > allowed to run down the screen, under the bezel, and into the display. In that case, I don't think there's anything you can do to fix it. Once the water has invaded the pixel area, it's all over. > that should have easily sucked all the gas and water vapor out even > with all the leaks. I had hoped to see some boiling near the hole, > but didn't see any. I was experimenting with making heat pipes years ago. I don't remember the numbers, but 0.5 PSI sounds WAY higher than I was trying. As a test, I put the vacuum gauge right on the suction port of the pump. It went down to where water was supposed to vaporize and stuck there until I gave up. Reading about it suggested that you have to suck all the water (and other contaminants) out of the pump oil before you can do anything useful. They recommended FRESH oil for every evacuation. I bought some pump oil, but never got around to trying it. |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 07 10:46PM -0700 >On 6/7/2018 4:32 PM, Jeff Liebermann wrote: (...) >In that case, I don't think there's anything you can do to fix it. >Once the water has invaded the pixel area, it's all over. Yep. The secret to engineering is knowing when to give up. >> but didn't see any. >I was experimenting with making heat pipes years ago. I don't remember >the numbers, but 0.5 PSI sounds WAY higher than I was trying. Vapor pressure of water in Torr: <http://www.wiredchemist.com/chemistry/data/vapor-pressure> and in PSI: <http://www.pumpworld.com/vapor-pressure-chart.htm> 25 Torr or 0.5 PSI look right. >the water (and other contaminants) out of the pump oil before you can do >anything useful. They recommended FRESH oil for every evacuation. >I bought some pump oil, but never got around to trying it. That could have been my problem. At the time, all I had was the oil that was in the vacuum pump when I bought it used. It probably was rather dirty and likely contaminated with some water from condensation. Looking at the pump through the oil level sight glass, it looks dirty. New oil is about $30/gallon. I was eventually going to buy the o-ring and basic rebuild kit, at which time I would buy some new oil. However, I was getting a usable vacuum, so I didn't bother. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>: Jun 08 10:13AM -0400 > are all trash. But I am not gonna waste time on them computers. I may > salvege a few of the cards and the RAM, and send the rest of them to the > recycler. Blech. Sorry to hear that. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net |
| bruce2bowser@gmail.com: Jun 08 01:51AM -0700 On Thursday, June 7, 2018 at 1:26:39 AM UTC-4, Arlen Holder wrote: > Any advice for what makes the main #1 span spin? > (Could it be the twisted pair of wires coming off the graphics board?) > If the machine runs without the fan, will it shut off when it gets hot? The surface that you set a computer on is important. If the surface is dust-free and porous, it will allow more air to circulate around the cpu and power processor, keeping things cooler. But if you put a computer on the bed or the sofa with plenty of fibers, the system could overheat easier and fibers could clog everything, etc... |
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