Topband: Inexpensive low noise preamp
I can't build one (disabled to the point I can't operate tools or handle componenmts of any size) so wondering if anyone has an inexpensive and spare low noise preamp I could purchase? I need it for a small delta loop receive antenna I am going to put up next month. Inexpensive = something in the range of $20.00 Replying off-line works for me. Thank you, in advance, for looking around your shack! 72, Jim R. K9JWV _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
Another couple of points. About 10 years ago, at a local ham-fest, there was a guy selling brand new Lambda power supplies. They were adjustable from 10-15 V and he had models ranging from 20-50 amps. They were switching supplies. I couldn't pass these up and bought 7 or 8 of them. They were a bit on the noisy side RF wise...nothing horrible but enough to be noticeable. I ended up wiring in some CorCom line filters that I had around the house and it completely removed the noise. I've used these supplies for years including being used on a number of different DX-peditionsthey are light and fairly small. This fix worked just great. The CorCom filters are frequently seen at ham-fests and surplus outlets although you can buy them new through component distributors like Digi-Key and Mouser. There are many models and they differ in mainly two categories. Voltage/Current capacities and the mechanical connections for bringing line voltage in and out. The most common have Fast-On type spade terminals or solder posts but I've seen many variations. On 7/20/2013 4:11 PM, Gary K9GS wrote: Hi Clay, One thing you might want to check. See if you can get inside the power supply...disconnect it first. Take a look on the PCB near the power connector. There may be a space on the PCB where you can install a power line filtersomething like a CorCom or similar. Sometimes they leave them out on some models to save money. If you Google CorCom you find info on the different models...just be sure to get the correct ratings. They also sell filters with built-in IEC connectors. An IEC connector is what the power cord plugs into. you may be able to get one that works. On 7/20/2013 9:27 AM, Clay Melhorn wrote: Hello to the group.I recently built an AMD quadcore machine I intend to eventually replace my trusty XP Pro machines. Foolishly got in a hurry to complete the build and purchased a PS from a local shop.It supplies the power required without issue, I have discovered why the price was so good.Jim Brown will love this one, virtually no RFC filtering, you get what you pay for and I know betterjust didn't realize the noise from 40m and down would be SO intense particularly on a Delta pennantthat points back toward the shack's general direction. The XP machines are very quiet.Live and learn. Question: Looking at another good deal how do the COOLER MASTER PS's rate for RFC filteringor are there others brand I should be looking at? http://www.newegg.com/Product/Product.aspx?Item=N82E16817171031nm_mc=EMC-EXPRESS072013cm_mmc=EMC-EXPRESS072013-_-EMC-072013-Index-_-PowerSupplies-_-17171031-L04B Will likely not waste time trying to make a Cadillac out of the Yugo I purchased. Thankyou in advance, Clay Melhorn N9IO Bonfield, ILWebmaster: KARS - Kankakee Area Radio Society - W9AZ http://www.w9az.com/ _ Topband Reflector -- 73, Gary K9GS Greater Milwaukee DX Association: http://www.gmdxa.org Society of Midwest Contesters: http://www.w9smc.com CW Ops #1032 http://www.cwops.org _ Topband Reflector
Topband: Fwd: Re: Desktop Power Supply Brand/Noise Question
I think Pete meant to send this to the list. if not, my apologies Pete. Original Message Subject:Re: Topband: Desktop Power Supply Brand/Noise Question Date: Sun, 21 Jul 2013 09:52:25 -0400 From: Pete Smith N4ZR n...@contesting.com To: garyk...@wi.rr.com I did exactly what Gary suggests to clean up the power supply on my homebuilt octo-core machine (back when it was a dual core Pentium hi). Corcom is one of several brands - even the best costs only ~$10. I had to do a little surgery on the IEC connector hole in my cheapo supply, but it was worth it!. 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. On 7/20/2013 5:11 PM, Gary K9GS wrote: Hi Clay, One thing you might want to check. See if you can get inside the power supply...disconnect it first. Take a look on the PCB near the power connector. There may be a space on the PCB where you can install a power line filtersomething like a CorCom or similar. Sometimes they leave them out on some models to save money. If you Google CorCom you find info on the different models...just be sure to get the correct ratings. They also sell filters with built-in IEC connectors. An IEC connector is what the power cord plugs into. you may be able to get one that works. On 7/20/2013 9:27 AM, Clay Melhorn wrote: Hello to the group.I recently built an AMD quadcore machine I intend to eventually replace my trusty XP Pro machines. Foolishly got in a hurry to complete the build and purchased a PS from a local shop.It supplies the power required without issue, I have discovered why the price was so good.Jim Brown will love this one, virtually no RFC filtering, you get what you pay for and I know betterjust didn't realize the noise from 40m and down would be SO intense particularly on a Delta pennantthat points back toward the shack's general direction. The XP machines are very quiet.Live and learn. Question: Looking at another good deal how do the COOLER MASTER PS's rate for RFC filteringor are there others brand I should be looking at? http://www.newegg.com/Product/Product.aspx?Item=N82E16817171031nm_mc=EMC-EXPRESS072013cm_mmc=EMC-EXPRESS072013-_-EMC-072013-Index-_-PowerSupplies-_-17171031-L04B Will likely not waste time trying to make a Cadillac out of the Yugo I purchased. Thankyou in advance, Clay Melhorn N9IO Bonfield, ILWebmaster: KARS - Kankakee Area Radio Society - W9AZ http://www.w9az.com/ _ Topband Reflector -- 73, Gary K9GS Greater Milwaukee DX Association: http://www.gmdxa.org Society of Midwest Contesters: http://www.w9smc.com CW Ops #1032 http://www.cwops.org _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
I ended up wiring in some CorCom line filters that I had around the house and it completely removed the noise. I've used these supplies for years including being used on a number of different DX-peditionsthey are light and fairly small. This fix worked just great. I can't understand why throwing some ferrite beads at a problem, or changing the supply, are the only two solutions. Many times, if not most times, a few .01 uF line voltage rated bypass capacitors are significantly better than a sting of cores, or a winding through cores. In the first place, we can add cores over power cords or other multi-conductor cables until the cows come home, and it won't change differential mode suppression. Differential excitation can be as bad as common mode excitation, because lines are always unbalanced some small distance away from the noise source. There was a computer about a mile or two from me, perhaps further, and it was exciting the telco and power lines in differential mode. The lines acted like transmission lines with fairly low loss, and the noise went for miles. I bought the lady a lighting protection outlet strip with internal bypass capacitors, no series beads added, and the problem vanished. There are two excitation modes that cause problems, and beads across multiple conductors don't do a thing for differential mode. Beads also have a varying effect on common mode, because the common mode impedance of the system has to be very LOW in comparison to bead series impedance in order for beads (or any series impedance) to have a large effect. A high CM or DM system impedance, or an uncontrolled impedance, is what causes us to have poor results, or what makes a system require astronomical and/or impractical choking impedances. I solved all my computer issues 15 years ago. I built a line filter box that has individual series chokes on each power mains lead, and bypasses the line source side of the lines to the safety ground and box ground. The computer side ground pin floats from the chassis by a high current RF choke, and the socket is bypassed only to the cord's safety ground on that side. In conjunction with proper shack wiring, enclosures, and RF cables, I can use any supply or computer I like. A few hours proper work saved me years of problems. Some line filters, by the way, are not built correctly. Some fail to address the common mode, others fail to address the differential mode. But the poorest and most unreliable system of all is the system that just throws beads at a problem. 73 Tom _ Topband Reflector
Topband: Desktop power supplies
It is my opinion that there are two kinds of switching power supplies---the kind that are messing up your radio today and the ones that will at a later time. I believe they are not compatible with HF radio at a fundamental level, thought we must learn to live with them. Two instances...one noise related, the other not. A few years back I setup a packet node at a remote BC location, and was blessed with a high quality switching supply. Every time the radio was keyed, the supply would sense the load increase as a short and briefly pulse the DC output. This reset the packet controller, which created several trips to the site before I scoped the DC and figgered out what was going on. In the second instance, this past field day somebody managed to get a switcher hooked up to our 6M radio without my knowledge. When the radio was keyed, the noise from the normally quiet supply clobbered the adjacent SSB station. Reason: The supply did not like the square wave from our generator (rather than the utility sine wave) and the switcher would panic when the load was high. Problem not apparent on the 6M or HF radio while 6M was receiving...only a couple amps load. Never would have thought of those problems. Switching power supplies are very sneaky as well as potentially noisy. They work well with steady loads under ideal conditions. They work well when new when all the line-filter caps are in tact, but the quality of those little caps isn't always the best and they get popped at the worst time. Switchers are a fact of lifebut any time you can avoid one on your operating table, I say do it. Same is true of the little curley-Q lightbulbs (with a switcher inside)... One man's opinion de K8RYU _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
On 7/21/2013 8:49 AM, Tom W8JI wrote: I can't understand why throwing some ferrite beads at a problem, or changing the supply, are the only two solutions. Many times, if not most times, a few .01 uF line voltage rated bypass capacitors are significantly better than a sting of cores, or a winding through cores. Yes, IF the problem is differential-mode coupling to the power line. But often it is NOT -- if the trash is coupled to the power cable as a common mode voltage on the green wire, those capacitors won't do a thing. There are also times that because of the way a product is built, it is not practical to modify it. Or because the owner might wish to avoid a warranty issue. If the problem is common mode, a ferrite choke is by far the best solution, and often the only solution. A very common way that trash ends up as common mode on the green wire is when the green wire fails to contact the chassis (or shielding enclosure) where it enters the unit, but instead wanders around circuit common before it MAY or may not find the chassis. All three of my linear Astron supplies have this problem -- the green wire goes to the retaining lug of a traditional terminal strip, that is insulated from the chassis by paint. Circuit common also goes to that lug. More often the problem is intentional, and the result of cost-cutting in the design process. Yes, opening up the unit and correcting it fixed those Astrons, but many products with this sort of problem cannot be fixed without major surgery. For all of these reasons, I continue to recommend the use of common mode chokes that are optimized for the frequency range of the interference. 73, Jim K9YC _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
On 7/21/2013 8:49 AM, Tom W8JI wrote: I can't understand why throwing some ferrite beads at a problem, or changing the supply, are the only two solutions. Many times, if not most times, a few .01 uF line voltage rated bypass capacitors are significantly better than a sting of cores, or a winding through cores. Yes, IF the problem is differential-mode coupling to the power line. But often it is NOT -- Bypass capacitors will cure common mode also, because common mode cannot be generated without differential mode someplace in the system between two points. In virtually every situation, the power supply is in a metal box. The trash is between the power line leads, and also between those leads and the case. This is the nature of switching supplies, because they tie a chopper with squarewaves across the power mains, and the system is not well balanced. As a general rule the stuff exiting the dc side is much less problematic. If it is problematic, it needs cleaned up. Bypassing to the cabinet, groundplane, or case fixes or greatly assists in fixing it, too. If a line is properly bypassed to the case, the system can't produce much common mode or differential mode on that particular line. In the rarer case, where two or more lines are involved, they all must be suitably bypassed. The same things that work for lightning protection work for RFI issues, and vice versa. Payback for doing things right, rather than just tossing beads at wires, is much wider than the initial target. 73 Tom _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
On 7/21/2013 4:52 PM, Tom W8JI wrote: Bypass capacitors will cure common mode also, because common mode cannot be generated without differential mode someplace in the system between two points. But you're re-engineering someone else's design, without knowledge of all the issues.That's a questionable practice unless you're a circuit designer -- it's easy to open a can of worms. Few hams are qualified to do that, and I would be the last to recommend it. 73, Jim K9YC _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
Not a new problem for hams. For most of a century consumer stuff had poor to nonexistent RFI compatibility... And if the equipment itself wasn't so bad, it was connected with huge loops of wires that made the installation susceptible. Adding a few bypass capacitors and helping the consumer use decent differential wiring has been part of the solution since at least the 1930's handbooks. Except today we are more often worried about radiation and not susceptibility of consumer stuff. Tim N3QE - Original Message - From: Jim Brown [mailto:j...@audiosystemsgroup.com] Sent: Sunday, July 21, 2013 08:37 PM To: topband@contesting.com topband@contesting.com Subject: Re: Topband: Desktop Power Supply Brand/Noise Question On 7/21/2013 4:52 PM, Tom W8JI wrote: Bypass capacitors will cure common mode also, because common mode cannot be generated without differential mode someplace in the system between two points. But you're re-engineering someone else's design, without knowledge of all the issues.That's a questionable practice unless you're a circuit designer -- it's easy to open a can of worms. Few hams are qualified to do that, and I would be the last to recommend it. 73, Jim K9YC _ Topband Reflector _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
On 07/21/2013 08:37 PM, Jim Brown wrote: But you're re-engineering someone else's design, without knowledge of all the issues.That's a questionable practice unless you're a circuit designer -- it's easy to open a can of worms. Few hams are qualified to do that, and I would be the last to recommend it. 73, Jim K9YC _ Hi, Unless I missed something we are talking tampering with our own gear - our own possessions. I would be reluctant to ever so much as touch somebody else's consumer equipment. However I have bought brand new radio gear and after running a day or two turned it off, opened it up, and customized it. None of that stuff failed to run as expected. Other gear I just opened up, tearing the Do not open - no user serviceable parts inside nonsense tag. I satisfied my questions about how it works and how it was built. How awful that some of us actually build electrical equipment from scratch! YMMV. 73, Bill KU8H _ Topband Reflector
Re: Topband: Desktop Power Supply Brand/Noise Question
I think that both W8JI and K9YC have made good points and a discerning ham can make an intelligent choice. Next topic ! Dale N3BNA From: Bill Cromwell wrcromw...@gmail.com To: topband@contesting.com Sent: Monday, July 22, 2013 12:41 AM Subject: Re: Topband: Desktop Power Supply Brand/Noise Question On 07/21/2013 08:37 PM, Jim Brown wrote: But you're re-engineering someone else's design, without knowledge of all the issues.That's a questionable practice unless you're a circuit designer -- it's easy to open a can of worms. Few hams are qualified to do that, and I would be the last to recommend it. 73, Jim K9YC _ Hi, Unless I missed something we are talking tampering with our own gear - our own possessions. I would be reluctant to ever so much as touch somebody else's consumer equipment. However I have bought brand new radio gear and after running a day or two turned it off, opened it up, and customized it. None of that stuff failed to run as expected. Other gear I just opened up, tearing the Do not open - no user serviceable parts inside nonsense tag. I satisfied my questions about how it works and how it was built. How awful that some of us actually build electrical equipment from scratch! YMMV. 73, Bill KU8H _ Topband Reflector _ Topband Reflector
