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#1
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#2
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![]() Bob wrote: wrote: Glad to have helped. As people have helped me over the years, I try to pass my bits of useful knowledge on to those who can use them. Thanks again! In your discussions with Charles Counselman, has he added anything yet to his document? He had some blank sections that were to come later, just wondering if he mentioned anything. Bob We covered many topics, but it would be hard to extract anything to post here. He does intend to post info on his search antenna. A simple 20 turn loop wound on a pill bottle will suffice to get you started. Is your Email valid? I will ask Charles if it is OK to forward you his B-field noise sensing diagram. Depending on how serious, or demented, you are, you might benifit from rereading my prior posts on RF hunts. The 20 turn loop is good for finding noisy devices. A smaller loop made from a salvaged 100uH axial ferrite inductor is great for sniffing around inside a device to find the exact noise source. I built mine in a old Sharpie dry marker case. While I added BNC females connectors to all my probes because I was in the process of trading for a spectrum anylzer and wanted to be able to use my probes with that test gear, a cheaper and more effective option for most people would be to use ~3' of RG174 terminated in the coorect connector for your noise sniffing receiver. I choose to use a DX398 because I have one and becuase it it reasonbly well shielded and does a good job as a sniffer. Maybe 99% of devices radiate RFI over a very wide frequency range. Digital noise tends to be very broadband. Every so often you will find a device that produces a strong signal on a specific frequency and does not radiate general RFI. One common frequency is 3.58MHz, US color refference burst. I had one early Apex DVD that I never could quiten down enough to live with. I suppose I ought to dig through my notes and list the more common "CPU' frequencies. As NTSC goes away, and TV horizontal moves away from 15.73426KHz, (from a grass valley "NTSC Studio Timing:") the harmonics that we are used to at ~15.73KHz increments will vanish. ATSC can be a can of snakes. (http://www.atsc.org/standards.html) Butfrom what I have seen so far ATSC will bigger VHF/UHF RFI issue. Plasma big screens have their own nasty noise signature. LCDs are cold cathode florescent illumintated and the drive oscillators tend to be in the 35~50KHz range and are fairly well shielded and (most) don't radiate too badly.Perhaps the best thing for modern SWLs is the move from over the air TV to cable and satellite. Older tube sets had very poor internal shielding and radiated sweep and color burst back out the antenna and that 300 ohm ribbon lead made a pretty effective antenna. Good hunting Terry |
#3
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#4
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Terry -
Have you found any specific wall warts that you would consider reasonably electrically quiet? Thanks again, Bob |
#5
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![]() Bob wrote: Terry - Have you found any specific wall warts that you would consider reasonably electrically quiet? Thanks again, Bob Even with wall warts that appear to be identical, the RFI varies a great deal. I go to the local good will store once every couple of weeks with my trusty DX398 and check out their constantly changing stock for quite ones. Stay away from switch mode wall warts. They are very light weight and are RFI demons. I try to keep a selection on hand of the more common voltages and try to limit my purchases to those that are fastened with screws. At home I have modifed nearly everything in the radio room to run from +12V so I only have to worry about the one big supply. It also makes operation during power outages easier as I have several GellCells on constant float ready to take over when the grid goes down. I will try to assemble/edit down a list of usefull links and email, or get Will to email, them to you. The r2000swl/swler accounts are dead. Too much hate filled spam. What type receiver are you using? What type antenna(s).... What is your special interest... It is hard to overestimate how much a good ground can improve every situation. "Good" is difficult to define, but in my mind it is much more then a single 8' ground rod or a cold water pipe. A triad of three 8' ground rods arranged in a equalateral 12" triangle, interconnected by #8 solid copper wire is a good start. An alternative can be made with one 8' rod, and ~20' of soft copper tubing buried at lease a foot. The use of balanced antennas makes the ground less critical. I am not a big fan of loops, but I have found that active, broadband dipoles, in the right places can reduce the need of a good ground nearly completly. And while I don't care much for loops, many first class DXers swear by them. Good, well balanced loops don't require much in the way of a ground. Terry |
#6
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#8
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wrote:
For bang for the buck the North Country Active antenna works pretty well. According to Yodar from RHFs Yahoo antenna group they will assemble it for you. It is small enough to hide and will work much better then the PA0RDT. In my opinnion, based on the tests that I have made, the PA0RDT simply doesn't have enough antenna to overcomm the internal noise in the active electronics. The North country would be my first choice if I couldn't get a Lankford, or it's near clone the AMRAD. Thanks for reminding me of the North Country! I had seen Yodar's note about them building him one, but had forgotten about it. I think I'd prefer the AMRAD or Dallas' design if the builder can do, but it's another option and only a little over $100 at that. While poking around the North Country site after reading your message, I came across this page in their tech section: http://www.northcountryradio.com/Articles/actant3.htm It is a clear, concise explanation of how and why to use a "Bryant type choke" and a seperate ground rod on an active antenna to knock down noise on the shield. The only critical comment I would have is they never actually call the noise common mode noise. You could save some typing by referring someone there :-) One variation I am going to try and build of Dallas' active dipole is to build it like a VHF coaxial dipole. The lower element will be an outer sleeve over a center support member. It would be very easy to hide in plain sight, and with some care in routing the coax, you might get away with calling it a bird feeder. Hard to put into words, but I ought to be very doable. My problem is that since the Homeowners Association does all lawn and driveway maintenance, free standing things that require any extra effort to mow or trim around are frowned upon. Bird feeders need to be attached to home or deck. As time goes on, and trees grow a bit, something in a tree with buried coax may be possible. The R8B is a SWEET receiver. 95% of the time anything I hear on the R8B I can hear on my R2000. But that other 5% of the time is heaven! Yeah, right now it's on my "future budget list"...... How do you rate its' synchronous detector vs what you have seen? Bob |
#9
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#10
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Some of those cheap no good wall warts will mess up and blow out your
equipment.I have seen it happen before. cuhulin |
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