Re: Topband: Thanks!
Hi Charlie, You are right, and you can thank Jim, K9YC for that. I used 14 turns of CAT5 on a 2.4 OD #31 ferrite core, per his suggestion. Photo attached. Out of all the info I have ever read on ferrite materials and common-mode chokes --either in print or on the Web-- Jim's info at http://audiosystemsgroup.com/RFI-Ham.pdf has been the most valuable to me. 73, Mike www.w0btu.com On Wed, May 22, 2013 at 12:34 AM, Charlie Cunningham charlie-cunning...@nc.rr.com wrote: I would think 31 material would be great for RF control and suppression on things like CAT5 cables, telephone circuits, audio circuits etc.! Regards, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Mike Waters Sent: Wednesday, May 22, 2013 1:01 AM To: topband Subject: Re: Topband: Thanks! That's true, but 31 material is the closest thing I've come to a magic cure here, for several applications in the past year! :-) It's the ONLY material that kept 75 meter RF from getting into my shack computer's CAT5 LAN cable (etc.), and it worked perfectly as a choke balun on a G5RV-type antenna I experimented with last year. 31 almost ought to be one of the definitions of magic in the dictionary. :-) 73, Mike www.w0btu.com On Tue, May 21, 2013 at 9:07 PM, Tom W8JI w...@w8ji.com wrote: 31 isn't a magic cure-all, ... All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Magnetic Loops
Gary wrote on May 21. I've had a Wellbrooke loop for a few years at 20' on a TV rotator. It nulls a single nearby QRN source NW at 300 deg true. EU is about 15-30 deg from here. When 160 or 80 are open over the N Pole, it often helps me hear the weak. It's less effective on multi-source QRN, but still helps at times if I rotate the loop to null the loudest noise and max the received signals. No room for other receiving antennas, and the loop ignores legal limit transmissions on a 120'x120' lot. What more can I ask? 73, Gary NL7Y Gary, Deploying the loop at ground level can sometimes reduce local QRN compared to mounting it high up where it can pick-up noise radiated from sources below. Also it may be prudent to make sure you have mains filter on the rotator, receiver and Loop power supply. Preferable one with a Earth line choke, so it can have a separate ground connexion to the equipment isolated from the powerline Earth. 73 Andrew G8LUG All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Thanks!
I think that 31 material is probably a good choice for cleaning RF from wiring that isn't handling RF power and where there isn't much in the way of shunt impedance for the choke to work against -like a line from an electricity meter carrying a much as 480 VAC (530 VAC at 480 high-line).` That line has shunt impedances. Almost everything does. A main area for shunting impedance is the entrance ground. The individual wires couple together fairly tight, so even the hot wires have shunt impedance. This is one of the reasons antenna systems, with system design flaws causing common mode issues, have better reception (less noise) with improved grounding on the mains. The shunt impedance is as important as any series bead or choke string. The better the ground, the less important choke impedance is. Another common point is downstream at the station. If the feeders have common mode from poor feed arrangements, reducing shunt impedance on the path from antenna feeders to power mains reduces noise. Common mode chokes are part of a system. Because I have a good entrance layout and cable bonding, just a single bead makes a large difference. If I had a sloppy arrangement with high shunt impedances, I could have fifty beads and not change much. This is the problem with small antennas, or antennas with high common mode impedance. The antenna itself doesn't present much shunt impedance. The series part of the pi filter or attenuator formed by the shunt impedances and series beads or chokes is in a high impedance path, and has very little attenuation even with astronomical series impedances. It is a system with huge variables if the variables are not controlled, not something that generally the same where one rule fits every system. That's also an issue on high-speed digital circuits that can't tolerate much in the way of shunt capacitance. Not on individual lines, but when the lines are properly grouped they can have low shunt impedance for common mode and high shunt impedance for desired signal modes. Although we might not always think about it, we do that all the time in systems. Not so sure about it as a balun on coax carrying much RF power! Every different system has to be looked at as a unique system, but the best way to avoid troubles is to design feedpoints and equipment entrance points properly. Proper basics are far better than randomly peppering a mess of a system with beads. The nice thing is what we do for lightning also works for RF, and vice versa. An air coil choke is just as good as beads when the system is planned. As a matter of fact, we can build a nearly perfect single band balun with no beads and no solenoid chokes at all. An 80 meter dipole with a feedline in air and a ground ~~40-80 feet from the antenna has virtually no common mode without any balun at all. As a matter of fact, a balun could make it worse. We need to think about the system more, and guess less. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Thanks!
All good and valid points, Tom! Thanks! Regards, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Wednesday, May 22, 2013 9:35 AM To: Charlie Cunningham; topband@contesting.com Subject: Re: Topband: Thanks! I think that 31 material is probably a good choice for cleaning RF from wiring that isn't handling RF power and where there isn't much in the way of shunt impedance for the choke to work against -like a line from an electricity meter carrying a much as 480 VAC (530 VAC at 480 high-line).` That line has shunt impedances. Almost everything does. A main area for shunting impedance is the entrance ground. The individual wires couple together fairly tight, so even the hot wires have shunt impedance. This is one of the reasons antenna systems, with system design flaws causing common mode issues, have better reception (less noise) with improved grounding on the mains. The shunt impedance is as important as any series bead or choke string. The better the ground, the less important choke impedance is. Another common point is downstream at the station. If the feeders have common mode from poor feed arrangements, reducing shunt impedance on the path from antenna feeders to power mains reduces noise. Common mode chokes are part of a system. Because I have a good entrance layout and cable bonding, just a single bead makes a large difference. If I had a sloppy arrangement with high shunt impedances, I could have fifty beads and not change much. This is the problem with small antennas, or antennas with high common mode impedance. The antenna itself doesn't present much shunt impedance. The series part of the pi filter or attenuator formed by the shunt impedances and series beads or chokes is in a high impedance path, and has very little attenuation even with astronomical series impedances. It is a system with huge variables if the variables are not controlled, not something that generally the same where one rule fits every system. That's also an issue on high-speed digital circuits that can't tolerate much in the way of shunt capacitance. Not on individual lines, but when the lines are properly grouped they can have low shunt impedance for common mode and high shunt impedance for desired signal modes. Although we might not always think about it, we do that all the time in systems. Not so sure about it as a balun on coax carrying much RF power! Every different system has to be looked at as a unique system, but the best way to avoid troubles is to design feedpoints and equipment entrance points properly. Proper basics are far better than randomly peppering a mess of a system with beads. The nice thing is what we do for lightning also works for RF, and vice versa. An air coil choke is just as good as beads when the system is planned. As a matter of fact, we can build a nearly perfect single band balun with no beads and no solenoid chokes at all. An 80 meter dipole with a feedline in air and a ground ~~40-80 feet from the antenna has virtually no common mode without any balun at all. As a matter of fact, a balun could make it worse. We need to think about the system more, and guess less. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
