Re: Topband: Best Outlet sttrip
This discussion is beginning to confuse me. I thought the issue being debated was the optimal way to provide surge protection to safeguard our radios from unexpected line transients, and not how to reduce hum in unbalanced audio circuits caused by ground loops or ground return currents. It's actually a related issue, because it is common mode and bad port design. I'm perplexed by recent trends to impose unrealistic requirements in consumer installations to work around poor port designs. Wide ranges of real-world installations are just not going to be able to have zero potential between chassis on isolated pieces of gear. Once a cable is out of a cabinet, the designer has to face the fact he has little control over common mode and surges. The port should be designed with reasonable immunity, rather than telling the rest of the outside world they need to be perfect in every way. I believe the conventional wisdom is that both whole-house surge protectors and local surge protectors in combination provide the most effective safeguard. I'm afraid I don't understand how a surge protector that clips an, e.g., 1KV spike on a 120 VAC line can end up doing more damage than no protection all. I understand that the clipped current pulse returns through the ground line and will cause a voltage spike on the ground, and I also understand that other interconnected equipment connected to different grounds may potentially see part of the spike, but on balance that seems to me to be a less dire situation than having no protection at all. I agree with you 100%, Jim. I have MOV protected surge protection outlets at every computer and entertainment group in my house. I also have outlet strips like that in my shop and in my house. While I generally do not depend on MOV's, and do not have lightning arrestors on my feed cables, I do use outlet strips like that for two reasons: 1.) To protect a device that is particularly sensitive to power line surges 2.) As a common point for RF grounding and bypassing in a hub, usually with a piece of gear that generates or receives RFI from a poorly filtered power line connection I think advising against MOV protected strips because some remote piece of gear might have a bad port design is not a good first choice. The trend to correct for bad port designs by demanding the rest of the world have zero or nearly zero cabinet ground potential differences is unrealistic, and will only lead to progressively worse port designs as blame for any damage or operating maladies is shifted to use of reasonable installations. There is a radio, for example, that has a ~0.7 volt logic threshold on a QSK transmit activation line. The manufacturer blames external interfaces and wiring when the radio malfunctions, but they are the ones who used an unreasonable 0.7 volt threshold in their design. This blame-shifting trend by people who do poor port designs is seemingly expanding. This is really why we are having so many problems with noise or damage on ports. 73 Tom _ Topband Reflector
Re: Topband: Best Outlet sttrip
I'm afraid I don't understand how a surge protector that clips an, e.g., 1KV spike on a 120 VAC line can end up doing more damage than no protection all. I understand that the clipped current pulse returns through the ground line and will cause a voltage spike on the ground, and I also understand that other interconnected equipment connected to different grounds may potentially see part of the spike, but on balance that seems to me to be a less dire situation than having no protection at all. I think it comes down to the surge protection device (SPD) wiring configuration in relation to its placement in the electrical system. First, in most NA power systems, neutral and ground are connected at only two places: (1) the secondary of the utility company's transformer; and (2) at the premises main panel board. An SPD, if used, should first be placed at either the electric meter or panel board so that surge currents near the utility entrance may divert on a short path to ground/neutral. On a branch circuit, the problem potentially becomes worse the further the distance of a common secondary SPD from the main panel (so-called 3 modes of protection from devices using three MOVs). Surge currents being induced from say...a shack entry point can divert a large current onto the grounding conductor, causing a large voltage differential to other grounding points on the same branch circuit. On a branch circuit, surge current should never be diverted to a grounding conductor. It may be safely diverted to the neutral conductor and even then, it's best managed if at least a portion of the surge potential can first be stored and then bled onto the neutral where that neutral is connected to ground at the main panel. Common secondary protection SPDs meant for use on branch circuits don't meet this requirement, despite IEEE's recommendation that common 3 modes of protection are safe for use on a branch circuit. Secondary SPDs that do accomplish this goal are made by BrickWall, ZeroSurge, and SurgeX. In a nutshell, my recommendation (for what little it's worth) is this: (1) a secondary SPD on a branch circuit should only be used when a primary SPD is used at the utility company's meter or at the premises main panel; and (2) assuming condition 1 is met, then the secondary SPD should divert surge current only onto the neutral, and never the grounding conductor. Finally, on the issue of balanced audio: it costs manufacturers of consumer electronics and ham gear no more to balance all audio inputs with a 3-stage instrumentation op-amp circuit. It's far more important to balance each input this way than to balance audio outputs although balanced outputs are preferred for best system matching, especially on long cable runs or where distribution is complex (e.g., a broadcast or recording studio with cross-point switchers). With a true instrumentation input, the input circuit does not care if the source is balanced or unbalanced. It's simply a two terminal, floating device with extremely high common-mode rejection (CMRR) performance. The best laid out instrumentation circuits carry that high rejection well into the HF range. Paul, W9AC _ Topband Reflector
Re: Topband: Best Outlet sttrip
First, in most NA power systems, neutral and ground are connected at only two places: (1) the secondary of the utility company's transformer; and (2) at the premises main panel board. Sorry, should have read ...neutral and ground are connected *together* at only two places... Paul, W9AC - Original Message - From: Paul Christensen w...@arrl.net To: TopBand topband@contesting.com Sent: Wednesday, October 09, 2013 9:55 AM Subject: Re: Topband: Best Outlet sttrip I'm afraid I don't understand how a surge protector that clips an, e.g., 1KV spike on a 120 VAC line can end up doing more damage than no protection all. I understand that the clipped current pulse returns through the ground line and will cause a voltage spike on the ground, and I also understand that other interconnected equipment connected to different grounds may potentially see part of the spike, but on balance that seems to me to be a less dire situation than having no protection at all. I think it comes down to the surge protection device (SPD) wiring configuration in relation to its placement in the electrical system. First, in most NA power systems, neutral and ground are connected at only two places: (1) the secondary of the utility company's transformer; and (2) at the premises main panel board. An SPD, if used, should first be placed at either the electric meter or panel board so that surge currents near the utility entrance may divert on a short path to ground/neutral. On a branch circuit, the problem potentially becomes worse the further the distance of a common secondary SPD from the main panel (so-called 3 modes of protection from devices using three MOVs). Surge currents being induced from say...a shack entry point can divert a large current onto the grounding conductor, causing a large voltage differential to other grounding points on the same branch circuit. On a branch circuit, surge current should never be diverted to a grounding conductor. It may be safely diverted to the neutral conductor and even then, it's best managed if at least a portion of the surge potential can first be stored and then bled onto the neutral where that neutral is connected to ground at the main panel. Common secondary protection SPDs meant for use on branch circuits don't meet this requirement, despite IEEE's recommendation that common 3 modes of protection are safe for use on a branch circuit. Secondary SPDs that do accomplish this goal are made by BrickWall, ZeroSurge, and SurgeX. In a nutshell, my recommendation (for what little it's worth) is this: (1) a secondary SPD on a branch circuit should only be used when a primary SPD is used at the utility company's meter or at the premises main panel; and (2) assuming condition 1 is met, then the secondary SPD should divert surge current only onto the neutral, and never the grounding conductor. Finally, on the issue of balanced audio: it costs manufacturers of consumer electronics and ham gear no more to balance all audio inputs with a 3-stage instrumentation op-amp circuit. It's far more important to balance each input this way than to balance audio outputs although balanced outputs are preferred for best system matching, especially on long cable runs or where distribution is complex (e.g., a broadcast or recording studio with cross-point switchers). With a true instrumentation input, the input circuit does not care if the source is balanced or unbalanced. It's simply a two terminal, floating device with extremely high common-mode rejection (CMRR) performance. The best laid out instrumentation circuits carry that high rejection well into the HF range. Paul, W9AC _ Topband Reflector _ Topband Reflector
Re: Topband: Best Outlet sttrip
In a nutshell, my recommendation (for what little it's worth) is this: (1) a secondary SPD on a branch circuit should only be used when a primary SPD is used at the utility company's meter or at the premises main panel; and (2) assuming condition 1 is met, then the secondary SPD should divert surge current only onto the neutral, and never the grounding conductor. Paul, The issue I have with this is ***thinking*** ( incorrectly) that unwanted surge is on the hot or neutral, and is diverted to the safety ground because we call that ground. That's a big stretch, and probably mostly never true. The suppressor doesn't pluck something off a hot lead and drop it there just because we call it ground, or because we want it all to be collected and go there. A suppressor only clamps or limits voltage across its terminals. It goes low resistance where a transient comes along. I can have two suppressors, one each from hot and neutral to safety ground (although that is a poorly thought-out system) and it will simply clamp the three wire ends together. It does not back-feed the safety ground or neutral with any grossly upsetting currents, because almost certainly any **power line** sourced surge already came from the direction of the breaker panel. The clamps would divide currents by wire impedance and clamping voltage differential, so the neutral and other two wires would be part of it any way we wire the clamping system. To illustrate how misplaced the concept of protection devices increasing damage actually is, the safety ground is already connected to the chassis! It is a thinner bare wire that closely parallels the other two wires for some significant distance, and already connects to the neutral at the box. Suddenly we are supposed to believe that clamping it to wires it already parallels (and already has a low impedance to) will cause or increase damage. Additionally, there is a bunch of stuff inside devices that lowers impedance or voltage breakdown between all conductors anyway. There isn't anything wrong with clamping the lines at a common point in the shack, or at any equipment cluster, no matter what else we have in the system. Most of the damage we get is common mode from our antenna grounds and antennas. The potential from that sees a voltage differential from the mains. That differential already occurs between the antenna and chassis common connection to all three wires almost equally. If you DON'T have the MOV device, the safety ground and chassis is actually the best path to the box. After all, that safety ground already is directly tied to the chassis, and to out antennas, or in consumer gear to Telco lines or CATV lines. The only thing the MOV's do for nearly all of the problems is keep the snap out of the power line wiring and components inside the cabinets. I'm just baffled why any theory would propose allowing two wires of a three wire line float from the chassis is an improvement, when the bulk of the problem is a ground loop from the antennas or cable/Telco grounds to the power mains, and most mains surges are the same. A secondary but lesser mains issue would be between the neutral and hot, and that surge would primarily flow back on the heavier neutral rather than the lighter safety. This entire thing defies common sense. The next thing I expect to hear is them telling us to cut the safety ground off to protect their ports. 73 Tom _ Topband Reflector
Re: Topband: Best Outlet sttrip
Tom, You have probably already seen references like this: http://www.zerosurge.com/technical-info/how-surge-suppression-works/ One can either believe it, or dismiss it as voodoo engineering. I'll not try and persuade its use other than to point out that if a whole-house SPD is installed at the power meter or entrance panel, and if its clamping devices are working without failure, then there's probably no need for additional SPDs anywhere else on a branch circuit. But if that protective entry device does fail, and I'm left with only secondary SPD protection on a branch circuit, I would rather clamp to neutral where it's still at ground potential by virtue of the neutral-to-ground bond at the entrance, but not potentially raise the potential of the branch circuit's grounding conductors. Paul, W9AC - Original Message - From: Tom W8JI w...@w8ji.com To: Paul Christensen w...@arrl.net; TopBand topband@contesting.com Sent: Wednesday, October 09, 2013 3:01 PM Subject: Re: Topband: Best Outlet sttrip In a nutshell, my recommendation (for what little it's worth) is this: (1) a secondary SPD on a branch circuit should only be used when a primary SPD is used at the utility company's meter or at the premises main panel; and (2) assuming condition 1 is met, then the secondary SPD should divert surge current only onto the neutral, and never the grounding conductor. Paul, The issue I have with this is ***thinking*** ( incorrectly) that unwanted surge is on the hot or neutral, and is diverted to the safety ground because we call that ground. That's a big stretch, and probably mostly never true. The suppressor doesn't pluck something off a hot lead and drop it there just because we call it ground, or because we want it all to be collected and go there. A suppressor only clamps or limits voltage across its terminals. It goes low resistance where a transient comes along. I can have two suppressors, one each from hot and neutral to safety ground (although that is a poorly thought-out system) and it will simply clamp the three wire ends together. It does not back-feed the safety ground or neutral with any grossly upsetting currents, because almost certainly any **power line** sourced surge already came from the direction of the breaker panel. The clamps would divide currents by wire impedance and clamping voltage differential, so the neutral and other two wires would be part of it any way we wire the clamping system. To illustrate how misplaced the concept of protection devices increasing damage actually is, the safety ground is already connected to the chassis! It is a thinner bare wire that closely parallels the other two wires for some significant distance, and already connects to the neutral at the box. Suddenly we are supposed to believe that clamping it to wires it already parallels (and already has a low impedance to) will cause or increase damage. Additionally, there is a bunch of stuff inside devices that lowers impedance or voltage breakdown between all conductors anyway. There isn't anything wrong with clamping the lines at a common point in the shack, or at any equipment cluster, no matter what else we have in the system. Most of the damage we get is common mode from our antenna grounds and antennas. The potential from that sees a voltage differential from the mains. That differential already occurs between the antenna and chassis common connection to all three wires almost equally. If you DON'T have the MOV device, the safety ground and chassis is actually the best path to the box. After all, that safety ground already is directly tied to the chassis, and to out antennas, or in consumer gear to Telco lines or CATV lines. The only thing the MOV's do for nearly all of the problems is keep the snap out of the power line wiring and components inside the cabinets. I'm just baffled why any theory would propose allowing two wires of a three wire line float from the chassis is an improvement, when the bulk of the problem is a ground loop from the antennas or cable/Telco grounds to the power mains, and most mains surges are the same. A secondary but lesser mains issue would be between the neutral and hot, and that surge would primarily flow back on the heavier neutral rather than the lighter safety. This entire thing defies common sense. The next thing I expect to hear is them telling us to cut the safety ground off to protect their ports. 73 Tom _ Topband Reflector
Re: Topband: Best Outlet sttrip
On 10/9/2013 1:08 PM, Paul Christensen wrote: You have probably already seen references like this: http://www.zerosurge.com/technical-info/how-surge-suppression-works/ This technology is quite well proven, and widely used in pro audio. A company called SurgeX pretty well owns the pro audio and video market. I began specifying their products to protect racks full of equipment for the large systems I designed nearly 20 years ago. IEEE studies have shown that with proper bonding and grounding at the service entrance, the highest voltage that can be induced on branch circuits is in the range of 3-6 kV. 73, Jim K9YC _ Topband Reflector
Re: Topband: Best Outlet sttrip
On 10/8/2013 8:11 AM, Tom W8JI wrote: Why would that be true? I can't understand any mechanism that would consistantly increase damage because an MOV protected stip is added. MOV from phase to green wire dumps current onto green, IZ drop on green back to the panel raises potential of that chassis. It has a low voltage (signal cable) to another box, plugged into another MOV strip at a different location, more current on green, probably not the same, probably not the same IZ drop. The difference appears on the low voltage interconnection and fries I/O for that interconnection. Same issue happens if the interconnection is to equipment with a different ground connection. I've seen MANY reports from engineers of destructive failures in small wired Ethernet systems in homes and small offices with no radios or towers involved. Likewise, large audio and video systems with equipment at widely separated locations have this issue. I worked in that field for many years, and we solved it by using series-mode protection on branch circuits. MOVs are fine IF the bonding of grounds and equipment is properly done, and if everything is at a single outlet. I have long advocated a scheme for AC power in shacks whereby all power comes from outlets that share the same green wire, or from outlets whose green wires are bonded together. Likewise, I have long advocated a scheme whereby every equipment chassis is bonded to every other chassis by short fat copper, and to station ground, and to all other grounds. That works well both for lightning protection and for the prevention of noise coupled by leakage currents into unbalanced interconnects, and into Pin One Problems. The mechanism for the leakage current side of it is quite similar. We know that the AC line is full of the harmonics of 60 Hz because current is drawn by capacitor-input supplies in pulses at the peaks of the cycle, and that the triplen harmonics add both in the neutral and in the ground of 3-phase systems. Few of us have 3-phase in our homes, but a LOT of power distro to us uses high-leg delta on the street to feed us. High leg delta is 240V delta, where one side of the delta has a center-tapped transformer to feed single phase customers, and 3-phase customers get all three phases. These single phase customers have no neutral, so much of their harmonic current shows up on our neutral. In our homes, we have equipment with intentional capacitors (line filters) and stray capacitance (mostly transformers mounted to the chassis) between line and neutral, and between line and green. This capacitance dumps the line voltage, including the harmonics present in the voltage waveform, onto the neutral, increasing linearly with frequency. So when we stick a scope between the two ends of a green wire, we see those harmonics. Now, when we make a signal interconnect between gear plugged into different outlets, we have different IR drops due both to differences in the relative strength of the harmonics on those outlets, and to the lengths of the green wires, and the difference is the familiar power line buzz that we have long called ground loops. I prefer to call it what it is -- noise coupled by leakage current -- because we can now understand the mechanism, and knowing the mechanism, know how to prevent it. With unbalanced interconnects, this buzz is added to the signal. And if the gear has Pin One Problems, it's also coupled into gear by that mechanism. The power distro scheme (same green wire, or bonded outlet boxes) typically reduces the buzz by 20 dB (by taking the drop in the long green wires to the panel out of the equation). Bonding the gear is typically good for another 20-30 dB. 73, Jim K9YC _ Topband Reflector
Re: Topband: Best Outlet sttrip
Hi Jim, MOV from phase to green wire dumps current onto green, IZ drop on green back to the panel raises potential of that chassis. It has a low voltage (signal cable) to another box, plugged into another MOV strip at a different location, more current on green, probably not the same, probably not the same IZ drop. The difference appears on the low voltage interconnection and fries I/O for that interconnection. Same issue happens if the interconnection is to equipment with a different ground connection. I've seen MANY reports from engineers of destructive failures in small wired Ethernet systems in homes and small offices with no radios or towers involved. Likewise, large audio and video systems with equipment at widely separated locations have this issue. I worked in that field for many years, and we solved it by using series-mode protection on branch circuits. I understand your concern now, but that problem is really rooted in a design issue with the equipment. The system should not be that sensitive to common mode issues on ports. It is foolish or poor planning to think, by simply not clamping a distant line for surges, we somehow protect poorly designed input systems. A design sensitive to common mode places a burden on everyone else in the world to protect the poorly protected or designed ports. It's like saying I'm going to do a bad job, so watch out for me. It is like the unrealistic dream that unbalanced audio lines from chassis-to-chassis, grounded at each chassis, is a good system and that all that needs to be done is be sure that all of the world's chassis are at virtually zero potential to each other. That just sets everyone up for problems. It is unrealistic to expect every piece of gear and system to ensure all non-clustered pieces of gear are at the exact same chassis potential. If something as simple as a MOV clamp causes a problem, you can bet the same gear will have problems from dozens of other causes. I suspect the real root of this is cheapness, where they want to avoid isolation and protection on the port and pass the blame or burden off on the rest of the world. MOVs are fine IF the bonding of grounds and equipment is properly done, and if everything is at a single outlet. I have long advocated a scheme for AC power in shacks whereby all power comes from outlets that share the same green wire, or from outlets whose green wires are bonded together. Likewise, I have long advocated a scheme whereby every equipment chassis is bonded to every other chassis by short fat copper, and to station ground, and to all other grounds. That works well both for lightning protection and for the prevention of noise coupled by leakage currents into unbalanced interconnects, and into Pin One Problems. That's true, and that's good advice. Although proper grounding for lighting belongs at the entrance and not on the desk. Now, when we make a signal interconnect between gear plugged into different outlets, we have different IR drops due both to differences in the relative strength of the harmonics on those outlets, and to the lengths of the green wires, and the difference is the familiar power line buzz that we have long called ground loops. I prefer to call it what it is -- noise coupled by leakage current -- because we can now understand the mechanism, and knowing the mechanism, know how to prevent it. The easiest way to prevent it, because there are dozens of causes, is to not have port designs sensitive to common mode. In broadcasting, we would have nearly been taken out and put in front of the firing squad for running audio lines with shields grounded at each end, or unbalanced low level lines between equipment that was not on the same rack when the shield was grounded at each end. Sometimes we need to rethink the point of ingress, and not make the rest of the world responsible for our cheapness or lack of planning. :) 73 Tom _ Topband Reflector
Re: Topband: Best Outlet sttrip
On 10/8/2013 2:42 PM, Tom W8JI wrote: the system should not be that sensitive to common mode issues on ports. Right. But first, we're not talking about common mode, we're talking about chassis-to-chassis noise coupling into unbalanced interconnects, like computers feeding radios, with or without various interfaces. And yes, unbalanced interfaces are a lousy way to do it, but I don't know of a single ham rig that has balanced interconnects for audio or accessories. So unless a ham wants to rebuild every rig and all accessory gear with balanced interfaces, the simple power and bonding concepts I've outlined are the lowest cost, most reliable, and a very robust solution. Yes, we could add transformers, but transformers cost more, and shielded transformers cost a LOT more. As Vice Chair of the AES Standards Committee Working Group on EMC, I was a principal author of all AES Standards on the topic. It took a while to reach a consensus, because some purists were unwilling to write Standards to work with real world equipment. The path we took, and that the cool heads worked very hard to achieve, was to write Standards defining the RIGHT ways to do it, both inside and outside of equipment, but to define the right way to work with vintage gear that was badly designed/built. Our first EMC Standard, AES48, attacked the Pin One Problem, which was the most critical root cause, both at baseband and at RF. We then wrote the protocols for balanced interconnects, including the advice that when the cable shield needed to be interrupted to prevent shield current, the interruption should always be at the receiving end. This is counter-intuitive, but Bill Whitlock showed that it is the only right way. The point of this digression is that there's no way in hell that hams are going to replace our gear with stuff having balanced I/O for audio and control, simply because it doesn't exist, and to assume that such gear will exist in the foreseeable future is wildly unrealistic. Heck -- we can't every get manufacturers to build gear without Pin One Problems. 73, Jim K9YC _ Topband Reflector
Re: Topband: Best Outlet sttrip
FlexRadio equipment has balanced audio i/o 73 Peter -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim Brown And yes, unbalanced interfaces are a lousy way to do it, but I don't know of a single ham rig that has balanced interconnects for audio or accessories. _ Topband Reflector
Re: Topband: Best Outlet sttrip
Sent from my iPad On Oct 8, 2013, at 19:06, Jim Brown j...@audiosystemsgroup.com wrote: On 10/8/2013 2:42 PM, Tom W8JI wrote: the system should not be that sensitive to common mode issues on ports. Right. But first, we're not talking about common mode, we're talking about chassis-to-chassis noise coupling into unbalanced interconnects, like computers feeding radios, with or without various interfaces. And yes, unbalanced interfaces are a lousy way to do it, but I don't know of a single ham rig that has balanced interconnects for audio or accessories. So unless a ham wants to rebuild every rig and all accessory gear with balanced interfaces, the simple power and bonding concepts I've outlined are the lowest cost, most reliable, and a very robust solution. Yes, we could add transformers, but transformers cost more, and shielded transformers cost a LOT more. As Vice Chair of the AES Standards Committee Working Group on EMC, I was a principal author of all AES Standards on the topic. It took a while to reach a consensus, because some purists were unwilling to write Standards to work with real world equipment. The path we took, and that the cool heads worked very hard to achieve, was to write Standards defining the RIGHT ways to do it, both inside and outside of equipment, but to define the right way to work with vintage gear that was badly designed/built. Our first EMC Standard, AES48, attacked the Pin One Problem, which was the most critical root cause, both at baseband and at RF. We then wrote the protocols for balanced interconnects, including the advice that when the cable shield needed to be interrupted to prevent shield current, the interruption should always be at the receiving end. This is counter-intuitive, but Bill Whitlock showed that it is the only right way. The point of this digression is that there's no way in hell that hams are going to replace our gear with stuff having balanced I/O for audio and control, simply because it doesn't exist, and to assume that such gear will exist in the foreseeable future is wildly unrealistic. Heck -- we can't every get manufacturers to build gear without Pin One Problems. 73, Jim K9YC _ Topband Reflector _ Topband Reflector
Re: Topband: Best Outlet sttrip
This discussion is beginning to confuse me. I thought the issue being debated was the optimal way to provide surge protection to safeguard our radios from unexpected line transients, and not how to reduce hum in unbalanced audio circuits caused by ground loops or ground return currents. I believe the conventional wisdom is that both whole-house surge protectors and local surge protectors in combination provide the most effective safeguard. I'm afraid I don't understand how a surge protector that clips an, e.g., 1KV spike on a 120 VAC line can end up doing more damage than no protection all. I understand that the clipped current pulse returns through the ground line and will cause a voltage spike on the ground, and I also understand that other interconnected equipment connected to different grounds may potentially see part of the spike, but on balance that seems to me to be a less dire situation than having no protection at all. 73, Jim W8ZR Sent from my iPad On Oct 8, 2013, at 19:06, Jim Brown j...@audiosystemsgroup.com wrote: On 10/8/2013 2:42 PM, Tom W8JI wrote: the system should not be that sensitive to common mode issues on ports. Right. But first, we're not talking about common mode, we're talking about chassis-to-chassis noise coupling into unbalanced interconnects, like computers feeding radios, with or without various interfaces. And yes, unbalanced interfaces are a lousy way to do it, but I don't know of a single ham rig that has balanced interconnects for audio or accessories. So unless a ham wants to rebuild every rig and all accessory gear with balanced interfaces, the simple power and bonding concepts I've outlined are the lowest cost, most reliable, and a very robust solution. Yes, we could add transformers, but transformers cost more, and shielded transformers cost a LOT more. As Vice Chair of the AES Standards Committee Working Group on EMC, I was a principal author of all AES Standards on the topic. It took a while to reach a consensus, because some purists were unwilling to write Standards to work with real world equipment. The path we took, and that the cool heads worked very hard to achieve, was to write Standards defining the RIGHT ways to do it, both inside and outside of equipment, but to define the right way to work with vintage gear that was badly designed/built. Our first EMC Standard, AES48, attacked the Pin One Problem, which was the most critical root cause, both at baseband and at RF. We then wrote the protocols for balanced interconnects, including the advice that when the cable shield needed to be interrupted to prevent shield current, the interruption should always be at the receiving end. This is counter-intuitive, but Bill Whitlock showed that it is the only right way. The point of this digression is that there's no way in hell that hams are going to replace our gear with stuff having balanced I/O for audio and control, simply because it doesn't exist, and to assume that such gear will exist in the foreseeable future is wildly unrealistic. Heck -- we can't every get manufacturers to build gear without Pin One Problems. 73, Jim K9YC _ Topband Reflector _ Topband Reflector
