It's a mistake to think of plumbing pipework to be necessarily a good ground. Wet ground is a better ground than dry ground, sure, but RF travels on the outside of pipes (skin effect) so the water in the pipes is irrelevant except at DC. Pipework may be the best available local ground, but taking a wire to a pipe doesn't necessarily help at RF either, sometimes a wire (such as in a mains coble) isn't sufficient, particularly if it is thin gauge, single stranded or long. A short piece of tape or braid or Litz wire to provide a low impedance to a proved good ground may be required.
w
A bit more reading material:
Designing for Interference-free Audio System Components
A Practical Interference Free Audio System (Part 2)
One you get up to 1MHz the return current will follow the path of least inductance, this is not the path of least resistance nor quite often the path you think it is.
Designing for Interference-free Audio System Components
A Practical Interference Free Audio System (Part 2)
One you get up to 1MHz the return current will follow the path of least inductance, this is not the path of least resistance nor quite often the path you think it is.
Water is only a good conductor when you want an insulator. When you want a conductor water is almost useless. Better to regard it as a lossy dielectric (epsr~80). I suspect that a significant part of the difference between a 'good' ground and a 'bad' ground for RF purposes is not due to conduction but permittivity.
Grounding to water pipes relies on the pipes being metal, with good joints, all the way back to the ground. Not necessarily true of modern water systems. In the UK we are now taught to regard water pipes as a potential electrocution hazard, made safe by earth bonding (very thick cables to a true earth).
Grounding to water pipes relies on the pipes being metal, with good joints, all the way back to the ground. Not necessarily true of modern water systems. In the UK we are now taught to regard water pipes as a potential electrocution hazard, made safe by earth bonding (very thick cables to a true earth).
DF96 is right, ground is only ground if its really ground; do not assume! Just my penny/3 cents worth on how RF sees ground. I spent a few years laying out PCBs for signal handling equipment to work at L-band 850-2150 Mhz. Many of the designs involved switched multiple paths with amplification.
My experience is that RF will explore and exploit every bit of geometry in our electro physical world. We just aren't used to thinking of electronics in those terms, but that's how electro-magnetism at high frequencies works. Even a few square millimetres of copper on a circuit can turn into an antenna unless it is hard bonded to ground. Our rule of thumb was a a via to nail the ground plane top and bottom together every 10mm.
In one case we had cross talk of -60dB between two PCBs. Input and output were on DIN RF connectors soldered directly to PCB and the ground plane on the bottom of the PCB. The customer wanted -80db. Many areas of the design were scrutinised and no areas for improvement could be seen, the active circuitry was already screened with cans. In the end a solder fillet on the top of the connector body reliably saw -90dB, even though millimeters away the rest of the connector body was already tied hard to ground! Those two little stubs of brass either side of the center pin were the cause all along.
My experience is that RF will explore and exploit every bit of geometry in our electro physical world. We just aren't used to thinking of electronics in those terms, but that's how electro-magnetism at high frequencies works. Even a few square millimetres of copper on a circuit can turn into an antenna unless it is hard bonded to ground. Our rule of thumb was a a via to nail the ground plane top and bottom together every 10mm.
In one case we had cross talk of -60dB between two PCBs. Input and output were on DIN RF connectors soldered directly to PCB and the ground plane on the bottom of the PCB. The customer wanted -80db. Many areas of the design were scrutinised and no areas for improvement could be seen, the active circuitry was already screened with cans. In the end a solder fillet on the top of the connector body reliably saw -90dB, even though millimeters away the rest of the connector body was already tied hard to ground! Those two little stubs of brass either side of the center pin were the cause all along.
AVE...
For me grounding to pipe works. There are about 15 square kilometers of ground my pipe is grounded to...
Anyway, if I can't hear my cellphone and my plasma lamp discharges, then shielding is sufficient for audio equipment. Add some RC low-pass filters in circuit and there should be no problems. Even if some RF noise is present, it will be not heard or will be removed by filters. This noise can be problematic, when equipment works in the same bandwidth or has high-gain amplifiers (or both). I experienced problems when I experimented with wireless EKG. AM transmitter caused interferences with input amplifier. Some part of op-amp demodulated the radio signal. Series of huge RC low-pass filters helped, but I abandoned this project because it transmitted only one signal...
For me grounding to pipe works. There are about 15 square kilometers of ground my pipe is grounded to...
Anyway, if I can't hear my cellphone and my plasma lamp discharges, then shielding is sufficient for audio equipment. Add some RC low-pass filters in circuit and there should be no problems. Even if some RF noise is present, it will be not heard or will be removed by filters. This noise can be problematic, when equipment works in the same bandwidth or has high-gain amplifiers (or both). I experienced problems when I experimented with wireless EKG. AM transmitter caused interferences with input amplifier. Some part of op-amp demodulated the radio signal. Series of huge RC low-pass filters helped, but I abandoned this project because it transmitted only one signal...
I haven't but they look good. Kind of pricey though.
jkeny said:
I don't. If it hurts don't listen to it, I say. I'm also curious about the noise that was produced by our amps. Just too lazy to hook it up to my 100Mhz scope to check for ringing or check it out for noise problems. I kinda doubt I'd find anything, also.
Want to do an interesting experiment? Find a toroidal power transformer of a fairly low power (under 25VA for good HF response) and low voltage (6 volts or so). Place a voltage divider across the secondary to act as a load (100 mA or so) and drop the output to a level that your computer sound card can eat. Plug the primary into your wall outlet and have a look at the secondary with any test equipment you have, scope, distortion analyzer, and FFT analyzer.
The distortion on my line voltage runs about 5% in the winter afternoon when the demand is low and TV sets aren't on. At 8 PM on a hot evening when everyones AC unit is humming it hits 10 to 12% here with obvious flat topping. My FFT analyzer goes to about 90 KHz and I can see crud on my power line all the way to the upper limit. Some of the spikes are only 15 db below the 60 Hz. That new flat screen TV is one of the worst polluters, so is this computer!
The distortion on my line voltage runs about 5% in the winter afternoon when the demand is low and TV sets aren't on. At 8 PM on a hot evening when everyones AC unit is humming it hits 10 to 12% here with obvious flat topping. My FFT analyzer goes to about 90 KHz and I can see crud on my power line all the way to the upper limit. Some of the spikes are only 15 db below the 60 Hz. That new flat screen TV is one of the worst polluters, so is this computer!
Sheesh. I would take that one up with the public service commission if your utility does not take 10% THD seriously. They are constrained by IEEE Red Book (indirectly, not sure the actual root source), which states 5%.
The fact the AC is running should not affect your THD appreciably; that load is highly linear. Sure, you may end up with low voltage on the grid, but not high THD. But in general, everyone is suffering with harmonic distortion, especially residential users ironically enough. With the exception of our largest appliances, our entire house is cap input rectifiers.
Johnloudb
The Mosquito - Wikipedia, the free encyclopedia
The US navy report was from a few years ago, when super tweeters started coming out, I'm plowing through some stuff to try and find it.
When we hear sounds our bodies also add to the sensation, with low frequency effecting the squashy bits and the higher frequencies effected by bone conduction. We do communication systems and have to take these effect into consideration when the equipement is being used with high ambient noise and audio frequency range vibration. So while not hearing the extremes they do effect the overall impression of sound. That is why older people who dont 'hear' high frequencies still find that music with these highs removed sounds naff. Standard audio and communications often dont use bone conductions for the transmission of sound, so quite a lot of info tends to be classified unfortenatly.
This is some stuff on bone conduction protection etc.
http://ftp.rta.nato.int/public/PubFullText/RTO/MP/RTO-MP-HFM-123/MP-HFM-123-14.pdf
microwave hearing (Frey effect), especially voice modulation
The Mosquito - Wikipedia, the free encyclopedia
The US navy report was from a few years ago, when super tweeters started coming out, I'm plowing through some stuff to try and find it.
When we hear sounds our bodies also add to the sensation, with low frequency effecting the squashy bits and the higher frequencies effected by bone conduction. We do communication systems and have to take these effect into consideration when the equipement is being used with high ambient noise and audio frequency range vibration. So while not hearing the extremes they do effect the overall impression of sound. That is why older people who dont 'hear' high frequencies still find that music with these highs removed sounds naff. Standard audio and communications often dont use bone conductions for the transmission of sound, so quite a lot of info tends to be classified unfortenatly.
This is some stuff on bone conduction protection etc.
http://ftp.rta.nato.int/public/PubFullText/RTO/MP/RTO-MP-HFM-123/MP-HFM-123-14.pdf
microwave hearing (Frey effect), especially voice modulation
Try driving through Times Square in NYC during the evening -- the RFI is staggering, knocking out even the 50kW transmitters of WABC (770 a.m.)
Apparently, no one complains to the FCC.
Our local utility used to state the 5% spec on their web site. All specs are now gone from their web site.
It didn't until about 4 years ago. Before then there was a giant metal transformer on the pole. I never measured the distortion but the wave form always looked sinusoidal. Lightning zapped that transformer and it was replaced by this plactic can that was about half the size of the original.
It serves 11 houses with 240 volts at either 100 or 150 amps each, depending if the house has gas for hot water and cooking. That POS transformer probably operates on the edge of saturation and goes into saturation during high demand. The scope traces shows flat topping slightly before and leading into the peak of the wave just like a smallish OPT does when you whack it with 20 Hz.
They put in a new UHV bus to bring power from the nuke in south Dade up to Broward county. There is a UHV station on the edge of the everglades that transforms the multi mega voltage down into the 100KV range for distribution to the individual sub-stations around the county. They run two sets of these distribution lines within 100 feet of my house. Any frequency on my ham radio below 40 meters (7MHz) is now useless, and 40 is for strong signal use only. AM broadcast radio is useless too but there are only a few English speaking stations left there anyway.
Another cause of RF problems is communications over power lines. here in the UK we have BT Vision which is causing problems for radio hams, and others I suspect. One firm has been given an exclusion from EMC requirements by Offcom (UK FCC equivelent) because it works on adding high frequency noise (sorry data) to the mains!! Basicly what everybody else has to avoid.
The increase in home wireless, wireless TV senders, also dosn't help.
I do believe that following EMC engineering guidlines, even for DIY projects, to stop noise getting in to equipement is the only way to solve the problem.
As cost become more critical I think that to get ever increasing power to more people, the regulations regarding clean power will diminish.
The increase in home wireless, wireless TV senders, also dosn't help.
I do believe that following EMC engineering guidlines, even for DIY projects, to stop noise getting in to equipement is the only way to solve the problem.
As cost become more critical I think that to get ever increasing power to more people, the regulations regarding clean power will diminish.
Unfortunately our "regulator" in the UK is on the side of the pollutors (big business). This means that they are allowed to pollute. If someone fought back Ofcom would find the part of the regulations which forbids deliberate interference and take them to court. Of course, selective application of laws to people who upset the government only happens in police states, and the UK is not a police state, so I must be mistaken.
Thankfully, I think CFL is a dying breed. Will be replaced by LED lighting; much more friendly to the grid and less radiated noise.
Good riddance.
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