Does the thickness of wire affect electromagnetic emission from it?  - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: August 25, 2022, 08:02:19 pm
content: Would a 8AWG wire give out less electromagnetic emission than a 22AWG wire having the same voltage, current, length, etc. running trough it?and if yes, would it outsway the benefit that would be from a closer proximity between opposite phase wires for a thinner wire ?

author: fourfathom
author_rank: Super Contributor
timestamp: August 25, 2022, 09:26:02 pm
content: Quote from: ELS122 on August 25, 2022, 08:02:19 pmCan you clarify what you mean by this? Are you talking about a two-wire balanced transmission line of a particular impedance?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 25, 2022, 10:18:24 pm
content: Antenna radiation of RF does vary with the size of the radiator. Bigger diameter wire or bigger antenna parts like aluminum tubes, radiate better than thin wire.Some isolation is accomplished by using Coax or twisted pairs.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 26, 2022, 12:12:52 am
content: Here is a low frequency AC magnetic model.Current in copper pairs: 1000 ArmsFrequency: 1 MHzDistance between pairs: 80 mm for both the large and small rectangular copper pairs.There is an aluminum plate at bottom of model.https://app.box.com/s/yhncfnxlsxcmozcdbsfi4dj2fmhcrl10

author: B J
author_rank: Contributor
timestamp: August 26, 2022, 01:51:50 am
content: Are you referring to AC or Dc? If AC, what frequencies are you looking at?

author: EPAIII
author_rank: Super Contributor
timestamp: August 26, 2022, 09:44:56 am
content: This is a difficult question, at least partially because it is not well stated. You say the same Voltage, current, and length. I have to assume you mean the wires' length. But with different wire sizes/gauges, that is not normally even possible. The larger wire will have less resistance so Ohm's law will prevent the Voltage and current from both being the same. One or the other MUST change.It seems that you have some reason for asking this, but your question is not framed well.A wire or a transmission line that is radiating is acting somewhat like an antenna. You further talk about "closer proximity between opposite phase wires for a thinner wire". This suggests that you are talking about a twin lead transmission line.When the radiation from a twin lead transmission line is considered, a distinction is usually made between the near field and the far field. Often the dividing line between these two areas is considered to be about ten times the wavelength of the signal(s) involved. This is not a precise, mathematical point but just a convenient way for engineers to think about the situation. The twin lead transmission line is usually thought not to have significant radiation in the far field, but the near field can be present. That may sound contradictory and in a way it is. But it is good at least as a first approximation. And because wavelength and frequency are inversely proportional, the 10X distance is dependent on the frequency or frequencies involved.The center to center spacing or overall dimensions of the pair of conductors will vary if their insulation jackets are in contact. But again, just how much of an effect this will have will depend a lot on the wavelength(s) which is just another way of saying frequencies. Higher frequencies will have shorter wavelengths so the spacing between the wires will become more significant. So the difference between the two wire gauges you mention may have a real significance when you talk about the near field.On the opposite end, the 50 or 60 Hz power lines, which usually use three wire/phase transmission lines, will have wavelengths measured in thousands of kilometers. So their near field can extend for tens of thousands of kilometers and you simply can not escape that on the entire planet. We are all immersed in the near field of every power transmission line on the planet.Another thing to consider is that transmission lines are usually constructed to have a characteristic impedance. That is a way to prevent power from reflecting back and forth on the line, creating standing waves, and also to provide a maximum amount of power to be transmitted to the load end of the line, from the source end. There are design calculations that take the physical size of the conductors and their spacing into account to provide a specific characteristic impedance. Thus, your two twin lead transmission lines, made with different wire gauges and with the same surface to surface (but not the center to center) distances between the conductors will have different characteristic impedances. For a given frequency, a given source impedance, and a given load impedance this will produce a different standing wave pattern on the line and that will have an effect on the amount of radiation that escapes from it.Communication transmitters must be connected to their antenna with a transmission line. The power amplifier of the transmitter has a specific impedance. The antenna also has a specific impedance. Normally those two impedances are the same, usually 50 Ohms. And the transmission line also is designed to have that same characteristic impedance, again usually 50 Ohms. And that insures that a maximum amount of the transmitter's power is radiated into space by the antenna while little or none is radiated by the transmission line. That is how things normally work. We do not just change wire sizes willy-nilly. In a high power transmitter, if just one element in the transmission line is mis-matched, there will be a hot spot there and it could actually MELT the conductor(s).So there is so much more to your question than just the wire gauges. Perhaps if you could be more specific about the situation you have in mind a better answer may be possible.Quote from: ELS122 on August 25, 2022, 08:02:19 pmQuote from: ELS122 on August 25, 2022, 09:34:05 pm

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 26, 2022, 11:33:52 am
content: OK, my first crystal ball was a bit off at 1000A 1 MHz.I scaled model down to 3 A 50 Hz.The left side conductors are 1mm^2 spaced 2mm. The right side conductors are 5mm^2 spaced 2mm.Added two chassis plate materials under the pairs, each 1mm thickThe left side plate is steel with permeability of 66. The right side plate is Al.Notes: The steel chassis plate heavily attenuates the field under it, but actually increases the field strength around the pairs.The Al is too thin for useful attenuation of 50 Hzhttps://app.box.com/s/h0ao3ngctj174fuqn8syu9r1kyf2f8mc

author: Gyro
author_rank: Super Contributor
timestamp: August 26, 2022, 12:27:21 pm
content: You could have saved people a lot of time if you had simply said in your OP that you were looking at minimising the stray fields from twisted pair heater wiring!The thickness of the wire is simply determined by its voltage drop (resistance) for a given heater current. Tightly twisted solid core wire is much better than stranded for this application. It holds its twist and is stiff enough to be neatly routed around the chassis. Also there is no danger of stray strands at the tube holders.I recommend buying 'Building Valve Amplifiers' by Morgan Jones. It will save you a lot of time and questions. It covers amplifier physical and electronic construction, measurement and testing in great detail. There is a sister book called 'Valve Amplifiers' by the same author, which concentrates more on their electronic design.

author: fourfathom
author_rank: Super Contributor
timestamp: August 26, 2022, 02:59:18 pm
content: With 50Hz filament wiring, the issue might be magnetic-field coupling to nearby components and wiring. This is a concern on boats when routing DC power near a magnetic compass, and the solution for boats and HiFi amps is to run the two power/filament wires as a a pair in close proximity -- twisted if practical. This way the magnetic fields cancel. The electric fields also cancel but at 50Hz this isn't an issue and the near/far field concepts as mentioned above still come into play for both E and M fields.But it sounds like the OP is aware of this, at least sort of, so the question is what effect the wire gauge will have. There will be no practical difference at 50Hz, the magnetic field will depend on the current and as long as the wires are heavy enough there will be little difference. Larger diameter wires will be further apart even when twisted so I suppose there will be less near-field cancellation but I truly doubt that you could detect the difference unless the wires were absolutely huge and run for some difference within a millimeter of your most sensitive input wiring.Consider that the (not twisted) filament within a vacuum tube is already extremely close to the cathode and fairly close to the grid.

author: mag_therm
author_rank: Frequent Contributor
timestamp: August 26, 2022, 03:11:34 pm
content: On a vintage shortwave receiver, I converted the RF, Osc and mixer tubes to regulated 6.2 V DC.Along with regulated plate voltage and temp control, it made a big improvement to stability.I also converted a 1962 era FM tube radio from 120V filament string to 6.3 V AC tubes.In that radio, with one side of some filaments already at chassis potential, some of the filament leads are single wire runs.If doing a new build tube job (not anticipated!) , I would use a regulated 6.2 V DC and run single wire DC for all indirectly heated tubes.

author: Gyro
author_rank: Super Contributor
timestamp: August 26, 2022, 04:13:27 pm
content: In practice, AC filaments are fine for line level [Edit: audio] and above (especially if given a positive DC bias). DC filaments are helpful for high gain, low signal level stages - microphone amps etc. Even then, valves like the EF86 were constructed with a folded helical heater to minimise loop area within the cathode.

author: Gyro
author_rank: Super Contributor
timestamp: August 26, 2022, 08:00:44 pm
content: Quote from: ELS122 on August 26, 2022, 07:03:14 pmI've had zero problems with Soviet 6n2ps in the input stage of my amp. Remember that the area (and so capacitance) of any proximal crossing of the wires is absolutely minute (and in a vacuum too). The time constant, in combination with the grid resistor makes any coupling at 50Hz miniscule (as in unmeasureable). You need to worry much more about the quality of your wiring to the socket.QuoteI don't know of any convincing evidence one way or the other.

author: Gyro
author_rank: Super Contributor
timestamp: August 27, 2022, 08:46:22 am
content: Quote from: ELS122 on August 26, 2022, 10:39:47 pmOf course I'm not implying that there is no current flowing through the heater connections (why on earth would I do that?). What I am saying is that connections inside the base of the tube are so tiny that any influence - capacitive or inductive will be miniscule. I have a 6n2p-EV sitting in front of me and the grid connections are bent away from the heater connections (at 90' to them). With a high impedance node like the grid, capacitive coupling is likely to dominate - but as grid to cathode capacitance, wth their very close proximity and shared area along the whole length of the cathode is <2.5pF any coupling in the tiny base connections is extremely tiny.There are far more opportunities for introducing coupling by careless socket wiring because the structures (wires) are so much larger and longer - the heater connections might not have been tightly twisted right up to the heater connections, one wire might be carelessly looped around the other side of the socket, with the grid wire close for instance, not to mention the coupling opportunities in the chassis in general due to poor layout. Resistive coupling (leakage) also becomes a possibility outside the tube.The only other possible mechanism for couplingwithinthe tube is from the ends of the heater itself acting as hot cathodes relative to the grid (or to the cathode interior). As I mentioned previously, this can be avoided by DC biasing the heater supply centre tap so that it is always positive with respect to the grid and cathode, say +20 to 30V. That way, any possible parasitic diode effect is reverse biased. The DC bias of the heater supply may need to be raised in any case, to accomodate the maximum heater - cathode voltage specs in SRPP or cathode follower stages for instance.I really do recommend that you purchase the Morgan Jones book as he covers a lot of this stuff in detail (and / or look at some of the older valve/tube texts on the web - Peter Millett has an excellent collection...http://www.tubebooks.org/).

author: EPAIII
author_rank: Super Contributor
timestamp: August 27, 2022, 09:54:42 am
content: Tube heater connection!Considering the frequency and the use of a twisted pair, like others I highly doubt that there will be any measurable difference. The routing of the pair may make more difference than anything else. I would try to run it near the chassis, which should be grounded. And, of course, keep them as short as possible while avoiding proximity to the signal wires or components.If it really bothers you, mag_therm beat me to suggesting that DC would be better than AC. I suspect that would be the single biggest factor you could change.

author: radiolistener
author_rank: Super Contributor
timestamp: August 27, 2022, 07:04:53 pm
content: Quote from: ELS122 on August 25, 2022, 08:02:19 pmelectromagnetic emission/reception depends on wire geometry dimensions. Larger dimension == more emission. This is because larger dimension can get energy from more large volume of space. But if you compare the same length wire with 8 AWG and 22 AWG the difference will be too small, so you can just ignore it.But there is also another aspect. More thicker wire diameter leads to more wide bandwidth on wire resonant frequency. So if you use wire for antenna, it has a sense to use more thicker wire, because it can be used for more wide bandwidth with no need to tune physical length and no need to use tuner.And third aspect is that more thicker wire has less energy loss. Because it uses more cross section area of wire for current transfer, so it has less resistance and as result less thermal losses. It is even more important for higher frequency, due to skin effect, because current flows primary at thin layer of wire surface.If you're talking about RF frequency, there is more important thing - you're needs to keep fixed distance between wires along all transmission line length. It helps to keep fixed line impedance. Otherwise your transmission line will have high losses for RF emission.Note, that any change in distance between wires leads to emission loss and reflections in the line. This is much more important than wire diameter. The same, you're needs to keep fixed wire diameter along all length of the transmission line.Quote from: ELS122 on August 25, 2022, 08:02:19 pmyes, wire diameter and distance between wires affects transmission line impedance. This is because RF energy is transfered not through wires, but through space between wires. More thicker wire has more surface area, so it's interaction with environment space between wires will be different than for thin wires, because thin wire has less surface area.