Grounding questions - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: June 25, 2017, 07:13:30 pm
content: The place where I live has a standard electrical service box thats grounded to two long copper poles that are hammered - maybe two meters into the ground where the power line comes in. Those grounds are connected to the ground wire in the electrical service box and also bonded to the cold water pipe coming in to the plumbing system via two thick copper wires and a hefty clamp.All strictly to the electrical code and installed by a licensed electrician when the service was upgraded a few years ago.However, recently when I got back into radio stuff I immediately gave up on using the house ground for HF because its noisy as all hell.Now I am reading up on standard ham radio practice and its not consistent. And now its my understanding that the new way of doing this has all grounds tied together...Rather than give a lengthy explanation of what is I am sure a fairly generic situation, I am just wondering, what does the task of satisfying both safety needs when lightning strikes, electrical codes and practical need for quiet RF friendly grounding?-----------Update:Doing a little more reading I suspect the weakest link in the chain for me may be the grounding in the audio cables between my SDR and my computer. The problem is both sides of the connection use audio mini plugs and the audio mini plug to audio mini plug options that I have are all crap. It might also help to literally bond the case of the SDR to a binding post somehow bonded to the computer case using a thick conductor. Going to give that a try.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: June 27, 2017, 01:08:52 pm
content: There is a lot of issues in your post , so keeping it simple is going to leave a lot out .The lack of consistency is mostly got to do with your choice of reading .The way I think of it is , grounding starts with 3 separate catagories in theory [ think about 3 circles that have overlapping edges ] , depending on your circumstances , you may give one more or less priority .Electrical ground , lightning ground & RF ground .Wiring up a building for AC may have some limited codes for lightning and RF , lightning does not cover wiring a building for AC - but does tell you to bound all grounds , and RF is just another subject - but again bounding grounds between all 3 is required .For lightning the Motorola R56 document can be bought / downloaded .https://www.rrmediagroup.com/Features/FeaturesDetails/FID/449For ham radio the problem is finding how to do as much as you can afford , using R56 costs a lot in labor & copper .

author: cdev
author_rank: Super Contributor
timestamp: June 27, 2017, 02:59:47 pm
content: So I forgot to add an important fact in this post. The worst of the spurs is a SMPS-like wavering noise that repeats itself across the spectrum that appears to be influenced by my movement. Yesterday I discovered that its modulated a tiny bit by my grabbing different wires and placing my hands on the leftmost portion of my keyboard. However when I unplugged (and replaced the keyboard with another) it didn't go away.Yesterday and today, Ive gone from one device to another unplugging them to see if any was clearly the cause but so far no luck. It doesnt seem to be he monitor - at least when Ive switched monitor resolutions it doesnt change but it may be the monitor. Anyway this particular spur seems certain to be right at my computer desk if its frequency is influenced (very slightly) by my motions. So I think I am very close to finding it.I've dug out of my boxes a substantial gold plated triple RCA jack video dubbing cable from decades ago and that and adding a thick ground between SDR and computer to my existing ground wires seems to have helped noticeably enough for the noise to have decreased by >20 db or so but its still there.Both the SDR and the computer use stereo miniplugs for their audio output and input respectively which I suspect is non-optimal.So at opposite ends of the gold plated audio cable there are these nickel plated cheap mini-plug to RCA adapters.So I am going to try to find either a top quality miniplug to miniplug cable that's gold plated or two gold plated RCA to miniplug adapters.They will likely not be that expensive so is worth a try.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 27, 2017, 03:45:06 pm
content: Galvanic grounding, as normally practiced, is exclusive to low frequencies ("DC" as it were), and is only intended for safety -- providing a low resistance fault path to ground.At RF, the impedance of all those wires adds up, both picking up ambient and wiring noise, and not really grounding your stuff (any RF ground currents your stuff produces, is dropped across that impedance, again generating voltages rather than sinking it to zero).A more comprehensive grounding practice is required. Theory, perhaps.It's not enough to run wires between points, that much is obvious. But what are you actually intending? You want a low impedance path, which separates a ground current from a signal current. You want a shield. A ground plane.The ideal system, then, is one of shields -- Faraday cages -- which carry ground currents along their low-impedance surfaces. A shield has two surfaces: inside and outside. You want the ground currents to stay outside, and the signal currents to stay inside.The Earth is conductive, and acts as ground. It's not ideal, because soil resistivity isn't very low. Suppose it were -- suppose you covered the ground with a continuous metal sheet so this becomes true. Then, anywhere you stick an antenna on top of this ground, its return (ground) current is sunk into the sheet, and spreads out over an area.Ideally, you'd connect to the antenna at the underside of this ground sheet. Underground, as it were. This keeps the ground current on the outside, and the signal current on the inside.That's not very convenient. But anything we construct, by a process of transforming the geometry, moving things around, without breaking the continuity of the ground/shield surface, will be identical to that situation.Suppose, instead of routing the signal connection beneath the ground, we raise a bump, an emboss, on the metal ground. We run the signal inside this channel. Suppose we further raise and pinch this bump, so that it fully encloses the signal wire: now we have a coaxial cable, laying on top of (and still bonded to) the shield/ground surface.Suppose we completely cut the coaxial cable away from the shield, so that it is only bonded to ground at the ends (at the antenna, and at the transmitter). As long as the cable is contiguous (full shield coverage over the inner conductor), it doesn't see anything different -- even though there is now a loop between shield, bond, cable, and bond, which can have EMF induced into it. The ground-loop current flows along the outside of the shield, leaving the signal undisturbed. (We can also reduce this ground-loop current by wrapping ferrite around the cable: the EMF drops across the ferrite instead.)If we break the ground bond near the antenna, we have a big problem. Now the antenna's ground current must flow along the transmission line. The transmission line becomes a radiating element, and its orientation matters. Moreover, it brings ground current up very close to the transmitter. (The transmitter doesn't care, as long as the ground bonding is still good at that end. But anything on the antenna side of that bond, may be affected!)Now, antennas don't all have ground currents. Good antennas are balanced, so that they produce very little (intentional) ground current. (There will always be some residual, though.) This is a more direct concern for unbalanced antennas, like 1/4 wave monopoles and such, which require a ground plane of some sort.Suppose we leave the antenna-end ground bonded, and unbond the transmitter end. As long as the antenna bond is good, we won't have energy traveling back to the transmitter, along the shield. We will have ground-loop voltage (which may be ambient noise, or the transmitter's own output connection), though, which may affect the transmitter and connected equipment.Now, to go from the imaginary to the practical:Suppose we have an antenna tower, and a shack.Ideally, the tower should be well grounded. It should be based deep enough into the Earth that earth acts like electrical (RF) ground. Any transmission lines coming down from the tower should be bonded to it, at the base.The tower could also be installed on top of a large ground plane, or something equivalent to that, like an array of radials: wires laid on top of the ground, radiating away from the tower base, which serve the same purpose of shunting ground currents away. (Many monopoles, designed for insulated towers, or too short to use earth as ground, have radials in their design. They aren't so much monopoles as asymmetrical dipoles.)Transmission lines coming up to the shack, should be grounded to the shack. The shack itself should be a Faraday cage, i.e., made of metal, so that the transmission lines are bonded to it on the outside, and only the signals penetrate inside the cage.Inside the shack, we may again apply the same principle. The transmitter itself should be in a metal box: its output should be bonded to that box, and the cable simply connects from there, to the shack.Indeed, we might optimize away the requirement that the shack itself be a cage, as long as the equipment within follows the same principles of shielding. This can be complicated to ensure, though: any box that has more than two connections, has more than two paths for ground currents (accidental or intentional) to flow away from it. You can very quickly get a complicated network, between mains (or whatever supplies your equipment runs from), various signal cables, audio cables, and etc., that accidentally contains ground loops that couple into the signal paths and cause problems.Note that differential and balanced signals are no panacea. You might put the signal between two physically balanced wires, but you can't avoid the fact that the two wires act together, with respect to ground, or to the environment if nothing else. An exposed (unshielded) pair picks up 100% of the EMF around it, and that EMF will upset anything that's not prepared to handle it (e.g., a poorly made balun; an industrial RS-485 transceiver with its limited (usually ~12V) common mode range; an audio cable going to a solid state amplifier that tends to rectify RF on the inputs; etc.).(Note that it's not enough to simply use shielded pairs; the shield must be bonded at each end, otherwise the break in shield allows 100% of that ambient EMF to enter the (common mode) signal path.)Household ground is useless, because it's lengthy, not wide and contiguous. All these shields should, of course, be bonded galvanically, for safety purposes -- something that should happen naturally because you'll be connecting a lot of beefy shielded cables between everything -- but in addition, you need to set up the system so that there is a strong separation between signal currents inside the shield, and ground currents outside the shield. A properly wired system should not care if there's somehow a large RF voltage to Earth, because it's all within a Faraday cage that blocks any current that might flow as a result. The shielding must be solid and contiguous, at least at the circuit level (the equipment must be built so that ground currents flow around the active circuitry, while signal currents flow only to the active circuitry), but preferably (and often?) also the enclosure. The circuits or enclosures, then, are contiguous with the interconnecting cables, which are shielded. The interconnects can, in turn, be contiguous with the shack (if you choose to use / build a shielded shack), which is in turn contiguous with the transmission line(s) to the antenna/tower (which should be bonded to Earth).Tim

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 04:29:09 pm
content: The easy option may well be to use wide band audio isolating transformers to break the PC<=>SRR ground connection, with about ten turns of the whole cable through a good sized ferrite ring at both the PC and SDR ends as close as possible to the plugs to attenuate conducted common mode EMI from the PC.Unfortunately gold plate on audio cable connectors doesn't mean a dammed thing any more except as an indicator of audiophool bling. If you want a good quality fully screened cable, make up your own using metal bodied 3.5mm jack plugs and double screened twin cable - two individually screened cores often with foil screens and an overall braid or lapped stranded screen.For a ground strap to be low impedance and effective at HF RF, due to skin effect concentrating the RF current in its surface, it *MUST* have a large surface area - which means it needs to be tinned copper wide flat braid, or wide copper foil. Also the total length of above ground strap to the actual ground rod, buried radials or mesh, or other ground plane needs to be a small fraction of a quarter wave at the highest frequency of interest. Once the length is comparable to a halfwave or longer, the strap may even be worse than no ground at all.

author: cdev
author_rank: Super Contributor
timestamp: June 29, 2017, 04:14:24 am
content: You all have convinced me, I am going to order a bunch of braid so I have it handy to use. This will be interesting because an SDR is a particularly sensive RF testbed for grounding issues. Speaking of which, today a new toy arrived, a PA0RDT Mini whip kit. Its now undergoing a not very rigorous test procedure in the back yard, around a meter off the ground on a wooden stick pushed a few inches into the ground. It will go onto some kind of better temporary mounting tomorrow pending purchase of some some real grounding rods.First impression- its surprisingly good considering the location.

author: Electro Detective
author_rank: Super Contributor
timestamp: June 29, 2017, 05:23:09 am
content: Another option is to source those cheapie ready made audio isolation transformers (RCA to RCA) they use in car stereosand see if that helps nuke your problemPlease ensure you can get a refund as Step #1 before you try itIf it's a fail, it cost you nothing to try, one solution less to think about..and continue on with the troubleshoot

author: CopperCone
author_rank: Super Contributor
timestamp: July 09, 2017, 06:34:40 pm
content: What you need to do is get a network analyzer or make an equivalent (ie sa noise source sweeper something), take your braid or ground wire, and determine its impedance. It might be completely useless at the frequencies you are interested in, or highly effectivethen you can see how much your ground will work at the frequencies you are interested in, simply getting to the grounding rod.As for the grounding rods in the earth, I don't know. Electrician do measurements using high current sources and sampling rods, but I don't know how this works at RF. Perhaps you can do the same thing with a massive power amplifier (like 100 amps of rf current) to determine earth impedance. It seems difficult to do however.It comes down to how much energy wants to go into the ground, otherwise, the long thing you are hanging off your instrument is just an antenna/inductor/capacitor that will radiate and pick up some amount of energy to free space/other circuits

author: cdev
author_rank: Super Contributor
timestamp: July 10, 2017, 03:38:03 am
content: I think my issue is a fairly generic dirty powerline problem. I live kind of near a large light industrial building and they have a lot of machinery in there. Its quite possible that a ground that works - kind of when its normal moisture in the soil stops working well when it dries out, enough to make it impossible for me to get decent HF without a balanced antenna of some kind because of common mode noise. I think thats what is happening because Ive been able to reduce it significantly since those pictures were taken - but not get rid of it.I'm still losing at least 40-50 db of noise floor because of it. So i've been focusing on learning other, non RF stuff.Also, VHF/UHF is much better, as far as this specific issue, and so although some of this noise makes it up into the very bottom of VHF, its mostly HF thats messed up.Thank you all for all the good suggestions! Improving grounding has made improvements. I'm going to try using braid if I can find an appropriate one and buy it. Ive noticed substantial improvements from using thicker wire and both crimping and soldering the spade lugs on the ends.Also, I am going to try to make a different power injector (to send 12 v up the coax cable) that isolates the antenna using a battery. Ive gotten good results using 9volt batteries but my problem is I constantly forget to turn them off and run them down. And my various 12v gel cell type batteries all need replacement. (if anybody has any tips that could revive them, specifically gel cell 12v lead acid batteries, using a constant current power supply, if its possible, I'm all ears.)I am so bad with rechargeables but I really need a system so that I dont put alkaline batteries in devices that typically get a lot of use once in a while and then sit for months or even years unused, batteries going dead, wasting money.I guess you can tell I am really trying to economize.I really don't like spending money needlessly.Like for example, $20 for a copper plated steel (or whatever it is) grounding rod now.. when we already have two.. no way. I am sure that I can accomplish the same level of grounding with stuff I already have.Necessity is the mother of invention.I think that the weak link in the chain - Electro Detective I know you are likely right on this, is the common mode - Audio isolation transformers. In the audio chain. Definitely. Don't need a money back guarantee, I am certain I already have some somewhere. I found them a while back and put them aside. They are probably in a ziplock bag in one of endless plastic storage containers of parts I have. I just have to find them.Definitely will help.And also RF galvanic isolation. A 1:1 RF isolation transformer done right will be very broadband. A toroid works but regular iron powder toroids tend to work best at either MW/low HF, or HF, of HF/VHF but now MW. Ive had the best luck with balun cores of #43 iron powder material, not that many turns to keep the capacitance low.This can also be done with ferrite beads of #43 iron powder material. Which I have a bunch of. Two or better four or six ferrite split beads is basically the same inductance increase as a balun core. You can also double or triple them up.I am almost sure that somewhere in my box, I also have at least two audio isolation transformers. They are 600 ohm transformers I think. I have had them for ages..