Testing for a good earth ground - Page 1
Forum section: electronics / rf-microwave

author: petert
author_rank: Regular Contributor
timestamp: April 02, 2020, 03:49:47 pm
content: Hello,I couldn't find a forum category that would really match this question, but since it comes up a lot with radio builds, I thought I might get answers here.How can you electrically test if a given earth ground is a "good" ground? When "building" one, you are usually adviced to put a metal rod deep in the earth below the common freezing level around your location. But what if you want to test if a water pipe or some other metallic installation would make a good earth ground?Is there some standard way to test? What properties can I test for say, using an oscilliscope/signal generator or multi-meter, to determine if it has the properties to make a good earth ground (for example, to act as earth for an antenna for a radio, but really, circuits in general)?

author: coppercone2
author_rank: Super Contributor
timestamp: April 02, 2020, 04:04:31 pm
content: for safety ground, rf ground might be different but measurement principles might helpnot sure if good rf ground is good safety ground, because safety is more about fault current not breaking conductors

author: petert
author_rank: Regular Contributor
timestamp: April 03, 2020, 06:23:14 pm
content: If anybody else could comment on what way to measure a good RF ground, that would help as well

author: gdewitte
author_rank: Unknown
timestamp: April 03, 2020, 08:56:04 pm
content: Check outhttp://www.teli.us/GroundOhms.htmby Jim Satterwhite K4HJU

author: Lord of nothing
author_rank: Super Contributor
timestamp: April 04, 2020, 06:27:53 pm
content: In my Office Room, Basement is beside of the Home Electrical Wiring no Ground Rail.Thankfully there is an unused Pipe for Ventilation I could use to get some Wire out.What do I need to build my own Ground Rail?What kind of Metal should I take? Sorry for the Stupid Question I am not want make anything wrong and die.

author: Monkeh
author_rank: Super Contributor
timestamp: April 04, 2020, 06:28:54 pm
content: Quote from: Lord of nothing on April 04, 2020, 06:27:53 pmA phone and the number of a competent electrician.

author: El Rubio
author_rank: Regular Contributor
timestamp: April 05, 2020, 05:12:28 am
content: There are tests that take measurements by driving rods into the ground. Typically, the soil in an area will have similar characteristics, so whatever is commonly used in your area, is probably sufficient. Most commonly at a home, it will be a single copper clad steel rod about 8 feet long. Some less conductive soils and rock require a hole to be drilled and it will be filled with a more conductive material that the rod is set into. I believe this is called doping.Do you have an existing ground already. If you are considering driving a second or more ground rods to supplement your ground system, or even an RF counterpoise ground, it MUST be bonded to the existing ground system. Bonded means at the same electrical potential. Different grounds create ground loops which can bleed mains voltage and create alternate paths to ground through whatever is connected to it.

author: tkamiya
author_rank: Super Contributor
timestamp: April 06, 2020, 10:55:20 pm
content: You will do a great service to yourself and fellow enthusiasts by deciding which one you want to know first; safety ground or RF ground.The reason I say that is that requirement and method used for each is quite different. What is good for one isn't necessary good for the other. It will get quite confusing fast.People who do this professionally (safety ground) have "ground tester" that is specially made for this purpose. Most qualified electricians should have one. However, this is not usually how it's done. For example, in Florida USA, the code calls for two 8 foot ground rods and call it done. No actual measurements are taken. In Japan, when lightening protection grounds are dug, usually a thick large copper plate is burried and something called "Earthlon" is poured. This is a conductive gell.For hams, this is where you just do the best job you can within your budget. As long as RF ground and safety grounds are tied together (called bonded), you cannot do any harm. For me, I just added 3 ground rods and bonded them with existing ground system. I have no idea how much better they are. My purpose is safety ground and some degree of lightening protection.

author: coppercone2
author_rank: Super Contributor
timestamp: April 06, 2020, 11:03:47 pm
content: I think you can make the equipment shown in video, I believe its just a variac used to make a really beefy ohm meter. Useful to know how to do that anyway, i.e. chassis safety bonding you might wanna pass 10-20A through it to make sure the resistance does not vary with current. They sell a meter for this, but there is no reason you cannot make one.. actually a good project since its not a high decimal point thing and you get to work with coils etc.I thought this might be a good use of saturable reactor possibly.If you want to test a chassis you made, try hooking up a supply thats low voltage high current (low Z load stable) to a point on the chassis, say with a test screw (you splice in a connector under a screw) and the other end to the end of the ground cord, and see what the impedance is when you push 10-20-30A + through it (I kind of thought about it before, and it might be interesting if there is a capacitor.. can the ground take a shorting capacitors surge current?). For a scary example, I have seen arc/burn damage inside of fast-on connectors before (use grease).If its safety you want, you need to test the whole chain, not just have a really low Z ground with a weak connection in the equipment. I find it really interesting because I do my own fabrication. If you put alot of panels on a box, its important to know they are actually bonded electrically.

author: TheMG
author_rank: Frequent Contributor
timestamp: April 07, 2020, 12:47:16 am
content: Quote from: petert on April 03, 2020, 06:23:14 pmIt's no simple task and depends on the antenna type, design, and usage frequency. At frequencies above HF, RF "ground" doesn't really matter because the the antennas used either don't need them, or incorporate their own ground plane on the antenna itself. You just need your safety ground for lightning protection and that's it.With some antennas at HF and lower, for example a dipole antenna at a good height above ground, no RF ground is needed. But for something like a vertical antenna, with the exception of that using a resonant counterpoise wire, a good RF ground is essential to performance of the antenna so multiple ground radials are usually buried around the base of the antenna. The lower the soil conductivity, the more radials you need to make an effective RF ground plane. Note that ground rods are primarily for lightning and electrical safety ground, ground rods alone make a rather poor RF ground in most cases.How much ground plane is necessary for good performance depends on antenna characteristics (for example, lower impedance will be more affected by RF ground quality), type of soil, etc.What I would do is do some research on the type of antenna you intend to use/build and what kind of ground plane is required for good performance with your soil conditions, and follow "tried and true" recommendations.Quantitatively measuring RF ground performance is not something that is particularly easy. Commercially, this is done for example on AM broadcast towers by measuring antenna characteristics of an installed system such as impedance and capacitance, factoring in the theoretical antenna characteristics and calculating the expected performance that way. Unlike most amateur radio installations, a great deal of money is spent in the commercial world engineering and installing a very large number of very long ground radials (we're talking hundreds of them!) to guarantee good performance, along with the site selection preferring low-lying areas with soil that is relatively damp year round.Even then, the only true measure of the actual overall antenna system performance comes when it is actually transmitting, and then field strength measurements taken in various locations away from the antennas, compared with the theoretical/calculated values for signal coverage.Since a calibrated field strength meter and other specialized test gear is not something most hams have access to, nor the flexibility of choosing an optimum antenna location, or endless sums of money installing extensive ground systems, the best thing to do is to learn from others in terms of what works and what doesn't, what is a good compromise considering your location and money, and finally to experiment and test on the air to gather a relative idea of your station's performance. For example, start with a handful of ground radials, try it out. Add a few more... did performance noticeably increase yes/no? Go from there.