Discussion in 'General Technical Questions and Answers' started by KF5LJW, Oct 29, 2019.
As you requested. This should turn on a few lights and help understand there are two ways to do this. All connections shown. Two completely different circuits with just one modification.One circuit puts th eradio equipment in the Ground Loop serially connected. The other takes the equipment out of the loop and connects radially to the Ground Loop.I added the antenna circuit for clarity.
This short piece of 12ga wire that Dereck is saying is electrically equivalent to the single ground point will frequently NOT be a shot piece of wire. Think of many shacks were the wire would have to be many feet long, sometimes tens of feet. Not only would this then have to better than 12ga to get a low enough DC resistance, but it would also seem to cause issues with RF pickup on certain frequencies with a ground wire now into quarter, or half, or even full wavelengths of length depending on the band.
Won’t you get RF current on this wire if it is long?
I mean, it’s great it you can make this a 6in piece of wire, but my shack is on the second floor.
Isn’t ARK’s “bus bar” even better than this short piece of twelve gauge? He presumably has a fat copper pipe, and the a #6 wire to the ground rod. I see it provides more of a loop, though
What if this low DC resistance “bus bar” were connected to the “yoke.” Then it would be a single point at least by your definition of having a very low resistance path. Of course there IS still a loop with what you describe. (To the breaker box). I assume at DC at least these two act a voltage divider based on Ohm’s law. At RF there is all kinds of other stuff going on, include even the reactance due to the inter-winding capacitance of the AC transformers (which I think ARK alluded to earlier).
Question about what you are referring to as the “yoke.” This is just the ground lug of the outlet, right? It is connected to both the ground wire going back to the breaker box, and the ground pin, and the center screw of the outlet wall plate (typically). Right? Or is this something else?
Interesting thread. There is a lot to consider, probably *far* more than anyone has addressed here when it comes to RF currents (Antenna proximity, which at low bands are always in the near field, other house wiring picking up RF, power company wiring picking up RF, ground effects, inter-antenna effects (when multiple antennas are present, etc., etc.))
K9YC's paper. Starting on page 138 especially:
Appears to be the inspiration for Dreck's ranting.
So, I have been called ignorant, and now I am supposed to be blind, too.
Since Dereck doesn't seem to be able to understand anything but a cartoon schematic, I have redrawn a super-simplified version of my station's ground paths using Derecks method:
So Dereck, can you see that my ham equipment is not in the series loop created by the coax and line cords? It is in-fact bypassed to the "Ground Rod Outside Shack" by a very-low impedance copper bus bar, and a few feet of #6AWG! Only the AC-line-cord ground wire is in series with the "loop".
Here is my station diagram again, this time with Dereck's jumper (blue line) added.
Notice that all that blue wire does is effectively connect 10 to 20ft of #12awg in parallel with the original loop, which consists of coax shield and line-cord ground wire. Yeah, it lowers the impedance between the "Ground Rod Outside Shack" and the "AC Wall Plate Yoke" a bit at DC, but not at RF. It is anything but a "Single Point RF Ground". In the event of a direct lightning strike, my existing bus bar provides much more protection than would exist without with just the blue line.
Currently, I do not have either the blue or pink wire. No Computer crashes, no RF in the shack, no buzzing speakers, etc...
In my specific installation, if I was going to add Dereck's wire, I would do better with the pink wire than the blue one, because the RF and DC impedance of my existing red bus-bar and my orange #6 bare Copper is lower than Dereck's magic blue #12AWG!
That is because the author is saying what I was saying about the consequences are for bonding the negative terminal inside the power supply will do be injecting current into ground conductors. That is not an opinion, it is fact well known and documented. So yeah click the link, go to page 138 and start reading for details how it can tear up SSB TX Audio. That was the whole point of the thread until W7ARK trying to convince fools running current through ground circuits is no problem. Pure rubbish.
Well I hope it is not shot or in disrepair. Here is the point you and everyone seems to be missing. When you use Multipoint-Grounding, you are using two different reference points with a considerable distance between them. There will be a voltage difference between them. There is 180 and 60 Hz AC current flowing through the dirt. The source of the current is the utility, and our service drops. Utilities are allowed to use dirt as a conductor and use dirt to transport and distribute electricity. Saves them lots of money. We use what is called a Grounded System where one circuit conductor is bonded to earth called neutral. On the utility pole, the utility will bond the transformer secondary center tap to pole butt ground. That neutral conductor is one of three wires we use for service. Code requires for us to bond the Neutral again at our service. That means ground is in parallel with the neutral and thus current will flow as earth is now a conductor for our service.Funny thing is the NEC forbids us to use earth as a conductor. No current is allowed on ground conductors. This is why the NEC only allows you to bond the Neutral One time where it enters. If it were bonded again down stream would put ground in parallel with neutral and carry normal load current. Big no no and and a huge amount of common mode noise if allowed.
Here is the point. You AC service is on the West side of house, and the shack on the east side some 60 feet away. We drive a rod where the AC enters, drive a rod where our coax enters on east side, then bond the two together. Those rods separated 60 feet are at two different voltage potentials and when you short them together a current will flow. So here is where the big problem comes in. The AC ground in the Yoke (your wall receptacle) you plug the power cord into is reference to earth some 60 feet away, while your RF ground is inches away.
You have two ground reference points with a voltage difference between them because they are referenced to two different reference point located considerable distance from each other. That voltage difference is pure noise. Throw some RF into the picture and now you have a huge common mode noise to deal with because all that distance between the two reference point will have considerable RF voltage difference.
It should not take you long to figure out the problem and solution for it. You do not want any difference in potential between any two reference points and in the case is AC and RF Ground. So how do you accomplish that? Stupid simple right? You reference both Grounds to the same point. Since this is a multi-point application, it is impossible to have a pure Single Point Ground to reference both AC and RF Ground together as we can do if we had thought to run the coax out with the AC Service. However you can make a simple modification and cut the distance between the two grounds from 60-feet to a few inches up to a couple of feet.
So the jumper you use needs to be as short as possible because AC ground will be at one end, and RF Ground at the other end. A good way to keep it short is use a Power Strip with a long enough pig tail to position it right where the Coax Enters. Now you got the distance down to a few inches.
But wait we can even make it much shorter to the point it is the exact same point. You install a 2' x 2' x 3/4' plywood right where the coax enters. You cover the surface of plywood with galvanized sheet metal. I used a copper sheet stuck on plywood with contact cement. Get a power strip with a metal case, or can be insulated, you will just have to bond the ground buss to the sheet metal. Then mount a Coax Surge Protector or a Ground Block on the the plywood making sure you get a good bond to sheet metal. Now you have a pure SINGLE POINT GROUND where RF and AC Ground use the same reference point with 0 voltage potential difference aka Common mode noise. Without out any voltage potential difference means there is no current flowing. That translate to a good clean ground circuit free of noise. Exactly what you want.
Where and how you connect things matter.
I checked my rs50 this morning and it's floating. Thanks for the info and the sideshow that followed.