Discussion in 'General Technical Questions and Answers' started by KF5LJW, Oct 29, 2019.
Looks like the contest went sideways.
The guy on the bottom is at a major disadvantage.....unless that contest was modeled in free space and there's no gravity.
I did. Much more understandable than anything you've presented.
Probably because he doesn't present it in a holier than thou manner and without a condescending attitude.
Then you have a problem. Without the Blue or Pink Jumper means your AC ground is on one side of the house, and RF Ground is on the other side. The two grounds are at different voltage potentials because they are separated by 50, 60, 100 feet apart or whatever your actual distance is in the dirt. When they meet at the radio completes the loop, and common mode current begins to flow through your radio equipment.
With the Jumper, brings them closer together with less voltage potential difference. If they are terminated to the same point, there is no voltage potential. That is what you are not seeing. You have two different reference points. You AC Ground is at one potential, and your RF Ground at the end of the coax where you bond it to the Ground Rod are a considerable distance apart. There is a Voltage difference between the two point, and you have your two reference points as far apart as you can possible make them. Ideally you want them to come from the same point so there is no current flowing or voltage difference between the two. So by adding the Blue Jumper shortens that distance considerably. You want the two points as close together as possible, and it is possible to make them the same point.
Well sorry about that, but W7ARK started it spouting stuff off he has no clue about. I was trying to keep hams up to date and inform them Astron has a serious design flaw and inconsistency that is easy to fix and can solve some noise problems.
Yes but it is a voltage difference caused by current flowing where it should not be flowing. Lets try a different approach. In a multi-point ground, you have two reference points in the dirt separated by DISTANCE. The greater the distance, the greater the voltage gradient is going to be. Now lets define Common Mode Noise is created and seen as a voltage gradient along the length of a ground circuit that should not be carrying any current. CMN is not unique to RF but also a problem from DC to Light frequencies. The higher in frequency you go, the higher the impedance will be at a given frequency. Example a 100 foot 6 AWG conductor in parallel with a 12 AWG conductor of equal length at 60 Hz is roughly .02 Ohms. While at say 10 Mhz may be 1000 Ohms so even a little current results in very large voltage difference and radiating on you because there is a high amount of common mode noise being injected when you transmit. At resonance my dip to 30 Ohms which is still way to high.
So now look at W7ARK rendition of my drawing. Look and see where AC ground is (On the left side of the house with the AC meter) RF Ground is on the right side of the house where the coax is bonded to the ground Rod. See it? No find the point where AC Ground and RF Ground join. Where do you see them come into contact? Did you say the DC Power Supply is where they meet. If you did, you are correct. That completes the Ground Loop circuit and heck yeah you have current flowing through your radio equipment. that flow roight from th eDC Power Supply out to the Coax where it is bonded to the RF Ground Rod.
So some like W7ARK might say the voltage difference an current is small and he would be right, but any voltage or current is a big deal and can really much things up. Example lets talk about TX/RX audio circuit. In fact lets pick on receive audio and use some realistic data. Lets say with the two distance ground reference develop .0001 volt @ 60 Hz difference with .0000001 amps of current. Now you might laugh and say that is not enough to do anything and you would be dead wrong. That .0001 Volt AC signal is picked up buy the radio audio amp stage and amplified 50 db. So now that .0001 volt signal you thought is no problem is now .0001 volts x 10,000 = 1 volt @ AC 60 Hz blasting into your speaker and all you can hear is a loud HUM. Realistically the audio stage has a gain greater than 50dB which means the problem gets a lot worse. Example say the audio gain is 50 db now that 60 Hz signal is now a deafening 10 volts and blew your 8-ohm 1 watt speaker coil to smitherings.
OK move to RF and the problem gets worse, a lot worse. Since we moved from 60 Hz to say 14 Mhz, when we key the transmitter the ground impedance skyrockets and the voltage difference is now measured in 10' and 100's of volts. We are dumping a lot of RF energy across the the 60-foot ground wire connect the two ground together. You now have one nice little RFI problem with all your ground conductors radiating energy.
So hopefully by now you see the core root of the problem? It is the Distance between the two ground reference points and running that common mode current through your radio equipment that you are now aware of causing all the problems. The fix is stupid simple, shorten the distance between the two ground points. In fact if you use the same point for both grounds, and you completely eliminate the problem. If you use the same point to reference both AC and RF ground, it is impossible to have a voltage difference between the two ground points No voltage difference and there is no current or noise on your ground circuit where you tap the Ground Loop.
So now look what I have recommended to shorten the distance between AC and RF Ground. We go from say 60 or 100 feet apart to a few inches or couple of feet. I shorted the loop out with the short jumper thus removing the current from flowing through our radio equipment. and shortened the distance between AC and RF Ground.
You can take that one step further and create a psuedo Single Point Ground so RF and AC ground seen by the radio equipment is a pure Single Point Ground with no Common mode noise period. Again that is simple and uses the same technique. This time you use a peice of Plywood cover with sheet metal or copper or splurge a copper bus bar. Both make excellent ground planes. You run a Jumper from the Ground Rod where the coax is terminated too, run it in with the coax and terminate the Jumper to the Buss Bar or sheet metal on plywood. So now you have a Nice Single Point Ground Plane. Now mount a Coax Surge Protector and AC Power Strip onto the the Ground Bus or sheet metal covered plywood. Bond the Ground Bus inside Power Strip to the Ground Bus you mounted the Power Strip onto. Terminate Coax to Surge Protector or Ground Block. Now both your AC and RF Ground are the exact same point free of any voltage and current.
Understand now? Hope that helped.
So YES is the answer to your question, and the further apart the two grounds are, the greater current and voltage will be.So you gotta a choice, You can do it W7ARK way with the two grounds as far apart as he can possible make it, or take my advice and make the distance as short as possible. Or do like me and just make them the same point.
One is coming at it from a "safety" angle and the other the "elimination of potential noise" angle.
The two sort of go hand in hand it seems.
My power supply output is floating, but at the transceiver, about 12 inches of wire away, the DC input negative is bonded to the chassis. Probably a dumb question, because all this back and forth and ‘LJW’s explanations changing several times has left me confused, but wouldn’t that have nearly the same effect as if it were bonded to the chassis of the power supply?
The reason I don't want my power supply negative lead tied to the AC mains ground is because if my negative lead lost connection from the radio to the power supply, the negative connection would be through the AC wiring ground back to the radio through station ground or coax if it is properly bonded to service ground. The AC ground connection is not meant to be a current carrier and it is most likely only 14ga wire and a very long run. If the power supply is not bonded to the ground and you lose the negative connection to the radio it wont power up and you will know if you have a problem with the negative lead. With the negative lead bonded to the chassis ground, the AC ground is sharing the load of the radio just as if two resistors in parallel even with the negative lead from the radio connected to the power supply.