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Shack Grounding
- Thread starter Crambone
- Start date
Shadetree Mechanic
Delaware Base Station 808
I read this a while ago, I had to find it again.
https://helpdesk.flexradio.com/hc/e...n-the-Ham-Shack-Paradigms-Facts-and-Fallacies
https://helpdesk.flexradio.com/hc/e...n-the-Ham-Shack-Paradigms-Facts-and-Fallacies
So to refine my question, how much length do I need to be away from the wavelength in feet to not be resonant? I have to apologize, my math is very weak and copper is expensive and I only want to buy this once.
So 27.185 at 1/2 wave is 18 feet and 1/4 wave 9 feet will I be ok using a 14 foot run?
So 27.185 at 1/2 wave is 18 feet and 1/4 wave 9 feet will I be ok using a 14 foot run?
Shadetree Mechanic
Delaware Base Station 808
You will want it to be a 1/2 wave multiple so closer to 18 if you can. Here is another link that might explain it better.
http://www.radioworks.com/nbgnd.html
http://www.radioworks.com/nbgnd.html
(1) The ground wire should be as short as possible, preferably much shorter than a quarter-wavelength long on the highest frequency band operated.
Whatever conductor has the most surface area is the best for RF. If you have 50 feet you aren't RF grounding anything. You may redirect some stray RF and think you did good.
At 50 feet it doesn't matter if it's welding cable or light gauge wire. Any grounding you do should be for lightning protection. As long as there is no common mode current you shouldn't have to do anything special inside the shack.
The reason for bonding the coax shield to the electrical system at the entry point is so that lightning doesn't find a better path to ground through radio equipment if it hits your house, or a better path through your household appliances if it hits your antenna.
The only ground straps in my shack are between each piece of audio gear in my rack. They don't actually go to ground. They just bond each piece of gear. I wouldn't need those if the rack wasn't made of wood.
Thank you, yes ive read that several times and ill have to read it many more times before I understand some of it. Ill book mark the page.
When I say my math is bad I mean a lot is non existent.
To make a long story short, rough childhood, drunk abusive mom, runaway at 14 and never made it past 10th grade and a rough time getting that far. I feel I owe some explanation for my level ignorance.
Some of the time google is my friend and Ill always try to figure stuff out my own before asking. Numbers and math have always been my nemesis unfortunately.
Not trying to dump a bunch of personal stuff here but sometimes knowing some of a persons situation helps to understand why they might not comprehend things they should or why they ask certain questions. You folks have always been helpful and im very thankful for that. I probably shouldve picked a different hobby but I didnt and now you're stuck with me
Shadetree Mechanic
Delaware Base Station 808
Short as possible unless that distance is a quarter wave multiple. Then you would have to make it longer to prevent an impedance rise that would render it useless.
http://www.radioworks.com/nbgnd.html
http://www.radioworks.com/nbgnd.html
Where would such a long ground wire be needed? If this solves any rf problems your fooling yourself. It doesn't seem much different than the guys that would tie a 1/4 wave piece of wire to their amp case to get rid of rfi.
Shadetree Mechanic
Delaware Base Station 808
If your ground wire works out to be a quarter wave, the impedance will cause it to be ineffective. What ever that length works out to for the frequency you are using. Are you saying that a 9 foot ground wire is longer than anyone would need?
Are we strictly talking about rf grounding?
I think a long piece of wire it is more of a radial or counterpoise. My thinking is that if such a long ground wire improves anything you have other issues that are being ignored.
If you lengthen it to a half wavelength wouldn't there still be high impedance/high voltage at the center of the half wave wire? I doubt anything bad will happen unless you run high power but I still don't think this is a good thing.
If you bond all of your gear together with long wires it seems like you may be making an unnecessary ground loop. I have solved more rfi problems by choking audio and power cables between different pieces of equipment. When making an rf bond I don't like the strap to be more than a couple of inches. I'm not an expert so talk all this with a grain of salt.
Shadetree Mechanic
Delaware Base Station 808
Shadetree Mechanic
Delaware Base Station 808
The thing about RF is that it has a different set of rules than DC or even conventional ac. With RF everything depends on the reactance. The wire itself has inductance just running straight across the floor all by itself. This inductance causes the impedance to change at different points along the wire. The impedance will be highest at a quarter wave distance. The impedance will be lowest at a half wave distance. Add another quarter wave and it goes up again. The thing about grounding all the equipment is that it will cause ground loops with the interconnecting coax. The coax needs to be choked between each device. That way the RF stays on the ground and not the coax shield. These are considered best practices. Many stations get away with no ground at all. But if you have a CMC problem and want to fix it and make it the best it can be then the science behind what is happening needs to be considered. I am no expert either but this is how I understand it.
I think we're mostly on the same page. My opinion is that there should not be that much rf in your shack. What you say about the impedance transforming along the wire every 1/4 wave is true. The same is true for an antenna. If this is happening along that long ground wire it's likely radiating. It may provide a lower impedance path for rf than your tv, pc speakers or whatever but it's only eliminating the symptoms. The real problem is still there.
My main point is the long ground wire can radiate RF and pick up noise. With enough power that high voltage point in the center can burn you, arc to nearby cables and even start a fire. That's extreme but possible.