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K5KEN
01-28-2010, 01:05 PM
Quick question,
what would be better to ground my station to the outside ground with, Braid or solid? My run is only going to be about 7' from my below grade cellar shack over the foundation, through the sill plate and out to the grounding rod. I have removed the copper braided jacket from some old RG-8 wire and I also have #6 solid copper uninsulated wire.
Thanks and 73's
Ken
K5KEN

G7LSR
01-28-2010, 01:50 PM
Very little differences, I would go for the one with the lowest resistance.
It's only a short run, so do a test!

AF6LJ
01-28-2010, 01:57 PM
Depends on the width of the braid and the size of the wire?
Not much difference between quarter inch braid and number ten wire.

One advantage to flat braid is it's flexibility.
Surface aria does matter the length is also somewhat important.
If you are going to operate on twenty meters and below, that length is still good to ensure a reasonably good RF ground. For ten meters that is almost a quarter wave and would in my opinion not be as good an RF ground without ether shortening it or adding a means to tune the ground wire.

My two cents :)

KA4DPO
01-28-2010, 02:19 PM
The critical factor for a good ground is surface area. You would want to use the conductor that has the largest surface. You can use large copper braid like automobile ground strap or, another way to do it is to use a couple of large diameter wires instead of just one. Six guage wire is pretty large, two runs of that should make an excellent ground conductor.

K0RGR
01-28-2010, 04:52 PM
Some folks believe that the braid presents a higher impedance to ground, which is not actually desirable in RF applications, which is the only reason you're dong this.

To be absolutely honest, particularly if the run is more than a few feet long. I find that a piece of large coax is the most effective ground. In cases of stubborn RFI, I will even employ a 'shielded ground', an 'old wives tale' that can't possibly work, and has been proven scientifically to be a total fraud. It just seems to work, and sometimes appearances are more important than science. I've had cases where replacing braid with a 'shielded ground' cured stray RF in the shack. Coincidence? Quite llikely -

To create a 'shielded ground', you solder a .01 ceramic capacitor across each end of the coax, and use the center conductor as the ground strap. Again, it's an old wive's tale, and I will deny you heard it from me.

AF6LJ
01-28-2010, 04:56 PM
Some folks believe that the braid presents a higher impedance to ground, which is not actually desirable in RF applications, which is the only reason you're dong this.

To be absolutely honest, particularly if the run is more than a few feet long. I find that a piece of large coax is the most effective ground. In cases of stubborn RFI, I will even employ a 'shielded ground', an 'old wives tale' that can't possibly work, and has been proven scientifically to be a total fraud. It just seems to work, and sometimes appearances are more important than science. I've had cases where replacing braid with a 'shielded ground' cured stray RF in the shack. Coincidence? Quite llikely -

To create a 'shielded ground', you solder a .01 ceramic capacitor across each end of the coax, and use the center conductor as the ground strap. Again, it's an old wive's tale, and I will deny you heard it from me.
:)
/Sue scratches her head....


That is one I have never heard before.
So you have a DC isolated shield over your RF/DC ground.
Hmmmmmmmm:confused:

If it works, who cares how. :)

KR2D
01-28-2010, 05:00 PM
Some folks believe that the braid presents a higher impedance to ground,

This should not be a "belief", as it is easily measurable. A length of braid, a length of wire, and one of the ubiquitous MFJ analyzers will give you the truth.

No, I don't know which has a higher impedance - I haven't measured it yet. For what it's worth, I use 4 AWG solid copper wire for grounding because I have a bunch of it.

W0LPQ
01-28-2010, 05:11 PM
As Glen (K9STH) and others have said in previous posts in other threads, aluminum flashing works great also ... it is wide thus reduces the inductance. Better than wire also.

Braid has a side detriment, with moisture and air, it can oxidize which is not good. Makes for little diodes along the length between conductors.

AF6LJ
01-28-2010, 05:14 PM
....

Braid has a side detriment, with moisture and air, it can oxidize which is not good. Makes for little diodes along the length between conductors.

Actually I have never heard that happening with similar metals.
The main issue would be keeping the inside and outside joints clean and moisture free.

WB2WIK
01-28-2010, 05:22 PM
To create a 'shielded ground', you solder a .01 ceramic capacitor across each end of the coax, and use the center conductor as the ground strap. Again, it's an old wive's tale, and I will deny you heard it from me.

If you're caught or killed, the Secretary will disavow any knowledge of your action. Good luck, Jim. This tape will self destruct in five seconds.:p

KI6USW
01-28-2010, 09:05 PM
The critical factor for a good ground is surface area. You would want to use the conductor that has the largest surface. You can use large copper braid like automobile ground strap or, another way to do it is to use a couple of large diameter wires instead of just one. Six guage wire is pretty large, two runs of that should make an excellent ground conductor.
Exactly. The 'skin effect' dicates that there is more surface area on the braided wire that the single thick strand of wire. More conductive surface on the braided one - no doubt.
But that begs another question; how much is enough?

K0RGR
01-28-2010, 09:21 PM
This should not be a "belief", as it is easily measurable. A length of braid, a length of wire, and one of the ubiquitous MFJ analyzers will give you the truth.

No, I don't know which has a higher impedance - I haven't measured it yet. For what it's worth, I use 4 AWG solid copper wire for grounding because I have a bunch of it.
Yes, I suppose so, though I'm not sure how I would arrange a meaningful measurement. In any case, it's going to vary based on frequency and length.

Now, if you tinned the braid, that would probably give you a different result.

K0RGR
01-28-2010, 09:26 PM
:)
/Sue scratches her head....


That is one I have never heard before.
So you have a DC isolated shield over your RF/DC ground.
Hmmmmmmmm:confused:

If it works, who cares how. :)

Yes, I never heard of it either, until someone with an original 1X2 call told me about it one afternoon. I was having very stubborn RFI issues in the shack - probably due to the use of an OCF antenna very close to the shack - and this was suggested. My ground run was only a few feet long, but switching to the 'shielded' ground out to my ground rod/radial field eliminated all traces of RF in the shack.

When operating as a feed line, there is no way coax can work like this. But, I wonder if it's working as a feedline or something else. I've also tried just grounding one end of the shield, and that seems to work too.

N8CPA
01-29-2010, 01:08 AM
Yes, I never heard of it either, until someone with an original 1X2 call told me about it one afternoon. I was having very stubborn RFI issues in the shack - probably due to the use of an OCF antenna very close to the shack - and this was suggested. My ground run was only a few feet long, but switching to the 'shielded' ground out to my ground rod/radial field eliminated all traces of RF in the shack.

When operating as a feed line, there is no way coax can work like this. But, I wonder if it's working as a feedline or something else. I've also tried just grounding one end of the shield, and that seems to work too.

I had never heard of it either, but it's well illustrated at W8JI. Very interesting.

AF6LJ
01-29-2010, 01:11 AM
It's a real head scratchier.....

WF7A
01-29-2010, 01:16 AM
Exactly. The 'skin effect' dicates that there is more surface area on the braided wire that the single thick strand of wire. More conductive surface on the braided one - no doubt.
But that begs another question; how much is enough?

Just for an education:

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/skineffect/page1.html (http://www.st-andrews.ac.uk/%7Ewww_pa/Scots_Guide/audio/skineffect/page1.html)

http://en.wikipedia.org/wiki/Skin_effect

AD7N
01-29-2010, 02:24 AM
It seems using the center conductor of large-diameter coax would be the way to go. You get large surface area, but you also don't get anything radiating. One of the tricky annoyances of any RF ground is as Sue touched on, that you have to calculate wavelengths that you will be operating on to make sure the length of the ground doesn't interfere.

Or, do I have this all confused-discombobulated? A shielded ground wouldn't radiate anything, so it seems like it the optimal ground conductor as it wouldn't effect the pattern of the antenna.

Time to invest in ~15ft of Andrews LDF6-50 Heliax!

KI4WCA
01-29-2010, 03:19 AM
Use the solid wire.Wide copper strap is better, as is large diameter copper tubing.Avoid the braid.It does not have as low a loss at rf as big wire.

Or really lose control and use what I use...silver plated power plant buss bar.
(uncle worked at westinghouse...hee hee)

K9KJM
01-29-2010, 07:27 AM
WCA has the correct "BEST" answer. Flat copper strap is the BEST material to use. (Found at home supply stores in the roofing department... Copper roof flashing. About .022-.025" or so thick. Last time I checked, About 30 bucks for a 10 foot long roll, 6 inchs wide. That would make a Dandy ground conductor, OR you can just take a tin snips and make two 3 inch wide strips for 20 lineal feet, Or cut it into three 2 inch wide strips for 30 lineal feet, etc)

The flat aluminum roof flashing mentioned also works really good, Almost as good as copper. The big PROBLEM with aluminum is how difficult it is to transition to copper ground wires once outside near the soil. (NEVER run aluminum underground! Turns to a white powder in short order in most all soils)

As already pointed out, "Braid" will oxidize outdoors and cause real problems sooner or later. At commercial tower sites nowadays, Braid is only used where a conductor has to flex. Like grounding/bonding a steel door to a steel door frame, etc.

While #6 gauge copper wire is generally considered the minimum size to use for grounds, It is really far too small for any type of effective RF ground. If you cannot find or get some flat copper strap, My second choice would be some low cost copper TUBE. As already pointed out, It is the surface area you are after. The soft flexible copper tube is a fair substitute for a really nice wide copper strap.

AG3Y
01-29-2010, 04:20 PM
I worked in several different broadcast stations in the past, and every one of them used flat copper strapping in an extensive ground system. The copper strapping ran under each of the rack panels, and the transmitter itself, and then out to the base of the tower where a triangle of the stuff surrounded the base of the tower, and then took off in several different directions to ground rods. The chain link fence and everything metal , including the flashing on the roof was tied to the strapping!

That may be considered a bit extreme, but repeated lightning strikes did minimal damage, and often a fierce storm could be all around, and nothing would even flicker.

Of course there was that one time . . . . .

K5KEN
01-29-2010, 07:01 PM
Thanks everyone, I have some flat copper from an old copper tank I will cut down into strips and use:D

73's everyone

WA9CWX
01-30-2010, 12:43 AM
Sounds like a great idea......Several years ago when putting together my new shack, I spent a LOT of time reading all kinds of different opinions on RF, and lightning grounding. Finally I reached a decisison concerning flex braid and solid/ stranded wire.
Therefore I settled the debate for myself and wound up with three parallel ground wires, all going to and doing the same thing. A solid wire, braid and a stranded wire, all big, all well clamped, all obnoxious. If you have decent house wiring, probably the prong on your AC plug is all you need for any grounding, unless your antenna is an unballanced single wire, then you need radials, not an earth ground.


Frank

WA9CWX
01-30-2010, 12:56 AM
Usually more important for 'ground loops', which are obnoxious paths for RF, based on where you need it NOT to be, like in your pilot lights, mic cable, keyer cables, etc. The most important issue is a common ground point for ALL the gear, including incidentals, like the rotor box, audio boxes of various types, and just about anything else in the shack, including the cat. In addition those grounds sometimes need to be by more than one path, and not just the coax connection. The tuner will need a seperate wire for certain, and do not daisey chain them (series), instead ONE common point for the several ground wires to avoid 'loops'. :D
For the 'outside ground' your copper strips will work great.

AD7N
01-30-2010, 02:49 AM
A "cheap" copper flat bar can be had with standard copper plumbing pipe, if you don't mind some "sweat equity" :D

clamp down the pipe with a bench vise, cut a seam all the way down long wise, take it out of the clamp and pound the pipe flat :D

WA3MEJ
01-31-2010, 05:13 AM
Regardless of what you have heard braid is NOT the way to go if you have a choice especially if it will be used outside in the weather.

The reason for this is that even if the braid is silver or tin plated it will corrode. You will see this as blue/green mung on the braid (often you have to open the weaves up to see it)

Ok so why does this matter... well when braid corrodes little semiconductor surfaces (consider them diodes) are formed with the surface of the braid. What happens is when you transmit in close proximity to this corroded braid you all of a sudden generate a 3 harmonic that is radiated and could even get you speeding ticket.

Now why would I know this. Well because it happened about 30 years ago to me. It took me about 2 weeks to find the problem. AND.. funny thing when I replaced the braid the funny background noise I had in my receiver cleared up as well. See I was in the near field of a broadcast band station and even thought it was only rated at 1000w it caused me grief.

The navy used to have similar problems on their ships... ever wonder why their lifeline chains and wire ropes is replaced periodically? It is also why solid copper strap is used on crypto equipment instead of braid.

So what do you do.. use flat 2" wide copper strap.. no it is not as flexible but it also does not promote 3 harmonic radiation either.

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