Best way to secure RF ground from 2nd floor?
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Best way to secure RF ground from 2nd floor?
 
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HI all:
I am re-doing all my 20 year old connections here in the shack, which is on the 2nd floor of my house. Can anyone point me to a resource for the "best way" to ensure a proper RF ground from the 2nd floor? I have lots of holes in the walls going outside (rotor cables, control lines, many coaxes, etc), so going through the wall is not an issue. If fact, maybe I can use the shield of a coax to help with an earth ground? I"m not looking for "resonant" inside radials....I want a genuine RF ground. Looking forward to your comments. Since I suspect this may a topic of wider interest, I'll ask you post your comments here (or you can always post to me directly if you disagree with "filling up the reflector"). Thanks so much! de Doug KR2Q _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Best way to secure RF ground from 2nd floor?
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I'm not on a 2nd floor, but I use 2" wide copper strap.
It comes from a sheet metal shop, which cuts it with a sheer from the side of a 4' x 8' sheet. The strap is run along the back of my desk with brass 1/4 x 20 bolts soldered at 12" intervals. I use brass wing-nuts on the bolts. 73! Ken Kopp - K0PP [hidden email] or [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by DOUGLAS ZWIEBEL
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On Mon, 18 Feb 2008 20:44:55 -0800, Ron AC7AC wrote:
> >Another approach for an RF ground is to use your connection to the ground >rod, but tune out the reactance. MFJ made a small "tuner" for just that >purpose: a coil and capacitor in series that one adjusted as needed to >produce maximum ground current at the rig. That can be very effective, but >it is frequency-sensitive: it requires readjustment for every band. And, >because the circuit involves a capacitor in series with the coil, it is not >a d-c ground if that's what you are looking for. But it can produce a good >RF ground. > >Ron AC7AC An automatic ground tuner might be nice-- a GTU, i guess you would call it. 73, Drew AF2Z _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: Best way to secure RF ground from 2nd floor?
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In reply to this post by DOUGLAS ZWIEBEL
Why do you need a "proper RF ground" for your radios? It's not needed unless you are using something like an end-fed wire for an antenna. Here's what I do (also have a 2nd-floor shack): I built a box just outside the house near to where the coaxes come in from the towers. On a piece of copper sheet I mounted all my coax switches, surge supressors, coax stub filters, etc. This is all connected to the ground system with a very short connection. 3 coaxes and a lot of control wires go up to the shack. I don't have any "ground connection" inside. Inside the shack I do bond all the grounds for each piece of equipment together. It all seems to work. I can transmit and receive simultaneously on different bands (SO2R) running 1500 W without problems. Tor N4OGW |
Re: Best way to secure RF ground from 2nd floor?
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In reply to this post by DOUGLAS ZWIEBEL
DOUGLAS ZWIEBEL wrote:
> HI all: > > I am re-doing all my 20 year old connections here in the shack, which > is on the 2nd floor of my house. > > Can anyone point me to a resource for the "best way" to ensure a > proper RF ground from the 2nd floor? I have lots of holes in the > walls going outside (rotor cables, control lines, many coaxes, etc), > so going through the wall is not an issue. If fact, maybe I can use > the shield of a coax to help with an earth ground? I"m not looking > for "resonant" inside radials....I want a genuine RF ground. > > Looking forward to your comments. > > Since I suspect this may a topic of wider interest, I'll ask you post > your comments here (or you can always post to me directly if you > disagree with "filling up the reflector"). > > Thanks so much! > > de Doug KR2Q > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > > for me. My shack is on the 2nd floor and I run several rigs w/ amps . I was having RF everywhere until I tried this: - Run coax ( RG-8 or similar) from rig to a real good ground . Put a .01 cap across the shield and center conductor at both ends. Cap needs to be 2KV or better. You will be using the center conductor as your connection to rig and the ground rod.You should also use an ATU as mentioned in an earlier reply. 73 Dale K5AJZ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by DOUGLAS ZWIEBEL
In a message dated 2/19/08 8:50:41 PM Eastern Standard Time,
[hidden email] writes: > Here is a solution from a very old QST, It's not from QST. and all I can say is it works > > for me. My shack is on the 2nd floor and I run several rigs w/ amps . I > was having RF everywhere until I tried this: > - Run coax ( RG-8 or similar) from rig to a real good ground . Put a > .01 cap across the shield and center conductor at both ends. Cap needs > to be 2KV or better. You will be using the center conductor as your > connection to rig and the ground rod.You should also use an ATU as > mentioned in an earlier reply. Have you tried just using the coax as a ground conductor, without the capacitors, and the center conductor tied to the shield? 73 de Jim, N2EY ************** Ideas to please picky eaters. Watch video on AOL Living. (http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/ 2050827?NCID=aolcmp00300000002598) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by DOUGLAS ZWIEBEL
> > Here is a solution from a very old QST, > > It's not from QST. > > and all I can say is it works > > > > for me. My shack is on the 2nd floor and I run several rigs w/ amps . I > > was having RF everywhere until I tried this: > > - Run coax ( RG-8 or similar) from rig to a real good ground . Put a > > .01 cap across the shield and center conductor at both ends. Cap needs > > to be 2KV or better. You will be using the center conductor as your > > connection to rig and the ground rod.You should also use an ATU as > > mentioned in an earlier reply. If it is not from QST, do you know where it is from? Do you know where (or how) I can get a reprint of it? My shack is on the second floor, too. And I believe that The Wireman used to sell a kit containing the capacitors! Dan Allen KB4ZVM K2 S/N 1757 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I ran a TR-3 with no gnd at all for 4 yrs from higher floor with no problems. The AC had a gnd pin. I say, if u have no problems with no gnd, forget it. Of course, my Thailand 230VAC is supplied with no separate 3rd wire gnd.... The guy who installed my water pump here ran the gnd wire from it to a plastic water pipe. The guy who installed my outside air cond condenser ran the gnd wire to a screw in the concrete wall. Then my dog chewed the wires in two. Buzzzzzz, zap.Charles Harpole [hidden email] > From: [hidden email]> To: [hidden email]> Subject: RE: [Elecraft] Best way to secure RF ground from 2nd floor?> Date: Tue, 19 Feb 2008 20:44:34 -0800> > -----Original Message-----> > > Here is a solution from a very old QST,> > > > It's not from QST.> > > > and all I can say is it works> > > > > > for me. My shack is on the 2nd floor and I run several rigs w/ amps > > > . I> > > was having RF everywhere until I tried this:> > > - Run coax ( RG-8 or similar) from rig to a real good ground . Put a > > > .01 cap across the shield and center conductor at both ends. Cap needs > > > to be 2KV or better. You will be using the center conductor as your > > > connection to rig and the ground rod.You should also use an ATU as > > > mentioned in an earlier reply.> > If it is not from QST, do you know where it is from? Do you know where (or> how) I can get a reprint of it? My shack is on the second floor, too.> > And I believe that The Wireman used to sell a kit containing the capacitors!> > Dan Allen> KB4ZVM> K2 S/N 1757> > ---------------------------------> > Those capacitors look like "shorts" at RF. So the center conductor is tied> to the shield at RF, but not at D-C. Direct current isn't the problem. Tying> the shield to the center makes the impedance of the cable slightly less> because it's slightly bigger to the RF. > > Even so, at RF it's still just a wire from the second story to ground. > > If you force a wire to either a low impedance (grounded) or high impedance> (insulated) at one end, it will show at the opposite end the opposite> impedance if it's 1/4 wavelength long or an odd multiple of 1/4 wavelength> long, and it'll show at the opposite end the *same* impedance if it's 1/2> wave long or a multiple of 1/2 wavelength long. Everything in between will> be something "in between". > > Even a marginal RF ground will cure problems caused by no RF ground in some> situations. Even a hunk of coax. > > The things you can do to provide a low(er) impedance ground than a wire is> to make the wire larger, or parallel a lot of wires to ground, all> separated, such as running a large wide sheet of metal from the rig to the> ground. If you're on the second floor, that's seldom practical for those who> live in the same building with our "shacks" ;-) My shack is, fortunately, on> the ground floor about 3 feet from where the large metal conduit for the> underground utilities emerges from the earth. It's also where all the other> services - telephone, cable, etc. - are grounded along with the mains> ground. And my RF ground goes there. Since it's only a few feet away, I use> a 2-foot wide strip of copper attached to the wall from the rig to a point> on the wall opposite the mains conduit. Then a pair of ground wires makes> the run through the wall to the mains conduit. Each wire is about 12 inches> long. Two in parallel reduce the impedance of one. To RF, they look like on> FAT conductor. > > I didn't suggest that because, from the 2nd floor, it'd take very large> piece of metal to show low enough impedance.> > But all is not lost. You can operate free from RF when you aren't close to> ground. It's been done by everything from rigs in Zeppelins to Hams stuck in> the attic! > > The "trick" is to keep the impedance of all RF antenna circuits at the rig> low. > > A 50 ohm dummy load does that, but it's a lousy radiator. But it> demonstrates the concept: keep the impedance low.> > Feeding an antenna at a current loop (low-impedance) point will do that.> That's why Hams seldom have trouble with center-fed dipoles. The impedance> at the center of a dipole is low - typically not far from 50 ohms. Bringing> the feed point of the dipole directly to the rig or through a length of coax> that has a low SWR keeps the impedance at the rig low. The impedance is low> because each half of a dipole is 1/4 wavelength long. The far ends are> insulated, forcing their impedance high. So the ends at the rig are low> impedance - typically 20 to 30 ohms. Two of them makes a 50 ohm load for the> rig. > > The famous "Zeppelin" antennas did the same for a rig floating high in the> sky held aloft by a bag of hydrogen. An open wire feed line, exactly 1/4> wavelength long, was connected to the rig. At the far end one side of the> feeder was connected to nothing at all: it was well insulated. The other> side of the feeder was connected to a 1/2 wavelength hunk of wire floating> out behind the ship in the air stream. The 1/2 wavelength long wire showed a> high impedance to the feeder at its end. The feed line, being 1/4 wave long> matched that high impedance while showing a low impedance at the rig. The> other side of the feed line, being insulated at the far end, also showed a> low impedance at the rig in the airship. Low impedance at the rig meant no> RF to cause sparks and burns which meant the airship didn't catch fire. > > If your not using a "Zepp"eline antenna you can do the same thing. Just hook> a 1/4 wave long piece of wire to the chassis of your rig. Yes, that means> you need one for each frequency you operate on. That's the bad news. The> good news is that it's generally adequate to use only one for each Amateur> band. As I mentioned above, you don't need a perfect ground. > > The "problem" with such counterpoises, other than the need to string them> out and insulate the far ends, is that they, too can radiate, just like 1/2> of a center fed dipole radiates. If the end, hot with RF, is near house> wiring, etc. that can pick up the RF voltage, you might still see troubles.> Also, a portion of your power will be radiated by the counterpoise which> might be largely absorbed by the building or other nearby objects.> > In an ideal counterpoise, you'd have two 1/4 wave wires running in opposite> directions with the ends out in the clear. The RF in each wire would be in> phase, so their RF fields would cancel, resulting in little radiation and> loss. That's why "Ground Plane" types of antennas show more than one radial> arranged in a symmetrical pattern. When that's done, the center point of the> radials, typically at the base of the radiator, is at a very low impedance> for RF and the radials radiate very little power. > > Moxon and others have studied the needs of such "ground" systems and come up> with some interesting suggestions that might apply to you. One point is that> the counterpoise can be much shorter than 1/4 wavelength if you resonate it> with an inductor. Moxon suggests using several identical radials less than> 1/4 wave long tied together and all resonated in common with an inductor.> The multiple radials minimize the power radiated by the system while the> inductor resonates the system at 1/4 wave for the lowest impedance at the> rig. > > That can be a lot of work, which is why most Hams in "attic" situations rely> on some sort of balanced feed with a low impedance, like the famous Zepp> antenna, or a center fed 1/2 wave, etc. > > Keep in mind, if you are using an antenna that is designed to be a low> impedance, the SWR on the coax must be very low. If it's allowed to rise,> then voltage maxima will appear along the line. That's exactly what we're> measuring when we measure the SWR. If a voltage maxima appears near the rig,> you'll likely find "RF in the shack". In that case the SWR on that feeder> isn't low enough. You need a better match out at the antenna. > > Ron AC7AC> > > > > > _______________________________________________> Elecraft mailing list> Post to: [hidden email]> You must be a subscriber to post to the list.> Subscriber Info (Addr. Change, sub, unsub etc.):> http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm> Elecraft web page: http://www.elecraft.com_______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: Best way to secure RF ground from 2nd floor?
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In reply to this post by AC7AC
Grounds can serve three purposes: lightning protection, power line
safety, or RF ground. These are three very different things, requiring very different ground methods. For an RF ground, forget about a wire to earth ground. It will almost always be too long to present a low impedance at RF. Even if you can tune out the reactance by adjusting the length to a multiple of 1/2 wavelength or by using a tuner, it will still have RF current flowing in it and so will still radiate RF. A better method is to use a counterpoise wire. This is like a single radial, 1/4 wavelength long, connected to the chassis of the antenna tuner. One counterpoise is needed for each band of interest. Al N1AL _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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There is an exhaustive article about the counterpoise,
written by L.B. Cebik (W4RNL) in the Winter 2008 issue of the QRP QUARTERLY. 73! Ken Kopp - K0PP [hidden email] or [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: Best way to secure RF ground from 2nd floor?
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In reply to this post by Alan Bloom
> > > Grounds can serve three purposes: lightning protection, power line > safety, or RF ground. These are three very different things, requiring > very different ground methods. > > ... > > Al N1AL > > True. But should we go a step further and avoid even using the phrase RF ground? Long ago I asked an old Zen master about the best way to RF ground my station. His answer was "What do you mean by ground?" This was the best possible answer because it made me think about the physics that's going on: You don't want to seek some elusive "ground" potential. What you want is to keep unbalanced feedline current out of your shack or at least as far from your equipment as possible. 73, Carl WS7L No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.20.9/1290 - Release Date: 2/20/2008 8:45 PM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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i believe the originator had said that he has a centerfed dipole with a
balanced feedline. i think the first thing the lead wire should come to is a suitable matching device. i use an elecraft t1 which works well for my qrp activities. the coaxial input to my t1 has 10 inches of suitable ferrites on it to act as a common mode rf choke to keep rf off the exterior of the coax regardless of it's length. that ensures that whether the feedline is perfectly balanced or not all of the rf is properly contained inside the coax. the tuner itself is likely a bit hot but it is of no consequence. my next oft delayed project is to build up a simple insertion/extraction pair for a bit of dc onto the coax to remotely trigger the t1 tuning cycle. 73 jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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