Rubber Tires.
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On the subject of tires to add to the existing K2 VFO knob, I received an
interesting e-mail from Geoff, K7KBS who has difficulty posting on the Elecraft Reflector, so passing on his comments. Bob G3VVT Message was: Just read your submission on today's Elecraft Reflector and all the talk about asparagus and broccoli solutions to the K2 knob's shortcomings gave me an idea. I have some old bicycle inner tubes in my garage that I often cut up to make rubber bands for various things like holding tow ropes in a coil and other odd uses. I cut a piece just the width of the K2 knob and it makes a nice tight fitting "tire" for my K2. Perfection! What's even better, it came from an "English racing tire", so no need to look for an "American" solution to the problem. Balloon tires such as the standard for American bikes are too big. This, along with a stick-on finger dimple makes the standard K2 knob as good as the Yaesu replacement, and much cheaper. Another "homebrew solution". _______________________________________________ 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 recently up graded my house electrical panel from 100 to 200 amp
service. In order to do the up grade I had to install a Ufer ground which was 20 feet of bare #4 copper wire in cement. Our local code allowed a 10 foot run of wire in a U shape in a 9 inch wide trench. The wire had to be 3 inches above the dirt 3 inches from the side of the dirt 3 inches between the wires and three inches away from the dirt on the other side of the trench. That allows for 3 inches of cement all around the bare copper wire. The more I found out about Ufer grounds the better they seem to be to me. The PH factor in the cement and the fact that the cement never completely dries out and retains moisture make it an excellent ground. This leads me to my question. Is anyone out there using a Ufer ground as a counterpoise or to ground their tower and station? This seems way better than the old ground rod pounded in the dirt. Any comments would be appreciated. Glenn WA7SPY Sacramento, CA _______________________________________________ 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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Glenn Maclean wrote: (much snipped by Dave) > This leads me to my question. Is anyone out there using a Ufer ground > as a counterpoise or to ground their tower and station? I have been for the last 12 years or so; I highly recommend them. In my installation, it approximates a commercial station I toured prior to starting construction. Some notes: 1. in setting all the rebar for the foundation, as it was tied, and before the concrete was poured, all the points at which the rebars touched each other were cad welded (I think this is the term but it has been a while); the process uses little molds that are filled and then fired, resulting in a corrosion free weld (no oxide in between) huge "cage" that is in the concrete, similar to your normal rebar structure as far as structural strength, but, electrically bonded. This is apparently capacitively coupled to ground (fairly low inductance as well). 2. the advantage for lightning strikes seems to be that the whole ground system floats and then drops back down, so there is little differential (ground loop currents) so most stuff in the house is better protected. 3. My tower (its base is part of the Ufer ground) has an excellent counterpoise from it; I have 70' tower, with a 8 element LP for 20 - 17 - 15 - 12 - 10, and a 6 el. Yagi on 6 M.; a full wave loop on 60 M, and an inverted L on 80 and 40, and a 160 - 10 M. B&W wide band dipole set for NVIS. They all appreciate the better ground it offers. 4. the cable entry to the shack (feed lines, coax switch, rotor control, etc.) all come in at a common entry point with all shields grounded prior to entering the shack, common ground, etc. 5. I have taken several direct strikes (on top of a hill; all the trees in my yard have evidence of having been hit sometime); the first one was sufficiently strong that it took out a cable TV distribution amp 50 yards away that was buried - it took out the AC compressors, (lightning jumped to them as a supplemental path to ground?), the telephones, and the burglar alarm, but almost everything else in the house survived it by floating with the changing ground. It even blew a chunk of concrete out of the tower base, where the rebar was too close to the outside of the concrete, and some water had gotten in, becoming superheated steam. That chunk weighed over 20 lbs, and it went over 50 yards away (unhappy neighbors). I am convinced (and more importantly, so is the xyl) that without it, the house would have burned for sure. We are building another home, but it is in an area with the dreaded C&R stuff, so no tower; we chose not to do Ufer grounds there, but I wish I had; I now figure I will have to run a ground wire under the long wire antenna to help it out... (and, yes, the search is on for about 10 acres so I can get a competitive 160 and 80 meter array with a good ground going.) > This seems way better than the old ground rod pounded in the dirt. Definitely way more expensive too, but seriously better in terms of both an RF ground, and lightning protection. > Any comments would be appreciated. > > Glenn WA7SPY > Sacramento, CA 73 de W5SV, Dave -- David F. Reed - W5SV - cell: 512 585-1057 _______________________________________________ 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 a message dated 7/14/05 12:39:32 AM Eastern Daylight Time,
[hidden email] writes: > all the points at which the rebars > touched each other were cad welded (I think this is the term but > it has been a while); the process uses little molds that are > filled and then fired, resulting in a corrosion free weld (no > oxide in between) > > That's cadwelding, aka thermite welding. A mixture of powdered iron and aluminum is set afire (usually by a bit of magnesium powder) and the resulting reaction will weld the steel. 73 de Jim, N2EY _______________________________________________ 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 David F. Reed
Ufer grounds:
The question of grounding comes up often, and it's important to distinguish between the various functions of a ground for a ham station. They are 1) Safety (utility) ground. This is the solid connection to the ground wire from the AC service entrance. All equipment enclosures must be bonded to this ground so that if leakage occurs from a hot wire to a chassis (etc.) the enclosure will not become hot with AC. Note that the grounding of the service entrance itself is important. 2) Lightning ground. This is the connection of antennas, towers, and lghtning suppression devices to a low-impedance ground to divert induced potentials and even direct strikes (if the system is built properly). A lightning ground needs to be implemented with a single entrance panel and appropriate suppressors on all incoming lines, including antenna, power, telephone, rotor, etc. in order to be effective. 3) RF ground. This is the 'ground return' for antenna currents. Some antennas (balanced ones) do not need an RF ground at all. Others (e.g. simple verticals) need an elaborate one. Normally the ground systems used for 1) and 2) are NOT effective as RF grounds, although all ground systems should be bonded together. 4) Common potential ground. All equipment on an operating desk should be connected by short wide straps to a common ground bus (not daisy chained), which is connected to the other grounds. This helps reduce hum, noise, and RF getting into equipment. A Ufer ground can be used to ground the service entrance or as part of a lightning ground system. If it happens to be located near the base of a simple vertical or random wire it can be connected to the radial system and be helpful as part of the RF ground system. It isn't especially useful as an RF ground otherwise. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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 WA7SPY
Hi Glenn
Seems a lot of work for a relatively simple rf ground. Why not just take a piece of copper tubing and lay it in a shallow trench and bond your ground wire to it? RF doesn't penetrate the ground very far, so a deep trench wouldn't be needed. Glad to see you're still around. Haven't heard you on in a while. 73, Bob N6WG -----Original Message----- From: [hidden email] [mailto:[hidden email]]On Behalf Of Glenn Maclean Sent: Wednesday, July 13, 2005 7:48 PM To: [hidden email] Subject: [Elecraft] Station grounding question I recently up graded my house electrical panel from 100 to 200 amp service. In order to do the up grade I had to install a Ufer ground which was 20 feet of bare #4 copper wire in cement. Our local code allowed a 10 foot run of wire in a U shape in a 9 inch wide trench. The wire had to be 3 inches above the dirt 3 inches from the side of the dirt 3 inches between the wires and three inches away from the dirt on the other side of the trench. That allows for 3 inches of cement all around the bare copper wire. The more I found out about Ufer grounds the better they seem to be to me. The PH factor in the cement and the fact that the cement never completely dries out and retains moisture make it an excellent ground. This leads me to my question. Is anyone out there using a Ufer ground as a counterpoise or to ground their tower and station? This seems way better than the old ground rod pounded in the dirt. Any comments would be appreciated. Glenn WA7SPY Sacramento, CA _______________________________________________ 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 |
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Glenn, Bob and all,
What constitutes a good utility ground or a protective lightning ground will not always (you can substitute usually) provide an effective RF ground. See Vic Rosenthal's posting today on this same subject. For example: Consider that a good RF ground can be provided by a properly tuned counterpoise wire - an electrical 1/4 wavelength long and open at the free end (just like half of a balanced dipole) and separated from earth along its entire length. The near end will present a low impedance at the frequency the wire is tuned to and thus presents a good RF Ground. This near end can be (should be) attached to the tuner (or transceiver) grounding point to provide the RF ground - THE CHASSIS SHOULD ALSO BE CONNECTED TO THE AC MAINS AND LIGHTNING PROTECTIVE GROUND at the same point. The point here is twofold: 1) Each type of ground will have different characteristics, and 2) An RF ground need not have any relationship with what we normally conceive as 'ground' - the British commonly use a separate word - 'earthing' which I believe helps keep the distinctions separate and a bit closer to correctness - earthing is good for AC, DC and lightning grounds, but may or may not have any relationship to an RF ground. I doubt that a Ufer ground would serve as a good RF ground, although it may do so at some particular frequencies - I would want to test it before depending on it. 73, Don W3FPR > -----Original Message----- > > Hi Glenn > Seems a lot of work for a relatively simple rf ground. > Why not just take a piece of copper tubing and lay it in a shallow trench > and bond your ground wire to it? > RF doesn't penetrate the ground very far, so a deep trench wouldn't be > needed. > > Glad to see you're still around. Haven't heard you on in a while. > 73, Bob N6WG > > -----Original Message----- > > I recently up graded my house electrical panel from 100 to 200 amp > service. In order to do the up grade I had to install a Ufer ground > which was 20 feet of bare #4 copper wire in cement. Our local code > allowed a 10 foot run of wire in a U shape in a 9 inch wide trench. The > wire had to be 3 inches above the dirt 3 inches from the side of the > dirt 3 inches between the wires and three inches away from the dirt on > the other side of the trench. That allows for 3 inches of cement all > around the bare copper wire. The more I found out about Ufer grounds the > better they seem to be to me. The PH factor in the cement and the fact > that the cement never completely dries out and retains moisture make it > an excellent ground. > > This leads me to my question. Is anyone out there using a Ufer ground as > a counterpoise or to ground their tower and station? This seems way > better than the old ground rod pounded in the dirt. Any comments would > be appreciated. > > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.8.15/49 - Release Date: 7/14/2005 _______________________________________________ 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 WA7SPY
Hi Glenn,
Let me jump in here and comment. A Ufer ground is for 60 Hz and safety grounding only. It probably is not such a good RF ground, as that would depend on its wavelength relationships, ie how big is it in terms of wavelengths you use, what is it's capacitance to the dirt, what is the inductance of its embedded rebar, what is your local ground conductivity. How well are the rebar elements bonded to each other, and are they cad welded, so that rusting of tie wires holding rebars is not an issue re the resistance of the conductors? Many hams probably confuse RF ground and earth/ safety ground, (or AC grounding). They are separate issues, although the RF ground should bond, for lightning safety, to the AC ground per the National Electrical Code. (All house grounds to be bonded). A single ground rod has poor chances of being low enough inductance and high enough capacitance to be adequate for RF coupling to the earth. Its area is too small. Grounds thru an intermediate medium, as the Ufer ground is, are also not the best candidate to be an RF ground, depending on local conditions. To have a good RF reference or counterpoise, we have to have a resonant or near resonant conductor. This is usually taken to be a quarter wave of insulated conductor leading out from the chassis of the transceiver. That will lessen RF on the rig problems. This can be used and then a simple bonding of the rig to the other AC safety grounds can be used. That keeps your rig from having a greatly different voltage upon its case than the AC wiring in case of lightning. If we have a connection to a rod, it does not have a good RF earthing characteristic, because of the small area of the rod, the usually round conductor used to bond the rod, and the length of the run of conductor to the rod. The grounding (RF) conductor must not be odd multiples of a quarter wave for the band in use or you will have a high impedance possible at the rig. The goal in safety grounding for lightning mitigation is to spread out the current from a strike or surge into the earth. One such method that satisfies the 10 ohm rule for AC earth grounds is 200 feet of bare no. 10 conductor put around the building perimeter. It does not have to be buried many feet deep, for it works by area in contact with earth. Such an extensive added earth conductor would augment your Ufer ground and give you added protection by bonding to it. Depending on the local state of earth at your QTH, this may or not, be adequate for your RF ground. The compounds of the earth around you may be poor RF conductors. In those cases, you generally have to add more low inductance area to your grounding scheme. Wide flat copper is one of the best conductors to use. Plates can be buried, and multiple rods are sometimes used. Hope that distinguishes the two types of grounding you need for safety and for low RF impedance to earth. Stuart K5KVH _______________________________________________ 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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