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#11
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Earth rods, etc
On Fri, 7 Sep 2018 09:21:15 +0100
"Jim GM4DHJ ..." wrote: On 9/7/2018 9:06 AM, Stephen Thomas Troll wrote: On Thu, 6 Sep 2018 18:14:51 +0100 Gareth's Downstairs Computer wrote: On 06/09/2018 17:22, Jeff Liebermann wrote: On Thu, 6 Sep 2018 14:46:33 +0100, Gareth's Downstairs Computer wrote: Interesting because between the house TT earth, a steel rod and the copper RF earth is now about 0.4 volts, making the ohmmeter go haywire trying to measure the resistance between them. That's only true if there's an electrolyte between the copper and steel. When bonded together, there's no galvanic action or voltage. If you're using two or more ground rods, all electrical codes specify that they need to be connected together with some heavy gauge wire. Separate RF earths to reduce noise on RX and protect family members from RF hazard if touching central heating radiator 1/4 wavelength away. Gareth, get some double glazing, Gareth, that would stop them huddling around the radiators, Gareth. Gareth, Thanks, Gareth. I had a radiator that rusted through....just thought you would like to know that .... Jimbore, too tight to buy inhibitor, Jimbore? Jimbore, Thanks, Jimbore. |
#12
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Earth rods, etc
"Stephen Thomas Troll" wrote in message ... On Fri, 7 Sep 2018 09:21:15 +0100 "Jim GM4DHJ ..." wrote: On 9/7/2018 9:06 AM, Stephen Thomas Troll wrote: On Thu, 6 Sep 2018 18:14:51 +0100 Gareth's Downstairs Computer wrote: On 06/09/2018 17:22, Jeff Liebermann wrote: On Thu, 6 Sep 2018 14:46:33 +0100, Gareth's Downstairs Computer wrote: Interesting because between the house TT earth, a steel rod and the copper RF earth is now about 0.4 volts, making the ohmmeter go haywire trying to measure the resistance between them. That's only true if there's an electrolyte between the copper and steel. When bonded together, there's no galvanic action or voltage. If you're using two or more ground rods, all electrical codes specify that they need to be connected together with some heavy gauge wire. Separate RF earths to reduce noise on RX and protect family members from RF hazard if touching central heating radiator 1/4 wavelength away. Gareth, get some double glazing, Gareth, that would stop them huddling around the radiators, Gareth. Gareth, Thanks, Gareth. I had a radiator that rusted through....just thought you would like to know that .... Jimbore, too tight to buy inhibitor, Jimbore? Jimbore, Thanks, Jimbore. it was at the van and the previous owner didn't even have anti freeze in it never mind inhibitor....no big deal the rad was £20 at screwfix..... |
#13
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Earth rods, etc
On 9/6/2018 5:46 AM, Gareth's Downstairs Computer wrote:
Unearthed the previous fan of plumbers' copper microbore tubes and associated ground rod to find a corroded and non conductive mess and raised the question of how to protect underground junctions from the worst that nature could throw at them? Firstly, resurrecting a technique from school metalwork lessons from 53 years ago when brazing things together, dig out the gas torch, soldering flux***** and solder and connect all together electrically. Secondly, to protect the now-relatively-massive joint, smear with petroleum grease. Was this a good idea, and is there something better? ***** Curious as to whether could be combined with one's radio interest to nake a flux capacitor to go time travellingg :-) I don't know how to protect it, I recently installed ground rods and figure to periodically test them and replace as needed. I ran a 253ft BOG antenna, I needed a ground at each end. I started with 1-five ft 1/2" copper pipe, with predrilled 1/8" hole running down and around the pipe. I used the method on page 25 of this pdf to measure the ground resistance. http://www.weschler.com/_upload/site...owntoearth.pdf I had a pair of wires ran from my home to each end of my BOG antenna so it was convenient to connect it to a variac driven by an isolation transformer. I used that as my voltage source*. I set it at about 40V, but measured the voltage at the ground rods for calculations, because of the voltage drop of the feed wire. My first measurement was 112 ohms, both ends 253 apart were basically the same even though I had 3 rods at one end and 1 rod at the other. I added 2.5lbs of Calcium Chloride at one end by pouring the water/Calcium Chloride solution into the three copper pipe ground rods. After a few hours a retest showed a drop from 112ohms to 73 ohms. The next day it was down to 60 ohms. About a week later I added another 3.5lbs of the Calcium Chloride solution into the copper pipes, this brought the resistance down to 34 ohms. I added 2 more rods to the other end and added more Calcium Chloride, that brought the end down to 24 ohms. The measurement at one end 22.35V and 660ma for 33.9 ohms. The other end 13.14v and 580ma for 23.9 ohms. Lower voltage because my 240ft feed line was a much smaller gauge and had more voltage drop. * I know 60hz drive voltage is not ideal but, I didn't have a signal generator with enough power do the job. http://www.esgroundingsolutions.com/...stance-meters/ There are some papers saying DC better to measure earth ground, I don't know. |
#14
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Earth rods, etc
On 9/6/2018 8:46 AM, Gareth's Downstairs Computer wrote:
On 06/09/2018 13:59, Rambo wrote: On Thu, 6 Sep 2018 11:46:55 +0100, Gareth's Downstairs Computer wrote: Unearthed the previous fan of plumbers' copper microbore tubes and associated ground rod to find a corroded and non conductive mess and raised the question of how to protect underground junctions from the worst that nature could throw at them? Firstly, resurrecting a technique from school metalwork lessons from 53 years ago when brazing things together, dig out the gas torch, soldering flux***** and solder and connect all together electrically. Secondly, to protect the now-relatively-massive joint, smear with petroleum grease. Was this a good idea, and is there something better? ***** Curious as to whether could be combined with one's radio interest to nake a flux capacitor to go time travellingg :-) cathodic protection? Interesting because between the house TT earth, a steel rod and the copper RF earth is now about 0.4 volts, making the ohmmeter go haywire trying to measure the resistance between them. Yet another ground to contend with is whatever may come with a cable TV connection. (Sorry for my ignorance, I am not sure how to translate for the other side of the Atlantic! In the US we typically have a 75 ohm coax coming in for this purpose.) At another residence I had about 3 volts between that ground and the ground for AC power. When I connected the coax to an FM tuner in the music system, to play an FM station that was carried at baseband, that put 3 volts between the tuner's antenna connection and its power connection (until I eventually put in some isolation...) There was a lot of hum out of the system with a 300 watt audio amp feeding the speakers! Bob Wilson, WA9D |
#15
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Earth rods, etc
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#16
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Earth rods, etc
On 09/09/2018 22:32, Bob Wilson wrote:
... There was a lot of hum out of the system with a 300 watt audio amp feeding the speakers! Somewhat reminiscent of the opening sequence in one of the Back To The Future films! Or, going back some years to the April Edition of Wireless World and the article by the Dutchly-named George Izzard O'Veering. |
#18
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Earth rods, etc
Bob Wilson wrote:
Yet another ground to contend with is whatever may come with a cable TV connection. (Sorry for my ignorance, I am not sure how to translate for the other side of the Atlantic! In the US we typically have a 75 ohm coax coming in for this purpose.) At another residence I had about 3 volts between that ground and the ground for AC power. A modern cable TV demarcation point has galvanic isolation. With a TV there usually is no problem because it usually has galvanic isolation in its input circuit as well (some ferrite bead transformer between the input and the tuner). For radio tuners that may be different. |
#19
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Earth rods, etc
On Fri, 7 Sep 2018 09:37:53 -0500
amdx wrote: I ran a 253ft BOG antenna, What DX did you hear with it and on what band(s)? -- Mouse. Where Morse meets House. |
#20
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Earth rods, etc
On 9/10/2018 3:19 PM, A. non Eyemouse wrote:
On Fri, 7 Sep 2018 09:37:53 -0500 amdx wrote: I ran a 253ft BOG antenna, What DX did you hear with it and on what band(s)? I ran it for the AMBCB. It was clearly directional. I'm in the Panhandle of Florida and I pointed it North. It is a quiet antenna and the best of the 3 antennas I have. I suspect It will work well on 160 and 80 meters, but My R-71A has a SSB problem and until I fix that, I can't check. Mikek |
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