Re: Topband: Stainless Steel for coil taps.
On 11/16/2020 7:58 AM, Wes wrote: Nickel is not OK. I could tell a war story about gold plating over a nickel barrier where the plating shop skimped on the gold. Wes N7WS On 11/16/2020 4:05 AM, Rob Atkinson wrote: EF Johnson and perhaps others used steel nuts and bolts that were plated with nickel. I have a war story to tell: HP used to have pretty gold plated PC boards, which of course had the obligatory nickel barrier. I was the project manager for the HP5334B frequency counter, which was a cost lowered version of the 5334A model that used gold plated boards. By the time of the B model, HP was doing all new products in "Solder Mask Over Bare Copper" (aka SMOBC). No gold or nickel. I had the front end section of the 5334A PC board leveraged to use in the 5334B. Exact same schematic and layout. Only difference was the SMOBC process. Upon turn on of the first SMOBC board, I was not especially surprised to find out that the front end circuits now oscillated because the lossy PC board containing nickel was replaced with just copper. I had to add back in some loss with damping resistors to make it stable. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
I use a zinc ground clamp on each tower leg to attach the tinned #4 solid copper ground wires. N2TK, Tony -Original Message- From: Topband On Behalf Of Steve London Sent: Monday, November 16, 2020 10:58 AM To: Topband Subject: Re: Topband: Stainless Steel for coil taps. Tower leg ground clamps all have stainless steel between the tower and the copper strap. Seems like the lower conductivity of stainless could be a huge issue during a lightning event. Yet, I haven't heard of this being an issue. 73, Steve, N2IC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
> Rob, are you implying that I shouldn't use a steel lattice tower to conduct > RF as a radiator? Good question and I wondered the same thing. Firstly not "implying" that at all. It comes down to mass and surface area. The problem with steel, iron, etc. is when you have a lot of RF current over a small area like a narrow piece of steel strap or a steel nut, bolt and washer. The surface area of a tower is so big that it doesn't present the same amount of problem. 73 Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps
Roger, I have gone through the school of hard knocks on alligator clips, especially as my home station went from 100W to making major efforts at legal limit RTTY contests. While the BU-27C end serrations are great for 10-14AWG copper wire, I would like to add that the BU-27C also has a lipped stretch that is good for 1/4" copper tubing. I think copper clips do help dissipate any heat generated at the interface point. So it's not just electrical conductivity that helps power handling, it's also the thermal conductivity. I will also say that I am mystified at those here who think that steel has some incompatibility with RF circuits. For example all of my old-school EF Johnson/etc tuning capacitors use steel rods/threaded-rod as the backbones, and most all ring lugs are plated steel. Tim N3QE On Mon, Nov 16, 2020 at 10:32 AM Roger Parsons via Topband < topband@contesting.com> wrote: > Tim N3QE wrote: > > "I would recommend something different for coil tapping for a 10AWG coil: I > am a big fan of the Mueller BU-27C copper clip, rated for 40A DC. If you > are going onto thick copper tubing, Mueller the BU-27CGW (the "geophone > clip") works well." > > I really wish I had known about these years ago! > > 73 Roger > VE3ZI > > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
Nickel is not OK. I could tell a war story about gold plating over a nickel barrier where the plating shop skimped on the gold. Wes N7WS On 11/16/2020 4:05 AM, Rob Atkinson wrote: We all learn this sooner or later: Don't use ferrous metals to conduct RF. If a metal fails the magnet test, it's out. Every time I get some item of homebrew or something that's had a previous owner, (transmitter or matching network) I go through with a magnet and see if a previous owner or builder used steel around RF stages or matching networks. Some steel alloys may be better than others but it's impossible to tell, so out they go. Brass, copper, aluminum, silver, nickel all okay. EF Johnson and perhaps others used steel nuts and bolts that were plated with nickel. That's okay as RF current has the skin effect. What's wrong with ferrous metals? They don't conduct as well but more important, at the microscopic level, they vibrate at the RF frequency. This does two things: Generate heat, and slowly loosen clamp, as in the case of a nut, bolt and washer for example. Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
Tower leg ground clamps all have stainless steel between the tower and the copper strap. Seems like the lower conductivity of stainless could be a huge issue during a lightning event. Yet, I haven't heard of this being an issue. 73, Steve, N2IC _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps
Tim N3QE wrote: "I would recommend something different for coil tapping for a 10AWG coil: I am a big fan of the Mueller BU-27C copper clip, rated for 40A DC. If you are going onto thick copper tubing, Mueller the BU-27CGW (the "geophone clip") works well." I really wish I had known about these years ago! 73 Roger VE3ZI _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
I agree Rick.. Too “clever” but just enough to fool me.. once. After I get the new coil ready (Using brass hardware to replace the stainless bolts also) and find the sweet spot again using the proper coil clips, I will SOLDER the clips onto the copper at that time without shorting out any other coil turns. Since this is a series coil at the base, I will use a shunt coil to match the swr.. I hope that is what I am going to do and not blow up something else . From: Richard (Rick) Karlquist Sent: Monday, November 16, 2020 10:02 AM To: Tim Shoppa; Larry-k1uo Cc: topband@contesting.com Subject: Re: Topband: Stainless Steel for coil taps. I _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
I need to correct some misconceptions: On 11/16/2020 6:24 AM, Tim Shoppa wrote: Conductivity of Copper: 5.85 x 10^7 mho/m Conductivity of 301 Stainless: 0.14 x 10^ mho/m Stainless is 42 times worse conductor than copper. 1. Because of skin effect, the surface resistance is inversely proportional to the SQUARE ROOT of the conductance at RF. There, in the calculation above, the square root of 42 should have been used. 2. But that would still be incorrect because any magnetic material will have additional loss at RF above and beyond mere RF skin effect. This loss is difficult to quantify but should be assumed to be substantial. [BTW, does anyone know if so-called "non magnetic" stainless steel is free of this effect at RF by virtue of not being attracted to a magnet?] There was also some mention to the effect that nickel was a "non-ferrous" metal and therefore would be good at RF. Nothing could be further from the truth. Although technically "non-ferrous", nickel is nevertheless "ferromagnetic". I once measured some nickel strap material for RF loss and it was horrific. Much worse than even what its DC resistivity would suggest. An additional factor with various stainless steels is that some alloys naturally form an oxide layer, along the lines of aluminum. I can easily imagine wrapping a stainless clamp around copper tubing and have high contact resistance on account of this. This is no mechanism for puncturing the oxide and forming a gas tight seal like you would have in a crimped connection. IMHO, this is the more likely reason for the pyrotechnics. My conclusion is that the technique is in the "too clever by half" category. 73 Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
@Tim, For the sake of my “experiment” I was indeed using the band clamp to hold a small aluminum eyelet soldered onto#14 wire for the tap wire. The wire used for the coil is solid copper 10 gauge wire. I found some clips that would work up to #10 wire at DX engineering called coil clips if you are looking. I believe after I rebuild a coil and tap it “properly” that things will indeed work ok. Not top dog ok but Home Owners Association ok. Thanks all for both private and public help with suggestions and helpful information for this old guy… aren’t we all. From: Tim Shoppa Sent: Monday, November 16, 2020 9:25 AM To: Larry-k1uo Cc: topband@contesting.com Subject: Re: Topband: Stainless Steel for coil taps. Conductivity of Copper: 5.85 x 10^7 mho/m Conductivity of 301 Stainless: 0.14 x 10^ mho/m Stainless is 42 times worse conductor than copper. Larry, was the band clamp holding a copper conductor onto the coil, or was the band clamp actually being relied on for conductivity. If current was being carried by the hose clamp: Typical 301 stainless band clamp (say one that will accomodate both 1/2" and 3/4" tubing) is .023" thick by 5/16" wide. For an area of 0.007 square inches carrying the current. Because copper is 42 times better conductor, a equivalent copper conductor would be just a little more than 0.00017 square inches. So that stainless band clamp is a worse conductor than AWG 26 copper wire. The tables list 26AWG as having an ampacity of 0.36A. So even at 100W and 50 ohms you are past the limit. Go to legal limit and 50 ohms and you are way past. Go to a high Q circuit and you are way way past. I would recommend something different for coil tapping for a 10AWG coil: I am a big fan of the Mueller BU-27C copper clip, rated for 40A DC. If you are going onto thick copper tubing, Mueller the BU-27CGW (the "geophone clip") works well. Tim N3QE On Sun, Nov 15, 2020 at 6:40 PM Larry-k1uo wrote: Probably everyone but me knew or knows this but it seems it is NOT a good idea to use stainless steel band clamps as coil taps. Especially on a large 160M Base coil. Oh well…. The ss band only got red hot and caused the #10 wire coils underneath it to melt into the pvc form and did not start a fire at least. Regards Larry K1UO _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
Conductivity of Copper: 5.85 x 10^7 mho/m Conductivity of 301 Stainless: 0.14 x 10^ mho/m Stainless is 42 times worse conductor than copper. Larry, was the band clamp holding a copper conductor onto the coil, or was the band clamp actually being relied on for conductivity. If current was being carried by the hose clamp: Typical 301 stainless band clamp (say one that will accomodate both 1/2" and 3/4" tubing) is .023" thick by 5/16" wide. For an area of 0.007 square inches carrying the current. Because copper is 42 times better conductor, a equivalent copper conductor would be just a little more than 0.00017 square inches. So that stainless band clamp is a worse conductor than AWG 26 copper wire. The tables list 26AWG as having an ampacity of 0.36A. So even at 100W and 50 ohms you are past the limit. Go to legal limit and 50 ohms and you are way past. Go to a high Q circuit and you are way way past. I would recommend something different for coil tapping for a 10AWG coil: I am a big fan of the Mueller BU-27C copper clip, rated for 40A DC. If you are going onto thick copper tubing, Mueller the BU-27CGW (the "geophone clip") works well. Tim N3QE On Sun, Nov 15, 2020 at 6:40 PM Larry-k1uo wrote: > Probably everyone but me knew or knows this but it seems it is NOT a good > idea to use stainless steel band clamps as coil taps. Especially on a > large 160M Base coil. Oh well…. The ss band only got red hot and > caused the #10 wire coils underneath it to melt into the pvc form and did > not start a fire at least. > Regards Larry K1UO > > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
Rob, are you implying that I shouldn't use a steel lattice tower to conduct RF as a radiator? For coil taps, I like to solder. Luke VK3HJ On 16/11/2020 10:05 pm, Rob Atkinson wrote: We all learn this sooner or later: Don't use ferrous metals to conduct RF. If a metal fails the magnet test, it's out. Every time I get some item of homebrew or something that's had a previous owner, (transmitter or matching network) I go through with a magnet and see if a previous owner or builder used steel around RF stages or matching networks. Some steel alloys may be better than others but it's impossible to tell, so out they go. Brass, copper, aluminum, silver, nickel all okay. EF Johnson and perhaps others used steel nuts and bolts that were plated with nickel. That's okay as RF current has the skin effect. What's wrong with ferrous metals? They don't conduct as well but more important, at the microscopic level, they vibrate at the RF frequency. This does two things: Generate heat, and slowly loosen clamp, as in the case of a nut, bolt and washer for example. Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Stainless Steel for coil taps.
We all learn this sooner or later: Don't use ferrous metals to conduct RF. If a metal fails the magnet test, it's out. Every time I get some item of homebrew or something that's had a previous owner, (transmitter or matching network) I go through with a magnet and see if a previous owner or builder used steel around RF stages or matching networks. Some steel alloys may be better than others but it's impossible to tell, so out they go. Brass, copper, aluminum, silver, nickel all okay. EF Johnson and perhaps others used steel nuts and bolts that were plated with nickel. That's okay as RF current has the skin effect. What's wrong with ferrous metals? They don't conduct as well but more important, at the microscopic level, they vibrate at the RF frequency. This does two things: Generate heat, and slowly loosen clamp, as in the case of a nut, bolt and washer for example. Rob K5UJ _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: Stainless Steel for coil taps.
I found some small aluminum coil taps at DX Engineering I will try on the #10 solid copper coil wire I am using so as not to short multiple turns this time. The ss band clamp thing I saw on uTube (lol) but obviously he was not running 1500 watts and, with me not having tried to load an 80M vertical for 160 before, I bought it hook, line and sinker. At 72 I hate asking for help. The schedule 40 pvc form is 3.5 in OD with 35 turns of #10 wire spaced ¼ in so 4 turns per inch. I assume because the Band clamp was shoring multiple turns was what started the heating process early? I don’t know for sure but I am winding another coil as I had the machine shop make me an extra form. I terminate the #10 solid copper wire at each end of the form with a 1/1 inch stainless bolt. Hopefully I am on the right track to get back on 160M with something that the HOA wont ban me for. Thanks to all. Larry K1UO From: Roy Morgan Sent: Sunday, November 15, 2020 10:16 PM To: Larry-k1uo Cc: topband@contesting.com Subject: Re: Topband: Stainless Steel for coil taps. L _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
