+++++++++++++++++++++++++++++++++++++ Date: Tue, 15 May 2001 21:34:54 -0600 From: "James E. Fuller" Subject: Re: [Elecraft] Dummy Load for K2? At 09:04 PM 5/15/01, Darrell Bellerive wrote: >What are K2 owners using for a dummy load? > >I would like something that would handle the full 15 watts or so, be as >small as possible, and shielded. Would also like something that worked >up into the UHF range. I've been using a Radio Shack gizmo, part number 940-0912, http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F001%5F002%5F004%5F000&product%5Fid=940%2D0912 It seems to work very well. It's small, inexpensive, and it appears to be durable, and it gets just barely warm to the touch with a few minutes of about 10-12 watts, but it needs a BNC adapter, part number 278-120, http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F005%5F003%5F001%5F001&product%5Fid=278%2D120 A BNC 'L' is handy, also, 278-116, http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F005%5F003%5F001%5F002&product%5Fid=278%2D116 - -- Jim Fuller +++++++++++++++++++++ Date: Wed, 16 May 2001 10:57:36 -0400 From: Mark Dulcey Subject: Re: [Elecraft] Dummy Load for K2? Darrell Bellerive wrote: > > What are K2 owners using for a dummy load? > > I would like something that would handle the full 15 watts or so, be as > small as possible, and shielded. Would also like something that worked > up into the UHF range. I use a Radio Shack 21-506. It's a little black cylinder, about 2 inches long and 1.25 inch in diameter, with lots of fins and a PL-259 connector on the end. (No, they don't have a version with a BNC, so you'll need an adapter.) Rated to 15w continuous use (and up to 100W for 30 seconds), DC-500MHz. They don't sell them in the stores any more, but radioshack.com still lists something similar-looking (same appearance and ratings) as catalog number 940-0912, RSU# 11269479, which sells for $21.95. Search for "dummy" on their site to find it. > Any kits on the market? Commercial units? > > I have thought about sandwiching a bunch of resistors between 2 PC > boards, but am a little concerned about capacitive effects of the PC > boards and the enclosure, and heat dissipation. That approach can certainly work at the QRP level - or even the 100W level, if you use LOTS of resistors. The ARRL has published a number of dummy load projects that work that way. You want to use metal oxide resistors; they're evidently the least reactive of the readily available types of resistor. Oak Hills Research (http://www.ohr.com) makes a 100W dummy load kit, the RFL-100, that uses the lots-of-resistors approach. It's rated for use through 144MHz. It sells for $34.95. If you want a ready-made dummy load for that power level, there is the MFJ-260C, which also sells for $34.95. MFJ sells it as a 300W load, but that's only for 5 minutes, whereas the OHR load rating is for continuous use, so they can probably both actually handle about the same amount of power. Down at the milliwatt level, you can use a thin Ethernet terminating resistor. They're usually built with 1/2 watt resistors; they should be able to handle 1W for a little while. - -- Mark J. Dulcey mark at buttery.org Visit my house's home page: http://www.buttery.org/ Visit my home page: http://www.buttery.org/mark/ +++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 16 May 2001 09:49:03 -0700 From: Kevin Swesey Subject: RE: [Elecraft] Dummy Load for K2? I use a 10-watt MOX resistor bought at RS for a buck or so soldered across a BNC panel mounted jack for my K1. Kevin Swesey, K6RXL K1 #474 kevin.swesey at sigtech.com ++++++++++++++++++++++++++++++++++++++ Date: Tue, 05 Jun 2001 15:29:41 +0000 From: Darrell Bellerive Subject: [Elecraft] Re: Dummy Load for K2? Follow-up Thanks to all who answered my question; There were many! Thought I would post a quick summary for anyone else who may have the same question. The most recommended choice was to build my own. Seems not too difficult a project. Some very interesting designs! The most recommended commercial solution was the Radio Shack dummy load (stock number 940-0912 at http://www.radioshack.com.) Also suggested was the Ethernet terminating resistors in a BNC case. The only kit suggested was from Oak Hills Research (http://www.ohr.com) for a 100W dummy load kit, the RFL-100. I ended up buying two dummy loads, a Diamond Antenna DL-30A and a Workman DL-52. The Diamond is similar in appearance to the Radio Shack unit. It can handle 15 watts continuously and 100 watts for 30 seconds. It is also spec'd to 500 MHz. The Workman is a 5 watt dummy load built into a PL-259 connector. If anyone wants details please email me directly. Darrell VE7CLA K2 #1973 Darrell Bellerive wrote: > > What are K2 owners using for a dummy load? > > I would like something that would handle the full 15 watts or so, be as > small as possible, and shielded. Would also like something that worked > up into the UHF range. > > Any kits on the market? Commercial units? > > I have thought about sandwiching a bunch of resistors between 2 PC > boards, but am a little concerned about capacitive effects of the PC > boards and the enclosure, and heat dissipation. > > Ideas? > > Thanks! > > Darrell > VE7CLA > K2 #1973 ++++++++++++++++++++++++++++++++++++++ Date: Mon, 02 Jul 2001 14:55:39 -0400 From: "Mark J. Dulcey" Subject: Re: [Elecraft] dummy load freddybrown at juno.com wrote: > > What are the pros and cons for using a 15-25 watt incandescent lightbulb > as a dummy load to align the K2 transmitter? Although light bulbs were popular as dummy loads in the old days, it is no longer a recommended practice. 1. Light bulbs are not a good 50 ohm match. It didn't matter to tube rigs with tuned outputs, but modern broadband solid state finals don't like them. 2. Light bulbs are not shielded, and can radiate a significant signal. They can cause interference to other spectrum users, and possibly earn you a pink slip if you generate a signal outside the ham bands, as you might if your rig isn't fully aligned yet. People have made contacts using light bulbs as antennas. The bottom line: use a proper dummy load. Some suitable QRP recommendations: the small Radio Shack load (not in stores, but available from radioshack.com), the dry MFJ and Vectronics loads (I've heard bad reports on their oil-cooled Cantenna clone), the Oak Hills Research kit. ARRL publications have printed plans for making your own low-to-medium power load, using multiple resistors. At milliwatt power levels, you can use a Thin Ethernet terminator, but it's not up to handling full output from your K2. ++++++++++++++++++++++++++++++ From: "Don Brown" To: , "'Andrey Stoev'" , Date: Thu, 7 Nov 2002 13:37:02 -0600 Subject: [Elecraft] Re: [Elecraft]Yet another Dummy Load Idea Hi I built a dummy load by mounting a chassis mount BNC on a large fender washer. Then I connected 4 51 ohm resistors in series parallel. (you could also use three 5 watt 150 ohm resistors in parallel which would be better) In other words make 2 sets of parallel connected resistors then connect the parallel resistors in series. I used 3 watt MOS resistors because they are non inductive. Connect one end to the center pin of the BNC and run the other end down to the washer and solder close to the BNC. Then I slipped the the assembly into a piece of 3/4 inch schedule 40 PVC pipe about 3 or 4 inches long. Now fill the pipe with GE silicone rubber II and allow to set up overnight. This makes a convenient load and it is good to 15 watts or 25 to 30 for a short time. The silicone forms a heatsink so the resistors will dissipate a little more than their rating. I have one of the Radio Shack loads but the home made on works just as will and you don't need a PL-239 to BNC adapter Mouser P/N for 5 watt 150 MOS resistor is 286-150 or 51 ohm 3 watt is 283-51 Don Brown KD5NDB ----- Original Message ----- From: "Ron D'Eau Claire" To: "'Andrey Stoev'" ; Sent: Thursday, November 07, 2002 12:59 PM Subject: RE: [Elecraft] Dummy load for Part III > Andrey, it sounds like a dummy load I built many years ago using 2 watt > 'composition' resistors (not made any longer) for my Viking Ranger. > Worked FB. Your choice of metal film is the key here from what I > understand. > > The "proof" is easy to test. Check the VSWR of your dummy load. If it's > reasonably low up through the highest frequency you want to use, you're > in business. For the K2 that means 1.5:1 or better is fine. Maybe even > 2:1 although that's the limit of the acceptable SWR range without > matching if I recall correctly. > > For ops looking for a pre-built dummy load, Radio Shack does make a > nifty little factory-built dummy load. I bought one 15 years ago to use > checking VHF radios on ships. It's round, about 1.5 inch in diameter > (mostly black cooling fins) and about 2.5 inches long with a male SO-239 > coax connector built in one end. It's rated for 15 watts and will handle > that easily for longer than one should hold the key down on the K2 at > that power level. The stores don't carry them any longer, but I know a > fellow who bought one on-line from Radio Shack not too long ago. They're > about US $20. > > Ron AC7AC > K2 # 1289 +++++++++++++++++ To: elecraft at mailman.qth.net Date: Thu, 7 Nov 2002 13:57:24 -0800 Subject: Re: [Elecraft] Dummy load for Part III From: k6se at juno.com Audrey Stoev wrote: "The dummy load is build from the T-Connector, using 20 pieces of 1/2 W 1kOm Resistors." ========== A couple of years ago I needed a low power 50-ohm load to dissipate any reflected power on one of the ports on the hybrid coupler phasing unit I built for my 160m phased array. I used twenty 1000-ohm 2-watt 5% carbon-film resistors purchased from Mouser. I sandwiched the resistors between two small (about 2" x 2") pieces of perfboard, soldered the resistors together and (happily) measured 50.0 ohms for the parallel combination of the twenty resistors. I added an SO-239, and voila - a 50-ohm, 40-watt dummy load (I recommend that the key-down power you apply should not exceed 20 watts to carbon-film resistors). This dummy load, which has a 1:1 SWR from .5 kHz to 30 MHz (as measured by my Autek RF-1), came in very handy when aligning my K2. 73, de Earl, K6SE +++++++++++++++++ From: "Don Brown" To: , "Jeremiah J McCarthy" Subject: Re: [Elecraft] Dummy load Date: Fri, 8 Nov 2002 21:29:59 -0600 Hi Carbon comp resistors are getting scarce especially the 2 watt type but you can use MOS resistors. They are non inductive and more accurate than the carbon comp resistors. They are available in 1, 2, 3 and 5 watt sizes. Something else you may want to consider for a dummy load are the Ohmite TO-220 resistors. These resistors are in the the same package as a TO-220 transistor and are rated at 35 watts when mounted to a heatsink of the proper size. You could mount 3 150 ohm resistors to a heatsink and wire them in parallel for over 100 watts They are about $6 each. Don Brown KD5NDB ----- Original Message ----- From: "Jeremiah J McCarthy" To: Sent: Thursday, November 07, 2002 10:56 PM Subject: [Elecraft] Dummy load > Popular Electronics published an article in 1970 on how to build a dummy > load into a paint can ala the Heathkit Cantenna...Very simply it > consisted of 2 large copper washers, a short length of 1/2" copper pipe, > and ten 510 ohm, 2 watt composition resistors soldered in parallel > between the two copper washers, which were drilled to accept the resistor > leads...A PL-259 was mounted in the center of the paint can lid and the > pipe/washer/resistor assembly was soldered to and suspended from the > bottom the PL-259...This assembly was immersed in transformer or mineral > oil in the can, raising the power handling from 20 watts to 200 watts...I > built one of these and still use it, although I made mine with twenty > 1000 ohm resistors, making it capable of 400 watts...In those days I was > running Drake Twins, rated at 200 watts PEP, and never heated the oil... > > I recently saw a variety of 2 watt composition resistors at a flea > market... > > Jerry, wa2dkg > K2 #2549 ++++++++++++++++ Date: Wed, 27 Nov 2002 20:18:15 -0700 From: Larry Benko To: Jeff Burns Cc: elecraft_list Subject: Re: [Elecraft] Cantenna vs. Oak Hills Research RFL-100 Jeff, If you want a quality dummy load for 100W I would look at the surplus ones used in the cell phone industry. I see them all the time at hamfests for $15 to $25. They look like a heatsink that is about 3"x3"x8" and always have an N connector on the end. I bought several a year or so ago and made some measurements on them. I don't know what the ratings are but they will take 100W forever and get barely warm. Better yet they actually look like 50.0 ohms. Measurements made on a $40K Agilent network anaylzer shows SWR less than 1.02 thru 200MHz and 1.1 at 1 GHz. They have absolutely no liquid inside them so spillage is no problem. Any dummy load kit which actually may measure 50.0 ohms is very likely to be slightly reactive. Not really a big deal but these other dummy loads are definitely superior. You will need to buy a N to UHF adapter. 73, Larry, W0QE Jeff Burns wrote: > I have a Heath Cantenna HM-31-A RF load resistor I purchased when I built my > K2. To do the K2 alignment I ended up using a network-terminating resistor > instead because the Cantenna measured 52 ohms at DC. > > Now I am thinking of getting a KPA100. To use the Cantenna at 100W I suppose > I need to put some oil in it. The thought of keeping an oil filled can for > just a 100w rig does not excite me much. Especially with a two year old in > the house. I am thinking of selling the Cantenna and getting a the Oak Hills > Research RFL-100. > > Any comments on the Oak Hills RF load? Am I being short sited moving down in > power handling capability? > > Jeff Burns > AD9T +++++++++++++++ From: "COLIN WHITMORE" To: Cc: "Elecraft" Subject: RE: [Elecraft] 50 Ohm Dummy Load Date: Fri, 16 May 2003 05:56:26 -0600 Daniel, You can build up your own QRP dummy load with a couple of 5 Watt 100 ohm = resistors in parallel. Alternatively, you can go to the Colorado QRP webs= ite (http://www.cqc.org/cqc_shop.htm) and order their QRP dummy load kit.= It's designed using an 20-239 connector and comes with both, an SO-239 a= nd, a BNC adapter. It's a nice small package and made for taking with you= into the field. Also, look in about any ARRL Handbook and I'm almost sur= e they'll have a dummy load project that'll fit your needs. Cheers, Colin N0YGY From: Daniel Reynolds I'm working on the ATU and read ahead last night and discovered that I'll= need a 50 Ohm dummy load. Up til now, I've used test equipment at work, but it= seems like I really ought to have a QRP dummy load. Thanks for your help (I know I'll get a few answers), - Daniel/AA0NI ++++++++++++++++