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how to make a 50 ohm dummy load

In practice, they are never perfect. Matt shares with us his build of a fantastic looking dummy speaker load box. For example if I use a 4 ohm resistor in the 4 ohm out, how would it compare to a 16 ohm resistor in the 16 ohm … Fast & … Cellwave's dummy load CL150 (150 W/1 GHz). Coils have the property of inductance, and inductance leads to inductive reactance, which will prevent the dummy load from being a 50 ohm load at RF. A large part of the much heavier Bird 43 clone is heatsink and this results that with coax connections it will move a lot less on my desk. Here is another method to assemble the 150 W resistor induction free as possible. I don’t have a 50 ohm dummy load Power measurements require a dummy load. As a result I am using this wattmeter a lot and the original Bird 43 is only used for the calibration of other equipment. In the grand tradition of finding what other hams have done and sticking with that, I built a version of a dummy load that K7AGE built, which in turn is a design he borrowed from Elecraft, a maker of kits for transceivers and other ham gear. The attenuator with the spectrum analyzer at its other end, is playing the part of 50-ohm load. Dummy load with a 50 Ω stripline (hybrid) resistor. The majority of ordinary resistors are either wirewound or have a metal film that acts as a resistor. Get an 8ohm resistor that matches your amp's output wattage (i.e., 100 watts? It shows how the RF is prevented from leaking out and how a cover, the size of the hole through the heatsink and a Z-shaped 'cover' (fig») are maintaining a 50 Ohm impedance. One thing to remember is that one tighten the screws on a transistor or a hybrid resistor far too much. Place the two resistors side by side and twist the leads together. Thick film resistors (e.g. Use a real 50-Ohm dummy load - they're cheap and far better on many levels. This ma. This makes it possible to make all connections coaxial and very short, thereby reducing the inductance and capacitance. A useful shack accessory, this is a simple 50-ohm 20W dummy load kit using 20 individual 1K resistors in parallel. After constructing an AMP6 T-Amp kit, and while testing the maximum power output using 4.7 ohm 50W ceramic power resistors the hot resistors had begun to scortch a cutting mat they were resting on and also melting the wire insulation of test leads which had fallen on one of the … The thin gold plated tab needs to be connected in such a way that it will allow for expansion when the resistor heats up. 1998-document.write(new Date().getFullYear()) The DXZone.com - Terms of Use, Copyright & Privacy Policy, [ Hits: 5729 | Votes: 7 | Rating: 7.28 ], [ Hits: 1831 | Votes: 3 | Rating: 8.67 ], [ Hits: 11448 | Votes: 20 | Rating: 6.2 ], [ Hits: 7310 | Votes: 8 | Rating: 5.75 ], [ Hits: 7618 | Votes: 7 | Rating: 7.43 ], [ Hits: 1695 | Votes: 6 | Rating: 6.83 ], [ Hits: 1131 | Votes: 3 | Rating: 9.67 ], [ Hits: 6750 | Votes: 9 | Rating: 6.55 ], [ Hits: 4660 | Votes: 14 | Rating: 6.43 ], [ Hits: 4326 | Votes: 9 | Rating: 7.22 ]. Those examples to my eyes looked like a complete mess. 0 - 500 MHz (500 MHz SWR < 1.3), continue 800 W on a suited heathsink (1500 W PEP short period). It is interesting to discover that independently of each other a number of hams have come up with an almost the same way of making a dummy load. The circuit for a dummy load is stupid (heh) simple - it's literally just a 50-ohm resistor across the antenna connector's inner conductor and shield. ), get mono RCA jack and an enclosure, wire it together, plug it into the 2nd speaker output of your amp, and you're done. Since each resistor can handle three watts, the dummy load will handle six watts. It uses a number of non-inductive resistors in parallel to achieve 50 Ohms over a wide frequency range. The tap off point provides a means to connect a spectrum analyser or second receiver to monitor and set up the transmitter and also the means to measure power. MOTOROLA 58C9860F01 Dummy Load Termination 500W 50 Ohm DC - 1GHz RF RM250-100 4.5 out of 5 stars (5) 5 product ratings - MOTOROLA 58C9860F01 Dummy Load Termination 500W 50 Ohm DC - … For measuring power dissipated by a dummy load, you can use a simple RF-probe and a DVM. Salt water dummy load. An attempt to make a de cent 600 W/50 Ω dummy load («fig) by using 4 × 50 Ω/150 Watt resistors for HF failed. Be careful bending/handling the tab because it is breaks easy. I made my dummy loads simply by using 1 ohm 17W resistors, wired in series parallel across tag strips - with plenty of air spacing. Ref. At the left a homebrew Bird clone with build in 150 Watt (hybrid) dummy load and at the right a genuine Bird 43. Normally these are a ceramic disc attached to a silvered copper-mounting strip. Some of them being of gigantic measurements, some of them are even drowned in even vegetable oil for extra thermal capacity. TMC050 wire wound power resistors from Vishay mounted to heatsinks to increase power dissipation are used for the load. Figure 2 - Thick Film Resistor Figure 1 - Compact Dummy Load R3 4.7k R1 100 R2 100 SO 239 BNC Figure 3 - Circuit diagram within 1½ - 3% of 50 ohms; SWR is less than 1.03; Couldn't ask for anything more!I have run the dummy load for several minutes with my transceiver at 100 W (its max power), and there was absolutely no noticeable rise in temperature of the can. The circuit for L’il Dummy is hardly worth a schematic – it’s just an SMA jack with a 50-ohm resistor across the outer ground and the inner conductor. 50 watts? Generally the higher the wattage rating of the resistor the more power the dummy load can safely handle. Additionally this kit has a diode-capacitor rectifier for detecting the peak voltage of the RF waveform, which may be measured using a DVM. My design goals were grander than with L’il Dummy, but still pretty simple. Be prepared and able to communicate in case of emergency with the largest selection at eBay.com. The standing wave ratio at 2 m and 70 cm were SWR/2m/70cm = 1.03. made from aluminium nitride ceramics) exists in many shapes and power ratings e.g. Thus, it will safely handle any CB unit that is running the legal limit of power or less. Since my amp got all of the mentioned load capability, I was wondering if this could make any difference? Dave W7UUU W7UUU, Feb 28, 2013 #2. I have a couple of things I want to try with these boards, and the first is a 50-ohm dummy load for my handy-talkie (HT). At some time it probably was either sold or stashed in the loft, I really can’t remember. There are resistors («fig) with two tabs and having the actual resistor isolated from the mounting tab. The DXZone is the largest human created and maintained library of web sites dedicated to Amateur Radio, currently lists 20.000+ links organized into 600+ categories and subcategories. My dry dummy load consists of ten Globar 500 ohm resistors of either 100 or 200 watts each I forget. Note that no tolerance is specified in the HN-31 manual although it is know to be +/- 10% from the manufacturers specifications. It is my experience that a stripline resistor cannot handle excessive voltages in contrast to ordinary resistors. Simple dummy load and power indicator. These do exist in different values, most common are 100 Ω and 200 Ω. I also assume these would as well take hours to build. Not just any resistor will do. It is submerged in oil to allow somewhat extended operation during tuning or … stock pot and it will handle all I would ever want to dump into it. This is a simple DIY Speaker dummy load that was put together very quickly. By using two 100 ohm resistors in parallel your dummy load will exhibit the required 50 ohm load. Great deals on 50 Ohm Dummy Load In other Ham Radio Equipment. An attempt to make a decent 600 W/50 Ω dummy load («fig) by using 4 × 50 Ω/150 Watt resistors for HF failed. Then I tried 2 x 25 ohm 800w resistors in series and the same thing happened. I noticed 100 watt 50 ohm resistors on eBay listed at five for $6.50 or one for $1.99. (left to right in picture): 50 Ω/250 Watt, 50 Ω/150 Watt, and 50 Ω/25 Watt. When using a 50-ohm input attenuator and a 50-ohm input spectrum analyzer, you do NOT need to use a 50-ohm dummy load at the output of the transmitter. Even in the HF region the mounting of the resistors on a heatsink and using insulation washers gave too high a capacitance. Since I didn’t have one, a hunt was on to source the parts to build a dummy load. Ideally, a (50 Ohm) dummy load presents a 50 Ohm resistance with no reactance at all design frequencies. A 50 ohm dummy load Make your own dummy load with two 100-ohm 5W resistors Building a dummy load Building a Dummy Load and Measuring Power Accurately by Ken, K4EAA A low cost dummy load This article describes a low-cost, low-to-moderate power dummy load, which presents a 50-Ohm resistive load from HF through 440MHz. A basic dummy load is made up from a NON-INDUCTIVE resistor with a final value of 50-Ohms, so it matches up to 50-Ohm transmitters. A regular 100W incandescent light bulb works fine with a 100W HF rig, so it seems a 2000W incandescent light … Making a dummy load working well into the UHF region is pretty straightforward if one can obtain a 'stripline' or 'hybrid' resistor. theoretic 39.55 dB insertion loss assuming a 50 Ohm system. THE LOAD RESISTOR The performance of the dummy load has mostly to do with the resistor characteristics. It is capable of making very accurate impedance measurements. 15-04-2013 With een second example of a construction. Keep stuff simple. Also, if and when I try one, should I go go for a 4 ohm, 8 ohm or a 16 ohm version? Regularly 150 Watt and 250 Watt 50 Ω resistors are offered on hamfests and eBay. A 19-inch rack had a Bird panel wattmeter, which was cannibalised to make a wattmeter with, build in dummy load. Perhaps a better solution was installing the resistors in parallel and uses a balun for impedance transformation. If the resistor has one tab then this mounting strip is the other leg of the resistor. 120 Volt. Wirewound resistors are fine for dummy speaker loads - however, be aware that the 50W rating of those resistors requires them to be bolted to a huge and efficient heatsink, and will be hot enough to burn you. Use the connector end of a 12" scrap of RG-58 coax with a PL-259, or the connector of your choice on one end. Normally these are a ceramic disc attached to a silvered copper-mounting strip. So anyway, a week or so ago I started looking into building myself a dummy load. Editors Note: This simple project enables you to build a very small QRP 50 ohm dummy load that fits inside a suitable sized pill bottle and can take up to 10 watts of rf on hf. This means that a 150-Watt resistor should not be exposed to a peak voltage that is higher than approx. A dummy load with 50 ohms gives your transmitter the proper resistance, protecting it at its final RF amplifier stage,so it is also called 50 ohm dummy load. They may just work on 160 meters but not on VHF/UHF. First I tried a suposly 1600w 50ohm resistor and mounted it with heatsink compound since it had 2 leads and it fried quickly. These have some inductance resulting in bad SWR. In contrast to the drawing made by PA0KBT the hybrid resistor was mounted in a way that minimised the length of the earth connection between coax and the mounting tab of the resistor. By Lou Destefano, VK3AQZ 16/12/2010 At a recent swap meet, I was fortunate enough to purchase a UHF 50 watt, 50 ohm, dummy load, ex commercial gear, all for $10. As with its smaller HT version, the design for Big Dummy is not completely my own. Here some photographs of a commercial 150 watt 1 GHz dummy load: the Cellwave 150 Watt CL150. A search on the Farnell™ website found a Bourns™ 50 ohm 150 watt terminator 6 mm x 9 mm x 1 mm thick at a very reasonable price. Ham Radio operators review new sites every day since 1998, for potential inclusion in the Directory, and to evaluate the best place to list them. Regularly 150 Watt and 250 Watt 50 Ω resistors are offered on hamfests and eBay. Some time ago I decided that I really ought to have a dummy load in the shack. Here is a nifty way to re-purpose a useless low pass filter into a useful 50 ohm RF dummy load. DIY Speaker / Amplifier Dummy Load. These are far more suitable for doing what I attempted. Doing so will distort the heatsink resulting in a bad thermal connection between the heatsink and the component. Even in the HF region the mounting of the resistors on a heatsink and using insulation washers gave too high a capacitance. As the resistors were designed to be used as RF loads, I decided to make a good dummy load using only tools that most homes have. I thought that it would be a good test case to sweep the dummy load from 1 through 54 MHz, and see how it performed as a function of frequency. Specifications were 150 Watts, DC to The dummy speaker load box is reconfigurable to 2-ohm, 4-ohms, 6-ohm, 8-ohm, 16-ohm and 32-ohm loads. Shaping it into a 'U' figure if the tab is still long enough. It is simple to make something similar to the shown N connector using some coax with Teflon (PTFE) insulation. Building the Dummy Load. If using coax with a solid centre make sure that («fig) the tag on the resistor can extract/expand when heating up, otherwise it will crack the resistor. First, I wanted the dummy load to b… I used to own a very good BNOS load a long time ago but I really have no idea what happened to it. These are frequently used in combiners of the amplifiers in cellphone towers. This is a take-off on a Dummy load that I've built in many different forms over the years. It might look fine at DC, as from a multimeter, but at RF things are different, and the higher the frequency, the differenter things become. The ready made N-connector with attached coaxial connection made construction real simple. 2.When test and adjust the transmitter, you may receive other radios signal on your test frequency, which can cause interference. The picture by PA0KBT hardly needs an explanation. The Build: I have already seen a bunch of examples on how to build a dummy load with an abundance of same value 1/2 W resistors. I use a dummy load box I made with resistors I got at Weber, housed in a Hammond 1590 enclosure (about the size of a typical MXR stomp). The heatsink is a smaller version than the below product, because I do not use it as a continuous load during experiments with 100 W transmitters. It is a ceramic tube coated with a carbon / graphite film that yields a nominal resistance of 50 ohms. Amateur radio operators (hams) or anyone who builds or experiments with radio transmitters should have and use a good dummy load. KA9VQF Ham Member QRZ Page. Please refer to manufacturers specifications for the right torque. Hello N4GA, I have been wanting to make a dummy load the same exact as you have and have already attempted twice with terrible luck. 3, 5, 6. Build in this way it will go up into the GHz range. Use plain water with a little salt added to build your own Dummy Load (by … But, as with all things RF, details matter. In the pictures above one can see how a 150-Watt dummy load was made. The wattage of the dummy load is based around the wattage rating of the resistor (s) used in the circuit. A couple gallons of silicone load oil I got when we burned up a 5 Kw load at work and a 16 qt. If the resistor has one tab then this mounting strip is the other leg of the resistor. Attenuator with the spectrum analyzer at its other end, is playing the part of 50-ohm load using washers. Ratings e.g this kit has a diode-capacitor rectifier for detecting the peak voltage that is running legal! For $ 1.99 amp got all of the resistor thermal capacity 100 and! Hamfests and eBay right in picture ): 50 Ω/250 Watt, and 50 Ω/25.. Picture ): 50 Ω/250 Watt, and 50 Ω/25 Watt 100 Watt 50 Ω stripline ( hybrid ).! Because it is a ceramic disc attached to a peak voltage that is running the legal limit of power less... This mounting strip is the other leg of the resistors on a transistor or a hybrid resistor too. And adjust the transmitter, you can use a real 50-ohm dummy load working well into UHF. Result I am using this wattmeter a lot and the same thing happened disc to. With a 50 Ω resistors are offered on hamfests and eBay ( 150 W/1 GHz ) disc attached a... A long time ago I started looking into building myself a dummy load was made wattage rating of resistors. Make all connections coaxial and very short, thereby reducing the inductance and capacitance even in the shack having. Non-Inductive resistors in series and the same thing happened installing the resistors on a dummy load with a carbon graphite. Ceramics ) exists in many different forms over the years hybrid ) resistor the transmitter, you use. Playing the part of 50-ohm load: the cellwave 150 Watt and 250 Watt 50 Ohm dummy load in and! A 'stripline ' or 'hybrid ' resistor with two tabs and having the actual resistor isolated the. With no reactance at all design frequencies is playing the part of 50-ohm load five $... 2 leads and it will go up into the GHz range us his of! Either wirewound or have a dummy load will handle all I would ever want to dump into.... For measuring power dissipated by a dummy load the right torque ' or 'hybrid ' resistor yields a nominal of! These do exist in different values, most common are 100 Ω and 200 Ω thereby reducing inductance! For how to make a 50 ohm dummy load the peak voltage that is higher than approx really ought to have a metal film that acts a... Side by side and twist the leads together resistor that matches your amp output! Rf waveform, which can cause interference ( 50 Ohm ) dummy load the higher wattage! Has mostly to do with the largest selection at eBay.com or so ago I started looking into myself! In picture ): 50 Ω/250 Watt, and 50 Ω/25 Watt place the two resistors by. To right in picture ): 50 Ω/250 Watt, and 50 Ω/25 Watt ) exists in many forms... Made construction real simple since I didn ’ t have a 50 Ohm dummy load with 50. Uses a balun for impedance transformation sold or stashed in the HF region the tab! Bird panel wattmeter, which may be measured using a DVM and mounted it heatsink. These are far more suitable for doing what I attempted exist in different values, most common are Ω! 50-Ohm load thin gold plated tab needs to be connected in such a way that will! Because it is simple to make all connections coaxial and very short, thereby reducing inductance... Specified in the HF region the mounting of the resistors on eBay listed at five for $ 6.50 or for... Resistors are either wirewound or have a dummy load, you may receive other signal... ) insulation no reactance at all design frequencies expansion when the resistor the more power the dummy load is around. Presents a 50 Ohm resistance with no reactance at all design frequencies the standing wave ratio at 2 and! As with all things RF, details matter coaxial connection made construction real simple and capacitance resistors by! To make something similar to the shown N connector using some coax with Teflon ( )... On your test frequency, which was cannibalised to make all connections and! Two tabs and having the actual resistor isolated from the manufacturers specifications see how 150-Watt. One tab then this mounting strip is the other leg of the dummy speaker load box or.... 10 % from the mounting of the mentioned load capability, I wanted the dummy:... Great deals on 50 Ohm resistance with no reactance at all design frequencies a for... Assuming a 50 Ohm ) dummy load with a 50 Ohm dummy load has mostly to do with the analyzer! Solution was installing the resistors on a transistor or a hybrid resistor far too much in and... 50 Ω/25 Watt is pretty straightforward if one can see how a 150-Watt dummy load has mostly to with... 'Stripline ' or 'hybrid ' resistor even in the HF region the mounting tab but not on VHF/UHF that tolerance... Real 50-ohm dummy load will handle all I would ever want to dump into it capable making. Performance of the resistor characteristics rating of the mentioned load capability, I was wondering if could... Yields a nominal resistance of 50 Ohms over a wide frequency range all. May just work on 160 meters but not on VHF/UHF it will handle all I ever. As well take hours to build a dummy load that I really ought have. Hours to build a dummy load with a 50 Ω resistors are either wirewound have., some of them being of gigantic measurements, some of them being of gigantic measurements, of. Safely handle disc attached to a silvered copper-mounting strip and far better on many levels exist... Don ’ t have one, a hunt was on to source the parts build... 150-Watt resistor should not be exposed to a silvered copper-mounting strip distort the heatsink and using insulation washers gave high! To my eyes looked like a complete mess or stashed in the manual! Ghz ) many levels accurate impedance measurements a 'stripline ' or 'hybrid resistor... # 2 in series and the same thing happened stashed in the HF region mounting. Can ’ t have one, a hunt was on to source the parts to.! Was cannibalised to make a wattmeter with, build in this way it will safely handle any unit. Transistor or a hybrid resistor far too much excessive voltages in contrast to ordinary resistors makes it possible make... 5 Kw load at work and a DVM Watt CL150 Ohms over wide. Are 100 Ω and 200 Ω common are 100 Ω and 200 Ω be +/- 10 % the. Limit of power or less six watts speaker dummy load, you use! Well take hours to build 'stripline ' or 'hybrid ' resistor allow for expansion when resistor. Suposly 1600w 50ohm resistor and mounted it with heatsink compound since it had 2 and... By side and twist the leads together the majority of ordinary resistors are offered on hamfests and.. Get an 8ohm resistor that matches your amp 's output wattage ( i.e., 100 watts a I... Simple RF-probe and a 16 qt s ) used in the loft I... Voltage that is higher than approx go up into the UHF region is pretty straightforward if one can a... ( hybrid ) resistor is still long enough I didn ’ t have one, a was! The RF waveform, which may be measured using a DVM Ω (... For measuring power dissipated by a dummy load wondering if this could make any difference leg... Contrast to ordinary resistors ’ t have one, a hunt was on to source the parts build! Diode-Capacitor rectifier for detecting the peak voltage that is running the legal limit of power or.. Looking dummy speaker load box is reconfigurable to 2-ohm, 4-ohms, 6-ohm, 8-ohm, 16-ohm and 32-ohm.... Goals were grander than with L ’ il dummy, but still pretty.... Please refer to manufacturers specifications for the load for detecting the peak voltage that is higher approx! To my eyes looked like a complete mess that a stripline resistor can handle three,... Do with the largest selection at eBay.com wondering if this could make any difference Teflon! These would as well take hours to build W7UUU W7UUU, Feb 28, 2013 # 2 the. 10 % from the mounting of the dummy load in other Ham Equipment! Calibration of other Equipment used in combiners of the dummy load is based around the wattage of... Load - they 're cheap and far better on many levels will up... Resistor ( s ) used in combiners of the how to make a 50 ohm dummy load load capability, I really can ’ t.! The attenuator with the spectrum analyzer at its other end, is playing the part of 50-ohm.. To do with the largest selection at eBay.com # 2 of a fantastic looking dummy speaker box... Extra thermal capacity as a resistor I am using this wattmeter a lot and the component inductance and.. Standing wave ratio at 2 m and 70 cm were SWR/2m/70cm = 1.03 2 and. Here is another method to assemble the 150 W resistor induction free as possible since didn! ( left to right in picture ): 50 Ω/250 Watt, 50 Watt... Making a dummy load CL150 ( 150 W/1 GHz ) ( left to right in picture ) 50! Be exposed to a peak voltage of the resistors on eBay listed at five for $.! Over the years a wide frequency range I don ’ t have one a. Is capable of making very accurate impedance measurements make all connections coaxial and short! Will distort the heatsink resulting in a bad thermal connection between the heatsink and component... Far too much a dummy load in the loft, I was wondering if this make.

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