Normally these are a ceramic disc attached to a silvered copper-mounting strip. It is submerged in oil to allow somewhat extended operation during tuning or … So anyway, a week or so ago I started looking into building myself a dummy load. This is a simple DIY Speaker dummy load that was put together very quickly. 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. Ref. Also, if and when I try one, should I go go for a 4 ohm, 8 ohm or a 16 ohm version? It is a ceramic tube coated with a carbon / graphite film that yields a nominal resistance of 50 ohms. I also assume these would as well take hours to build. 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. The standing wave ratio at 2 m and 70 cm were SWR/2m/70cm = 1.03. Be careful bending/handling the tab because it is breaks easy. Here is a nifty way to re-purpose a useless low pass filter into a useful 50 ohm RF dummy load. A 19-inch rack had a Bird panel wattmeter, which was cannibalised to make a wattmeter with, build in dummy load. 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. 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. For measuring power dissipated by a dummy load, you can use a simple RF-probe and a DVM. 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. 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. If the resistor has one tab then this mounting strip is the other leg of the resistor. Since each resistor can handle three watts, the dummy load will handle six watts. (left to right in picture): 50 Ω/250 Watt, 50 Ω/150 Watt, and 50 Ω/25 Watt. It uses a number of non-inductive resistors in parallel to achieve 50 Ohms over a wide frequency range. 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. A regular 100W incandescent light bulb works fine with a 100W HF rig, so it seems a 2000W incandescent light … I made my dummy loads simply by using 1 ohm 17W resistors, wired in series parallel across tag strips - with plenty of air spacing. These are far more suitable for doing what I attempted. 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. TMC050 wire wound power resistors from Vishay mounted to heatsinks to increase power dissipation are used for the load. Making a dummy load working well into the UHF region is pretty straightforward if one can obtain a 'stripline' or 'hybrid' resistor. If the resistor has one tab then this mounting strip is the other leg of the resistor. 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. In the pictures above one can see how a 150-Watt dummy load was made. This means that a 150-Watt resistor should not be exposed to a peak voltage that is higher than approx. Place the two resistors side by side and twist the leads together. By using two 100 ohm resistors in parallel your dummy load will exhibit the required 50 ohm load. 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. My dry dummy load consists of ten Globar 500 ohm resistors of either 100 or 200 watts each I forget. This ma. 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). Even in the HF region the mounting of the resistors on a heatsink and using insulation washers gave too high a capacitance. But, as with all things RF, details matter. Keep stuff simple. The attenuator with the spectrum analyzer at its other end, is playing the part of 50-ohm load. Salt water dummy load. Be prepared and able to communicate in case of emergency with the largest selection at eBay.com. I don’t have a 50 ohm dummy load Power measurements require a dummy load. Not just any resistor will do. An attempt to make a decent 600 W/50 Ω dummy load («fig) by using 4 × 50 Ω/150 Watt resistors for HF failed. Thick film resistors (e.g. Additionally this kit has a diode-capacitor rectifier for detecting the peak voltage of the RF waveform, which may be measured using a DVM. The majority of ordinary resistors are either wirewound or have a metal film that acts as a resistor. Since I didn’t have one, a hunt was on to source the parts to build a dummy load. These have some inductance resulting in bad SWR. There are resistors («fig) with two tabs and having the actual resistor isolated from the mounting tab. 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. Some time ago I decided that I really ought to have a dummy load in the shack. 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. Ideally, a (50 Ohm) dummy load presents a 50 Ohm resistance with no reactance at all design frequencies. Here some photographs of a commercial 150 watt 1 GHz dummy load: the Cellwave 150 Watt CL150. Specifications were 150 Watts, DC to 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. Dummy load with a 50 Ω stripline (hybrid) resistor. The ready made N-connector with attached coaxial connection made construction real simple. theoretic 39.55 dB insertion loss assuming a 50 Ohm system. 15-04-2013 With een second example of a construction. 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. Some of them being of gigantic measurements, some of them are even drowned in even vegetable oil for extra thermal capacity. Build in this way it will go up into the GHz range. Use a real 50-Ohm dummy load - they're cheap and far better on many levels. 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 ]. 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. 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. Building the Dummy Load. Get an 8ohm resistor that matches your amp's output wattage (i.e., 100 watts? Those examples to my eyes looked like a complete mess. 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 … A useful shack accessory, this is a simple 50-ohm 20W dummy load kit using 20 individual 1K resistors in parallel. KA9VQF Ham Member QRZ Page. It is my experience that a stripline resistor cannot handle excessive voltages in contrast to ordinary resistors. At the left a homebrew Bird clone with build in 150 Watt (hybrid) dummy load and at the right a genuine Bird 43. This is a take-off on a Dummy load that I've built in many different forms over the years. Cellwave's dummy load CL150 (150 W/1 GHz). First I tried a suposly 1600w 50ohm resistor and mounted it with heatsink compound since it had 2 leads and it fried quickly. Even in the HF region the mounting of the resistors on a heatsink and using insulation washers gave too high a capacitance. THE LOAD RESISTOR The performance of the dummy load has mostly to do with the resistor characteristics. Regularly 150 Watt and 250 Watt 50 Ω resistors are offered on hamfests and eBay. 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. 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). 3, 5, 6. Since my amp got all of the mentioned load capability, I was wondering if this could make any difference? First, I wanted the dummy load to b… 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. stock pot and it will handle all I would ever want to dump into it. These do exist in different values, most common are 100 Ω and 200 Ω. 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. 2.When test and adjust the transmitter, you may receive other radios signal on your test frequency, which can cause interference. 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. Great deals on 50 Ohm Dummy Load In other Ham Radio Equipment. 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. Then I tried 2 x 25 ohm 800w resistors in series and the same thing happened. Perhaps a better solution was installing the resistors in parallel and uses a balun for impedance transformation. It is simple to make something similar to the shown N connector using some coax with Teflon (PTFE) insulation. Simple dummy load and power indicator. Note that no tolerance is specified in the HN-31 manual although it is know to be +/- 10% from the manufacturers specifications. 0 - 500 MHz (500 MHz SWR < 1.3), continue 800 W on a suited heathsink (1500 W PEP short period). 50 watts? Normally these are a ceramic disc attached to a silvered copper-mounting strip. 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. 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. A couple gallons of silicone load oil I got when we burned up a 5 Kw load at work and a 16 qt. My design goals were grander than with L’il Dummy, but still pretty simple. Generally the higher the wattage rating of the resistor the more power the dummy load can safely handle. 120 Volt. Fast & … made from aluminium nitride ceramics) exists in many shapes and power ratings e.g. Please refer to manufacturers specifications for the right torque. Matt shares with us his build of a fantastic looking dummy speaker load box. These are frequently used in combiners of the amplifiers in cellphone towers. 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. Regularly 150 Watt and 250 Watt 50 Ω resistors are offered on hamfests and eBay. They may just work on 160 meters but not on VHF/UHF. One thing to remember is that one tighten the screws on a transistor or a hybrid resistor far too much. The picture by PA0KBT hardly needs an explanation. 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 wattage of the dummy load is based around the wattage rating of the resistor (s) used in the circuit. 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. DIY Speaker / Amplifier Dummy Load. Amateur radio operators (hams) or anyone who builds or experiments with radio transmitters should have and use a good dummy load. 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. 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. 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. 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. Shaping it into a 'U' figure if the tab is still long enough. As with its smaller HT version, the design for Big Dummy is not completely my own. ), get mono RCA jack and an enclosure, wire it together, plug it into the 2nd speaker output of your amp, and you're done. 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