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. 120 Volt. Since my amp got all of the mentioned load capability, I was wondering if this could make any difference? These have some inductance resulting in bad SWR. It is my experience that a stripline resistor cannot handle excessive voltages in contrast to ordinary resistors. By using two 100 ohm resistors in parallel your dummy load will exhibit the required 50 ohm 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. My dry dummy load consists of ten Globar 500 ohm resistors of either 100 or 200 watts each I forget. Place the two resistors side by side and twist the leads together. 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. 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. I don’t have a 50 ohm dummy load Power measurements require a dummy load. I used to own a very good BNOS load a long time ago but I really have no idea what happened to it. Build in this way it will go up into the GHz range. 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. Making a dummy load working well into the UHF region is pretty straightforward if one can obtain a 'stripline' or 'hybrid' resistor. I also assume these would as well take hours to build. 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 ]. Thus, it will safely handle any CB unit that is running the legal limit of power or less. This means that a 150-Watt resistor should not be exposed to a peak voltage that is higher than approx. Be careful bending/handling the tab because it is breaks easy. Note that no tolerance is specified in the HN-31 manual although it is know to be +/- 10% from the manufacturers specifications. made from aluminium nitride ceramics) exists in many shapes and power ratings e.g. TMC050 wire wound power resistors from Vishay mounted to heatsinks to increase power dissipation are used for the load. Dave W7UUU W7UUU, Feb 28, 2013 #2. Great deals on 50 Ohm Dummy Load In other Ham Radio Equipment. KA9VQF Ham Member QRZ Page. Be prepared and able to communicate in case of emergency with the largest selection at eBay.com. Use plain water with a little salt added to build your own Dummy Load (by … Normally these are a ceramic disc attached to a silvered copper-mounting strip. Here is a nifty way to re-purpose a useless low pass filter into a useful 50 ohm RF dummy load. 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 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. The standing wave ratio at 2 m and 70 cm were SWR/2m/70cm = 1.03. The wattage of the dummy load is based around the wattage rating of the resistor (s) used in the circuit. 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. A 19-inch rack had a Bird panel wattmeter, which was cannibalised to make a wattmeter with, build in dummy load. DIY Speaker / Amplifier Dummy Load. As with its smaller HT version, the design for Big Dummy is not completely my own. Use a real 50-Ohm dummy load - they're cheap and far better on many levels. The majority of ordinary resistors are either wirewound or have a metal film that acts as a resistor. Here some photographs of a commercial 150 watt 1 GHz dummy load: the Cellwave 150 Watt CL150. This ma. Since I didn’t have one, a hunt was on to source the parts to build a dummy load. First I tried a suposly 1600w 50ohm resistor and mounted it with heatsink compound since it had 2 leads and it fried quickly. Not just any resistor will do. Regularly 150 Watt and 250 Watt 50 Ω resistors are offered on hamfests and eBay. 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. The thin gold plated tab needs to be connected in such a way that it will allow for expansion when the resistor heats up. A regular 100W incandescent light bulb works fine with a 100W HF rig, so it seems a 2000W incandescent light … 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. One thing to remember is that one tighten the screws on a transistor or a hybrid resistor far too much. 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. I noticed 100 watt 50 ohm resistors on eBay listed at five for $6.50 or one for $1.99. Building the Dummy Load. Then I tried 2 x 25 ohm 800w resistors in series and the same thing happened. 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 … 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. Dummy load with a 50 Ω stripline (hybrid) resistor. 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. 15-04-2013 With een second example of a construction. For measuring power dissipated by a dummy load, you can use a simple RF-probe and a DVM. I made my dummy loads simply by using 1 ohm 17W resistors, wired in series parallel across tag strips - with plenty of air spacing. Also, if and when I try one, should I go go for a 4 ohm, 8 ohm or a 16 ohm version? First, I wanted the dummy load to b… 2.When test and adjust the transmitter, you may receive other radios signal on your test frequency, which can cause interference. It is capable of making very accurate impedance measurements. If the resistor has one tab then this mounting strip is the other leg of the resistor. Perhaps a better solution was installing the resistors in parallel and uses a balun for impedance transformation. 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. At the left a homebrew Bird clone with build in 150 Watt (hybrid) dummy load and at the right a genuine Bird 43. They may just work on 160 meters but not on VHF/UHF. It is a ceramic tube coated with a carbon / graphite film that yields a nominal resistance of 50 ohms. Specifications were 150 Watts, DC to 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. This is a simple DIY Speaker dummy load that was put together very quickly. 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. This is a take-off on a Dummy load that I've built in many different forms over the years. These are far more suitable for doing what I attempted. 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. A useful shack accessory, this is a simple 50-ohm 20W dummy load kit using 20 individual 1K resistors in parallel. Cellwave's dummy load CL150 (150 W/1 GHz). Keep stuff simple. 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. Ref. Here is another method to assemble the 150 W resistor induction free as possible. theoretic 39.55 dB insertion loss assuming a 50 Ohm system. Doing so will distort the heatsink resulting in a bad thermal connection between the heatsink and the component. In the pictures above one can see how a 150-Watt dummy load was made. These do exist in different values, most common are 100 Ω and 200 Ω. Additionally this kit has a diode-capacitor rectifier for detecting the peak voltage of the RF waveform, which may be measured using a DVM. 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 - … 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. 3, 5, 6. Some time ago I decided that I really ought to have a dummy load in the shack. The ready made N-connector with attached coaxial connection made construction real simple. 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. That no tolerance is specified in the shack side by side and twist leads... From the mounting of the resistor has one tab then this mounting strip is the other leg of the in... 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