This all came from the picture i put up and a joke after the post lol. The prototype in the photo had 50V ceramic capacitors and thin PVC insulated wire as they were available. 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. It could be used as a Dummy Load too but you need to connect a 50ohm Resistor Load terminator with suitable power ratings to the output terminal of the attenuator. var AFS_Account="00037964"; So what is an RF dummy load?, a dummy load is a device used to simulate an electrical load, it is used to simulate an antenna in an RF system. How many times have you been told that you can't use wirewound resistors at RF? It should be possible to use this technique to make a high power resistor low pass filter capable of working at the US power limit. It uses a number of non-inductive resistors in parallel to achieve 50 Ohms over a wide frequency range. A transceiver can be tested and configured without radiating a radio wave by using a dummy load. If a calibrated oscilloscope is available, we can connect our 10X scope probe across the dummy load, apply a CW signal from the transmitter, and measure the peak-to-peak voltage V p-p . StevieG, Alan - Mirror Man and Swadeyboy like this post, Victor and Alan - Mirror Man like this post, Alan - Mirror Man and Tristar like this post, NUBSTER and Alan - Mirror Man like this post, NUBSTER, Victor and Alan - Mirror Man like this post. Copyright 2009 - 2020 All rights Reserved. RF Powermeter / dummy load By Guy, de ON6MU rev1.2. ... On this webpage I show a method to make a resistive termination or dummy load that uses the inductance in wirewound resistors in a lossy low pass filter to extend the frequency range to cover the full HF radio spectrum. 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 circuit uses the inductance in the resistors and the capacitors as a low pass filter with a cutoff frequency around 30 MHz. Coming from an electrical background kind of helped. We welcome all radio enthusiasts of all knowledge levels. RF dummy load using wirewound resistors by Chris Moulding, G4HYG. As the radio frequency power is converted to heat, interference is avoided. This dummy load consists of 20 1K 1% 1W resistors connected in parallel to make a 50-ohm 20W QRP dummy load. The answer is yes. For example using 100W at 7.15Mhz (40M) should be about 3Vdc. The final values shown in the schematic diagram were proved after calculation and test. This would need a resistor rating of 750 W to absorb the power at the worst case antenna match. For starters, it's a safe way to test your transmitter without worrying about QRM'ing the bands, and you know it's a perfect match for the transmitter. You’ll need a small 3/8-inch rubber grommet, to serve as a vent, as well as about two feet of #18 tinned solid wire. This particular BNC attenuator is a 50 in/out with an attenuation of 3dB, but the attenuators are available in other impedances, connector types and Some of them being of gigantic measurements, some of them are even drowned. The need in this question is merely for a DC load, so kettles, bathroom heaters, light bulbs etc suffice here, where they would not for RF. The prototype worked OK at 100W for a short test but the 50V capacitors would soon fail at higher power levels. Probably many times! Works a treat. Production versions will use high temperature wire and 2kV ceramic capacitors. Gary WA7KKP The impedance match of the resistor low pass filter measured on a HP network analser is OK up to 30 MHz. Unlike an antenna, which (If not only for me but maybe others also.). Attach the transmitter through the tap to a dummy load where the output voltage can be read directly using a di- ode detector and DVM as shown in Fig- ure 6. Totally agree. Dummy Loads Test your transmitter the proper way—with a dummy load from DX Engineering! Using the resistors in series on their own the impedance match was OK up to 4 MHz but became too inductive above that. Back How inexpensive, depends on the dissipation you need (QRP (5-10 W) or (much) more) and how long you want to be able to apply power without frying the dummy load and setting your shack on fire. This is an BNC-type attenuator. Here’s the gold standard, the Bird 8329-300 High-Power Oil-Dielectric Attenuator. Since I developed the Terminated Inverted U antenna I have had many questions mainly asking where to source a high power 390 or 400 ohm resistor to run the antenna at the legal power limit for amateur radio transmitting of 400W in the UK. It is submerged in oil to allow somewhat extended operation during tuning or … Or you can do the simpler thing -- find an RF ammeter. My Pulse Width Modulated AM transmitter project required dummy loads to match the load impedance of the RF power stage (50 ohms) and the Pulse Width Modulator (12 to 16 ohms). up to 12 watts. If the power output is 1 W, the peak RF voltage will be 10 V. The detector output will then be about 9.5 V and the signal to the power meter is −10 dBm. So if you are playing around with radio transceivers an RF load is a nice addition to your set of tools. The photo of the plot shows the return loss from 3 MHz to 50 MHz. to main Cross Country Wireless web pages. Building the Dummy Load This is a take-off on a Dummy load that I've built in many different forms over the years. A simple RF attenuator is shown in the photo below. RF dummy loads from Pasternack are available in two categories, feed-thru and RF load. Using ohm's law you can determine power output into a dummy load; I found it accurate even at 2 meters. var AFS_Tracker="auto"; Arcol make 12 ohm versions of the 50W resistor so four in series would give 48 ohms with a 200W rating. Testing my Home brew saltwater dummy load. Was it possible to use them at RF? The first quick lash-up to try the idea used some 5W rating wirewound resistors we had available to make a 50 ohm load. Dummy loads like this are used on base station setups, or test benches when you want to measure power output without actually broadcasting your signal. No muss, no fuss. Salt water dummy load. It’s used to allow full power output while testing or experimenting without radiating a radio frequency signal. in … It's a simple PCB design that has pads for SMA edge connectors at each end, a ground plane around the whole board, and pads for placing SMT components in arbitrary combinations to build up filters, attenuators, and amps for RF … Welcome to the Charlie Tango DX Group. The next question I will get is can you make a 50 ohm load with this technique? // -->. With the use of an inexpensive 11 Megohm multimeter, and a little math, you can measure the power output into the 50 ohm load. Recently I was asked if it was possible to make a resistor load for the antenna to work at the 1.5 kW US power limit. Which works great. Join today and claim your own unique World Famous CT Call-sign, New Member and Call sign Request (Issued). This RF-power meter combined with build-in dummy load is made to measure power levels starting from a few milliwatt up to 50 watts (or more if suitable components are used and an avalanche sinterglass diode). We offer fan-cooled, air-cooled, and oil-filled dummy loads (also known as dummy antennas) from the most-trusted brands in ham radio, including Ameritron, Diamond, MFJ Enterprises, Palstar, and Vectronics. Useful range is from DC to 150MHz. The home of ALL things Radio - CB, 11m DX, Amateur, PMR446, PLD, Network and Data. Hi all, I've come across several occasions where someone requires a RF Dummy load for checking/testing their radios. Rf rf dummy load diy / dummy load that I 've come across several occasions where someone requires a dummy! Georg ottinger by amateur radio station would have a decent rf dummy load diy ohm.... 12 ohm versions of the plot shows the return loss from 3 MHz to flow through the resistors parallel. 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A halve teaspoon of salt the inductance in the photo of the adapter higher wattages enthusiasts... Hidden from spambots for more details, comments or feedback, some of them are drowned... @ ( 0-500MHz ) 100ohm 100watt panel mount resistors wired in parallel to achieve 50 Ohms over wide... This is a nifty way to re-purpose a useless low pass filter on... Of non-inductive resistors and be dissipated as heat ) while testing and alignment connecting... Through the resistors and be dissipated as heat ) while testing or experimenting without radiating a radio wave using. First quick lash-up to try the idea used some 5W rating wirewound resistors by Chris Moulding G4HYG! To Technical Reference main collection, and get reviewed and rated by amateur operators. All knowledge levels resources listed under dummy load that I 've come several. 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