No muss, no fuss. The common RF Attenuator has the same input output Z which is 50 Ohm. 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). It’s used to allow full power output while testing or experimenting without radiating a radio frequency signal. Useful range is from DC to 150MHz. Using the resistors in series on their own the impedance match was OK up to 4 MHz but became too inductive above that. (If not only for me but maybe others also.). Hi all, I've come across several occasions where someone requires a RF Dummy load for checking/testing their radios. This would make an ideal terminating resistor for HF use for the Terminated Inverted U antenna to work at the UK legal limit of 400W even for higher duty modes such as RTTY or FT8. This all came from the picture i put up and a joke after the post lol. The basic design for this dummy load comes from the RF Biscuit project by @georg ottinger. The photo of the plot shows the return loss from 3 MHz to 50 MHz. A simple RF attenuator is shown in the photo below. Those examples to my eyes looked like a complete mess. Optionally you can also use an oscilloscope to measure the RF voltage at the Dummy Load (not shown, also dangerous voltages are present!). The metal box helps with any heat build up. Which works great. You choose the RF connector; type N or UHF female are the most common and flexible. The final values shown in the schematic diagram were proved after calculation and test. 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 . The home of ALL things Radio - CB, 11m DX, Amateur, PMR446, PLD, Network and Data. 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. Further tests running a constant 100W carrier into the resistor low pass filter circuit for ten minutes showed that the resistors were dissipating the power evenly and that the temperature rise indicated that the diecast box used would be suitable for running at the full rated power of 200W. I do have one at… Testing my Home brew saltwater dummy load. var AFS_Server="www"; 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 QRPGuys Dummy Load/Power Meter is a 50 Ω, 12W rated terminated load that is useful tool when setting up or diagnosing most low power transmitters. AN LF TO 2GHZ 250W DUMMY LOAD. ... 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. Victor if you look at one of my post in the Antenna section its says " Admin please feel to post this in the Information section but give the video maker Gary (Offplanet)the credit" the reason I ask Admin to do it was when I posted the Q code list Lee put it in the info section so I thought it was up to Admin to do it ,but also I got a bit of a impression that some thought I was talking cr*p and was more interested in making ones with diodes and heatsinks which cost money ,my info cost next to nothing and was use by radio operators (not just hams)years ago in fact it's common physics and not really electrical or radio . Resources listed under Dummy Load category belongs to Technical Reference main collection, and get reviewed and rated by amateur radio operators. It's not often that you can get 4 times the power rating for the same price! These dummy load attenuators can get very pricey. Building the Dummy Load This is a take-off on a Dummy load that I've built in many different forms over the years. Probably many times! 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. Surely any self-respecting amateur radio station would have a decent 50 ohm dummy load, I hear you ask incredulously. Using ohm's law you can determine power output into a dummy load; I found it accurate even at 2 meters. Well this was my attempt at building a dummy load. 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. Welcome to the Charlie Tango DX Group. This would need a resistor rating of 750 W to absorb the power at the worst case antenna match. Coming from an electrical background kind of helped. Figure 1. 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. 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. 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. Here is a nifty way to re-purpose a useless low pass filter into a useful 50 ohm RF dummy load. I used a metal alloy box which was a bit small but a bit of ingenuity made it fit. Using 1.5mm sq electrical cable. 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. 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. A dummy load is used at the output of a transmitter for testing purposes. 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). The new resistor low pass filter design works so well that we are going to manufacture it instead of the 50W thick film resistor unit for the same price. Since I didn’t have one, a hunt was on to source the parts to build a dummy load. This is an BNC-type attenuator. Dummy-loads are easy and relatively inexpensive to build yourself, using one or more suitable resistors. RF Powermeter / dummy load By Guy, de ON6MU rev1.2. Elecraft DL-1, MFJ-261) to submersion in non-conductive oil baths (e.g. If four resistors are used the ratio between the three capacitor values should be the same. You’ll need 30 dummy load resistors — 1.5k-ohm, metal film, 2-watt resistors soldered in parallel. Using a DMM you should see positive DC voltages at the output of the adapter. We welcome all radio enthusiasts of all knowledge levels. Join today and claim your own unique World Famous CT Call-sign, New Member and Call sign Request (Issued). Or you can do the simpler thing -- find an RF ammeter. var AFS_Account="00037964"; var AFS_Tracker="auto"; All materials cost about £30. Totally agree. \$\begingroup\$ An RF dummy load adds the substantial additional complexity of needing to be a matched, hopefully resistive impedance at frequencies of interest. The prototype in the photo had 50V ceramic capacitors and thin PVC insulated wire as they were available. The dummy load display case. It uses a number of non-inductive resistors in parallel to achieve 50 Ohms over a wide frequency range. I had a 0-2a Weston, mounted in a Mini-box, with very short leads to the SO-239 jacks. // -->. The roles of RF attenuators, terminations, matching pads and loads are important in radio communications test and measurement, as well as in equipment interconnection. The first quick lash-up to try the idea used some 5W rating wirewound resistors we had available to make a 50 ohm load. Some of them being of gigantic measurements, some of them are even drowned. The impedance match of the resistor low pass filter measured on a HP network analser is OK up to 30 MHz. 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. 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. IT has 3 scale readings: 0.5 watt, 5 watt and 50 watts. Special flange mounting RF metal film resistors like the Florida RF 32-1037 make an ideal resistor for a dummy load. The Minty Load DIY Version The minty load is basically a QRP+ dummy load with a RF detector circuit that allows a standard Voltmeter to be used to measure RF power out, ideal for anyone adjusting homebrew QRP Transmitters. As admin cant be bothered to put my contribution to making a dummy load which I ask for to be put in this section. It is submerged in oil to allow somewhat extended operation during tuning or … With the use of an inexpensive 11 Megohm multimeter, and a little math, you can measure the power output into the 50 ohm load. Dummy Loads Test your transmitter the proper way—with a dummy load from DX Engineering! Back High power dummy loads are expensive diy with a bit of water and a halve teaspoon of salt ! 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. Was it possible to use them at RF? The circuit uses the inductance in the resistors and the capacitors as a low pass filter with a cutoff frequency around 30 MHz. Here at Cross Country Wireless we make a 50 Watt rated 390 ohm resistor unit based on a noninductive thick film resistor.