Not cheap stuff, but not too bad, and I like the look of polished copper. To correct it, I put the whole thing into an enclosure made from 1″ copper pipe. I was able to hit a local repeater through the dummy load without any issues. To my surprise, once I soldered the resistor to the RF Biscuit board, the dummy load was almost as good an antenna as the stock rubber ducky on my Baofeng HT. That and an edge-mount SMA jack should have been all I needed to make a working dummy load. The resistive element I chose was a thick-film SMT device capable of dissipating 35 watts – way more than enough for this job. This is an open-source design that enables all kinds of handy little RF circuits - attenuators, filters, and as in this case, dummy loads. I chose to build the circuit on an RF Biscuit board. 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. The RF Biscuit board is a handy little thing. Looking down into L’il Dummy just before applying the torch. We’ll need to be clever in sourcing components. Trouble is, power resistors in that range are often wirewound, and a coil of wire will have too much inductance. The HT dummy load, which I’ve dubbed L’il Dummy, needs to handle the 5 to perhaps 8 watts an HT can output. But, they also need to be able to dissipate a lot of power. That means our resistive elements need to be as non-inductive as possible. This could lead to RF power getting reflected back into the final amplifier transistors in the transmitter, possibly damaging them or destroying them altogether. Any inductive or capacitive elements in the load will make it more reactive, changing the impedance as the input frequency changes. The reason that the load needs to be as resistive as possible is that it needs to continue looking like a flat 50-ohm load no matter what frequency is applied to it. In almost every case, that’s going to be 50 ohms. These builds are covered in depth on my Hackaday.io page, but join me below for the gist on a good one: the L’il Dummy.Īs Al points out in the article linked above, a dummy load is just a resistive element that matches the characteristic impedance of the transmitter’s antenna connection. But I did put my own twist on each, and you should do the same thing. Neither of my designs is original, of course borrowing circuits from other hams is expected, after all. We’ll be building two dummy loads: a lower-power one specifically for my handy talkies (HTs) will be the subject of this article, while a bigger, oil-filled “cantenna” load for use with higher power transmitters will follow. Al Williams covered the basics of dummy loads a few years back in case you need a little more background. They allow operators to test gear and make adjustments while staying legal on emission. Every ham eventually needs a dummy load, which is basically a circuit that looks like an antenna to a transmitter but dissipates the energy as heat instead of radiating it an appreciable distance. To get my homebrewer’s feet wet, I chose perhaps the simplest of ham radio projects: dummy loads. But neither of those feats require much in the way of electronics knowledge or skill, and at the end of the day, that’s why I got into amateur radio in the first place - to learn more about electronics. Or on the other end of the money spectrum, using a Yaesu or Kenwood HF rig with a linear amp and big beam antenna to work someone in Antartica must be pretty cool, too. Sure, it’s cool to buy a radio, even a cheap one, and be able to hit a repeater that you think is unreachable. This is an exciting day for me - we finally get to build some ham radio gear! To me, building gear is the big attraction of amateur radio as a hobby.
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