In our last post we built a dummy load using resistors and a paint can. Today we will build a dummy load with a Mason Jar and Saltwater. This dummy load is easy to build but has to set to the frequency it is going to be used. If you want to change frequencies the salinity has to be adjusted. One advantage of this dummy load is that it is very economical. The only part that had to be purchased was the SO-239 connector. Generally I keep these on hand, so no parts were ordered to build this dummy load.
Before we start building I would like to warn I have not tested this dummy load over 10 W. Since the body of the dummy load is glass, to much heat could cause it to shatter. Monitor the temperature of this dummy load and do not let it over heat.
The easiest way to get the holes in the lid is to make a template. This template fits into the ring of the mason jar with the lid.
It is easy the tear the thin metal of the lid so use a small drill bit to start of with.
The screw holes are easy to get to proper size. The center hole needs to be stepped up in size slowly. To get the hole big enough I use a sharp uni bit.
The saltwater dummy load requires 2 electrode to be place in the saltwater. For this project I used 16 awg solid wire and folded it 3 times to form the electrodes. The three folds are soldered together.
Connect one electrode to the center of the connector and the other to one of the mounting screws.
For this dummy load I am using a mason jar that was found on a shelf in the lab. After it was cleaned it was filled with warm water. Do not use hot water it can crack the jar.
Place a small amount of salt in the water and stir. Since I am using tap water not as much salt is needed. I slowly added salt from packets and checked the antenna analyzer to see were the SWR was. With a little patients you can get good results on your target frequency.
If you think you have added to much salt pour some of the water out and replace it with fresh water. This dummy load has not been tested at any levels above 10 W. Since the dummy load is constructed out of glass be very careful about heating. Over heating can cause the glass to crack and make a very big mess. Many other containers work well with this type of dummy load. A plastic peanut butter jar or jelly jar are free and have plenty of volume.
Links
https://km4nmp.com/2020/02/08/100w-hf-dummy-load/
https://km4nmp.com/2020/02/02/ps100-antenna-analyzer/
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