Salt Water Dummy Load
Cheap and Simple
I don't know if any of you have ever wondered if there was an easier and cheaper way to build or acquire a dummy load for your amateur radio equipment.
I have purchased several different types of dummy loads at various hamfests. I have some that are just large carbon resistors capable of around 100-150 watts. I also have 2 of the cantennas which consist of a metal can with a gang of resistors immersed in oil. All of these dummy loads work just fine. However, some drawbacks of these dummy loads are:
1. They are rather expensive for my limited budget
2. These resistive loads can and do burn out with use
3. Oil filled dummy loads invariable begin to leak and you end up with a puddle of oil on the ground
4. Sometimes I need to be able to tune a 1kw amp on a dummy load and the smaller ones can't handle the wattage.
Well, here is the solution!
It is possible and actually very simple to construct a dummy load using the resistance in salt water.
All you need are some really basic items:
1. a good size glass jar
2. Some 10 guage or any heavy guage wire
3. an so239 coax connector
4. Drill and soldering iron
All you have to do is bolt the so239 to the lid of the jar. Solder the electrodes to the so239, and then use an MFJ or other brand antenna analyzer to monitor the resistance and SWR as you begin to add the salt to the water. Begin with a small amount of salt. For a gallon jar, begin with about 1/2 teaspoon. Be sure to mix well before testing.
Below you will find step by step pictures of the project:
The finished Salt Water Dummy Load
Solder the copper electrodes to so239
Make sure copper electrodes are long enough to reach to the bottom of jar.
Add salt slowly to the water in the jar.
Slowly bring the solution up to 50ohms and 1:1 SWR
The first time I added the salt too fast and went way beyond 50 ohms.
All I had to do is pour it out and start with fresh water. If you only go a little too far, you could just pour out a little water and add some fresh.
So far, I have been very pleased with the operation of the dummy load. I hope that this information will be of interest or help to others.
Very simple and cheap to build.
Happy Hamming from ND4jS Jay
