Don’t Be a Dummy and Spend Too Much for Oil

Tim, N9PUZ writes to the HamRadioHelpGroup mailing list:

With new HF rigs being 100% solid state these days, the need for a dummy load in some shacks has gone away. However, if you have an amplifier they are very useful as you can do most of your tuning off-air and avoid causing QRM.

Recently, I bought a used Heathkit Cantenna. It is a dummy load similar to the MFJ-250 1kW “wet” dummy load. It did not come filled with oil due to shipping difficulties.

In many places, such as where I live, genuine transformer oil to fill the load is unobtainium. You can buy a gallon from MFJ but it costs $30 plus shipping.

According to the Heathkit documentation, a good substitute is mineral oil. I checked at the local pharmacy and they wanted $4.25 per PINT still making this an expensive proposition. I wouldn’t classify myself as cheap but I am frugal so I kept searching.

An Internet search led to my discovery that mineral oil is often used as a laxative for horses and other farm animals. A quick trip to our local farm store “Farm and Home” got me a gallon jug for just $15. I imagine any store of this type or even the local Vet would have some.

The amplifier tunes up into the Cantenna very nicely now. Life is good.

Tim, N9PUZ

This is a great tip, but I disagree that “the need for a dummy load in some shacks has gone away.” Every shack should have a dummy load. They are immensely useful, especially in situations where you’re not whether your antenna or your transmitter is what’s causing you not to transmit properly.


  1. David Brodbeck N8SRE says:

    They’re also handy for testing mics, setting transmit levels for digital modes, etc. You can test to your heart’s content without worrying about QRM. If you have a separate receiver you can couple some signal to it and hear what your transmitted signal sounds like.

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