21 Things to Do: Buy a DMM

21 Things to Do After Getting Your Amateur Radio LicenseA digital multimeter, or DMM for short, is the most basic piece of test equipment you can own, and every ham should have one. With a digital multimeter (DMM), you can make voltage, current, and resistance measurements. Some multimeters do even more, but that’s a topic for another book.

Why do you need a multimeter? Well, the multimeter is the first thing you’ll reach for when you have problems with your equipment. For example, let’s say you go down to your shack, switch on your radio, and nothing. It doesn’t turn on. The first thing you should check in this case is that the power supply is supplying the proper input voltage. To do this, you pull out your DMM, set it to measure voltage, place the probes on the + and – outputs, and verify that the power supply is working.

Klein DMM

This multimeter costs about $50 and features a rugged case that helps prevent damage should you accidentally drop it.

OK, now we’re sure that the power supply is working OK, but the radio still doesn’t power up. The next thing to check is the power cable from the supply to the radio. It’s possible that the cable has an open connection. To check that, you first disconnect the cable from the power supply and from the radio.

This multimeter costs about $50 and features a rugged case that helps prevent damage should you accidentally drop it.Then, set your DMM to measure resistance. Set it on the lowest resistance scale. Connect one test probe to one end of the cable and the other test probe to the other end. The resistance you measure should be very low—less than 2 or 3 ohms. An open connection will register an infinite resistance.

I think you get the picture. Without a DMM, you’re dead in the water. With a DMM, you can figure out what’s wrong and fix it.

There are a wide range of DMMs available. On the low end, you’ll find DMMs at Harbor Freight for $5 or less. On the high end, you could spend $300 or more for a Fluke multimeter. I would advise against both. The $5 multimeters are not very well-made and can be inaccurate. They tend to quit working just when you need them.

The $300 DMMs are great, but you needn’t spend that much. A DMM costing between $30 and $100 will do pretty much all you need to do at this point in your amateur radio adventure, and you can use the money you have left over for other things. You can buy them at any Lowe’s or Home Depot. Ask your friends or Elmer what kind of meter they own and whether or not they would recommend that you buy something similar.

Comments

  1. Be careful, some inexpensive DMM’s do not have a continuity tester, and that’s an absolutely invaluable tool for any ham to have.

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