Articles for Amateur Radio Newsletters aimed at new hams
 written by Gerry Crenshaw, WD4BIS, Rowlett, Texas

 

 

NHP #7: Test Equipment Stuff. Do I need it?

What's all this test equipment stuff anyway.! Do I need Test equipment for the shack? What kind of Instruments do I need?

As we get into this hobby, sooner or late we are faced with the prospect of needing some basic test equipment. It’s true that due to the complexity of our radios, the "State of the Art" has advanced to such a high degree that most repairs have been taken out of our hands. Do you still need any test and measuring equipment in the shack? You can always take it to the repair shop and pay $50.00 an hour to get it fixed.

If your equipment runs on AC or DC there is still the need for a volt/ohmmeter in the shack. Many of the problems that are encountered with our equipment all have to do with power. We use Batteries, Power supplies and Connectors of all kinds. Being able to do GO/NO GO checks can quickly prove were the problem really is, and can save you lots in repair bills. There is nothing worse than a repair ticket with "No problem found" or "Operator in error" or "Loose nut in front of control".

More often than not, problems with a handi-talkie can be traced to a Mechanical connection between the battery and a radio. Being able to prove that the battery is good with a VOM (Volt-Ohm-Meter) or DVM (Digital Volt Meter) prior to looking for a problem like this helps with the troubleshooting process. For many of us who have base radios, when a problem occurs there are usually several test points in the radio that the manufacturer may want checked before they make a suggestion as to a repair action. Some manufactures such as Ten-Tech, when calling the technical support hot-line with a problem will ask for several voltage readings. If there is one "Must Have" in the shack, it's a basic VOM/DVM. Many manufactures make them and the prices vary from $30.00 to several hundred dollars. Depending on your needs and skills the VOM/DVM can be of great asset in troubleshooting.

Analog Vs Digital

Of the Meters on the market what type is best for you? For those of us who have used them awhile the older Meter Movement VOM is the instrument of choice. It can be used to check AC and DC voltages, AC and DC Amperages, Check continuity of conductors and connectors and Resistance's and will check most semiconductors with a "front to back" check. The DVM will do all of the above checks, The display reads directly and in plain numbers, but the semiconductor check is based on a front to back voltage reading rather than a resistance reading. Some of the high end meters by Fluke will even read capacitance and frequency to 10,000 hertz. Another difference with the DVM is the input impedance is very high so it won’t load the circuit being tested. For most applications this is good. For others this can fool you in that it will read leakage voltages that don't show up with a VOM.

Power and SWR Meters

Another instrument in the shack that becomes a "Must Have" for most of us is the Power/SWR Meter. This meter is used to check the output power of a radio and also to check the Standing Wave Ratio (SWR) or Forward to Reflected power ratio of our transmitters. The name of the game here is to put Radio Frequency energy into the air. If you have a high standing wave, power is not being put into the air but the power is being reflected back toward your radio and that it has to throw off as heat. The better the SWR of your station radio and antenna system the more efficiently it is working.

Power/SWR meters come in a variety of sizes, shapes and prices from the inexpensive version sold by Radio Shack to the lab quality instruments built by Bird and Booton. Many of these instruments are designed for specific application or range of measurement such as VHF/UHF only or HF only. Depending on your use, care should be observed and follow the manufacture's recommendation. These instruments are broken up into two broad types, the Single meter and Dual Meter types. The dual meter shows forward and reflected power simultaneously and where the needles cross is the SWR. The single meter type has to a switch that changes the polarity of the sensing diode so forward and reflected power are shown as two separate measurements.

Before purchasing one of these instruments consider the highest power you will be running. Many of these instruments come in Low watt versions. Test instruments for many of the basic measurements will keep the station running at peak efficiency and can warn you to of degrading or marginal performance.

Keep that station running

Gerry WD4BIS

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Copyright 2005 Gerald Crenshaw WD4BIS. All rights are reserved.

Permission in advance is granted to those who use this for non-profit Amateur Radio club newsletters as long as it is used unmodified including this copyright notice and that notice is given to the author via email (wd4bis@arrl.net). In addition, please forward a copy of any newsletter this appears in to: Gerry Crenshaw WD4BIS, c/o GARC, 1027B W. Austin St, Garland, TX, 75040

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