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Fall 2003 Issue |
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Simple Test Gear and Techniques for Measurements above 50 MHz |
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Troubleshooting our ham radio equipment is often a challenge, at best.
Here K3YWY suggests several off-the-shelf items that greatly simplify the
task for our VHF-and-above radios. |
The
author’s test equipment. Top, left to right: multimeter, counter, bird
equivalent wattmeter, scanner. Bottom, left to right: 10-dB, 10-watt
attenuator; 144-MHz HT; |
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The prospect of building, modifying, or troubleshooting today’s ham gear is a daunting proposition for many. For average hams who lack what they perceive as the necessary test equipment, this challenge may be perceived as insurmountable in the realm above 50 MHz. Sophisticated equipment such as micro-wattmeters, noise-figure meters, and spectrum or network analyzers, even when obtained used, may cost many thousands of dollars, a price tag which many but the most dedicated are unwilling to pay.
It is possible, however, to use relatively
simple equipment and techniques to achieve success above 50 MHz as
outlined in this article. Figure 1 depicts my collection of “test
equipment” which has been used to build and repair our rover station.1 The
current rover station is QRV on 50 to 2304 MHz. The equipment shown in the
photo includes a multimeter; counter; Bird equivalent wattmeter; scanner;
a 10-dB, 10-watt attenuator; 144-MHz HT; and 220-MHz HT.
Harmonics are a ham’s best friend. For
example, the 7th harmonic of 40 meters can easily be heard on 50 MHz. A
2-meter HT will provide a usable 3rd harmonic on 432 MHz. I was able to
copy the 17th harmonic of my low-band rig, a Yaesu FT-920, on 6 meters on
903 MHz and its 25th harmonic on 1296 MHz. These harmonics tend to be
weak, so if you do hear them, it’s a good sign your receiver is working
well. Remember, though, any error at 50 MHz is multiplied by a large
factor, so tune slowly and use CW to locate the harmonic.
The Bird model 43 wattmeter is the de facto
choice of many hams for the HF bands, and it functions well into the
microwave realm with proper elements to cover a wide range of frequencies
and power levels. The problem is that the elements are fairly expensive,
costing about $70 new and $40 used. However, by a judicious choice of
elements, it is possible to cover a wide range of frequencies and power
levels with just a few elements. The trick is that the elements will work
over a wider frequency range than listed on the element, often with very
little degradation in accuracy.
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