Featured: Bird 2-30 MHz wattmeter elements on eBay.
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A plug-in element wattmeter such as the Bird Model 43 is really a system. The meter body provides the line section and the meter movement, but the element decides which band and how much power you can read. Elements are where buying a used meter gets confusing, and eBay has a great many of them listed, so it pays to know how they are marked.
What an element does
Bird describes an RF wattmeter element as the sensing component inside a wattmeter that measures RF power over a specific frequency and power range. As Bird's own example puts it, one element may cover 2 to 30 MHz while another supports measurements from 1 GHz to 4 GHz. Bird's standard elements are built for 7/8" line sections and wattmeters.
The H series for HF
For HF amplifier work, the letter to look for is H. Bird lists its H series standard elements with a frequency range of 2 MHz to 30 MHz, and the number in the name gives the full-scale power:
- 25H: 25 W
- 50H: 50 W
- 100H: 100 W
- 250H: 250 W
- 500H: 500 W
- 1000H: 1 kW
- 2500H: 2.5 kW
- 5000H: 5 kW
Choosing the right size
An element reads best when the power you are measuring lands in a useful part of its scale. Pick an element whose full-scale rating comfortably covers your amplifier's output, but not one so large that normal readings barely move the needle. With a reasonable match, reflected power is much lower than forward power, which is why many owners keep a smaller element on hand for reading it. A smaller element is also handy for checking the drive level from the exciter before the amplifier is switched in.
Buying used elements
- Read the label, not just the title. Confirm the band letter and the power number on the element itself in the listing photos.
- Look for damage. Bird warns that calibration could be disturbed if elements are dropped, so a cracked or dented element is a gamble.
- Expect calibration questions. Bird recommends calibrating the Model 43 and its plug-in elements every 12 months, and a used element may not have been checked in years.
- Check the maker. Other companies make elements for these meters too, so read the description for the brand and the rating as well as the photos.
Safety
Bird's element label reads: RF VOLTAGE MAY BE PRESENT IN RF ELEMENT SOCKET - KEEP ELEMENT IN SOCKET DURING OPERATION. Never pull an element out with RF applied. For low reflection measurements, Bird also cautions against rotating the reflected power element to read forward power, because damage to the element or wattmeter could result.
Store spare elements where they cannot roll off the bench, and keep them in a padded box when they are not in the meter.
And a reminder whenever amplifier power is discussed: external linear amplifiers are not legal for use on CB radio. Accurate power measurement belongs in any licensed amateur station.
Where to get it
Browse current listings: Bird 2-30 MHz wattmeter elements on eBay.
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