Changes in the ARRL Test Methodology
IMPORTANT: In 2007, the ARRL made significant changes to its DR3 testing Methodology.
APPLES TO APPLES COMPARISONS CANNOT BE MADE BETWEEN RADIOS TESTED WITH THE OLD METHODOLOGY (2006 AND EARLIER) AND RADIOS TESTED WITH THE NEW METHODOLOGY (2007 AND LATER) !!!
- What changed ?
- Why did it change ?
- What are the effective results?
- Which method is correct?
- SUGGESTION to avoid confusion:
- How can we convert new numbers to old numbers?
- Example based on the Ten-Tec Eagle.
What changed: Starting in 2007, the leage began testing 3rd order dynamic range using a 3-Hz (three Hertz) filter between the radio and its analyzer.
Why it changed: Beginning with the Omni VI+ (late 1990s), it became impossible to measure the actual DR3 accurately because the radio was "noise limited".
In an effort to gain an accurate measurement of the DR3, the league used a very narrow(3-Hz) audio filter to eliminate the noise. Without the noise, it was indeed possible to measure the true DR3 of the radio.
What the effective results are: If a radio is noise limited, then the measured DR3 using a 3-Hz filter will typically be about 6dB greater than when measured without the 3-Hz filter. This may vary a dB or two but 6dB is a good ballpark number.
If the radio is not noise limited, then the difference could be anything between 0 dB and perhaps 8 dB. In recent years, all new radios have been noise limited.
Which method is correct? Both are correct.
They are different measurements.
Suggestion to avoid confusion: Let's give the two different DR3 measuring methodologies two different names:
- "Theoretical DR3" (test using 3-Hz filter)
- "Usable DR3" (test without 3-Hz filter)
How to convert new DR3 numbers to old DR3 numbers: This is a rough estimate but good enough for our purposes:
New DR3 Methodology = Old DR3 Methodology + 6 dB
Example based on the TEN-TEC Eagle:
- Rob Sherwood measured DR3 = 92 dB
- The league measured DR3 = 98 dB
- Difference: 6 dB