ARLA/CLUSTER: Novos testes aos equipamentos pelos Laboratórios da ARRL em Outubro.

[João Gonçalves Costa]

[http://www.radiocronache.com/wp-content/uploads/2009/04/qst-review1.jpg]
New product review tests to begin in October QST

When you peruse the October issue of QST, you may notice a few extra lines in the Product Review data.

"Here at the ARRL Lab, we strive to make our test procedures relevant to current technology and to new
features common on today's transceivers," said ARRL Test Engineer Bob Allison, WB1GCM.

"We continue to research ways to improve our testing and to develop new tests that will benefit our members. I hope you will find these new measurements useful in evaluating and comparing transceivers."

* Receiver Sensitivity (MDS) at 137 and 505 kHz
Several countries now give amateurs permission to operate at and around 137 and 505 kHz. In the US, there is activity on 495 to 510 kHz by more than 20 stations around the country operating under the ARRL sponsored WD2XSH experimental license. In addition, there are other Part 15
experimental licensees operating in this range. The WD2XSH stations are on the air regularly, gathering propagation data. They are always looking for signal reports.

Allison said that with many of today's transceivers and a suitable antenna, you can listen for these experimental stations and submit reception reports via the Web site: "The new Product Review tests will help identify transceivers suitable for use on these frequencies. With equipment built over the last 25 years ago or so, I've noticed a wide variety of available sensitivity, from terrible to quite good. Many
receivers tune to 137 and 505 kHz; not all are proficient at receiving signals there. For you 'lowfers,' this measurement is for you."

* Spectral Sensitivity
Spectral sensitivity is the weakest signal that can be "seen" on a visual display of spectrum above and below the operating frequency. Often called a spectrum scope or panadapter, this feature is included on many mid-range and high-end transceivers. "This data represents the level, in dBm, at which the operator can see a signal poke up out of the display noise floor," Allison explained.

"Although the measurement is somewhat subjective, it works out to be about 3 dB above the noise floor at the bottom of the display when the scope is adjusted to show 100 kHz of spectrum. With software-defined receivers (SDRs), such as the FLEX-3000, the sample rate is set to the highest setting."

* Audio Output THD at 1 V RMS
Allison said that one of the ARRL Technical Advisors posed the question, "Who ever listens to their receiver at full volume?" Allison explained that audio output power and THD (total harmonic distortion) at the specified load impedances as specified by the manufacturer have been tested and reported.

"Generally, the specification is at or near the maximum audio output the receiver is capable of," he said. "If severe hearing loss isn't an issue, we normally listen with the volume control set to around the 9 o'clock to 11 o'clock position on most transceivers and not with the control cranked to maximum."

Allison explained that distortion at normal listening levels is an important factor, especially when you are listening for an extended period of time: "High levels of distortion can make signals more difficult to understand and add to fatigue. We'll continue to measure and report how audio output power and THD compare to manufacturers' specifications, but we have added a new test intended to show distortion
at more typical volume levels."

After testing several radios for comfort, Allison picked 1 V RMS as an output level for the new test. "It's an easy figure to remember," he said. "We will now also report THD at this level. Note that this test will appear with the next transceiver reviewed because the FLEX-3000 has only a low-level audio output and is dependent on external, user-supplied devices to amplify the audio to normal listening levels."

Look for these new tests beginning with October's QST Product Review featuring the FLEX-3000.

Fonte: The American Radio Relay League<http://www.arrl.org/>
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