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<H1>New product review tests to begin in October QST </H1>
<P><FONT face=Verdana>When you peruse the October issue of <STRONG>QST</STRONG>,
you may notice a few extra lines in the Product Review data.</FONT></P>
<P><FONT face=Verdana>"Here at the ARRL Lab, we strive to make our test
procedures relevant to current technology and to new<BR>features common on
today's transceivers," said ARRL Test Engineer <STRONG>Bob Allison,
WB1GCM</STRONG>. </FONT></P>
<P><FONT face=Verdana>"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." </FONT></P>
<P><FONT face=Verdana><STRONG>* Receiver Sensitivity (MDS) at 137 and 505
kHz</STRONG><BR>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<BR>experimental
licensees operating in this range. The WD2XSH stations are on the air regularly,
gathering propagation data. They are always looking for signal reports.
</FONT></P>
<P><FONT face=Verdana>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<BR>receivers tune to 137 and 505
kHz; not all are proficient at receiving signals there. For you 'lowfers,' this
measurement is for you."</FONT></P>
<P><FONT face=Verdana><STRONG>* Spectral Sensitivity</STRONG><BR>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.
</FONT></P>
<P><FONT face=Verdana>"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."</FONT></P>
<P><FONT face=Verdana><STRONG>* Audio Output THD at 1 V RMS</STRONG><BR>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. </FONT></P>
<P><FONT face=Verdana>"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."</FONT></P>
<P><FONT face=Verdana>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<BR>at more typical volume levels."
</FONT></P>
<P><FONT face=Verdana>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."</FONT></P>
<P><FONT face=Verdana>Look for these new tests beginning with October's QST
Product Review featuring the FLEX-3000. </FONT></P>
<P><FONT face=Verdana>Fonte: </FONT><A href="http://www.arrl.org/"
target=_blank><FONT face=Verdana>The American Radio Relay
League</FONT></A><BR></P></BODY></HTML>