Instruction manual

QST – Devoted Entirely to Amateur Radio www.arrl.org April 2012 55
In terms of blocking gain compression, the
IC-9100 turns in excellent numbers on 144
and 430 MHz, more than 100 dB even at
2 kHz spacing. It’s a bit lower on 23 cm. For
comparison, on HF (14 MHz), where you’d
expect better performance, the ’9100 comes
in at 142, 120 and 111 dB (preamp off) at 20,
5 and 2 kHz spacings, respectively.
The IC-9100’s VHF and UHF performance
is superior to that of the IC-910H. To see
how far we’ve come over the past decade, the
IC-910H’s two tone, third order IMD DR
came in at 85 dB (noise limited) at 144 MHz,
80 dB at 432 MHz and 78 dB (noise limited)
at 1.2 GHz — all at 20 kHz spacing.
To ALC or Not
In the wake of a report or two we’d over-
heard on the Internet, we checked for ALC
overshoot. This would cause the transmitter’s
output power to max out for a split second
before the ALC circuitry reins it in. Here’s
what we found: At various barefoot exciter
power levels, we observed no overshoot
whatsoever in the CW mode — the mode we
use in testing for power spikes. In SSB mode,
we found no overshoot at full output. At
power levels below 50 W and with the
speech compressor enabled, however, we
observed a power spike on the first syllable
of the word hello. We carefully observed the
ALC readout while transmitting, keeping it
at about two thirds of full scale. There was
no apparent power spike if we switched off
the speech compressor.
This particular issue might be a problem
when using certain amplifiers. If so, we
would recommend turning off the speech
compressor; this would also keep the linear
amplifier output within the legal power limit.
ICOM was still looking into this issue as this
review went to press.
Okay, Now for the Really Cool Stuff
ICOM’s optional RS-BA1 software makes it
possible to operate the IC-9100 remotely via
the Internet or a local network. The software
is actually two programs — a remote con-
nection utility and a virtual front panel to
control the radio. I had somewhat mixed but
overall gratifying results using it.
Your “server” PC must have a direct Internet
connection; for me this meant snaking an
extra long Ethernet cable down the stairs and
through the house. To load the software,
you’ll need to enter the product ID and
license key from the CD label. Our software
CD, labeled “Programming Software Icom
Cloning System,” came with the original
program version and an upgrade. The soft-
ware does not come with a hard copy man-
ual. A PDF manual was supposed to be on
the CD, but it was not, nor was it available on
ICOM’s website. I found it on a third-party
website, www.ab4oj.com. ICOM does offer
a RS-BA1 Quick Reference Guide online at
www.icomamerica.com.
Understanding the instructions in either
resource can require good intuition and even
outright speculation, and the English in the
software itself was occasionally hard to
decipher. What I saw on my screen did not
always comport with the instructions. All of
this aside, the software does work, although
setting everything up can be rather demand-
ing and requires some degree of computer
and networking savvy.
Help is at hand, however. After running into
a brick wall on connecting to the remote
Reciprocal Mixing Testing: What Is It?
You may notice two new color bars in the “Key Measurements Summary” at the top
of this review. These are for reciprocal mixing dynamic range (RMDR), with measure-
ments at 20 and 2 kHz spacing. We’ve reported reciprocal mixing since December
2007, but it’s easy to overlook these figures in the table. From this review forward, we
will include RMDR in the Key Measurements Summary.
We report three dynamic range measurements that determine a transceiver’s
overall performance. Along with blocking gain compression dynamic range and two
tone third order dynamic range, we must consider RMDR while evaluating how well a
receiver hears. Which of these measurements is the most important factor in compar-
ing receivers depends a lot on how you plan to use that receiver. For hearing weak
signals at or near the receiver’s noise floor, receiver noise typically is the limiting factor.
For the reception of stronger signals under crowded band conditions, two tone third
order DR is the most important number. To assess a receiver’s ability to perform well in
the presence of a single, strong off-channel signal (common within geographical ham
radio “clusters” or with another ham on the same block), blocking gain compression DR
is usually the dominant factor.
Reciprocal mixing is noise generated in a superheterodyne receiver when noise
from the local oscillator (LO) mixes with strong, adjacent signals. All LOs generate
some noise on each sideband, and some LOs produce more noise than others. This
sideband noise mixes with the strong, adjacent off-channel signal, and this generates
noise at the output of the mixer. This noise can degrade a receiver’s sensitivity and is
most notable when a strong signal is just outside the IF passband. RMDR at 2 kHz
spacing is almost always the worst of the dynamic range measurements at 2 kHz
spacing that we report in the “Product Review” data table.
We perform the reciprocal mixing test at 14.025 MHz, using a very low noise
Wenzel test oscillator with a measured output of +14 dBm. The test oscillator’s side-
band noise is considerably below the reciprocal mixing we’re measuring. We feed the
oscillator’s output into a step attenuator, which we adjust until an audio meter on the
receiver’s output indicates a 3 dB increase in background noise. The RMDR is the
output level at which we note this 3 dB increase.
Here’s an example: Suppose the receiver’s noise floor (minimum discernable signal,
MDS) is –133 dBm, and a strong station 2 kHz away causes a 3 dB increase in noise
at a level of –53 dBm into the receiver’s antenna jack. The reciprocal mixing figure is
MDS minus the 3 dB increase level: –133 dBm – (–53 dBm) = –80 dBm. We previously
would have reported this as –80 dBc. Since we now consider this as a dynamic range
number, we report it simply as 80 dB.
In our real-world example, if your receiver’s MDS is –133 dBm, a signal 2 kHz away
at 20 dB over S-9 will cause the noise in the audio output to increase by 3 dB. This
reduces your receiver’s MDS by that amount, resulting in an MDS of –130 dBm. A
stronger signal will create more noise, but our benchmark for testing is a 3 dB increase
in noise.
The upper end of the RMDR bar on the key measurements summary charts has
been set just above the highest RMDR seen in the ARRL Lab to date. SDR and analog
type receivers have different performance characteristics and design tradeoffs. For
instance, some I/Q SDRs have been observed to have rather mediocre third order IMD
dynamic range when tested in a laboratory environment with just two signals, but if
hooked to an antenna with multiple signals simulating real band conditions, have con-
siderably higher third order IMD dynamic range. RMDR, on the other hand, can be lower
under the same conditions than what is observed in the Lab. If choosing a receiver for
real world use, it’s important to consider all three dynamic range parameters.
Note how reciprocal mixing relates to the two-tone third order DR figures, especially
at 5 and 2 kHz spacing. A single, strong adjacent signal 5 or 2 kHz from the desired
signal with resulting reciprocal mixing has a greater impact on a your ability to hear a
desired weak signal than do two strong signals 5 and 10 kHz away (5 kHz spacing)
or 2 and 4 kHz away (2 kHz spacing) with a resulting intermodulation distortion (IMD)
product that covers up the desired signal. In many cases, reciprocal mixing dynamic
range is the primary limiting factor of a receiver’s performance.
— Bob Allison, WB1GCM, ARRL Laboratory Engineer