Centaur 411 HF User manual

Product Review Column from QST Magazine
Copyright © 1997 by the American Radio Relay League Inc. All rights reserved.
June 1997
Ten-Tec Centaur Model 411 HF Linear Amplifier
AOR AR7030 Communications Receiver
Radio Shack Model 21-527 Digital SWR/Power Meter

66 June 1997
Product Review
Edited by Rick Lindquist, N1RL• Senior Assistant Technical Editor
By Rick Lindquist, N1RL
Senior Assistant Technical Editor
The Centaur represents Ten-Tec’s at-
tempttogotheextramileinofferingalow-
end HF linear amplifier. The Centaur cer-
tainly is not the first “three-hole” 811A
amplifier on the market, but the folks in
Tennessee reckoned they could go a few
stepsbeyondwhat was already out there,at
thesametime keeping the price in thesame
general ballpark. The result is an economi-
cal 600 W class amplifier that offers QSK
as a standard feature—the only one in this
price category to do so—plus hot-switch-
ing protection, pi-section input filters and
other niceties.
Let’s face it. Not everyone can handle
the $2500 cost of a big-power amp—and
not everyone needs that kind of power any-
way. At this point in the sunspot cycle,
though, some ops would just like a little
leverage on the bands. Sometimes—just
sometimes—the few hundred additional
watts an amp like this can offer will make
the difference between snagging that new
one, making a sked or continuing an enjoy-
able ragchew under changing or less-than-
optimal conditions. A little desktop ampli-
fier like this can certainly fill a lot of gaps.
In typical Ten-Tec fashion, the Centaur
is a fairly compact, straightforward box—
nothing fancy. On the outside, it has ver-
nier-driven LOAD and TUNE controls (cali-
brated with 0-10 markings on each knob’s
apron); a bandswitch (marked for 160, 80,
40,20,15and10meters,buttheampshares
positions for 30, 17 and 12 meters); two
lighted multimeters (one reads either grid
Ten-Tec Centaur Model 411 HF LinearAmplifier
current or power output in watts; the other
reads either plate voltage or plate current);
arowofmini-togglefunctionswitches;and
a big rocker-style POWER switch to turn
the unit on.
Inside the box (and visible through the
ventilation holes in the top of the gray steel
cabinet) are three Svetlana 811A tubes, a
fairlyhuskytransformer(1.5kVACCSand
accounting for about half the weight of the
amplifier), the tuning capacitor, and other
components (see photo). The parallel
811As are operated in class AB
2
grounded-
grid configuration with a nominal 550 mA
of plate current and approximately 1700 V
of plate voltage (at full load). The Centaur
canoperate satisfactorily from either120
or
240 V ac input. A four-inch muffin-type
fan moves 100 CFM of air across the three
output tubes, so the amplifier runs quite
cool (much cooler than my Collins 30L-1,
which has four 811As in the output but a
rather insubstantial-looking cooling fan).
The excellent cooling should keep the
811As running for a long time, assuming
youdon’totherwise abusethem.Themajor
tradeoff here is in fan noise (more on that
subject later).
The Centaur is rated at 600 W output on
SSB and CW on 80 through 15 meters,
500Woutputon160,12and10meters,and
400 W output on FM, RTTY or SSTV.
(Ten-TecsaysthatbytuningupforfullSSB
orCWpower then settingthecarrieroutput
at 150 W, the amp can be used for AM as
well.) It takes the better part of the output
ofatypicaltransceivertodrivetheCentaur
to full output—90 W or so would do it in
most cases, we found. We got the rated
poweronallbandsexcept17meters,where
it was much closer to—but not quite—500
W.
While the Centaur manual advises
keeping the plate current at or below 550
mA during tuneup, we found that the tubes
drew up to 750 mA on some bands when
the linear was tuned for rated output. Ten-
Tec said this is normal. (My personal phi-
losophy with an amplifier like this would
be to run it at 450 to 500 W. There’s pre-
cious little to be gained by pushing it to its
absolute limits.)
Setting up the Centaur is pretty easy. It
comes from the factory wired for 120 V ac
use, but if you’ve got 240 V available in
the shack, it’s quite simple (and probably
advisable) to change two jumpers—acces-
sible via a rear-panel “inspection plate”—
plus a couple of fuses and the wall plug for
240-V operation.
As it comes from the factory, the Cen-
taur does not operate on 12 or 10 meters
(per FCC requirements). To add these
bands, users first must send a photocopy of
their Amateur Radio license to Ten-Tec
requesting the free modification package.
In return, they’ll receive a small circuit
boardthatinstallsviathe“inspectionplate”
access panel. It takes about five minutes
and involves no soldering.
The rear panel has SO-239 connectors
THE BOTTOM LINE
An economy-class “half-gallon”
811A linear amplifier with QSK stan-
dard.Worksgreat,runscool,butsome
ops might find the blower a little loud.

June 1997 67
Table 1
Ten-Tec Centaur Model 411 HF Linear Amplifier, serial number 01A10087
Manufacturer’s Claimed Specifications Measured in ARRL Lab
Frequency coverage: 160, 80, 40, 30,* 20, 17, and As specified (can be modified
15 meters; 12 meters and 10 meters by modification. by licensed amateurs for
operation on 12 and 10 meters).
Power output: 600 W on SSB and CW, 80-15 meters; As specified, except 500 W
500 W on 160 and 10 meters. 350-400 W on measured on 17 meters.
RTTY or SSTV (depending on band).
Duty cycle: SSB, continuous voice modulation, at As specified.
rated PEP output; CW, 50% duty cycle, no time limit
at rated PEP output (30 seconds maximum
continuous key-down).
Gain: Not specified. Approximately 8 dB, typical.
Drive power required for full output: 90-100 W, typical. As specified.
Spurious signal and harmonic suppression: ≥48 dB.
Meets or exceeds FCC requirements.
Intermodulation distortion (IMD): See Figure 1.
Not specified.
Power supply requirement: 120 V ac at 12 A; As specified.
240 V ac at 6 A.
Size (HWD): 6×15.5×13 inches; weight: 40 lb.
*The FCC-specified maximum legal output on the 30-meter band for US amateurs is 200 W PEP.
for the RF input and output. The rear panel
also has an
ALC input jack and an ALC
CONTROL
. If you plan to take advantage
of the QSK (for some users, this will be
the main reason for buying this amp), you
need to wire your keying line through the
Centaur. This is accessible through RCA
jacks on the rear of the amplifier. If you
have a late-model Ten-Tec transceiver
with
TX OUT and TX EN jacks (such as an
Omni VI), connecting these to the
KEY IN
and KEYOUT lines,respectively,takescare
of keying the transceiver for other modes.
For other transceivers, there’s a
PTT/VOX
jack. There’s a wing-nut connection for
ground.
The first thing you’ll notice when you
push on the
POWER switch is that the whole
box will shudder a bit. This is disconcert-
ing, but normal. The next thing you’ll cer-
tainly notice is the rapidly increasing deci-
bel level of the cooling fan as it accelerates
to warp speed. As noted, Ten-Tec moves a
lot ofairthroughthisamp, and it makesabit
of noise in the process. The high blower
noise level was the only major complaint
about this otherwise well-thought-out and
well-built economy amplifier. We checked
sound levels of some other amps and found
the Centaur to be noisier than even some
higher-power units. Ten-Tec acknowledges
that the fan is loud, but a spokesman said it
was a design decision to incorporate lots of
air flow. Ten-Tec says it’s been unable to
come up with a quieter means of doing so
that’s within economic reason and does not
compromise tube life and component lon-
gevity. Even so, many ops would probably
be willing to sacrifice some tube life for a
quieter-running amp. After all, new 811As
are relatively inexpensive.
The mini-toggle switch next to the
POWER switch selects STBY (standby) or
OPR (operate). By following the directions
Figure 1—The
Ten-Tec Centaur
Model 411 spectral
display during two-
tone intermodu-
lation distortion
(IMD) testing.
Third-order
products are
approximately
39 dB below PEP
output, and fifth-
order products are
approximately
45 dB down. The
amplifier was
being operated at
600 W output at
14.02 MHz.
Expanded Product Review
Report Available
TheARRLLaboffersanexpanded
test result report on the Ten-Tec
Centaur Model 411 HF Linear Ampli-
fier that gives in-depth, detailed tech-
nical data on the amplifier’s perfor-
mance,outlinesourtestmethodsand
helps you to interpret the numbers.
This report includes full-power spec-
tral purity charts for each band and a
chart showing how it stacks up
against similar, previously reviewed
units.
Reportsare$7.50forARRLmem-
bers and $12.50 for nonmembers,
postpaid. Request the Ten-Tec Cen-
taur Model 411 Test Result Report
from the ARRL Technical Depart-
ment, 225 Main St, Newington, CT
06111 (personal checks accepted).
For credit card orders only, call 860-
594-0278.
in the Operator’s Manual, any operator
who’s at all familiar with how a tube linear
like this tunes and works will pretty quickly
get the hang of the tuning procedure. If this
isyourfirstamp,justfollowTen-Tec’sclear
instructions in the Operator’s Manual. The
main thing (as Ten-Tec warns) is to avoid
overdriving the 811As. This is one excel-
lent reason for including separate meters to
simultaneously read the 811A grid current
andplate current. By theway, the
LOAD and
TUNE control knobs had rubberized grips
and spinner holes. Their vernier action was
silky smooth.
Another of the front-panel toggle
switches lets you select
QSK or PTT opera-
tion. For CW, the QSK was super. Other
ops—includingthose whotakeprideinhav-
ingacriticalearforkeying—saiditsounded
great. For a CW hand like me, not having to
shutoffmytransceiver’sfull-break-inwhen
running the amp was a gigantic plus. On
SSB, the amplifier performed well too. No
splatteror distortion was noted by other sta-
tions, and our Lab tests indicated good IMD
performance (see Figure 1).
Thebuilt-inwattmeterishandy.Theone
in our review unit measured to within ap-
proximately 10%, worst-case. It was most
accurate on 40 meters, where our Lab watt-
meter and the Centaur’s wattmeter agreed.
On other bands, it read up to 10% low.
Ten-Tec did quite a nice job on the
Operator’s Manual. It’s complete and to
thepoint.There’satuningcharttohelpyou
get in the ballpark while tuning up, plus a
chart where you can record actual settings
for each band; a troubleshooting chapter;
detailed descriptions of most individual
circuit boards—right down to pictures and
PC trace templates; and schematic dia-
grams of everything. There was no parts
list detailing the values of components
called out on the schematics, however. In-
TTC
–10 –8 –6 –4 –2 0 2 4 6 8 10
–80
–70
–60
–50
–40
–30
–20
–10
0
Frequency Offset (kHz)
Reference Level: 0 dB PEP

68 June 1997
structions are step-by-step. My favorite
line of the manual came in Chapter 1—In-
stallation: “If any of your home entertain-
ment electronic devices have RF leaks, the
Centaur will find them.”
Ten-Tec has done a fine job of design-
ing and putting together the Centaur, espe-
cially when you consider its price tag. At
the same time, the amp’s very efficient
cooling system comes at the cost of some
noise. The price and features are certainly
right, however, so if you can manage this
Reviewed by Paul Danzer, N1II
Assistant Technical Editor
Soundsgood!Thatwas my first impres-
sion when I turned on this little black box
withitsEuro-styledfrontpanelandafew—
very few—knobs and push buttons. In fact,
the radio’s exterior styling really distin-
guishes it from the traditional, utilitarian
approach of most general-coverage sets. It
also has a remote-control box, similar to
ones that commonly come with VCRs and
TV sets, something that sets it apart from
itspeers(andmakesitlookforalltheworld
like a satellite TV receiver). This is defi-
nitely not ham gear!
TheoveralleffectoftheAR7030—with
its swooping display window; black,
brushed-finishfrontpanel; textured-finish
case; and flush, hex-head hardware—is
striking. It’s compact, quite handsome
andunique, but its real beauty is more than
skindeep.TheAR7030performsverywell
too, and lives up to its designation as a
“high dynamic range general-coverage re-
ceiver.” Our relatively early production
unit AR7030 did not quite meet AOR’s
dynamic range specification of 100 dB
(measured at 12.7 MHz), but it came quite
close at 14.2 MHz (see Table 2).
To put it into a ham’s perspective, our
original AR7030’s dynamic range perfor-
mance was a bit better than that of the
Yaesu FT-1000MP (see “Product Re-
view,” QST, Apr 1996) but not quite as
good as the ICOM IC-756 (see “Product
Review,” QST, May 1997). That certainly
puts it in good company.
I may have set a new record. Within
threeminutesIhadpushedenoughcontrols
to have a totally unintelligible display on
the front panel, no output from the speaker
and no clue as to what to do. Okay, when in
doubt, read the manual—and there on page
2 is a paragraph with a bold-faced title:
“Overview—read THIS if nothing else.”
Then, three paragraphs down, is the sen-
tence: “If you really mess up the settings, a
LOAD DEFAULT facility has been in-
cluded so that you can return the set to its
out-of-box condition (except for memory
contents).”Pushone button,turnoneknob,
push a second button (all well marked) and
weare back inbusiness. I wonderhow they
knew I would do that?
AOR AR7030 Communications Receiver
What’s So Special about this
Receiver?
TheAR7030is the result of acollabora-
tion between AOR and well-known UK
designerJohnThorpe.TheAR7030isbuilt
in the UK, and it has just about every fea-
ture you want—IF gain, RF gain, BFO,
passband tuning, treble and bass controls,
and memory storage of frequency, mode
and all settings (100 memories!). You can
save (and load) up to three receiver setups
in the special setup memories (A, B or C).
Want to listen to music on a shortwave
broadcastband?SelectAMorsynchronous
AM, set the tone controls, memorize a few
frequencies and you are ready to go! SSB
your choice? Preset the filter bandwidth to
2.0 kHz, the mode to USB or LSB and
memorize the settings.
Wanttochange fromonepresetto another
orstartoverwithanewmode,frequency,gain
and filter? You can use either the front panel
controls or a remote control unit.
Normally, I would not open up a review
unit.WeusuallyleavethattoMikeGruber,
W1DG, and the other folks in the ARRL
Lab. But in this case, with so much
crammed into one small box—and the use
of hex-head screwsit was a challenge I
couldn’t resist. And, inside, it is beautiful!
Amixtureof DIPsandsurface-mountcom-
ponents sat on a shiny board with readable
component labels. Looking for test point
TP4? The label is fully visible, and not
under a nearby component. Even the thick-
ness of the metal case was impressive.
The AR7030 features dual conversion,
with IFs at 45 MHz and 455 kHz. AOR
claimstheIFfiltersare“self-aligned bythe
receiver, using advanced microprocessor
control.” According to AOR, the displayed
filter bandwidth actually represents the
bandwidth measured by the receiver!
As you would expect from a modern
receiver, two VFOs are included, A and B
(which AOR calls Active and Background,
respectively). Each VFO has an associated
memoryofmode,volume,tone,filterband-
width,passbandtuning,BFOfrequency,IF
gain,RFgainorattenuation,AGC,squelch,
scan delay time, scan mode and, of course,
frequency. These settings, depending on
the mode selected, can be stored in each of
the available 100 memory locations.
The front panel has a comfortably
weighted tuning knob with adjacent FAST
and MODE controls. The tuning knob has a
nice quality feel to it, and the faster you
spin, the greater the tuning rate. A FAST
button allows you to quickly move the fre-
quency to anywhere in the “dc” to 32-MHz
range. The AR7030 tunes in 2.7-Hz steps,
but you won’t hear any chuffing in this set.
Two MODE push buttons cycle through the
available modes—AM, synchronous AM,
NBFM, data, CW, LSB and USB.
One knob and four push buttons under
the display are keyed to the display. Their
usedepends on the menusettings. They are
trulymultifunctioncontrols,andthiswhere
this receiver gets interesting—or confus-
ing, depending on your point of view.
TheAR7030requires15Vdc,which,in
the case of our unit, was supplied by the
external ac adapter that came with the ra-
dio. AOR says the radio will operate using
apowersourcefrom12to15Vdcbut“with
degraded performance at 12 V.”
BOTTOM LINE
This is a slick, attractive, quality-
made receiver with practical and aes-
thetic appeal—and with a price tag to
match. It’s a terrific performer, but the
use of menus instead of dedicated
controls might confound some users.
shortcoming, the Centaur could be your
next—or your first—linear.
Manufacturer: Ten-Tec Inc, 1185 Dolly
Parton Pkwy, Sevierville, TN 37862;
tel [phone]; fax [phone]. Manu-
facturer’s suggested retail price, $750.

June 1997 69
Digital Displays—The Good
and the Bad
The front panel is attractive and stylish,
but at a cost of a more comprehensive dis-
play of information. The AR7030 sports a
green-backlighted LCD display that can fit
up to 48 characters—numbers, letters, S
meterbargraphandclocktime—atanyone
time,soit’sabitlimitedinwhatitcanshow
at any given time. The individual charac-
ters are a bit coarse (ie, not as bold) com-
pared to similar displays on transceivers
we’ve seen. The front panel has an effec-
tiveviewingangleofatleast45°fromhead
on, in any direction. In good lighting this
angle increases.
You can program this receiver to do
Table 2
AOR AR7030 Communications Receiver, serial number 100344
Manufacturer’s Specifications Measured in ARRL Lab
Frequency coverage: 0-32 MHz. As specified, with usable sensitivity to <20 kHz.
Modes of operation: AM (envelope and synchronous),USB, As specified.
LSB, CW, DATA, and NBFM.
Power requirements: 15 V dc, 1 A (max). As specified.
Size (HWD): 3.1×9.5×7.6 inches; weight, 4.9 lb.
SSB sensitivity, 10 dB (S+N)/N, 2.2-kHz filter: CW, minimum discernible signal (MDS),
20 kHz, preamp off, 1.9 µV, preamp on, 1.4 µV; 2.0-kHz IF filter:
100 kHz, preamp off, 0.73 µV, preamp on, 0.34 µV; 180 kHz, preamp off, –122 dBm, preamp on, –131 dBm;
500 kHz, preamp off, 0.5 µV, preamp on, 0.18 µV; 500 kHz, preamp off, –123 dBm, preamp on, –133 dBm;
1.0 MHz, preamp off, 0.52 µV, preamp on, 0.19 µV; 1.0 MHz, preamp off, –123 dBm, preamp on, –132 dBm;
5 MHz, preamp off, 0.5 µV, preamp on, 0.19 µV; 3.5 MHz, preamp off, –123 dBm, preamp on, –131 dBm;
14 MHz, preamp off, 0.58 µV, preamp on, 0.23 µV; 14 MHz, preamp off, –121dBm, preamp on, –129 dBm;
28 MHz, preamp off, 0.6 µV, preamp on, 0.23 µV.
AM sensitivity, 10 dB (S+N)/N, 70% modulation, AM sensitivity, 5.5-kHz IF filter, 30% modulation:
5.5-kHz IF filter: 3.8 MHz, preamp off, 1.84 µV, preamp on, 0.74 µV;
500 kHz, preamp off, 0.85 µV, preamp on, 0.33 µV; 1.0 MHz, preamp off, 1.84 µV, preamp on, 0.75 µV.
1.0 MHz, preamp off, 0.88 µV, preamp on, 0.36 µV; 70% modulation:
5 MHz, preamp off, 0.86 µV, preamp on, 0.35 µV; 1.0 MHz, preamp off, 0.78 µV, preamp on, 0.32 µV;
14 MHz, preamp off, 1.0 µV, preamp on, 0.42 µV; 3.8 MHz, preamp off, 0.78 µV, preamp on, 0.32 µV.
28 MHz, preamp off, 1.0 µV, preamp on, 0.40 µV;
FM sensitivity, 12-dB SINAD, 1.5-kHz deviation, 10-kHz IF filter: FM, 12-dB SINAD, 3-kHz deviation, 9.5-kHz IF
28 MHz, preamp off, 1.2 µV, preamp on, 0.48 µV. filter: 29 MHz, preamp off, 1.22 µV, preamp on, 0.42 µV.
Blocking dynamic range: USB mode, 12.7 MHz, CW mode, 14 MHz, 100-kHz spacing, preamp off,138 dB, preamp on,
2.2-kHz IF filter, 9.3-MHz spacing, preamp off, 137 dB. 135 dB; 20-kHz spacing, preamp off, 126 dB*, preamp on, 121 dB.*
Two-tone, third-order IMD dynamic range: CW mode dynamic range, 2.0-kHz IF filter:
USB mode, 2.2-kHz IF filter, 10 to 20-kHz spacing,
1.0 MHz, preamp off, 90 dB, preamp on, 96 dB;
preamp off, 100 dB, preamp on, approximately 98 dB. 3.5 MHz, preamp off, 94 dB, preamp on, 98 dB;
14.0 MHz, preamp off, 97 dB, preamp on, 97 dB.
Third-order intercept: Preamp off, +27 dBm, preamp on, 1.0 MHz, preamp off, +13.9 dBm, preamp on, +12.5 dBm;
approximately +17 dBm. 3.5 MHz, preamp off, +19.9 dBm, preamp on, +18.7 dBm;
14.0 MHz, preamp off, +28.1 dBm; preamp on, +22.0 dBm.†
Second-order intercept point: Preamp off, +85 dBm. Preamp off, +74 dBm; preamp on, +48 dBm.
FM adjacent channel selectivity: Not specified. 29 MHz, preamp off, 87 dB; preamp on, 88 dB.
FM two-tone third-order dynamic range: Not specified. 29 MHz, preamp off, 87 dB*; preamp on, 88 dB.*
IF/audio response: Not specified. Range at –6 dB points, (bandwidth):
CW, 2.0-kHz filter, 57-1934 Hz (1877 Hz);
USB, 5.5-kHz filter, 346-5826 Hz (5480 Hz);
LSB, 5.5-kHz filter, 101-5581 Hz (5480 Hz);
USB, 2.0-kHz filter, 179-2469 Hz (2290 Hz);
LSB, 2.0-kHz filter, 217-2517 Hz (2300 Hz);
AM, 5.5-kHz filter, 56-2805 Hz (2749 Hz);
AM, 6.5-kHz filter, 61-4000 Hz (3939 Hz);
AM, 9.5-kHz filter, 57-4400 Hz (4343 Hz).
First IF rejection: 85 dB or better. Preamp off, 88 dB; preamp on, 100 dB.
First IF image rejection: 85 dB or better. Preamp off, 81 dB; preamp on, 75 dB.
Squelch sensitivity Not specified. At threshold, FM, 29 MHz, preamp off, 0.4 µV, preamp on, 0.08 µV.
S-meter sensitivity: Not specified. 14 MHz, S9, preamp off, 94 µV; preamp on, 29 µV.
Audio output: 2.2 W into 8 Ω. 2.7 W at approx 10% THD into an 8-Ωload.
NOTE: Except as noted, all dynamic-range measurements were taken using the ARRL Lab standard spacing of 20 kHz.
*Measurement was noise-limited at value shown.
†Third-order intercept point was determined using S5 reference.
whatever you want, and it will memorize
yourfavoritesettings.However,ifyou for-
get your settings, you must step through a
menu to find out what you set a short time
ago, yesterday or last year.
Two buttons on the left-hand top corner
of the radio—one with a light and dark dot
and the other labeled MENU—select two
banks of functions. You use the “double-
dot” push button to shut off the receiver.
The labels of three buttons in the second
column under the display window are
FILTER, RF-IF and MEMORY. In combina-
tion with the “General” button (labeled
simply *) and a small rotary knob (which
AOR calls a “spin-wheel”), all receiver
functionsareavailablefromthefrontpanel,
assuming you follow the menu.
I found many functions to be more eas-
ily controlled by the remote control unit.
Frequency, memory selection, recall and
storage, mode and filter selection only re-
quire a few pushes of the remote control’s
buttons. In fact, direct frequency entry is
possible only via the remote control box.
Volumecanbecontrolledeitherbyasimple
rotary knob on the receiver front panel or
from the remote-control box (I happen to
like rotary volume controls).
How easy is control through a menu
system? Well, it’s a bit like using some of
today’s more compact radios and H-Ts,
wheremultifunctioncontrolspredominate.
It’s not always intuitive, but the manual is

70 June 1997
pretty helpful. Sometimes I found it easy,
but occasionally I got lost and had to start
theentireprocessover.Afterafewhoursof
usingtheradio,manycontrolsbecome sec-
ond nature.
One thing that made the menu system a
bit more confusing was the natural ten-
dency to try to make adjustments based on
the printed front-panel labels. That’s be-
causethemenus can change a button’snor-
mal function—something that was not
readily apparent, even from reading the
manual. For example, it was not immedi-
ately obvious that you use the RF-IF and
MEMORY buttons to turn on the receiver’s
built-in preamp or to kick in up to 40 dB of
attenuation. The trick is to pay attention to
the menu labels on the display window.
These tell you what the buttons and con-
trols are actually used for within a given
menu.
Within the confines of this menu sys-
tem, you can recall each setting, but not all
of them at the same time. Often, it took
many pushes and turns before I found my
current settings, and then had to push the
menu button one more time just to get back
to using the receiver!
Fingers and Eyeballs
If you plan to spend a lot of time using
a receiver, the feel of the controls and the
clarity of the display are very important.
Almost all receivers (and transceivers)
thesedays arebuilttooclosetothetablefor
myfingers,butafold-downbailismounted
under the AR7030. Many users will find
the bail very helpful to raise the controls to
a more comfortable level and to angle the
display for better viewing.
Since I found it easier to control many
functions from the remote control unit, it
was a strange feeling to take my hand off
the front panel and pick up the remote unit.
I’m not sure how quickly you can get used
to switching between ham-knob and
“VCR” modes of control. Maybe if you
watch a lot of TV, you’ll also feel at home
with the AR7030.
AOR does allow for using the remote
control box in an unconventional way.
There is a sensor at both the front and the
back of the receiver, and you can stand
to the side, with the front panel shielded,
and bounce the remote signal off the back
walloftheoperatingareaintotherearpanel
sensor!
Ins and Outs
The front panel has a 3.5-mm stereo
audio jack, a very nice touch. Audio for the
headphones and auxiliary output is pro-
vided in two channels, although the
AR7030 does not provide stereo output.
Since most inexpensive headphones these
days are wired for stereo—to work with
portable CD-players and tape decks—this
meansyou will not need oneof those pesky
stereo-to-mono adapters to use an ordinary
set of headphones.
Therearpanelhasaselection switch for
either a 50-Ωantenna connection or a ran-
dom-length wire. An RS-232 interface is
supplied.AOR’s Data-Mastersoftwarefor
Windows andWindows95isavailableasan
option. There’s also a contrast knob on the
rear panel, although you probably won’t
need it. The display is a black-on-green
LCDpanel,butfullcontrastseemedtogive
the best readability.
How Does It Sound and How Does It
Work?
It sounds good! The Lab measurements
tell the story in numbers, but the audio was
clean and full. SWLing was a pleasure, and
the 31/2-inch internal speaker was remark-
ably pleasant. The AR7030 lets you boost
orcut the treble and bass to shape theaudio
foryour listening taste. (WhenI plugged in
the external speaker I usually use with my
vintage ICOM receiver, it didn’t sound
nearly as good as the built-in speaker.)
Sideband signals sounded crisp. I did not
use it to listen during any contests, but the
standard “tune 20 SSB on a Sunday morn-
ing”test was impressive. Itworked fine for
listening to the standard AM broadcast
band, too—even at night (perhaps espe-
cially at night).
The AR7030’s synchronous AM detec-
tion helps to minimize problems with selec-
tive fading. Not only that, you can pick in-
dividual sidebands on AM signals and even
switch in different filters while in synchro-
nous mode to help dodge interference.
Qualitatively, there was a little less noise
apparentonsynchronousAMdetectionthan
on ordinary AM detection, but the audio
quality was the same. Tuning was a snap.
Just get close, press the button for
Snc and
the AR7030 will automatically tune in the
signal. Turn the tuning dial to look else-
where, and the radio will automatically
swap over to conventional AM mode.
The radio is not as sensitive as most of
thehamtransceiverswe’velookedatlately,
but engaging the preamp gives you about a
10-dB boost. If you’re planning to encoun-
ter very strong signals, the AGC is a must.
By the way, the radio offers four AGC set-
tings—fast, medium, slow and off.
Our AR7030 had no noise blanker, but
AOR has just come out with its optional
NB7030 “enhanced multi-function audio
notch and RF noise blanker” board. (The
NB7030 includes a new microprocessor
chip for the radio that also provides 400
memories and memory-naming, among
other features.)
Youcansetthetuningstep for changing
the frequency using the remote control.
Step tuning worked fine on the AM broad-
cast band (set to 10-kHz steps), but after
pushing the button a few times, we noticed
that the frequency on the display would
be off by 10 Hz (ie, 1079.99 instead of
1080 kHz).
The AR7030 can scan between its two
VFOs (which AOR calls dual-VFO opera-
tion),and youcansettheminimumtimethat
each VFO is monitored before it switches
to the other VFO (from 0.5 to 30 seconds).
You can also scan memories.
Wedidnot purchase any optional filters
for the AR7030, but the receiver can ac-
commodate two additional IF filters in the
455 kHz IF. AOR says that, “within rea-
son,” any 455-kHz filter can be used, but
the PC board is drilled to accept Murata
filters and Collins mechanical filters.
These days we expect receivers to be
stable. This receiver, which incorporates a
temperature-compensatingcrystaloscillator
(TCXO),claimsstabilityofbetterthan1part
per million from 10°to 40°C. My test was
very practical: when left in my basement
shack for a few days, will the AR7030 con-
tinue to copy weather RTTY without being
touched? I often leave a receiver on the
maritime information FEC broadcast on 518
kHz (in addition to the 8 MHz weather
broadcasts).This receiver was rock solid for
more than three daysthe only reason for
the three-day limit was that I needed to re-
covertheuseofthecomputerforothertasks!
Operating Manual
No discussion of the AR7030 would be
completewithoutafewwordsaboutthe37-
page OperatingManual.It’sthorough,and
it’s thoroughly British, complete with a
little wry humor from time to time. For
example, it suggests running through the
filter calibration procedure if “you have
justgotbored with listening to your radio.”
At another point, it asserts that the main
tuning dial “likes to be used…give it a few
turns once in a while.”
ChartsearlyonintheOperatingManual
reveal the mysteries of the menu structure.
There’s also a handy quick reference guide
that covers the essentials of operating the
AR7030. Another quick reference guide
explains remote-control box basics.
There’s a block diagram and four pages of
specifications (many more than the typical
transceiver),butnoschematic.Themanual
frequently includes sample display win-
dows to guide you through the intricacies
of operation. An index would have made
the manual more useful.
Is This Receiver for You?
The minimal controls combined with the
limitednumberofitemsonthedisplaydidn’t
appeal to me, but others who used the
AR7030 had fewer problems with this ar-
rangement. For many functions, using the
remote control was much less awkward. It’s
all a matter of style, and we hams often feel
more at home with lots of dials and buttons.
If you’re already acclimated to using a re-
motecontrol“clicker”foryourTVandVCR,
the AR7030 will likely be a breeze to oper-
ate. Many discriminating listeners would
find this a great set to have in their listening
post or even in their den, and it’s a superb
performer.
Thanks to Rick Lindquist, N1RL; and

June 1997 71
Mike Tracy, KC1SX, and Mike Gruber,
W1DG, of the ARRL Lab, for their help in
conducting this product review.
Manufacturer: AOR Manufacturing Ltd,
4E East Mill, Bridgefoot, Belper, Derbyshire
DE56 2UA, UK; tel [phone];
fax [phone]; e-mail [email protected].
uk; WWW http://www.demon.co.uk/aor/.
Reviewed by Steve Ford, WB8IMY
Managing Editor
SomeoneoncesaidthatSWRmetersare
the inventions of the Devil because they
cause so much suffering. There is a lot of
truth in that statement. Many hams grieve
needlesslyoverantenna systemsthatregis-
ter“horrible”1.8:1SWRs.Theirdiabolical
meters compel them to spend hours tweak-
ing and re-tweaking in desperate attempts
to reach Nirvana—the “perfect” 1:1 SWR.
And for what?
But bedeviling aspects aside, SWR
meters do serve useful purposes. Most
modern transceivers won’t tolerate more
than a 2:1 SWR before they begin reducing
output, so it pays to have some knowledge
of your SWR conditions. In addition, your
SWR meter often provides the first indica-
tion of trouble in your antenna system. If
you leave it in the line at all times, you can
watch for sudden variations that might sig-
nala broken wire, a corroded connector, an
arcing antenna tuner and so on. And if your
SWR meter includes a wattmeter function,
you can also use it to keep an eye on your
radio’s output level.
In recent years, the digital SWR meter
has been encroaching on a market domi-
natedbyanalogmeters.Digitalmeterstend
to be expensive, however, which limits
their appeal. Radio Shack hopes to win
the hearts of hams with a new approach—
an economical model known as the model
21-527. Can they succeed?
Features
The 21-527 lets you measure SWR and
power from 1.8 to 30 MHz in ranges from
1 W to 2 kW. You can select power ranges
manually (a button on the display unit steps
through the 20, 200, and 2000-W scales), or
leave it to the meter’s autoranging function.
I preferred the convenience of autoranging.
TheSWRreadingsappearonacompact,
easy-to-read, backlighted LCD display. If
the forward power input to the meter is less
than 0.5 W, it cannot calculate the SWR
and simply displays Lo. If the SWR is too
high, it displays InF. You can also select a
peak or average-power display (more on
that later).
The 21-527 includes a remote sensor
unit, which lets you sample the RF at one
locationandviewtheresultsatanother.The
sensor connects to the display unit via a
four-foot-long,three-wirecableandamini-
stereoplug.(Themanualstatesthatyoucan
Radio Shack Model 21-527 Digital SWR/Power Meter
BOTTOM LINE
Aneconomically priceddigital SWR/
wattmeterwithgoodaccuracyandgood
looks. It includes a remote sensor, and
it’s entirely adequate for typical, non-
critical ham use.
use a cable of greater length, but it doesn’t
mention a maximum length.)
A 12-V dc power cube is included with
themeter. For this review Isimply used my
station power supply. There are only so
many ac outlets to go around!
On the Air
The 21-527 was installed in minutes. In
my station, the only issue was finding a
placetohidetheremotesensor,whichtakes
up a bit more space than the digital control
box. The remote sensor has a mounting
bracket.Thecontrolboxhasthreadedholes
in each side that appear to be designed to
accommodateamountingbracket,butnone
was supplied.
I subjected the meter to power levels
from about 0.5 W to 600 W. Readings in the
average power-setting—the power-up de-
fault—were confusing. Unless it was read-
ing a steady carrier, the display flashed a
bewildering cascade of digits that never
seem to settle down. As a result, I used it in
the peak mode at all times. Tests in the
ARRL Lab indicated, however, that the
meter was not really providing a true PEP
reading, but something that was more than
average power but less than PEP. To put it
in perspective, however, the meter was
about as accurate on PEP readings as many
of the wattmeters we looked at in a com-
parative review of SWR/wattmeters a few
years ago (see “Product Review,” QST, Feb
1991).Theauxiliarybargraphat the bottom
of the display is a nice touch. It augments
the digital readout by providing a relative
indicationof powerorSWR—dependingon
the mode you’ve selected.
SWR readings were a snap. My only
complaint—and this applies to many other
digital SWR meters—was that the display
was slow to adjust to abrupt changes. I use
a venerable Johnson Matchbox antenna
tuner with a dipole that’s center fed with
450-Ωladder line. With my analog meter
it’s easy to see the sharp SWR dips as I ad-
just the Matchbox. If you rely solely on the
digital readout of the Radio Shack 21-527,
it’s possible to miss these tuning points be-
causeofthe display’s slow response. Onthe
21-527, however, you can use the auxiliary
bar graph across the bottom of the display
insteadofthe digital readouttoseetheSWR
“dip.” Of course, if you are using a resonant
antenna system, or an automatic antenna
tuner, this isn’t an issue.
We spot-checked the accuracy of the
wattmeter in the ARRL Lab, using it to
measure power from 10 W to 1500 W on
80, 20 and 10 meters. For the most part,
measurements made using the Model
21-527 were within 10% (in most cases,
well within 10%). Things started to veer
out a bit above power levels of 1000 W or
so on 28 MHz, but the meter still was only
approdimately 10% off at 1500 W. That’s
quite respectable for a meter that costs
around $60.
Conclusion
The Radio Shack 21-527 is a fine value
if you want the convenience of a versatile
digital SWR/power meter at a reasonable
price. But you’ll have to hurry to get one—
Radio Shack is closing out this product.
The±10% full-scale accuracy is more than
adequate for most amateur applications. It
certainly would be suitable for mobile use.
The ability of the 21-527 to provide read-
ings from QRP to QRO power levels is a
big plus not found on many HF SWR
meters. The stylish 21-527 design and the
remote sensor are icing on the cake.
A special thanks to ARRL Educational
Programs Coordinator Glenn Swanson,
KB1GW, for his contribution to this review.
Manufacturer:Tandy Corporation, 1900
One Tandy Center, Ft Worth, TX 76102; tel
817-390-3700. Manufacturer’s suggested
retail price, Model 21-527, $60.
Manufacturer’ssuggestedretailprice:$1400.
NB7030 audio notch and RF noise blanker
board, $315; SM7030 service kit, $90;
FPU-7030 enhanced features CPU, $110.