Palstar HF-Auto High Power HF and 6 Meter Automatic Antenna Tuner

by Mark
J. Wilson,
Palstar HF-Auto High Power HF and
6 Meter Automatic Antenna Tuner
Speed up band changes with this legal-limit auto tuner.
Reviewed by Joel R. Hallas, W1ZR
QST Contributing Editor
The Palstar HF-Auto
is a high-power automatic antenna tuner that
covers a continuous frequency range from 1.8 to
54 MHz. This includes
the 160 through 6 meter
amateur bands, as well as
Military Auxiliary Radio
Service (MARS) and
other frequencies outside
the amateur bands. While
most automatic tuners that we’ve seen
adjust the tuning through the use of relay
switched miniature fixed capacitors and inductors, the HF-Auto makes its adjustments
through the use of a full-size rotary inductor
and variable capacitor adjusted by precision
stepper motors. The only other high power
antenna tuner we’ve seen in this form was
its predecessor, the Palstar AT-Auto automatic antenna tuner we reviewed some
years ago.1 While functionally similar, and
about the same size, there are some significant differences that make a new review of
this tuner appropriate.
Here’s What’s New
A big change in capabilities from the ATAuto is that the HF-Auto expands coverage to include 6 meters. This makes sense
because more new linear amplifiers include
operation on 6 meters, as have most transceivers for some years. Another change is
that the HF-Auto includes three switchselectable antenna ports, rather than the two
provided in the AT-Auto.
While the AT-Auto allowed use with balanced antenna systems through an internal
1J. Hallas,
W1ZR, “Product Review: Medium to
High Power Auto Antenna Tuners — The Evolution Continues,” QST, Aug 2006, pp 56 – 63.
4:1 balun, all three antenna ports on the
newer tuner are for coaxial feed lines only.
This makes good sense to me for a couple
of reasons. First, many amateurs have no
need for a balanced output and thus don’t
need to pay for it. Second, if a balanced
output is desired, an external balun offers
the opportunity to select the most appropriate transformation ratio (Palstar offers
both a 1:1 and 4:1 model, each priced at
$90), as well as the opportunity to move the
transformation point a short distance from
the tuner. While extending the balun connection through coax does add loss due to
the generally mismatched coax, the loss is
small if the balun is just a few feet of lowloss coax away. This arrangement can help
avoid problems of coupling to and from the
unshielded (and often not quite balanced)
“balanced” feeders.
Bottom Line
The HF-Auto exhibits the quality of
construction, competent design, and
ease of operation we have come to
expect from Palstar. This smoothly operating tuner would be an appreciated
addition to most amateur stations.
QST ® – Devoted entirely to Amateur Radio
Another change is in the
metering. The AT-Auto included an analog, crossneedle SWR meter, while
the HF-Auto provides a
more precise digital power
and SWR indicator. The
power meter reads actual
peak power, a nice feature.
Another change is in the architecture of the control system.
The earlier unit offered both frequency sensing and direct control
of frequency-based tuning through
an Icom proprietary interface. The
HF-Auto is completely independent
of the radio type and quickly tunes based
on the measured transmit frequency.
What You’ll Find
The HF-Auto is constructed in a heavyduty powder-coated enclosure with a
straightforward front panel as shown in the
lead photo. There are four buttons and one
knob, which also functions as an additional
pushbutton. The MODE button selects operating mode between BYPASS, AUTO, and
MANUAL. It’s also used for entering SETUP
mode. In SETUP mode, you can choose
how close to 1:1 SWR you want the tuner to
target, as well as a number of other preference items, all described in the manual. The
LCD is used for mode and menu selection,
but in operational mode provides an indication of mode and antenna selection, the
measured transmit frequency, the tuner inductor and capacitor values, the peak power
and the SWR.
The inside view (see Figure 1) shows the
neat and high-quality construction we have
come to expect from the folks at Palstar.
Near the front, behind the control and display hardware, are the two precision stepper motors, one for the inductor and the
other for the differential capacitor. These
are driven by toothed fiberglass belts to
Reprinted with permission from May 2014 QST
avoid stretching and slippage. The rear contains the antenna relays and other interface
Figure 1 — The interior of the HF-Auto.
The rear panel is straightforward. Three
UHF (SO-239) sockets are provided
for the antenna outputs, plus another
for RF input. A jack is provided for the 12 –
14 V dc power connection, with a furnished
cable that includes RFI filtering. A current
level of 6 A peak is specified, but we measured a maximum of 3.6 A in the lab during
tuning. I found this compatible with my
25 A transceiver power supply, because I
was never adjusting the tuner and running
full transceiver output power at the same
time. There is also a serial connector for
software upgrades and a switch to select
Table 1
Palstar HF-Auto, serial number 20613
Circuit configuration: T network with shunt variable 16 µH inductor, fixed 10 µH
series inductor and 470 pF – 10 pF – 470 pF differential capacitor.
Frequency range: 1.8 to 54 MHz.
Matching range: Up to 8:1 SWR.
Power rating: 1800 W PEP SSB/CW (1.8 – 29.7 MHz), 800 W (50 – 54 MHz), 100%
duty cycle.
Measured threshold tuning level: 2 W (typical); maximum tuning level: 200 W single tone.
Measured insertion loss (bypass): 1.8 – 25 MHz, <0.1 dB; 28 MHz, 0.1 dB; 50 MHz, 0.35 dB.
Measured current usage: 13.8 V dc at 3.6 A (when tuning), 690 mA (standby),
475 mA (bypass).
Size (height, width, depth): 6.8 × 12.5 × 17.5 inches (incl protrusions); weight: 20 lbs.
Price: $1595.
ARRL Lab Resistive Load and Loss Testing
Load (W)
160 m 80 m
40 m
20 m
10 m
6.25 Power Loss%
Power Loss%
1.11.2 1.21.0 1.3
Power Loss%
1.11.1 1.11.1 1.2
Power Loss%
1.11.1 1.11.0 1.1
Power Loss%
1.11.3 1.11.1 1.1
Power Loss%
1.21.1 1.21.2 1.2
Power Loss%
1.11.2 1.21.1 1.2
Power Loss% 64 32 8
SWR 1.21.5 1.31.2 1.2
At 6 meters, the HF-Auto found a match for all resistive loads except 50 W. See text.
FrequencyShort Open
1.8 MHz
3.5 MHz
7.0 MHz
14 MHz
28 MHz
50 MHz
Will tune 1600 W resistive load 160, 80,
10 and 6 meters.
Yes = will tune into open or short circuit.
NT = no tuning solution.
Reprinted with permission from May 2014 QST
What It Does
The HF-Auto operates a bit differently from
most automatic tuners. Because it measures
frequency (in AUTOMATIC mode), a short
“dit” on CW or a few syllables on SSB will
let it know your frequency, and it will tune
until it gets to the settings last used for that
frequency. When it’s finished, a short key
down signal (2 W is usually enough, although I needed a little more in some cases)
will bring it to a match if more adjustment
is needed.
Depending on how far the rotary inductor
needs to move, the initial tuning can take
up to around 15 seconds. The second pass
is generally much shorter, but will somewhat depend on the accuracy you require.
A menu setting (TUNING LEVEL THRESHOLD) sets the target tuning goal from 1.05:1
to 1.64:1. That’s a nice feature, but obviously it can take a bit longer to find a 1.05:1
match than, say, the suggested 1.5:1 — but
it’s your choice. Though you can hear the
precision stepper motors advancing, I did
not find them offensive.
In addition to the AUTOMATIC mode, a
MANUAL mode is supported. Poke the
MODE button and you are into manual tuning mode. The single knob below the LCD
panel is used to change the inductance (L)
or capacitance (C). It comes up ready to
tune the L; push the knob in briefly and it
changes the C. The value of L and C are
displayed on the LCD as you change them,
so you can record the values for later reference. In the manual mode the HF-Auto
adjusts capacitance and inductance via
the stepper motors, so minimum effort is
ARRL, the national association for Amateur Radio® required — no heavy cranking needed with
this tuner.
Manual tuning can be useful to return to a
favorite net or DX frequency without causing interference, or it can be used with an
antenna analyzer to adjust to a match outside the ham bands, if desired. The MANUAL
setting can also be used to modify a previously memorized setting at a particular
frequency, if you need a better match for
some reason. The tuner includes more than
1000 frequency memory bins that vary in
frequency width from 4 kHz on 160 meters
to 500 kHz on 10 meters. There are also
bins allocated for frequencies outside of the
ham bands.
Three Coax Antenna Ports
Another nice feature of the HF-Auto is that
it has provisions for switch selection (via
the front panel MODE button) of any of three
unbalanced (coax connected) antennas. The
tuner can also remember which antenna to
select, based on frequency. Our original
firmware allowed selection based on ranges
of frequency, such as 1.8 to 13 MHz for antenna 1, 14 to 30 MHz for antenna 2 and 50
to 54 MHz for antenna 3. While that would
be useful at some stations, at W1ZR I use
my modified tribander for 20, 15, 10, and 6
meters and an 80 meter center-fed Zepp on
80, 60, 40, 17, and 12 meters. I was stuck
with manual antenna switching until firmware version 1.29, which allows antenna
selection by amateur band, a much more
flexible arrangement. Unfortunately, there
is no provision for 60 meters in this version
of the menu — hopefully the omission will
be remedied in the next release.
How It Performs
The ARRL Laboratory results are summarized in Table 1. There were few surprises,
although the loss with low impedance loads
on 160 meters suggests that it would be
prudent not to use high duty cycle modes
there with full power. A loss of 41% at 6.25
W with 1500 W applied, corresponds to a
dissipation of 615 W within the tuner —
probably not good for very long!
beyond the tuner’s specified 8:1 capability, yet it was able to find a 1:1 match. Not
many tuners can do that, especially on 160
meters. Note that, having learned from
my mistakes, I did not try this with high
power!2 I did run with up to 500 W, the
most I can generate, on multiple bands and
observed no problems.
navigate the many SETUP menus, all illustrated with color photos of the display and
indicating the choices. Some of the menu
choices were not yet available in our unit.
Most menus are of the “set and forget” type,
although some, such as ANTENNA selection,
are used frequently and are provided with a
dedicated button.
While the lab noted that tuning could take
up to 30 seconds, in my testing (with the
motor speed set to HIGH), the longest time I
found was 20 seconds between memorized
settings on 160 to 6 meters.
The manual includes a chronology of firmware revisions — the original went up to
version 1.25, the newer to version 1.29,
along with instructions for downloading
new software revisions to the serial port on
the rear of the tuner. We made a successful upgrade to version 1.27 before starting
Lab testing, and again to version 1.29 while
being evaluated at W1ZR. A serial-to-serial
cable for updating firmware is provided
with the tuner, while a serial-to-USB cable
is available from Palstar for those who don’t
have traditional serial ports. There is no
need to have a computer connection, other
than for firmware upgrades.
Lab testing had observed a problem tuning
on 6 meters into a matched load. I didn’t
have anything at my station (including my
dummy load) that provided an exact 1:1
match on 6 meters, but the tuner had no
trouble tuning my coupled resonator Yagi
with a 1.2:1 SWR on 50.2 MHz, nor my
Zepp with a higher SWR on that band. Of
course, if you have a perfectly matched
antenna, you are better off switching to
BYPASS mode. My guess is that with a 1:1
SWR, the differential capacitor needed to
have the same capacitance on each side, and
minimum capacitance was probably too
high to tune to 6 meters in that configuration. With a mismatch, the capacitance can
be lower on one side or the other.
The HF-Auto comes with a well-illustrated
15-page Technical Manual. The version
on the Palstar website that became available with the version 1.29 firmware release
is much more complete and user friendly
than the earlier version that came with our
tuner. The manual starts with an informative “Theory of Operation” section and follows with detailed descriptions of how to
2J. Hallas,
W1ZR, “My Tuner Tuned My Antenna
— But Now it Doesn’t!” QST, Aug 2012, p 46.
Manufacturer: Palstar Inc, 9676 N Looney
Rd, Piqua, OH 45356; tel 800-773-7931;
fax 937-773-8003;;
See the Digital
Edition of QST
for a video
overview of the
Palstar HF-Auto
High Power HF
and 6 Meter
Antenna Tuner.
On the air at W1ZR, this tuner worked very
well and was able to tune just about any
of my antennas on almost any band (possibly a mixed blessing for very low impedance combinations, as noted above). My
usual toughest test is to tune my 80 meter
center-fed Zepp on 160 meters, where its
impedance measures 5.2 + 65.8 W. That
corresponds to a 50 W SWR of 26:1, far
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On the Down Side
There are very few issues with this tuner.
One possible concern is that the tuner will
match into a short on 160, 10, and 6 meters.
This is not an uncommon problem, and
while we wouldn’t plan to do this, it can
easily happen by accident in a number of
ways. Not only will we make few contacts,
but the tuner will then be dissipating the full
transmit power. By making note of the L
and C values on the display during normal
conditions, you will know if something has
changed in your antenna system and can investigate it, or better yet, use a simple field
strength meter to make sure your antennas
are actually radiating.
Reprinted with permission from May 2014 QST
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