From March 2010 QST © ARRL
PRODUCT REVIEW
Mark J. Wilson, K1RO
Product Review Editor
Bottom Line
Reviewed by Phil Salas, AD5X
QST Contributing Author
QST has previously reviewed in-shack
and remote automatic antenna tuners de-
signed for various applications and power
levels.
1,2
Recent interest in 43 foot multiband
vertical antennas available from several
vendors has led to a corresponding interest
in remote auto tuners used specifically with
these antennas. This is because the 1:4 unun
(unbalanced to unbalanced transformer)
typically mounted at the vertical’s base for
matching to 50 Ω coaxial cable provides a
compromise SWR on 60 through 10 meters.
SWR is very high on 160 and 80 meters
resulting in corresponding coax and unun
losses.
This review will focus on three 200 W
auto tuners and specifically their suitabil-
ity for remote outdoor use at the base of a
43 foot multiband vertical antenna. The units
reviewed (from lowest to highest cost) are
the MFJ-927, CG Antenna CG-3000 and
SGC SG-230.
43 Foot Antenna
Measurement Methods
According to the EZNEC antenna mod-
eling program, a 43 foot vertical has an
impedance of 3 –j620 Ω on 160 meters when
installed over a perfect ground and not in
close proximity to other objects. For bench
testing a tuner’s ability to match this load on
160 meters, I built a simulator circuit with an
impedance of 14 –j590 Ω. I used 20 Ω and
50 Ω Caddock thick film resistors in parallel
to give the total real resistance of 14 Ω. This
simulates 3 Ω of radiation resistance plus
11 Ω of ground loss, which is probably bet-
ter than most hams have on 160 meters. To
Remote Automatic Antenna Tuners and the
43 Foot Vertical
Figure 1 — Test setup used by the author for measuring expected tuner loss with a
load that simulates the impedance of a 43 foot vertical antenna on 160 meters.
See text for details.
There are pros and cons to using a remote automatic antenna tuner with an un-
tuned antenna such as the popular 43 foot vertical. On the plus side are operating
convenience and reduced SWR related coax losses. Cons include limited reactive
tuning range and tuner losses. If you plan your remotely tuned antenna system
properly, a remote auto tuner can be an excellent answer for multiband operation.
1
J. Hallas, W1ZR, “Automatic Antenna Tuners
— A Sample of the Field,” Product Review,
QST, May 2004, pp 71-76. QST Product
reviews are available on the Web at www.
arrl.org/members-only/prodrev/.
2
J. Hallas, W1ZR, “Medium to High Power Auto
Antenna Tuners — The Evolution Continues,”
Product Review, QST, Aug 2006, pp 56-61.
simulate the reactive component, two 300 pF,
1 kV silver-mica capacitors in series provide
–j590, a compromise reactance between the
theoretical –j620 and the –j550 that I mea-
sured on my own 43 foot vertical.
Because maximum inductance and high-
est RF current occur on 160 meters due to the
antenna’s high capacitive reactance and low
resistive impedance, this simulator circuit
also permits the measurement of expected
auto tuner loss when used with a 43 foot
vertical on 160 meters. To measure the loss,
I used an Array Solutions PowerMaster
power/SWR meter and Tektronix TDS-2022
digital sampling oscilloscope as shown in
Figure 1. I first compared the TDS-2022
and PowerMaster by feeding a 50 Ω resistive
load directly and comparing the computed
power level from the TDS-2022 display to
the PowerMaster readings. The worst case
measurement difference between the two
instruments was 3%.
I set the PowerMaster to read net (forward
minus reflected) power and inserted a high
power 3 dB attenuator at the transceiver out-
put to ensure that reflected power from a less
than perfect auto tuner match is attenuated
6 dB further if re-reflected by the output cir-
cuitry. Actual power delivered to the load is
measured by the TDS-2022, which displays
not only the normal oscilloscope waveform
but also digitally displays the frequency,
RMS voltage and peak-to-peak voltage.
Resistive matching range and loss test-
ing was performed in the ARRL Lab with a
precision setup similar to that described in
February 2003 QST and used in tuner reviews
since then.
3
In the course of testing, ARRL
Test Engineer Bob Allison, WB1GCM, noted
that mounting the CG-3000 and SG-230 to a
metal plate improved auto tuner efficiency. It
also eliminated interaction with nearby metal
objects. Without the plate, SWR changed
dramatically with tuner movement on the
metal test bench. Bob suggests bolting the
mounting bracket of either of these tuners to
a metal plate if the unit is installed on a non-
conductive surface. (The MFJ-927, which is
3
M. Tracy, KC1SX, “Antenna Tuner Testing
Methods vs Accuracy,” Product Review,
QST, Feb 2003, p 75.
XCVR
3 dB
Pad
PowerMaster
(Fwd - Rev Power)
Autotuner
under test
14-j590 Ω
Simulator Circuit
TDS-2022 Scope
QS1003-Prodev01
(11 pages)
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