auto antenne tuner test

From March 2010 QST © ARRL
PRODUCT REVIEW
Mark J. Wilson, K1RO
Product Review Editor
k1ro@arrl.org
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
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 –
j
620
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 –
j
590
. I used 20
and
50
Caddock thick film resistors in parallel
to give the total real resistance of 14
. This
simulates 3
of radiation resistance plus
11
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
j
590, a compromise reactance between the
theoretical –
j
620 and the –
j
550 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
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
Po
werMaster
(Fwd – Re
v Po
wer)
A
utotuner
under test
14-
j
590
Simulator Circui
t
TDS-2022 Scope
QS1003-Prode
v01
From March 2010 QST © ARRL
Table 2
Testing with AD5X
43 Foot Vertical
MFJ-927
CG-3000
SG-230
Band SWR SWR SWR
160
No tune
No tune
1.4:1
80
1.3:1
2.0:1
1.4:1
60
1.0:1
1.2:1
1.2:1
40
1.0:1
1.2:1
1.3:1
30
1.5:1
1.1:1
1.5:1
20
1.5:1
1.3:1
1.0:1
17
1.2:1
1.5:1
1.4:1
15
1.1:1
1.3:1
1.9:1
12
1.2:1
1.7:1
1.8:1
10
1.2:1
1:9:1
1.3:1
Table 1
Tuned SWR with Short Circuit or Open Load
—– MFJ-927—–
—– CG-3000 —–
—– SG-230—–
Band Short Open
Short Open
Short Open
160
No tune
No tune
No tune
No tune
No tune
1.4:1
80
No tune
No tune
No tune
1.3:1
No tune
1.0:1
40
2.9:1
No tune
No tune
1.7:1
No tune
2.3:1
30
No tune
No tune
No tune
2.4:1
1.2:1
1.2:1
20
4.0:1
5.0:1
1.1:1
2.2:1
1.7:1
3.0:1
17
4.0:1
No tune
1.6:1
No tune
1.9:1
1.3:1
15
No tune
3.8:1
1:4:1
1.3:1
1.6:1
1.7:1
12
No tune
No tune
No tune
1.3:1
No tune
No tune
10
1.3:1
1.9:1
1.8:1
No tune
No tune
2.0:1
Figure 2 — Each auto tuner was tested at the base of the author’s 43 foot vertical antenna.
built on a metal plate with integral mounting
tabs, did not exhibit this behavior.)
The ARRL Lab also tested the auto tuners
with open and short circuit loads. With
loss
less
tuner components, an open/short tuning
solution is not possible. But no practical an
tenna tuner is lossless because it is built with
pedance of my 43 foot vertical on 60 meters
as 48 –
j
0
, which implies my ground loss
is 12
on that band. Once the tuner found
a match, I recorded the SWR measured in
my shack with the PowerMaster, as shown
in Table 2.
MFJ-927 REMOTE AUTOMATIC
ANTENNA TUNER
The MFJ-927 is the smallest of the three
auto tuners tested here. It is enclosed in
a weather protected container, but is not
O-ring sealed. For extended outdoor opera
tion, it would be a good idea to place the
tuner under a protective cover, such as an
inverted plastic storage bin.
Coaxial and random wire outputs are
provided, along with an SO-239 UHF
jack for the station feed line and a ground
post. The MFJ-927 receives dc power on the
coax feed line via an internal bias-T, so you
won’t need to run a separate cable for power.
MFJ supplies an MFJ-4117 bias-T for inserting
+12 V dc on the coax in the shack. The
outside of the unit and internal circuitry are
shown in the accompanying photos. Note
that the inductors consist of a mix of toroidal
and wide spaced air wound inductors.
Unlike the CG-3000 and SG-230, the
MFJ-927 does not specify minimum an
tenna lengths for tuning the ham bands, but
instead specifies a resistive tuning range on
all bands. A little calculator work shows
that with the 25 μH maximum inductance
available in the MFJ-927, the minimum
length antenna for 160 meters would need
to be about 80 feet. Therefore the MFJ-927
does not have the inductance range required
for using my 43 foot vertical on this band.
I verified this by connecting the simulator
circuit to the MFJ-927. The MFJ-927 tried
to find a match for about 10 seconds, and
then gave up.
Open/short test data is shown in Table 1.
Only on 10 meters did the MFJ-927 find an
open and short circuit tuning solution below
a 2:1 SWR.
Next I connected the MFJ-927 to the base
of my 43 foot vertical. Tuning was very fast,
with initial tuning typically occurring in less
than 2 seconds and tuning from memory
essentially instantaneous. As expected, the
MFJ-927 could not tune the 43 foot vertical
on 160 meters but found a 1.5:1 or better
match on 80 through 10 meters. Note that
an external inductance can be used to allow
160 meter operation (see sidebar on page
52). The results are shown in Table 2.
Last came the ARRL Lab testing of the
resistive load tuning range and loss mea
surements. As you can see in Table 3, the
MFJ-927 matched all resistive loads the Lab
presented to it. While there were a few cases
where the SWR didn’t reach the 1.5:1 target,
components of finite Q. The Lab discovered
that an antenna tuner can sometimes tune into
its own internal losses and present a matching
solution to the transmitter. Results of these
tests are shown in Table 1. Generally, fewer
cases where this happens indicates lower
intrinsic tuner losses.
Tuning sensitivity was also measured.
This is the RF power and SWR required to
automatically initiate a retune. All three auto
tuners specify a “must start a retune” when
the SWR exceeds 2:1.
For final testing, each auto tuner was
connected to the base of my 43 foot verti
cal and tested on each band (Figure 2) with
my 100 W transceiver. Sixty feet of
1
2
inch
Andrew Heliax connects my transceiver in
the shack to the auto tuners at the base of
the 43 foot vertical. Three ground rods and
approximately 20 radials provide my RF and
dc grounding at the antenna — certainly not
a perfect ground, but probably not atypical.
As a reference, I measured the resonant im
From March 2010 QST © ARRL
Table 3
MFJ-927
Manufacturer’s Specifications
Maximum power: 200 W PEP SSB/CW,
125 W continuous.
Minimum power for tuning: 2 W.
Frequency range: 1.8 to 30 MHz.
Tuning time: 6 seconds (initial tuning),
<0.2 second if memorized.
Impedance matching range: 6 to 1600
Ω.
Matching network: Reversible-L (series
L/shunt C or shunt C/series L).
Capacitor range: 0-3961 pF (256 tuning
steps).
ARRL Lab
Testing
Current draw: 200 mA when tuning, 13 mA static
Tuning sensitivity: At 10 W or higher, 2:1 SWR starts a retune.
Measured power loss into resistive loads (%) / Input SWR at match.
SWR
Load (
Ω)
160 m
80 m
40 m
20 m
10 m
16:1
3.125
47
21
26
13
*
1.6
**
1.6
**
1.6
8:1
6.25
31
14
27
15
*
**
**
**
1.7
**
4:1
12.5
*
*
*
*
16
**
**
**
**
1.8
2:1
25
*
*
*
*
*
**
**
**
1.6
**
1:1
50
*
*
*
*
*
**
**
**
**
1.6
2:1
100
*
*
*
*
27
**
**
**
**
1.6
4:1
200
11
13
*
*
22
**
1.7
1.6
**
1.6
8:1
400
12
*
*
*
20
**
**
**
**
1.6
12:1
600
*
12
17
14
24
**
1.6
**
**
**
16:1
800
30
12
17
14
24
**
1.8
1.8
**
1.6
*Power loss less than or equal to 10%.
**Matched SWR less than or equal to 1.5:1.
Inductor range: 0-24.86 μH (256 tuning
steps).
Tuning start: 2:1 SWR
Tuning target: Less than 1.5:1 SWR
Memory channels: 2500
Memory resolution: 2 kHz on 160 meters,
scaling to 28 kHz on 10 meters
Size: 7.5 × 5.5 × 9 inches; weight 3 pounds.
Power supply: 13.8 V dc ±10% at less than
750 mA.
Price: $230.
in most cases the 1.5:1 target specification
was met. The ARRL Lab also verified the
2:1 “must start tuning” specification.
The MFJ-927 has the ability to be remote
ly forced to retune on any given frequency
with its
Sticky Tune
feature. In software ver
sion 2.4 or greater, if Sticky Tune is enabled,
the MFJ-927 will always retune the first time
you transmit after a power cycle. This feature
is convenient if the SWR doesn’t settle as low
as you like and you’d like to force a retune. If
you want to try for a lower tuned SWR on a
given frequency, simply cycle power and then
transmit on that frequency. The MFJ-927 will
retune on that frequency only. Other memory
locations will be unaffected.
MFJ-927 Summary
The MFJ-927 is a fast-tuning, inexpen
sive remote auto tuner that will give good
performance from 80 to 10 meters when
used with a 43 foot vertical. Its Sticky Tune
feature provides a simple way to remotely
force a retune on any frequency without
affecting other memories. In a permanent
installation, some sort of cover for weather
protection would be a good idea.
Manufacturer
: MFJ Enterprises, PO Box
494, Mississippi State, MS 39762, tel 800-
647-1800;
www.mfjenterprises.com
.
CG ANTENNA CG-3000 REMOTE
AUTOMATIC ANTENNA TUNER
The CG-3000 is enclosed in an O-ring
sealed ABS plastic weatherproof container.
It includes attached stainless-steel mounting
brackets as well as two U bolts should you
wish to mount the CG-3000 on a mast. The
provided power cable, about 12 feet long,
plugs into the CG-3000 via a four pin connec
tor included on the cable. Next to the power
connector is an SO-239 for the station feed line
and a metric wing nut ground connection that
fits a #10 solder lug. The CG-3000 antenna
output is a single ceramic-insulated terminal
that is also a good fit for a #10 solder lug. As
seen in the accompanying photo, all inductors
are close wound air-core inductors.
CG Antenna specifies a minimum an
tenna length of 8 meters (26 feet) for 1.8 to
30 MHz operation, or 2.4 meters (8 feet) for
3.5 to 30 MHz. Those specifications, along
with the specified inductance range, indicate
that the CG-3000 will provide full coverage
from 160 through 10 meters with a 43 foot
vertical. Testing showed this was not the
case. When I connected the simulator circuit,
the CG-3000 was unable to find a match.
This implies that either the CG-3000 does
not have the advertised inductance range,
or the tuning algorithm fails to do the job
on 160 meters.
During resistive load testing in the ARRL
Lab (Table 4), you can see that the resis
tive tuning range on 160 meters is limited
compared to the other bands. There were
also some resistive impedances on 40 and
10 meters that could not be matched. ARRL
Lab open/short test results are shown in
Table 1. As you can see, tuning solutions at
or below 2:1 SWR are found on most of the
HF bands for opens or shorts.
Under some conditions the SWR settles
close to 2:1, which is the target SWR. In
those cases, I found that once the CG-3000
is tuned I could exceed a 2:1 SWR by mov
ing frequency within that band, but a retune
won’t occur until the SWR increases to
From March 2010 QST © ARRL
Table 4
CG Antennas CG-3000
Manufacturer’s Specifications
Maximum power: 200 W PEP,
125 W continuous.
Minimum power for tuning: 10 W.
Frequency range: 1.8 to 30 MHz.
Tuning time: 6 seconds (initial tuning),
<0.2 second if memorized.
Impedance matching range: Not specified.
Matching network: Low-pass pi or
reversible-L as needed (C-L-C)
Input capacitor range: 0-6300 pF
(100 pF increments).
Output capacitor range: 0-775 pF
(25 pF increments).
ARRL Lab
Testing
Current draw: 750 mA when tuning, 413 mA static
Tuning sensitivity: At 10 W, 3.2:1 SWR starts a retune; at 50 W, 2.5:1 SWR.
Measured power loss into resistive loads (%) / Input SWR at match.
SWR
Load (
)
160 m
80 m
40 m
20 m
10 m
16:1
3.125
No tune
*
No tune
48
No tune
n/a
**
n/a
2.0
n/a
8:1
6.25
13
18
20
36
No tune
**
**
**
**
n/a
4:1
12.5
12
20
17
20
25
**
1.9
**
**
**
2:1
25
29
17
27
19
12
1.9
1.9
2.0
**
**
1:1
50
24
*
*
13
*
**
**
**
**
**
2:1
100
24
*
14
31
15
2.1
**
**
1.9
**
4:1
200
No tune
11
12
11
22
n/a
**
**
**
**
8:1
400
No tune
11
14
14
18
n/a
**
**
**
1.6
12:1
600
No tune
20
14
15
35
n/a
1.8
**
**
2.0
16:1
800
No tune
38
23
24
42
n/a
**
**
1.6
1.9
*Power loss less than or equal to 10%.
**Matched SWR less than or equal to 1.5:1.
Inductor range: 0-64 μH
(0.25 μH increments).
Tuning start: 2:1 SWR.
Tuning target: Less than 2:1 SWR.
Memory channels: 200.
Memory resolution: 5 kHz on 160 meters,
scaling to 200 kHz on 10 meters.
Size: 12.2 × 9.5 × 2.8 inches; weight
13 ounces.
Power supply: 13.8 V dc ±10% at less than
800 mA.
Price: $330.
above 3:1. Unfortunately there is no easy
way to force a retune. The only way I could
force a retune was to short the output of the
CG-3000, let it try to tune, then reconnect
the load and let it tune again. I found one
other issue. The CG-3000 does not time
out if it cannot find a tuning solution. It just
continues to tune until you either remove RF
drive, or turn off power to the unit.
After completing bench testing, I con
nected the CG-3000 to the base of my
43 foot vertical and measured the tuned
SWR. Except for 160 meters, tuning solu
tions were found quickly. In most cases, the
final match was better than the 2:1 target.
Results are shown in Table 2.
The optional CG-CTU control unit adds
power and reset switches, along with power
and tuning LEDs. The reset switch puts the
tuner in bypass, but does not erase memories
or force a retune
CG-3000 Summary
The CG-3000 can reliably be used on 80
through 10 meters with a 43 foot vertical,
but not on 160 meters as advertised. The
solution presented in the sidebar may work
for the CG-3000 but this was not verified. Its
inability to time out when a match cannot be
found is an irritant, but not really a problem.
Its failure to meet its 2:1 “start tuning” speci
fication is an issue, however, especially since
there is no easy way to force a retune.
Manufacturer:
CG Antenna, 5/501, Lane
1800, Hanri Rd, 200336 Shanghai, China;
sales@cgantenna.com
;
www.cgantenna.
com
. We purchased the review unit from
Array Solutions, which is no longer handling
CG antenna products. At press time, CG An
tenna was working on details for distribution
of its products in the US.
SGC SG-230 REMOTE
AUTOMATIC ANTENNA TUNER
The SG-230 is enclosed in a rugged
O-ring sealed ABS plastic weatherproof con
tainer. Transceiver RF and power interface
through a 9 foot combination 4 conductor/
RG-58 cable that is permanently attached to
the SG-230. On the coax input side you will
find a
1
4
inch diameter bolt for the ground
connection, and the antenna output is a single
ceramic insulated terminal with a #10 screw
interface. Antenna and ground solder lugs
are provided with the SG-230. All inductors
are close-wound air-core inductors.
SGC specifies a minimum required an
tenna length of 23 feet for operation below
3.3 MHz, and 8 feet for operation above
3.3 MHz. With its specified 64 μH maximum
inductance, the SG-230 should be able to
match a 43 foot vertical on 160 meters. As
before, I first tried tuning on 160 meters with
the simulated load. This time I was success
ful — the SG-230 found a match within a
few seconds, just as it should. At 1.85 MHz,
I measured an SWR of 1.46:1 and 2.1 dB
loss (38% loss).
Table 5 shows the results of the ARRL
Lab testing. All resistive loads were matched.
In most cases the final tuned SWR was less
than 1.5:1, though there were two cases
where the tuned SWR settled close to the
2:1 SWR target. Open/short test results are
shown in Table 1. As with the CG-3000,
the SG-230 can find an open/short tuning
solution of less than 2:1 SWR on most of
the HF bands.
Just like the CG-3000, tuning doesn’t
restart if the SWR changes unless the SWR
From March 2010 QST © ARRL
Inductor range: 0.25-64 μH (0.25 μH
increments).
Tuning start: 2:1 SWR.
Tuning target: Less than 2:1 SWR.
Memory channels: 170.
Memory resolution: 10 kHz on 160 meters,
scaling to 1500 kHz on 10 meters.
Size: 16 × 12 × 3.5 inches; weight 8 pounds.
Power supply: 10-18 V dc at less than
900 mA.
Price: $540.
Table 5
SGC SG-230
Manufacturer’s Specifications
Maximum power: 200 W PEP, 80 W
continuous.
Minimum power for tuning: 3 W.
Frequency range: 1.8 to 30 MHz.
Tuning time: 6 seconds (initial tuning),
<0.2 second if memorized.
Impedance matching range: Not specified.
Matching network: Low-pass pi or
reversible-L as needed (C-L-C)
Input capacitor range: 100-6400 pF
(100 pF increments).
Output capacitor range: 25-800 pF
(25 pF increments).
ARRL Lab
Testing
Current draw: 900 mA when tuning, 450 mA static
Tuning sensitivity: At 10 W, 3.2:1 SWR starts a retune; at 50 W, 2.5:1 SWR.
Measured power loss into resistive loads (%) / Input SWR at match.
SWR
Load (
)
160 m
80 m
40 m
20 m
10 m
16:1
3.125
14
19
29
13
25
**
**
2.1
**
**
8:1
6.25
*
22
13
14
29
**
**
**
**
1.6
4:1
12.5
17
27
13
12
22
**
**
**
**
**
2:1
25
21
11
11
*
28
**
**
**
**
1.8
1:1
50
*
*
*
*
13
**
**
**
**
**
2:1
100
*
*
*
*
23
1.6
**
**
**
**
4:1
200
*
*
*
*
11
**
**
**
**
**
8:1
400
*
*
*
*
32
**
**
**
**
1.6
12:1
600
*
*
*
17
30
**
**
**
1.6
**
16:1
800
*
*
12
22
42
**
**
**
**
**
*Power loss less than or equal to 10%.
**Matched SWR less than or equal to 1.5:1.
increases to over 3:1. Unlike the CG-3000,
the SG-230 has an internal strapping option
that defeats memory tuning. Internal jumper
JP2 bypasses the SG-230’s memories, which
means that the SG-230 will always retune
rather than use previously stored data. This
setting will cause the SG-230 to retune every
time you transmit on a new frequency.
Final testing occurred with the SG-230
attached to the base of my 43 foot vertical.
I was able to find a matching solution on all
bands from 160 through 10 meters with no
tuning gaps. In all but two cases the final
match was under 1.5:1. Results are shown
in Table 2.
The optional Smartlock accessory pro
vides power and reset switches, a tuning lock
function and power and tuning LEDs. The
reset switch puts the tuner in bypass but does
not erase memories or force a retune.
SG-230 Summary
The SG-230 is the only auto tuner of
the three reviewed here that will match a
43 foot vertical on 160 meters. While it
did not meet its “must start retuning at 2:1
SWR” specification, it can be set to disable
memory tuning. This setting forces a retune
upon frequency change at the expense of
tuning speed but in some cases is neces
sary to keep the transceiver happy when
moving around a band. Tuning is almost
instantaneous when recalling previously
stored memory data.
Manufacturer
: SGC Inc, 13737 SE 26th
St, Bellevue, WA 98005; tel 425-746-6310;
www.sgcworld.com
.
Some Final Thoughts
I found this exercise to be very enlight
ening. Besides learning more about tuner
reactive tuning ranges and tuner losses, I also
had never considered that remote auto tuners
could possibly match an open or a short. This
means that you could have a failed connec
tion at the antenna without even knowing it!
Since there is probably at least one frequency
or band where you may have a high but
measurable untuned SWR, it would probably
be worthwhile to record the untuned SWR
so that you can verify connection integrity
if you suspect there might be a problem. All
three auto tuners discussed here come up in
the bypassed mode when power is cycled, so
this is an easy test to make from your shack
with an antenna analyzer (if you apply RF
power the auto tuners will start tuning).
There are definitely benefits to using a
remote auto tuner with an untuned antenna
such as the popular 43 foot vertical. First, of
course, is operating convenience. You simply
transmit a low power carrier for tuning and
then operate. And second, you will reduce
SWR related coax losses. There are always
trade-offs to consider, such as reactive tun
ing range and tuner losses. If you plan your
remote-tuned antenna system properly, a
remote auto tuner can be an excellent answer
for multiband operation.
From March 2010 QST © ARRL
Extending the MFJ-927 to 160 Meters
As discussed in the review, additional
inductance is needed to allow the MFJ-
927 to match a 43 foot vertical on 160
meters. I decided to add some external
inductance to see if this would help the
MFJ-927 tune the antenna on 160 me
ters. I chose to add around 30
μ
H, by
using a 2.5 inch length of MFJ 4004-0008
coil stock. This is an air core coil of #16
AWG tinned copper wire, 2.5 inches in
diameter, wound 10 TPI in series be
tween the tuner output and the antenna
base. If you order this product, you will
get a 10 inch length, so there is plenty
left over for other projects.
I mounted the coil in a 4 × 4 ×
4 inch plastic outdoor electrical box available from most home
improvement stores. I used #8 stainless steel hardware for
the I
N
and
OUT
RF connections. Two binding posts
(MFJ 606-0014) permit shorting the coil
for normal 80 through 10 meter auto
tuner
operation.
I made a simple shorting wire using a
pair of spade lugs. For mounting, I bolted
the assembly to one of the MFJ-927
mounting holes and then connected ev
erything to my 43 foot antenna as shown
in the photo.
How does this work? Absolutely great!
The MFJ-927 now easily tunes 160
meters just as on other bands. The only
disadvantage is that you must manually
select 160 meters or 80 to 10 meters by
adding or removing the shorting strap.
Finally, while this was built for use with my MFJ-927 this same
assembly can be used with any auto tuner that needs addi
tional inductance for matching low frequency, electrically short
antennas.
Phil
Salas,
AD5X

Geef een reactie

Het e-mailadres wordt niet gepubliceerd. Vereiste velden zijn gemarkeerd met *