Copyright (c), Ralph Holland, Mar 1997
Introduction
I have seen several Sailor 1500 Antenna Tuning Units circulating in
the second-hand market; this article describes how they can be adapted
for use with any amateur h.f. transceiver.
The Sailor 1500 ATU is a 400 Watt P.E.P. h.f. antenna tuning unit which
was designed to operate from 24 volts and be semi-automatically controlled
by the Sailor series of H.F. transceivers. This model ATU was designed
to feed wires such as the backstay on a ship and is still current shipboard
equipment. The ATU also operates as a dummy load when the higher inductance
coil, which contains a lossy laminated-iron core, is introduced into the
series arm of the "L" network and tuned to resonance.
With a few hours work the ATU can be modified and extended so it may
be manually controlled to tune a 3 metre whip at 1.8 MHz, or upwards, via
switched control wires driven from a 12 volt supply.
Summary of Modifications
Several modifications are necessary to adapt the ATU for stand-alone
operation.
12 volt operation
The relays must be "adjusted" so they pull-in reliably with
12 volts. The relay operation is adjusted by applying 12 volts to each
in turn and adjusting the tension of the spring and the contact travel
by the adjusting screw until relay action is satisfactory.
The d.c motor will operate on 12 volts, so no further modifications
are necessary.
Mechanical
The variable inductors are driven via a shaft connected to the d.c.
motor. This shaft is free-wheeling in one direction because one finger
has been removed from the driving arm. A replacement arm can be fashioned
from PCB material by modelling it after the other driving arms. This modification
locks the central tuning shaft to the motor preventing most platform movement
from accidentally detuning the ATU when it is operated on the bull-bar
of my four-wheel-drive (4WD) Landcruiser .
The unit must have the tuning shaft extension removed so the hole can
be blocked with with suitable sealing compound in order to ensure the unit
is waterproofed. Waterproofing will also be necessary around the control
plug inputs and any unused access holes. Now the unit can be used in any
position, not just the recommended vertical position and can be mounted
horizontally on the front or back of some mobile platforms (ie 4WD).
Electronic
The "L" match configuration is inverted from the expected
configuration with the shunt arm towards the load - this configuration
is normally used to match long length elements, but the ATU has a 4:1 transformer
at the transceiver side allowing it to drive shorter antenna lengths.
The ATU configuration should be modified to increase the flexibility.
The "L" can be configured to operate either way around. The iron
core in L101/L102 must removed so this maximum inductance coil can be used
at 160 and 80 metres. One series capacitance element must removed so an
additional shunt capacitance element can be added to permit the ATU to
operate on the lower frequeinces. The 4:1 input transformer must be removed
because the turns are insufficient for operation at 160 metres and barely
sufficient for 80 metres.
Tuning
Manual tuning is offered with twelve (12) switches to control the series
and shunt reactance elements, one (1) switch to select the direction of
the "L" network, one (1) DPDT centre-off switch to operate the
direction of the d.c. motor and one (1) master switch to turn off the system
power.

Figure 1 Original Circuit

Figure 2 Modified Circuit
Modification Steps in detail
Figure 1 shows the original ATU configuration while Figure 2 shows the
new ATU configuration. Perform the following steps to take the ATU from
Figure 1 to Figure 2.
- Remove all the stainless steel control plug and cover screws. Remove
the control plug and the cover.
- Check the operation of relays RE101 to RE112, by applying 12 volts
using negative ground. See Figure 1 for original circuit details. Adjust
the return spring tension with a pair of long-nose-pliers and adjust the
offset screws until the operation is deemed satisfactory.
- Remove board 200, the one above the d.c. motor, taking care to disconnect
the antenna input from RE112.
- Unsolder both small coaxes from this board, snip diodes D204, D205
and resistors R205 and R203.
- Bridge diode D203 with a wire strap. Wire the Violet/White wire, pin
12, to drive RE112 and check that the wiring harness is connected as follows:
Wire |
Pin |
Relay/Device |
Brown/White |
1 |
RE101 |
Red/White |
2 |
RE102 |
Orange |
3 |
RE103 |
Yellow |
4 |
RE104 |
Green |
5 |
RE105 |
Blue |
6 |
RE106 |
Violet |
7 |
RE107 |
Grey |
8 |
RE108 |
White |
9 |
RE109 |
Brown/Black |
10 |
RE110 |
Grey/Black |
11 |
RE111 |
Violet/White |
12 |
RE112 |
Yellow/White |
14 |
motor |
Green/White |
15 |
T201 |
Table 1 Existing Wiring
- Unsolder the coax and relay grounds from the subassembly board. Unsolder
the copper shims and leads on the relay contacts and remove relays RE101
to RE106 to permit access to the subassembly board containing the series
capacitors C101, C102 and C103.
- Remove T101 (4:1 transformer)
- Remove C103 (30pF)
- Remove C101 and C102, replaced C103 (100pF) with C103 (30pF) and reconnect
to the subassembly board.
- With the relays at the top and inductors at the bottom, place a solder
lug on the lower right-hand screw of the capacitor subassembly board.
- Remount the capacitor subassembly board.
- Solder approximately 2350pF / 1KV rating (5*470pF) or so between the
lower contact of RE106 (old C103 / 30pF relay) and the solder lug on the
right-hand screw. This capacitor is required for 160 and 80 metre operation
and shall be designated Cx.
- Connect inductor L103, with a shim or copper strap, to L104 (the small
rotating inductor).
- Remove L101 and then remove the iron cores from the bottom of L101
- they are no longer required.
- You will need to relocate and add new turns to the lower part of L101.
Remove the copper shim at the bottom and keep for the new winding. Relocate
the lower turns as high up the form as possible so you can add more turns
at the bottom. The relocated winding in terminated in a new hole. The turns
are extended by drilling a hole near the end of the relocated winding for
the start of the new winding. The old and new windings are then joined
by a bridge of solder across the gap and the shim is placed at the bottom
of the new winding, and the new winding is terminated in a new hole. Make
sure the ends of the winding do not have sharp points and are truncated
close to the inside of the former. I also coated the coil with estapol
and then baked it in the oven at 80 degrees Celsius for an hour. This prevents
tracking between the turns (take care not to coat the spindle contacts).
- Construct a PVC or Teflon insulator that will be placed under L101.
I made mine from the top of an ice-cream container. You will need to drill
two holes for the L101 mounting screws and you cannot make this insulator
too thick as it will prevent the rotation of the tuning shaft. This insulator
is necessary when the ATU is operating into highly reactive loads on 160
or 80 metres. (Ideally L101 should be mounted further from the case but
we have no choice.)
- Remove L104 and construct a new drive arm from a piece of insulated
PCB material. This drive arm should be double-fingered in the same profile
as the other coil drive arms; this will prevent coil movement when mobile
and will enable you to use the reverse the direction of the motor for fine
tuning adjustments.
- Replace the small teflon coax running between L101 and the input board
200 with RG58 U/C or preferably RG8 to prevent voltage breakdown when operating
on 160/80 m. Ensure the coax is routed so it clears the relay contact arms
and return springs - use the restraining strips provided on the chassis.
- Note GL201 is removed from the circuit as it will probably fire when
you are transmitting on 160 or 80 metres, particulary using short antennas
which mean highly reactive loads. RE201 is also removed as it is entirely
inadequate for the voltage levels expected at the ATU load.
- Reassemble all relays and wire them via shims or braid to the appropriate
components. (See Figure 2.) Note the modifications around RE106. L104 must
be bridged to L103 and the RE106 contact is between the shunt arm and the
new 1880pF capacitor Cx.
- Remove RE112 and modify it so it is a double-throw double-pole relay;
i.e cut the top, bottom and centre contact shims - do not cut the circuit
board though! The top and bottom shims are riveted and can be cut with
a hack-saw, while the centre (moving) contacts can be unscrewed and cut
with a pair of tin-snips. These contacts can be secured by a small amount
of super-glue - but do not allow any glue to cross between the contacts
as it offers a path for rf! Wire this relay so the antenna is connected
to L101 on the series arm and so the transceiver is connected to the capacitor
relays of the shunt arm when RE112 is off - as this is the default configuration
for mobile operation. Ie place the antenna and transceiver coax centres
on the moving contacts, the shields on the earth contact at RE112 and connect
the capacitor rail to one side and the L101 coax on the other side of the
stationary contacts. Construct loop-over wires from the insulated centre
conductor of RG58 or similar and loop one over the antenna relay and one
under the realy so the sense of the antenna and transceiver connection
changes when RE112 is switched on and off. Dress the loop-over leads so
they clear any metal contacts and each other - otherwise they will arc
and burn!
- Isolate the d.c motor from the chassis ground so it can be reversed.
Connect the former ground-pin to the control cable pin 16. Remove the former
motor end of R204 (12K) and connect it to ground.
- If you want the current sensor output then R204 must be grounded as
above and you must connect the sensor output to the control cable pin 15.
Note this senses load current and not transceiver current. If you want
to sense transceiver current you will have to move the sensor transformer
to the input terminal. (I omitted the transformer as I use the SWR and
power meter on my rig.)
- Make a switch box to organise control of the ATU components. You can
mark-up Table 2 for your future reference to aid cable wiring, while table
3 shows the layout and function of my control switches. The motor is connected
to a DPDT centre-off reversing switch to permit rotation in either direction
and the power for all switches passes trhough a master power switch (neither
shown in Table 3).
Control Wire colour |
Pin |
Device |
Component |
Switch |
State |
|
GND |
|
chassis |
|
|
|
1 |
RE101 |
L101 |
down |
off |
|
2 |
RE102 |
L102 |
down |
off |
|
3 |
RE103 |
30pF |
down |
on |
|
4 |
RE104 |
C101 (200pF) |
down |
on |
|
5 |
RE105 |
L103 |
down |
off |
|
6 |
RE106 |
Cx (2350pF) |
down |
on |
|
7 |
RE107 |
C104 (850pF) |
down |
on |
|
8 |
RE108 |
C105 (470pF) |
down |
on |
|
9 |
RE109 |
C106 (220pF) |
down |
on |
|
10 |
RE110 |
C107 (100pF) |
down |
on |
|
11 |
RE111 |
C108 (50pF) |
down |
on |
|
12 |
RE112 |
Long */ short changeover |
down |
off
(short)
|
|
13 |
sense |
|
|
|
|
14 |
Motor |
+ / - |
|
|
|
15 |
Antenna current |
|
|
|
|
16 |
Motor |
- / + |
|
|
Table 2 New wiring
C5 |
C4 |
C3 |
C2 |
C1 |
C0 |
L2 |
L1 |
L0 |
X1 |
X0 |
L/S |
Cx |
C104 |
C105 |
C106 |
C107 |
C108 |
L101 |
L102 |
L103 |
C101 |
C102 |
Long Short |
1880 pF |
850 pF |
470 pF |
220 pF |
100 pF |
50 pF |
13 uH |
10 / 34uH |
3 / 16uH |
200 pF |
30 pF |
… |
Table 3 My switch layout and function
- Remove the tuning shaft extension and plug the hole with suitable sealing
compound. I have found that liquid nails works but silicon compound (silastic)
may also be adequate.
- After wiring in accordance with the above table and the coax connection,
seal the control plug with suitable sealing compound around the cable entries
and any spare holes to prevent moisture ingress.
- You may now reassemble the unit.
Table 4 contains the reactance values of the series components.
Component |
1.8 MHz |
3.6 MHz |
7.5 MHz |
14.2 MHz |
L101 |
149j |
294j |
613j |
1160j |
L102 |
114/389j |
226/769j |
471/1602j |
892/3034j |
L103 |
34/184j |
68/362j |
141/754j |
267/1427j |
L104 |
12/46j |
23/91j |
47/158j |
89/356j |
C102 || C101 |
-3363j |
-1700j |
-816j |
-431j |
C102 |
-2915j |
-1474j |
-707j |
-373j |
C101 |
-874j |
-221j |
-106j |
-56j |
Table 4 Series component reactance values
Table 5 contains the switch settings for operation on my 2.64 m whip
mounted on the bull-bar; the switch values are designated in hexa-decimal
(one bit per switch) collected into capacitor, inductor, extension capacitance
and the Long / Short switch positions. (I keep table 5 as my cheat sheet.)
If you are having trouble matching on 160 m you can increase Cx until
it is 3290pF which is 7*470pF capacitors in parallel. This value is approximately
twice the value of all other capacitors so the switches will work in powers
of two or octaves.
(1 is down and 0 is up so 33 for C is the pattern 011011 which corresponds
to only C4, C3, C1, C0 connected and 2 for L represents 010 which is only
L1 connected; the * represents the preferred switch values for the nominated
frequency.)
Frequency MHz |
C |
L |
X |
L*/S |
SWR |
1.825 |
3F |
7 |
3 |
1 (short) |
1.5:1 |
3.570 |
37 |
3 |
3 |
1 |
1.2:1 |
3.608 * |
2F |
3 |
3 |
1 |
1.0:1 |
7.10 |
0F |
2 |
2 |
1 |
1.0:1 |
7.13 * |
17 |
1 |
3 |
1 |
1.5:1 |
8.7 |
16 |
1 |
3 |
1 |
1.0:1 |
14.112 |
07 |
3 |
2 |
1 |
1.0:1 |
18.25 |
07 |
1 |
2 |
1 |
1.5:1 |
21.121 |
00 |
0 |
2 |
1 |
1.7:1 |
27.00 |
05 |
0 |
2 |
1 |
1.5:1 |
Table 5 Settings employed for my 2.64m whip