Q-Mac TA-90 User manual

No part of this manual may be copied, transcribed, translated or reproduced in any manner or form
whatsoever, for commercial purposes, without obtaining prior written permission from Q-MAC
Electronics Pty Ltd. However, limited copying is permitted for private use providing authorship is
acknowledged.
© Copyright Q-MAC Electronics Pty Ltd, 2003.
142 Hasler Road
Osborne Park, WA 6017
PO Box 1334
Osborne Park Business Centre, WA 6916
AUSTRALIA
Australia: Phone [phone], Fax [phone]
International: Phone [phone], Fax [phone]
TA-90
Automatic Antenna Tuner for Vehicle Whip
First Edition
Print date: December 1997
Author: Rod Macduff
Literature Reference Number: TECH04.PUB
Part Number: QM1021

TABLE OF CONTENTS
Section 1 Introduction ...................................................................................................... 2
Section 2 Product specification.................................................................................... 3
Section 3 Mechanical assembly.................................................................................... 4
Section 4 Functional overview....................................................................................... 5
Section 5 Block diagram.................................................................................................. 7
Section 6 Circuit description and Schematic Diagrams ....................................... 9
Section 7 Fault finding.................................................................................................... 14
Section 8 Hints and tips................................................................................................. 15
Section 9 Parts list........................................................................................................... 16
Section 10 PCB overlays.................................................................................................. 19
Section 11 Installation Guide.......................................................................................... 21
-1 -

1. INTRODUCTION
The TA-90 Automatic Tuning Antenna System is designed specifically for use with the Q-
MAC HF-90 Transceiver allowing it to deliver maximum power to a range of short whip or
wire antennas. It is optimised for electrically short antennas and is normally used in vehicle
installations with the Q-MAC QM7131 continuously loaded 1.8 metre whip.
The HF-90 is significantly different from other Autotune Antenna Systems in the following
respects.
1The TA-90 allows a variety of mounting configurations as the antenna and tuner are
separate. On a vehicle the tuner can be mounted behind the bull-bar affording
considerable protection.
2The system is more economic to repair in the event of a vehicle rollover or antenna
decapitation as the whip is relatively inexpensive and readily available.
3Road visibility is not impaired by the tuner when fitted to a vehicle.
4The TA-90 is versatile. It can be used on trucks, buses, small vessels and aircraft or
helicopters (24volt version). Wire antennas may be used.
5Efficiency is comparatively good when operating into short whips on low frequencies.
Other autotuners are either unable to tune for these conditions or achieve poor
efficiency. Improved efficiency is due to the special low-capacitance switching
design.
6Antenna current and power transfer to the antenna are maximised. This ensures the
best radiation efficiency when compared to VSWR based tuning systems.
7The design uses Surface Mount Technology on a single PCB with toroidal inductors.
This ensures maximum reliability in a compact unit. It also minimises cost.
8The TA-90 autotuner box mounted on the stoneguard plate weighs only 2.2 kg.
-2 -

2. PRODUCT SPECIFICATION
Application:-Vehicle, Fixed, Marine or Aircraft used with HF-90 Transceiver.
Frequency range:-2 to 20 MHz continuous
Power rating:-70 watt PEP
Input impedance:-50 Ohm
VSWR:-Typically 1.6:1, Maximum 2.5:1 (antenna current always maximised).
Current drain:-500mA typical
Voltage:-10-15volt, from auxiliary connector on rear of HF-90 ( a 20-30volt model
is also available).
Tune time:-Less than 3 seconds.
Tuning method:-Binary weighted relay switched inductors perform tune, whilst transformer
achieves match.
Dimensions:-Tuner housing:-221 (L) x 146 (W) x 62 (D)
Tuner with mounting plate:-242 (L) x 206 (W) x 59 (D)
Whip Antenna:-1.8m (L)
Whip antenna with spring and insulator:-2m (L)
Weight:-TA-90 tuner box on plate 2.2kg.
Antenna mounting:-1/2” BSW screw
Environment rating:-IP67 (fully waterproof, limited immersion).
Antenna:-Continuously loaded 1.8 metre heavy duty CB type whip. Alternatively
may be used with wire antenna (up to 10 metres) or Marine HF whip.
Specifications are subject to change without notice
-3 -

The TA-90 tuner box comprises a single 2.4mm thick PCB which contains all the active
electronics mounted within a waterproof, aluminium diecast box with 6mm polymer lid.
The PCB is mounted in the box on four 20mm pillars using M3 screws.
DC power and input RF are taken to the PCB via a 10 way IDC connector.
The high voltage antenna feed is via a soldered connection to the PCB.
External RF input to the TA-90 is applied on a standard UHF S0-239 socket.
DC power from the HF-90 transceiver is taken to two 5/16 inch circular lugs. (this is also the
tune activation signal).
A 4mm high voltage binding post allows feeding of whip or wire antennas.
All connectors are protected by a heavy duty aluminium plate (stone guard) which has
mounting holes for U-clamp fixing to bull-bars.
The TA-90 can be mounted in any orientation but is best configured with the connectors to
the side and with the antenna feed topmost (see installation guide).
3. MECHANICAL ASSEMBLY
-4 -

The function of the TA-90 autotuner is to allow maximum power transfer between a Q-MAC
HF-90 transceiver and the 1.8m helical whip or a wire antenna.
The 1.8m continuously loaded whip when mounted on a vehicle has an equivalent circuit as
shown in Figure 1.
Figure 1 Equivalent circuit of 1.8 metre CB whip.
Below 8MHz the effect of the 1µH inductor and 440R resistor is negligible and the whip is
equivalent to 47pF in series with 6R. This is a highly reactive load.
In the frequency range 8-15MHz the L-R parallel circuit starts to raise the resistance and
cancel the reactance. At about 20MHz the LC elements are rear resonance and the reactive
value is very low and resistance is approximately 40 ohms.
In order to transfer maximum power to the above network the antenna tuner must:
Cancel the capacitive reactance.
-jXc = 1,000,000 (f in MHz)
2 x PI x 47 x f
Match the 50 ohm feed impedance of the HF-90 to the lower resistance left when the
reactance is cancelled. This resistance lies in the range 6-40 ohms.
Figure 2. Equivalent Circuit for TA-90.
The TA-90 contains a series of binary weighted toroidal inductors which are switched by
relays under control of the onboard microprocessor. These series inductors are adjusted to
exactly cancel out the capacitive reactance presented by the electrically short antenna. There
is also a 2:1 turns ratio step down transformer which is used on the lower frequency range to
obtain the requisite impedance match.
4. FUNCTIONAL OVERVIEW
-5 -

The TA-90 also incorporates a high to low impedance matching amplifier which is selected
to provide good receiver signal matching when the unit is untuned or the transceiver is in
scan mode. Tuning is performed purely by measuring the antenna current and by hill
climbing until a maximum value is obtained. This technique is superior to minimising
VSWR as it optimises the radiated power. Antenna current is measured using an improved
proprietary galvanic isolation technique whereby a current transformer excites a light
emitting diode coupled optically to a photo transistor via an optical fibre. The
phototransistor is connected to an A to D convertor via a dynamic range extension network.
The A to D convertor comprises an up-counter, D to A converter and comparator. A straight
up count is used (proceeding from high antenna current down to nil antenna current due to
inversion) because a successive approximation algorithm would give wildly erroneous codes
if the RF level changed slightly during the count. The counter is reset by a clear pulse from
the microprocessor and then the micro issues clock pulses to the counter until the comparator
goes low.
Circuit Operation
In the TA-90 the tuning sequence is initiated by a supply interruption of 400ms.
On turn-on all inductors are switched out and the matching transformer is switched out.
The TA-90 then goes through its tuning sequence.
The scan amplifier has RF protection. If RF power is applied when the scan amplifier is active thyristor
TH1 triggers and switches out the scan amplifier.
On the HF-90 transceiver when the TUNE button is pressed or on the first occasion when PTT is pushed
on a new channel, the +12volt auxiliary supply to the TA-90 is interrupted for 400ms. Following this, a
CW signal of three seconds duration is produced at approximately 20watt power level.
During this three second period, the TA-90 microprocessor monitors the antenna current and determines
the optimum inductor and transformer combination.
The analog to digital converter is a single ramp type. The measurement cycle is as follows:
First RST pin 11 on U9 is taken high momentarily, then counter U9 is incremented by pulsing pin 10 of
U9. This continues until the output of comparator U8:B pin 1 changes state on reaching the actual
current value level.
The resultant ramp can be seen on R27. The ramp proceeds from a low to high voltage with low
corresponding to high antenna current and low corresponding to low antenna voltage.
One measurement of antenna current is made for each relay setting chosen by the convergent tuning
algorithm.
-6 -

The RF chassis of the TA-90 auto-tuner comprises a selectable 2:1 matching transformer or 47pF series
capacitor, a selectable impedance matching receive preamplifier, a series of fifteen binary weighted
relay switched toroidal inductors and a current sensing transformer at the antenna output.
The control section of the TA-90 comprises of a sensor section, microcontroller section and output drive
section.
The sensor section consists of an optically linked antenna current sensor, dynamic range extendor and
analog to digital converter with -10volt charge pump.
A microprocessor with high order address latch and EEPROM are the programmed control element in
the circuit.
Output to the relays is effected via three darlington driver blocks.
A +5volt regulator supplies power to the PCB.
5. BLOCK DIAGRAM
-7 -

6. CIRCUIT DESCRIPTION + SCHEMATIC
DIAGRAMS
RF Section
The RF section of the TA-90 comprises fifteen separate relay switched toroidal inductors. These
inductors are approximately binary weighted. This means that up to 2 ↑15 inductance combinations are
possible with a minimum inductance of 144nH and a maximum inductance of 100µH.
Use of toroidal inductors ensures minimum coupling between adjacent coils and eliminates “suck outs”
or tuning holes.
All inductors have relays arranged to isolate them in bypass mode. This minimises the stray capacitance
and maximises the efficiency. The top four inductors in particular use a pair of relays resulting in
further capacitance reduction and improved high voltage handling.
A 2:1 turns ratio matching transformer T1 switched by relay RL1 steps down to 12 ohm allowing
effective matching in the 2-15MHz range when using short whip antennas. When the transformer is
switched out by RL1 a low loss 47pF capacitor C67 is switched in series with the RF input to allow the
tuning of antennas which are inductive.
A scan amplifier comprising JFETs Q2 and Q3 with associated passive components and protection
diodes D9-D14 provides impedance matching and gain in receive mode when the antenna has not been
tuned and when the HF-90 is scanning.
Antenna current is monitored using current transformer T2 and optical emitting diode D8. Galvanic
isolation is achieved by converting the current level to a light level and passing this down an optical
fibre. Optotransistor Q1 then converts the light signal back to a current level.
As the light level spans several orders of magnitude and it is necessary to detect very small currents and
yet be able to see change in very large currents then a dynamic range extender is necessary.
This network of D6, D7 and D15 with associated resistors R28, R29, R30 and R71 presents a very high
value of load (100K) for small currents and a very low value of load (1K) for high currents. In this way
the dynamic range is extended.
(see schematic diagram opposite)
-9-

Microprocessor Section
In the TA-90, tuning is controlled by a microprocessor U1. This microprocessor executes a program
stored in EPROM U2 which is addressed via latch U3.
Antenna current is monitored via the optical link resulting in a voltage in range 0-5volt on the collector
of phototransistor Q1.
A single ramp analog to digital converter comprising counter U9, DAC U10 and comparator U8 allows
the microprocessor to read the antenna current.
Control of the inductor relays, transformer relay RL1, and scan amplifier relay RL2, is implemented via
Ports 1 and 3 of the microprocessor, using darlington driver chips U5, U6 and U7.
A 5 volt regulator U11 provides a constant supply for the microprocessor and associated logic and a
-5volt charge pump U4 generates a negative rail for the ADC whilst the ALE line is active.
(see schematic diagram opposite)
-11-

MICROPROCESSOR I/0 DEFINITION
PORT 0 Address/Data Multiplexed Bus.
PORT 1 Inductor Relay Switching Outputs. High = inductor selected.
P1.0 L1
P1.1 L2
P1.2 L3
P1.3 L4
P1.4 L5
P1.5 L6
P1.6 L7
P1.7 L8
PORT 3 Inductor Relay Switching Outputs. High = inductor selected.
Plus A/D comparator Input on MSB.
P3.0 L9
P3.1 L10
P3.2 L11
P3.3 L12
P3.4 L13
P3.5 L14
P3.6 L15
P3.7 INPUT FROM A TO D COMPARATOR. LOW = THRESHOLD REACHED
PORT 2 Address High Order Outputs.
Plus miscellaneous high order memory mapped outputs.
P2.0 ADS8
P2.1 ADS9
P2.2 ADS10
P2.3 ADS11 4K top of memory limit for normal use.
P2.4 * A TO D clock output
P2.5 * A TO D clear output
P2.6 2:1 TRANSFORMER SELECT output.
P2.7 SCAN (NOT TUNED) output.
* A TO D max current is at count 00H and min at FFH. Count reset to 00H and incremented until P3.7 goes low.
-13 -

7. FAULT FINDING
1Check that an antenna or dummy antenna is connected (see Section 4, Figure 1 for schematic of
dummy antenna).
2Check that 12 volt DC nominal is present on 5/16 inch studs.
3Check that RF power is being delivered to PL259 connector in range 10-30watt when TUNE is
pressed.
4Disconnect and reconnect DC power feed to TA-90. Two phases of relay activity should be
heard. If this is not heard then proceed to step 6.
5Select a channel in the range 4 to 8 MHz and press the TUNE on the HF-90. Monitor VSWR or
antenna current during tune cycle. IF VSWR is less than 2.5:1 or antenna current is greater than
0.8 ampere then the unit is working satisfactorily. Repeat this test on a few more frequencies
between 2 and 20MHz.
6Open the TA-90 box by removing the six M4 countersunk screws.
7Check the 5V supply on R24.
8Check the 12V supply on R31.
9Check for 3.58MHz clock on both pins of X1.
10 Inspect relays and coils on topside and underside of PCB and on sub-boards for dry joints.
11 Check that two electrolytic capacitors on topside of PCB are correctly polarised or not fitted.
12 Ensure that R21 is 1K and not 10R. Change if necessary.
-14 -

8. HINTS AND TIPS
1Most problems associated with auto-tuners occur due to inadequate grounding or incorrect
antenna installation. Read the Installation Guide (Section 12) carefully to ensure that there are no
ground or antenna faults.
2In many cases faults turn out to be essentially mechanical problems rather than electrical
problems. Check that all connections and mounting bolts are tight and free from damage.
4If the radio is “hot” or gives RF burns on transmit or produces a howling noise from the
loudspeaker at certain frequencies particularly in the 8-12MHz range then it may be necessary to
ground the HF-90 at the radio transceiver end. There is a solder lug on the back of the BNC
coaxial connector. This will allow connection of a short ground wire directly to vehicle chassis.
Connection to the solder lug may be either using solder or a spade slide connector. If howling
persists, try replacing the microphone.
4Check that the 10-way IDC connector beneath the PCB is correctly located if no tuning activity
takes place.
5Some problems have been encountered due to vibration causing dry joints on the relay pins on the
subassembly circuit boards on the underside of the PCB. Check that all relay pins on these sub-
boards are well soldered and resolder as necessary. Any dry joint in this area will cause a mis-
tune.
6Earlier versions of the HF-90 prior to Serial Number 1700 had the +12volt switched power to the
TA-90 fed via a 2w 1R resistor. This should be replaced with a yellow Polyswitch which has a
lower resistance at normal operating current.
-15 -

9. PARTS LIST
DESCRIPTION QUANTITY
10R 1206 SMD 5% (00100) 36 R21 R23 R24 R26 R27
R31 R32 R33 R34 R35
R36 R37 R38 R39 R40
R41 R42 R43 R44 R45
R46 R47 R54 R65 R66
R67 R68 R69 R72 R73
R74 R75 R76 R77 R78
R79
33R 1206 SMD 5% (00330) 4R48 R49 R50 R53
100R 1206 SMD 5% (00101) 2R55 R56
330R 1206 SMD 5% (00331) 8R57 R58 R59 R60 R61
R62 R63 R64
1K 1206 SMD 5% (00102) 1R71
3K3 1206 SMD 5% (00332) 22 R1 R2 R3 R4 R5
R6 R7 R8 R9 R10
R11 R12 R13 R14 R15
R16 R17 R18 R19 R20
R22 R25
10K 1206 SMD 5% (00103) 1R28
33K 1206 SMD 5% (00333) 1R30
100K 1206 SMD 5% (10104) 1R29
330K 1206 SMD 5% (00334) 2R51 R52
10M 1206 SMD 5% (00106) 1R70
100P 0805 SMD NPO (10101) 3C1 C2 C27
10N 1206 SMD XTR (10103) 2C35 C40
100N 1206 SMD X 7R (10104) 49 C4 C5 C6 C7 C8
C9 C10 C11 C12 C13
C14 C15 C16 C17 C18
C19 C20 C21 C22 C23
C28 C29 C30 C31 C36
C41 C42 C43 C44 C45
C46 C47 C48 C49 C50
C51 C52 C53 C54 C55
C56 C57 C58 C59 C60
C62 C64 C65 C66
DESIGNATORS
-16 -

DESCRIPTION QUANTITY
330N 1206 SMD X7R (10334) 9C24 C25 C26 C32 C33
C34 C37 C38 C63
3U3 SMD TANTALUM (10335) 1C3
100U SMD ELECTRO (17107) 2C39 C61
47P6KV CERAMIC (17470) 1C67
INPUT MATCHING XFMR (37014) 2SK1 T1
CURRENT TRANSFORMER (37004) 1T2
144N TOROID (37012) 1L1
256N TOROID (37011) 1L2
400N TOROID (37010) 1L3
706N TOROID (37009) 1L4
1, 1U TOROID (37008) 1L5
1, 8U TOROID (37007) 1L6
2, 58UH/24T TOROID (37019) 1L7
3, 8UH/29T TOROID (37020) 1L8
5, 59UH/27T TOROID (37022) 1L9
8, 2UH/35T TOROID (37023) 1L10
12, 1UH/34T TOROID (37024) 1L11
17, 7UH/43T TOROID (37025) 1L12
26UH/55T TOROID (37026) 1L13
44, 2UH 58T TOROID (37027) 1L14
75, 7UH/80T TOROID (37028) 1L15
3.58MHz RESONATOR (80014) 1X1
RELAY-DPDT SMD (40003) 10 RL1 RL2 RL3 RL4 RL5
RL6 RL7 RL8 RL9 RL10
HV-SPST RELAY (40004) 8RL14 RL15 RL16 RL17 RL18
RL19 RL20 RL21
HV-DPDT RELAY (40005) 3RL11 RL12 RL13
BAV99 SMD DIODE (65001) 7D1 D2 D3 D4 D6
D7 D15
BAV103 SMD DIODE (65019) 7D9 D10 D11 D12 D13
D14 D16
BZD27C33 TRANZORB (65018) 1D5
637-142 OPTO EMMITTER (67020) 1D8
DESIGNATORS
-17 -

DESCRIPTION QUANTITY
BPW85 OPTO TRANSISTOR (67021) 1Q1
C236 SCR (61000) 1TH1
SST309 JFET (60200) 2Q2 Q3
N80C31 MICRO (76031) 1U1
27C64 EPROM (77064) 1U2
74HC14D INVERTER (73014) 1U4
74HC574DW LATCH (73574) 1U3
74HC4040D COUNTER (73040) 1U9
DAC0800M DAC (78800) 1U10
ULN2003L DARLINGTON (72003) 3U5 U6 U7
LM339M COMPARATOR (70339) 1U8
MC78L05ACD REGULATOR (79805) 1U11
DESIGNATORS
-18 -

10. PCB OVERLAYS
-1 -