Ameritron qsk 5 schematic

AMERITRON QSK-5PC Instruction Manual

AMERITRON QSK-5PC

T/R SWITCH PC BOARD

INTRODUCTION

The Ameritron QSK-5PC is a PIN diode QSK circuit board designed for use in Ameritron's
AL-80A, AL-80B, AL-82, AL-1500 and AL-1200 amplifiers. Ameritron can not assist
customers with the installation of the QSK-5PC in any amplifier other than these five units. The
QSK-5PC is rated to carry the full power of these amplifiers except on SSTV, RTTY and
PACKET. On these high duty cycle modes the QSK-5PC will handle a maximum of 1000 watts
with a 5 minute on and two minute off duty cycle.

Ameritron also offers a "stand-alone" PIN diode QSK adapter called the QSK-5. The QSK-5 is
an entirely self-supporting unit with an internal power supply. The QSK-5 is the best choice for
applications where maximum convenience and flexibility is desired. The QSK-5 connects to the
station equipment with standard connectors to facilitate installation and removal.

QSK BOARD OPERATION

Keying Circuit

Timing:

The timing of the transceiver keying circuit is critical with any QSK switch. The transceiver
MUST have the proper sequencing of RF and QSK output lines. The transceiver QSK line
must pull low BEFORE RF appears on the output connector and release AFTER the RF
envelope reaches zero to operate with any QSK switch. A few transceivers do not meet this
requirement even though they are advertised as QSK transceivers. There is no way to
completely correct this problem without modifying the transceiver.

One indication of improper timing is the flashing or failure of fuse lamps LP1 and LP2. These
lamps protect the transceiver from failure of the receive diodes. Any component failure that
causes the receive diodes to conduct during the time interval the transmit diodes are
conducting will connect the amplifier's output directly to the input. This may result in an
oscillation that can cause damage to the transceiver. NEVER REMOVE

OR DEFEAT THESE
LAMPS. They will only fail if there is a timing or component problem. If you remove the
fuse lamps, the transceiver may be damaged. If the lamps flash or fail, a simple test can be
made by sending a string of very slow dashes with a keyer. Slowly raise the power on the
transceiver until the lamps begin to flash. If the lamps flash at the beginning or end of each
dash, the timing of the QSK line from the radio is at fault. If the lamps light throughout the
entire length of the dash the QSK line should be unplugged and the RLY jack of the amplifier
should be grounded. If the lamps still light, then the QSK switch has a circuit problem. If the
lamps do not light, the problem is in the radio or the connection to the radio. Another

AMERITRON QSK-5PC Instruction Manual

indication of improper timing is the generation of clicks or leading or trailing edge "chopping"
of the signal. This indicates hot switching is occurring. This is strictly a timing problem.

Timing can be measured with a dual trace scope. The triggered trace should be connected to
the QSK output line of the transceiver(open collector lines will need a pull-up resistor con­nected to 12 volts) and the RF output monitored with the other trace. RF must not appear until
one millisecond after the QSK line is low. The QSK output line of the transceiver must not go
high before the RF envelope drops to zero.

RECEIVE:

In RECEIVE the QSK board functions as follows: When terminal
D is high, R10 and R16 bias Q5 into conduction. This holds the collector of Q5 below three
volts. IC1A and B are biased at 50% of the supply voltage with the inputs arranged so that
IC1B is on in this mode. IC1B turns Q4 on and this pulls the base of Q3 low removing the high
voltage from the receive diodes(D2, 3, 4 and 11) and grounding the junction at L6. This allows
12 volts to flow through the diode string from L5 and L7 to the common cathode point at L6.
This turns the receive diodes on. R17 and C19 control the time delay of the receive diode turn
on to insure the transmit diodes have time to turn off before the receive diodes are turned on.

IC1A will be off when terminal D is high and Q2 will not conduct. This allows Q1 to be
forward biased by R5 and pull L2 up to 400 volts. This voltage cuts off D1 first and then D10,
9, 8 and 7. This disconnects the input of the amplifier before disconnecting the output.

TRANSMIT:

In TRANSMIT the circuit functions as follows: Point D is held below 2 volts. This removes the
forward bias on Q5 and allows the collector to go high. IC1A turns on after a slight delay
caused by the charge time of R18 and C20. Q2 turns on and discharges the transmit diode
string through D5. Q1 is forced off by the removal of base bias by Q2. The 12 volt supply then
flows from R27 through the diode string to Q2. This places the transmit diodes in conduction
by biasing them with approximately 600 mA of forward current.

The receive diodes are disabled when Q5's collector voltage charges C19 quickly through D13.
This turns IC1B off which turns Q4 off. This allows R6 to pull the base of Q3 high and the
voltage at the emitter of Q3 rapidly turns the center junction of the receive diodes off by
applying 380 volts of positive bias to L6.
Voltage divider R8 and R12 allows IC1C to compare the status of the receive diode bias to the
voltage obtained through R11 from the transmit diode string. If the transmit diode string is
off and the receive diode string is on, the output of IC1C will be low and Q6 and Q7 will be
off. When the transmit diode string is on and the receive diode string is off Q6 and Q7 are
biased into conduction.

Q7 can be used to switch the bias in an amplifier. The source (terminal J) must be within 3 volts
of ground and the drain (terminal I) must be below 25 volts positive. The FET will safely carry
two amperes of current.

AMERITRON QSK-5PC Instruction Manual

Q6 can be used to pull up to 100 mA of current to ground (terminal K). The open circuit
voltage must be below 25 volts and positive polarity.

AMPLIFIER CONNECTIONS

The QSK-5PC installation requires modifications of the wiring to the phono jacks on the
amplifiers. The following is a list of the new functions of the amplifier rear panel jacks:

12 V:

This jack is used to supply 12 volts for external accessories. This jack can also be used for a
"hand-shake" that confirms the diodes have changed states. Optional instructions will connect
this jack to the open collector output of Q6 for the "hand- shake." This jack will then pull low
in the transmit mode. The maximum rating of this connection is 25 volts open circuit and 100
mA of current when low.

RLY:

CAUTION!! This jack must always be directly connected to the transceivers QSK output line.
NEVER attempt to operate the amplifier without this jack properly connected. Do not connect
any devices between this jack and the transceiver.

This jack provides the connection from the Key 2 terminal (D) of the circuit board. This jack
has 5 volts open circuit and supplies a maximum of 1 mA of current. This jack must be pulled
low (below 2 volts) at least 1 mS before RF is applied to the amplifier. The jack must not be
returned to an open circuit condition before RF is removed from the amplifier. Failure to
comply with these restrictions will damage the amplifier or the QSK board.
The QSK board will inhibit the receive signals for one mS after this jack returns to an open or
"high" condition.

RF IN:

This SO-239 connector should be connected to the RF out connector of the transceiver.

RF OUT:

The antenna will connect to this SO-239. The antenna SWR must be low if the QSK-5PC is
operated at full ratings. To calculate the safe power capability of the QSK-5PC use the
following formulas:

2800 divided by the SWR for SSB and high peak-to-average power modes.

2250 divided by SWR for CW and high average-to-peak power modes.

1000 divided by SWR for RTTY and other high duty-cycle, high average power modes.

AMERITRON QSK-5PC Instruction Manual

NEVER EXCEED 2000 WATTS ON CW, 2500 WATTS ON SSB OR 1000 WATTS ON
RTTY.

The following are some typical SWR values and power ratings:

SWR SSB CW RTTY

1:1 2500 W 2000 W 1000 W

1.5:1 1875 W 1500 W 667 W

2.0:1 1400 W 1124 W 500 W

3.0:1 950 W 750 W 333 W

Parts supplied: (1) QSK-5PC board
(1) QSK-5PC plate with mounting spacers (6)
(8) #6 INT lock washer
(2) #6 flat washer
(2) male/female spacer 1-3/4"
(8) male/female spacer 7/8"
(6) 6-32 5/16" screw
(6) 6-32 1/4" nut
(5) ferrite bead
10-1/4" RG-58 18" orange wire
16-3/4" RG-178 17-1/2" red/white wire
21" blue wire 7" red teflon wire
15" yellow wire 6" teflon sleeve

CAUTION: ALWAYS DISCONNECT THE AMPLIFIER FROM THE POWER MAINS
AND WAIT FOR THE FILTER CAPACITORS TO DISCHARGE BEFORE
REMOVING THE COVER.

Refer to fig. 4 for identification of the correct soldering post on the QSK-5PC during
installation.

QSK-5PC INSTALLATION FOR THE AL80A/82/1200/1500

1. Remove the Amplifier's power cord from the outlet. Check the high voltage on the
amplifiers internal meter. AFTER THE HIGH VOLTAGE HAS REACHED ZERO you may
safely disconnect all the station wiring and cables from the rear panel jacks. Place the amplifier
in a well lit area with adequate work space.