Hal Communications ST-7000 User manual

ST-7000
HF Demodulator for Packet Radio
Copyright © 1988 by HAL Communications Corp., Urbana, Illinois. Printed in
the United States of America. All rights reserved. Contents of this
publication may not be reproduced in any form without written permission of the
copyright owner.
870-07000
August, 1988 Printing

ST-7000 HF DEMODULATOR FOR PACKET RADIO
CONTENTS:
CHAPTER 1. UNPACKING AND INSPECTION................................... 1
CHAPTER 2. INSTALLATION ............................................... 2
2.1 DC Power............................................. 4
2.2
HF Radio Connection .................................. 4
2.2.1 HF Receive Audio .............................. 6
2.2.2
HF Transmit Audio ............................. 6
2.2.3
HF PTT Connection ............................. 7
2.2.4
HF GROUND Connection.......................... 7
2.3
Packet Controller Connections ........................ 8
2.3.1 TNC AUDIO Interface ........................... 8
2.3.2
TNC TTL I/0 Connections ....................... 9
2.3.3 RPC-2000 RS232
I/0 Connections ................ 12
2.4 VHF RADIO Connection................................. 14
CHAPTER 3. OPERATION .................................................. 15
3.1 Controls and Indicators .............................. 15
3.1.1 HF/VHF Switch................................. 15
3.1.2 SHIFT Switch.................................. 15
3.1.3 THRESHOLD Control............................. 16
3.1.4 Tuning Indicator .............................. 16
3.2 Use of the ST-7000 ................................... 18
3.2.1 General Considerations ........................ 18
3.2.2 HF Packet Operation ........................... 18
3.2.3 HF R TTY and AMTOR Operation ................... 19
3.2.3.1 HF PTT Control....................... 19
3.2.3.2 HF RX Data Squelch ................... 20
3.2.3.3
HF Transmit Tone ON/OFF .............. 20
CHAPTER 4. THEORY OF OPERATION........................................ 22
4.1 AF Input Filters ...................................... 23
4.2 Receive Audio AGC ..................................... 23
4.3 Mark Filter -600 Hz Shift ............................ 23
4.4 Space
Filter -600 Hz Shift ........................... 24
4.5 200 Hz
Detector and SHIFT Switch ...................... 24
4.6
HF Transmit Tone Generator............................ 25
4.7 RS232 and TTL I/0 Interface ........................... 26
4.8
TNC Audio Modem....................................... 26
4.9
TNC Audio Interface and PTT ........................... 27
4.10 Power Supplies ........................................ 27
4.11 Tuning Indicator ...................................... 28
4.12 Threshold Circuit ..................................... 28
4.13 ST-7000 Circuit Board Arrangement..................... 28
CHAPTER 5. TEST AND ALIGNMENT ......................................... 43
CHAPTER 6. SPECIFICATIONS ............................................. 49
LIMITED WARRANTY
........................................... 50

ILLUSTRATIONS:
FIGURE 2.I ST-7000 REAR PANEL.................................... 2
FIGURE 2.2 ST-7000 INTERNAL JUMPER LOCATIONS..................... 3
FIGURE 2.3 HF RADIO CONNECTIONS .................................. 5
FIGURE 2.4 AUDIO TNC INTERFACE CONNECTIONS....................... IO
FIGURE 2.5 TTL TNC INTERFACE CONNECTIONS......................... II
FIGURE 2.6 RS-232 TNC INTERFACE CONNECTIONS ...................... I3
FIGURE 3.I ST-7000 FRONT PANEL................................... I5
FIGURE 3.2 TUNING INDICATOR EXAMPLES............................. I7
FIGURE 4.I ST-7000 BLOCK DIAGRAM................................. 2I
FIGURE 4.2 AUDIO INPUT FILTERS................................... 29
FIGURE 4.3 RECEIVE AGC CIRCUIT................................... 30
FIGURE 4.4 600 HZ MARK FILTER .................................... 3I
FIGURE 4.5 600 HZ SPACE FILTER ................................... 32
FIGURE 4.6 200 HZ DETECTOR ....................................... 33
FIGURE 4.7 HF AFSK GENERATOR..................................... 34
FIGURE 4.8 RS-232 AND TTL 1/0 INTERFACE .......................... 35
FIGURE 4.9 TNC AUDIO MODEM....................................... 36
FIGURE 4.IOTNC AUDIO I/0 AND HF PTT .............................. 37
FIGURE 4.II ST-7000 POWER SUPPLIES ................................ 38
FIGURE 4.I2TUNING INDICATOR...................................... 39
FIGURE 4.I3THRESHOLD AND CARRIER DETECT.......................... 40
FIGURE 4.I4ST-7000 MAIN CIRCUIT BOARD............................ 4I
FIGURE 4.I5ST-7000 DISPLAY CIRCUIT BOARD......................... 42

HAL COMMUNICATIONS CORP.
ST-7000
HF Demodulator for Packet Radio
Operator's Manual
CHAPTER 1
UNPACKING AND INSPECTION
When
unpacking the ST-7000, carefully inspect the shipping carton and the
cabinet for shipping damage. Any evidence of shipping damage should be
immediately reported to your shipping carrier. Be sure to save all packing
materials if damage is found - the shipping carrier will want to inspect them.
Before discarding the packing materials check that you have all parts and
accessories listed below. If any are found missing, notify HAL Communications
Corp. immediately.
Be sure to fill-out and mail the enclosed Warranty Card to HAL Communications.
1 900-07000 ST-7000
HF Demodulator
The following accessories are included with the ST-7000:
1 770-05000
1 800-01002
1 960-07232
3 355-00054
1 870-07000
Spare 0.5A
fuse
115VAC to 12VDC Power Supply
5-pin
TTL I/0 Cable
5-pin
DIN to Phono Cable
ST-7000
Preliminary Operator's Manual
The following accessories are available at extra cost:
855-00006 RS232C Cable
333-20250 DB25
Connector
333-51228 DB25 Connector Shell
310-00064 5-pin DIN
Connector
327-05000 5-pin TTL Connector
You may also be interested in the following related HAL products:
RPC-2000
Radio Packet Controller Board (for PC-XT & DS-3200)
DS-3200
Radio Data Terminal (100% PC-XT Compatible)
HAL880815

ST-7000 OPERATOR'S MANUAL
PAGE 2
CHAPTER 2
INSTALLATION
The ST-7000 is a modem (MOdulator/DEModulator) device that connects between
your packet controller (also called "TNC") and an HF receiver-transmitter. The
packet controller is NOT included in the ST-7000. Proper installation of the
ST-7000 requires (a) DC power connection, (b) HF radio connection, and (c)
packet controller connection.
The rear panel of the ST-7000 is shown below in Figure 2.1. All connections to
the ST-7000 are made to one or more of these connectors.
FIGURE 2.1 ST-7000 REAR PANEL
Many of the 1/0 connections available on the ST-7000 will require changing of
internal jumpers. Therefore, when making the first installation, REMOVE the
ST-7000 top cover before starting. There are NO hazardous voltages inside the
ST-7000, but use care to avoid damaging components or accidently shorting out
circuits with stray wires while power is applied to the ST-7000. To remove the
top cover:
1. Remove all cables connected to the ST-7000 rear panel.
2. Remove the two screws at each side of the cabinet (4 screws total).
3. Lift from the front and swivel the top so that it lies upside down
behind the ST-7000.
4. Unplug the ground jumper wire and set the top cover aside.
5. Preliminary tests will be made with the cover OFF. The cabinet
cover may be re-assembled after all jumpers and connections are set.
Location of the internal jumpers is shown in Figure 2.2.
HAL880815

ST-7000 OPERATOR'S MANUAL
PAGE 3
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HAL880815
F1
.SASB

ST-7000 OPERATOR'S MANUAL
PAGE 4
2.1 DC Power:
The ST-7000 requires a minimum of 13 VDC @ 225 rna power. This is supplied by
the enclosed accessory DC Power Supply or from other sources of DC power. The
connector on the HAL DC Power Supply is already set-up for the ST-7000. If
using your own DC power source, be sure to observe correct polarity. The ST-
7000
DC connector uses the center pin as the oositive terminal. BE CAREFUL!
Other devices with similar appearing DC connectors may use a different polarity
as well as a different diameter center pin. If you accidently reverse the
power supply polarity, it should not damage the ST-7000 circuits, but it will
blow
the fuse inside the ST-7000! Any DC power supply used with the ST-7000
should supply 13.5 to 15 VDC at 0.250 A.
2.2 HF Radio Connection:
The HF Radio equipment is connected to the "HF RADIO" 5-pin DIN connector on
the rear panel. If you are preparing your own cables, pay close attention to
the pin numbers marked on the rear panel. The "industry standard" pin
numbering on these connectors does NOT go in a logical progression!
Connections are as follows:
PIN USE
1
Transmit tones to HF transmitter audio input
2 GROUND
3 Push-to-Talk (PTT) to transmit/receive control
4 Audio output of HF receiver
5 Not used
Shell
GROUND (Cable shields)
An accessory cable (P /N 355-00054) is supplied that conveniently converts the
5-pin DIN connections to individual "RCA-style" phono plugs. Some HF radio
equipment (notably Ten-Tee) have rear panel phono connectors to which this
adapter cable may be directly connected. Other radio connectors may require
that you either make your own complete cable set OR adapt the phono connector
to one that matches the connector on your radio. For HF radio connections, the
following color code applies to the HAL adapter cable.
CABLE
COLOR
RED
BLACK
WHITE
YELLOW
HF RADIO CONNECTIONS
DIN to PHONO Adapter Cable
USE
TONES
TO HF TRANSMITTER
Push-To- Talk (PTT)
AUDIO FROM HF RECEIVER
-- not used --
ST-7000
HF RADIO
PIN NO.
1
3
4
5
NOTE: Ground (pin 2) is connected to ALL phono connectors
A typical ST-7000 to HF Transceiver connection is shown in Figure 2.3. A
detailed discussion of the requirements for each connection is given in the
sections following Figure 2.3.
HAL880815

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ST-7000 OPERATOR'S MANUAL
PAGE 6
2.2.1 HF Receive .Audio:
The ST-7000 is designed to work equally well from either an 8 ohm or 600 ohm
audio output on your receiver. The simplest connection is direct to the
receiver speaker output terminals. Set the receiver volume control to a
comfortable speaker level and the ST-7000 AGC circuit will do the rest. If you
have a constant level 600 ohm audio output, by all means use it. Some radios
have a phone patch output on the rear panel - if so, use it. The ST-7000 may
also work with some "recorder" outputs provided on some receivers. However,
the output impedance and voltage level output may not provide sufficient audio
signal for the ST-7000 and may cause reduced performance during signal fades.
Be
sure to use shielded cables between the ST-7000 and the receiver audio
output connector.
2.2.2
HF Transmit Audio:
The ST-7000 is set at the factory for a level of -20 dBm (80 mY) to the
transmit audio output connector. This level may be reduced to as low as a few
millivolts (-50 dBm) by adjustment of the "HF AFSK" screw-driver control on the
rear panel. Conversely, if ypur transmitter system requires a higher level
output, internal jumper Jl2 may be installed to increase the maximum level
output to 0 dBm (800 mY). With J12 in place, the "HF AFSK" control will adjust
over the -30 to 0 dBm range (25 to 800 mY). The microphone input of most SSB
transmitters will require a level of between -40 and -20 dBm (8 to 80 mY). Be
sure to use a shielded cable between the ST-7000 and the transmitter audio
input.
Use the following procedure to set the "HF AFSK" level control.
1. Turn OFF transmitter VOX and SPEECH PROCESSOR features.
2. Set the transmitter to LSB mode.
3. Set transmit MIC LEVEL to "0".
4. Set ST-7000 to "200" SHIFT and turn ON ("HF" position).
5. Set ST-7000 HF AFSK to maximum (full CW as viewed from rear).
6. Be sure transmitter is connected to a load (antenna or dummy load).
7. Turn transmitter to XMIT.
8. Slowly increase MIC LEVEL until 50% of full transmitter power output is
noticed.
Note the position of the MIC LEVEL knob.
9. Turn transmitter OFF.
10. If 50% transmitter power is achieved in first third of the MIC LEVEL
rotation, change the setting of "HF AFSK" (CCW) and try step 8 again.
Keep adjusting MIC LEVEL and "HF AFSK" until 50% transmitter power is
achieved at between 1/3 and 1/2 rotation of the MIC LEVEL control.
HAL880815

ST-7000 OPERATOR'S MANUAL PAGE 7
11. If 50% transmitter power is achieved at greater than 1/2 rotation of
the MIC LEVEL control, install jumper Jl2 inside the ST-7000. Be sure
to turn OFF the ST-7000 before removing its cover. The jumper for J12
is
installed at the factory with just one pin covered. Unplug the jumper
and re-install it to short out the pins at Jl2. After installing the
Jl2 jumper, go back to step 8 and adjust MIC LEVEL.
12. If installing Jl2 still does not give adequate MIC LEVEL settings, turn
everything OFF and inspect your cables -something is WRONG!
13. Set the MIC LEVEL control to the desired transmitter output level. Since
most
transmitters are designed for SSB voice (50% duty cycle), using less
than full power for data is a prudent move and may greatly prolong the
life of your transmitter. The difference between 1/2 power and full power
is only 1/2 an S-unit on the other station's receiver, hardly worth the
risk to your transmitter!
2.2.3 HF PTT Connection:
The ST-7000 Push-to- Talk (PTT) output is a relay contact switched to ground.
The relay can adequately switch PTT control lines that have up to 50 VDC at a
maximum current of 0.25 amperes. This should switch virtually ANY transmitter
or transceiver available. A shielded cable is recommended but not required for
the PTT connection. Often, a two-conductor shielded cable can be used to carry
both transmit audio and PTT signals from the ST-7000 to the transmitter
microphone input jack.
The ST-7000 HF PTT output includes a 20 second safety timer for packet radio.
This timer prevents long key-down periods, even if your TNC or computer
malfunctions. This safety feature helps prevent transmitter burn-out in a
malfunctioning packet radio system. The timer resets after each packet is sent
and the TNC PTT control line returns to receive state.
However, the ST-7000 may also be used as an RTTY or AMTOR FEC modem. In this
case, long key-down transmitter periods are common and internal jumper J7 may
be installed to defeat the PTT safety timer. To defeat the timer, move the
jumper plug so that it shorts the two pins ·at 17. The jumper plug is
positioned at the factory to cover one but not both pins of J7 (PTT safety
timer ON).
2.2.4
HF GROUND Connection:
The ST-7000 MUST be adequately grounded to the HF transmitter and receiver.
Grounding is done in TWO steps - (I) an audio ground obtained through the
shielded cables between the HF RADIO connector and the transmitter/receiver
audio connections, and (2) an RF ground between cabinets. The importance of a
good
RF .ground cannot be over-emphasized! Use a short length of 1/4" shield
braid directly between the transmitter /receiver cabinet and the ST-7000 rear
panel ground screw. An earth ground for the entire radio station is a good
safety feature but does NOT replace the need for a seoarate RF ground
connection.
HAL880815

ST-7000 OPERATOR'S MANUAL
PAGE 8
2.3
Packet Controller Connections:
The ST-7000 includes three different I/0 interface connectors and jumper sets
for connection to your packet controller (TNC). Choice of which interface is
used is
left to the operator. If you need to use the same packet controller
for HF and VHF, use the TNC AUDIO interface. If you choose to dedicate a
packet controller specifically for HF use, a slight improvement in performance
may be gained by using the TTL or RS232 interface connections, but at the loss
of the VHF-Audio "pass-through" feature. The factory settings are for an AUDIO
interface and its use is described first.
2.3.1 TNC AUDIO Interface:
This interface connection makes use of a separate modem contained inside the
ST-7000. This modem converts the processed HF packet data into the tone
standards used for VHF packet radio -1200 Hz and 2200 Hz. This interface
allows use of virtually ALL currently available packet controllers with NO
internal modifications to the packet controller itself.
A
"standard" 5-pin DIN audio connector is used for the TNC AUDIO interface.
Pin connections correspond to those pins used on the popular TNC-2, MFJ-1274,
and KPC controllers. However, connectors and standards change -BE SURE TO
CHECK YOUR MANUAL! Connections to the TNC AUDIO connector are:
Pin Use
I
Transmit audio output from TNC
2 GROUND
3 PTT output from TNC
4 Receive audio input to TNC
5 Not used by ST-7000
Shell
GROUND (not used on some TNC devices)
Use
shielded cables to connect between the ST-7000 and the TNC. Be sure to
make an RF ground connection between the ST-7000 cabinet and the TNC cabinet.
No adjustments are necessary for the TNC AUDIO interface connection. Internal
jumpers at ST-7000 location JS are set at the factory. If your unit has been
changed from factory settings, check to be sure that:
l. ALL four (4) jumpers are installed at jumper field JS.
2. NO jumpers are installed at fields J9, JIO, and Jll.
3. If jumpers are not installed at J9, JIO, or Jll, connection of
external cables to either the TTL or RS232 I/0 connectors will
NOT affect ST-7000 operation.
Two DIN to Phono adapter cables (P/N 355-00054) are supplied to assist in
making the TNC Audio connection. In general, use of the adapter cable greatly
simplifies installation, even if some of the connectors must be changed or
further adapted. For TNC Audio connections, the following color code applies
to
the HAL adapter cable.
HAL880815

ST-7000 OPERATOR'S MANUAL
CABLE
COLOR
RED
BLACK
WHITE
YELLOW
TNC AUDIO CONNECTIONS
DIN to PHONO Adapter Cable
l!.SE
TX TONES from TNC
Push-To-Talk (PTT) from TNC
AUDIO 1Q TNC AF INPUT
-- not used --
ST-7000
TNC AUDIO
PIN NQ.
I
3
4
5
NOTE: Ground (pin 2) is connected to ALL phono connectors
PAGE 9
A
typical ST-7000 to TNC AUDIO connection is shown in Figure 2.4. Note that
connections to a VHF Radio are also shown. These connections will be discussed
further in section 2.4.
2.3.2
TTL TNC 1/0 Connections:
The ST-7000 may also be used in a direct connection to an external modem
connector on your packet controller. The connector and pin arrangement is
identical to that used on the PK232 controller. Cable 960-07232 furnished in
the accessories may be used to make a direct connection to the PK-232. Note
that internal jumpers in the PK-232 MUST be changed to use its external modem
connection.
Other TNC's may or may not support direct TTL external modem
connections. Be
sure to check your manual before making this connection. The
connector and pin numbering may be different; some jumpers inside your TNC may
have to be changed. The connections to the TTL TNC I/0 connector are:
Pin Use
I
Received HF data to TNC
2 Transmit data from TNC
3 HF Carrier Detect data to TNC
4 GROUND
5 Push-to- Talk (PTT) from TNC
Shielded wire is recommended for this cable connection. Be sure to run a
separate RF ground between the TNC and ST-7000 cabinets. The following jumpers
MUST be set inside the ST-7000 to use the TTL TNC 1/0 connection:
I. Plug-in
four jumper plugs at jumper field J II. If your ST-7000 is
"factory fresh", unplug the four plugs from jumper field J8 and move
them to field J II.
2. REMOVE ALL jumper plugs in fields J8, J9, and JIO.
3. External cables connected to ST-7000 TNC AUDIO or RS232 rear panel
connectors will have NO effect.
TTL TNC connections are shown in Figure 2.5.
HAL880815

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ST-7000
TNC TIL J/0 CONNECTIONS
CABLE
PIN USE COLOR
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HF RX DATA BLACK
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4 GROUND
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EI1IJ HAL COMMUNICATIONS CORP.
BCX 365, URBANA. IL 61801
ST -7000 FIGURE 2.5
TTL TNC I/0 CONNECTIONS
DATE
8/15/88 I SCALE NONE
DRN BY TFH
I NO. C1354 APP BY
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ST-7000 OPERATOR'S MANUAL PAGE 12
2.3.3 RPC-2000 RS232 1/0 Connections:
This connector is provided specifically for connection to the HAL RPC-2000
Radio Packet Controller, but may be used with ANY TNC that has an RS232C
external modem interface. The pin connections are:
Pin Use
1 Chassis Ground
2 Transmit data (TXD) from TNC
3 HF Receive data (RXD) to TNC
4 Request To Send (R TS) from TNC (+V = transmit)
5 Clear To Send (CTS) to TNC (constant +8V)
6
Data Set Ready (DSR) to TNC (constant +8V)
7
Signal Ground
8 HF Carrier Detect (CD) data to TNC
19 Push-to-Talk (PTT) from TNC (ground = transmit)
Other pins = NO CONNECTION IN ST-7000
TWO
different transmit/receive control inputs are provided RTS and PTT). The
RPC-2000 provides BOTH, but other TNC's may provide just one or the other.
This connector is designed so that a full 25-wire RS232 cable may be used
between the ST-7000 and the RPC-2000. For other TNC devices, be sure to
consult your manual and connect only those pins that are required.
Two jumper fields are provided for RS232 I/0 - a 4 position field (J9) for TXD,
RXD, CD, and PTT plus a 2 position field (JlO) to choose whether TNC RTS (pin
4) or TNC PTT (pin 19) is used to control the ST-7000 HF PTT circuit. To use
the ST-7000 with the RPC-2000, use the following jumpers:
1. Install four jumper plugs at field J9 (aligned front-to-hack in the
ST-7000 cabinet).
2. Install one jumper plug in the RTS position of field J10 (aligned
left-to-right in the ST-7000 cabinet).
3. Be sure that ALL jumper plugs are removed from fields J8 and J 11.
4. Connection of external cables to the TTL I/0 or TNC AUDIO connectors
on the ST-7000 will have NO effect.
Also, be sure to provide a good RF ground connection between the DS-3200 or
host PC for the RPC-2000 and ST-7000 cabinets. Use of the ST-7000 to RPC-2000
RS-232
Interface is shown in Figure 2.6.
HAL880815

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REV. DATE
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ST-7000
RPC -2000 RS232 I/0
PIN I USE
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19 PUSH-TO-TALK <PTI>
NOTES•
1. PIN 1 IS CONNECTED TO CABLE SHIELD.
2. SELECT EIIJ:lER RTS <PIN 4) DR
PTT <PIN 19) FOR HF PTT
<SEE SECTION 2.3.3>
3. DNL Y ABOVE PIN NUMBERS ARE USED
IN THE ST-7000.
I El1lJ HAL COMMUNICATIONS CORP.
BOX 365, URBANA, IL 61801
A
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ST- 7000 FIGURE 2.6
RPC -2000 I/0 CONNECTIONS E
DATE
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ST-7000 OPERATOR'S MANUAL
PAGE 14
2.4 VHF RADIO Connections:
The VHF radio connector works ONLY if the TNC AUDIO I/0 interface is also used.
It has NO effect if TTL or RS232 I/0 is used. The connector and pin-out are
identical to that used for a connection to popular TNC models. If such a
connector is already in use in your VHF to TNC connection, you may just unplug
the cable from the TNC and plug it into the ST-7000 VHF RADIO connector. If
you use a different connector, check your manuals and prepare a cable as
follows:
Pin Use
I
Audio input to VHF Radio transmitter
2 GROUND
3 Push-to- Talk to VHF Radio
4 Audio output from VHF Radio receiver
5 Not used
Shell
GROUND (may not be used on some TNC's)
To use the TNC with the VHF radio, set the ST-7000 front panel switch to VHF
position (button out= ST-7000 OFF) and change the TNC HBAUD to 1200 baud. No
ST-7000
circuits are used on VHF - the switch connects the VHF RADIO connector
to the TNC AUDIO connector. Connections and color coding of the DIN to Phono
adapter cable are shown in Figure 2.4.
This completes connection of the ST-7000 to the radio system. Temporarily
remove all connectors from the ST-7000, re-install the ST-7000 top cover, and
then restore the connections to the ST-7000. Be sure to reconnect the ground
wire between the ST-7000 circuit board and rear panel.
HAL880815

ST-7000 OPERATOR'S MANUAL
CHAPTER 3
OPERATION
PAGE 15
Operation of the ST-7000 is very simple. It is virtually a matter of hooking
it up, turning it ON, and tuning a signal. First, a brief review of the
controls and indicators:
3.1 CONTROLS AND INDICATORS
Refer to Figure 3.1 for the following discussion.
HAl COMMUNICATIONS CORP
TUNING
ST-7000
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200 - - 200
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FIGURE 3.1 ST-7000 FRONT PANEL
3.l.l HF/VHF Switch:
The HF /VHF switch serves the dual function of ST-7000 power switch and HF /VHF
radio switch if the TNC AUDIO interface connection (2.3.1) is also used. If
either the TNC TTL or RS232 TNC interface connections are used, the HF /VHF
switch only controls the power to the ST-7000. Power is turned ON when the
button is pushed IN (HF position), as indicated by the RED POWER front panel
lamp. If the TNC AUDIO interface connection is used and a VHF radio is
connected to the ST-7000 (Sections 2.3.1 and 2.4), this switch also diverts the
TNC audio signals to the VHF radio when the ST-7000 is turned OFF (button OUT=
VHF position).
3.1.2
SHIFT Switch:
This switch selects either 200 Hz or 600 Hz switch. The present "HF Standard"
is 200 Hz shift, so you will want to use this position to get started (button
in). However, when talking with another station who also has a HAL ST-7000,
switch to 600 Hz shift and see the difference! The ST-7000 200 Hz shift
performance is good, but the 600 Hz performance is even better! Both receiver
filters/detectors and transmit tones are switched by the SHIFT switch -you are
always transceive. Although polarity makes no difference to packet radio
HAL880815

ST-7000 OPERATOR'S MANUAL
PAGE16
signals, care has been taken to assure that receive and transmit data
polarities are identical -you may also use the ST-7000 for 300 baud Baudot or
ASCII RTTY (or 100 baud AMTOR).
3.1.3
THRESHOLD Control:
This control sets. the signal/no-signal detection threshold for the Carrier
Detect circuit. It operates in a similar fashion to a squelch control on a VHF
radio. Tune the receiver to an unoccupied frequency and rotate the control
clockwise (CW) until the CD LED comes on. Now, "back" the control CCW until
the CD light goes OFF. Tune to an active HF packet channel and confirm that
the CD LED flashes ON and OFF as bursts of packet signals are heard. The
setting of THRESHOLD will change with receiver volume control setting unless
you
have a constant audio output connection on your receiver. Practice setting
this control.
3.1.4
Tuning Indica tor:
The ST-7000 tuning indicator is a unique device, unlike any other ever offered.
A total of 20 LED segments are arranged in two parallel bars. A fully lit LED
segment corresponds to approximately 50 Hz change in the audio frequency of the
received tone(s). Picture the two parallel bars as the vertical "legs" of the
letter "U". The lowest audio frequency (approximately 900 Hz) will light the
top left LED segment. As you tune to increase the tone frequency, the
illuminated LED segment moves down the left bar and then back up the right bar
to the highest frequency (approximately 3000 Hz). The "center" of the display
(l/2 way between the bottom dots of the two rows) corresponds to the 1900 Hz
center frequency of the ST-7000. A packet radio signal will appear as a band
of dots, the width of which is proportional to the shift and data rate. The
dots actually correspond to the frequency spectra of the received signal.
Correct tuning of the receiver is achieved when the signal is centered on the
ST-7000 input filters - centered on the tuning display. Therefore, you need
only tune until an equal vertical deflection is obtained on the two parallel
bars.
When
correctly tuned, a 200 Hz shift signal will illuminate the bottom three
bars in both vertical lines - approximately to the "200" marks on the front
panel. A 600 Hz shift signal will have a balanced deflection near the "600"
marks on the front panel. With a little practice, it becomes VERY easy to
precisely tune an HF packet signal on the display. Use some patience when
tuning - a given packet burst may appear "biased" to one side or the other -
this is because of the bit-stuffing and NRZI format used for packet data. With
just a little practice, you can easily tune to within 20 Hz or closer. Watch
some
HF packet signals on a busy channel. You will be amazed at the frequency
error of some stations. The ST-7000 itself is very forgiving of minor tuning
errors (50 Hz on 200 Hz shift, 100 Hz on 600 Hz shift), but strive to be as
accurate as possible when tuning. The resolution of the tuning indicator is a
lot
better than the 50 Hz bar spacing might lead one to believe since each
segment partially illuminates as its "center frequency" is approached.
Resolution of 20 Hz or better is quite easy to achieve. If absolute frequency
accuracy is required on a net frequency, a crystal in the transmitter/receiver
is still the best approach. Examples of correct and incorrect tuning are shown
in Figure 3.2.
HAL880815

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TONE FREQUENCY TOO HIGH
I 5 I 6
7 I 8
REV. DATE
BY
El1IJ HAL COMMUNICATIONS CORP.
BDX 365, URBANA. IL 61801
ST -7000 FIGURE 3.2
TUNING INDICATOR EXAMPLES
DATE 8/16/88 I
SCALE
NDNE
DRN BY
TFM
NO. C1356
APP BY
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