2
Sound Card Interface Requirements
• Audio from Receiver to PC
– Signal level 5 Vp-p, typical signal is 1 Vp-p
– Audio frequency range from 200 to 4000 Hz, or whatever
the Rx passband will allow
– Cables need to be shielded
• Sound Card Accepts 5 Vp-p Before Saturating
– Software detects and warns against saturated signals at
around 1.5 V p-p
– Ways to control the maximum level to the sound card:
•RX RF/AF Gain
• PC Volume Control
• Interface Level Control
Sound Card Interface Requirements
• Audio from PC to Transmitter
– Sound Card output up to 5 Vp-p at max level
• PC slider set at mid level - output is about 1 Vp-p
– Rig expects microphone levels at about 2-10 millivolt p-p, so
signal must be attenuated in the interface
– Frequency range from 200 to 4000 Hz
• Max determined by Tx output bandwidth
, typically 2200 Hz
– Audio drive levels determine power output - usually run rig at
25% to 50% of CW rating for clean signal, and cool TX
– System is operating in an RF environment:
• Shielded cables - lengths under 6 feet.
• Good grounding of all components - Rig, PC & Tuner
– Care taken to mute other audio sources during transmit
Sound Card Interface Requirements
• SSB Rig Control
–TX On/Off
• Manual Switch - VOX - PTT via Serial Port Control
on PC
– TX Audio
• Input - Mic connector or Accessory Port
– TX Audio Drive Level
Set by combination of:
• Audio level from PC
• Attenuation level control on Interface
• Mike Gain on Rig
–RX Audio
to PC Provided by
• Line Out, Speaker/Headset Out, Accessory Port
Sound Card Interface
1:1 600 ohm
Audio Transformer
From
Sound Card
Spkr Out
3.5mm Stereo
Receptacle
Aud.
Out
Ret
Mic
To Xcvr
Ret
8
7
kk7uq Interface Model II - Schematic Diagram
14
From Xcvr
Spkr Out
(Alternate)
Ret
3.5mm Stereo
Receptacle
w/ switches
J4
R5 51
1:1 600 ohm
Audio Transformer
To
Sound Card
Line In
3.5mm Stereo
Receptacle
1
2
4
3
5
6
R7
X1
J2
1
2
3
Primary
Waterfall Drive
1k pot
Audio Taper
6
PTT
Ret
FSK
To Xcvr
All resistors
1/4W 5%
R6 51
To Xcvr
From Xcvr
R3 1.0 k
.0047uF
Tx Drive
1k pot
Audio Taper
1.0 uF
4
5
RJ45
Receptacle
3
25
6
R4 100
C1 C2
R8
X2
J3
J5
1
2
3
Primary
2
1
Up - Auto
Ctr - PTT Off
Down - PTT On
2.5mm
Stereo
Receptacle
D4
J1
External Cable w/ DB9
female serial port
conn shown for ref.
7
5
RTS
Gnd
DTR
4
Sleeve
Tip
Ring
3
Red
Yel
1N4148
1N4148
D3
Dual Color
T 1 3/4 LED
Red - PTT
Yel - FSK
LED 1
Photo Darlington
Opto-Isolator
U1
R2
2.2k
R1
2.2k
1
2
5
4
4N33
1
2
5
4
4N33
D2 1N4148
D1 1N4148
C3 10 uF
C5 .0047uF
C4 10 uF
+
+
Q1
2N3904
R11
2.2 k
R12
10 k
R10
2 meg
R9 4.7 k
AT 20 Audio
Transducer
U2
SW1
PTT Control
(SPDT Ctr Off)
Org
Wht
Grn
Wht
Blu
Wht
Brn
Wht
Org
Grn
Blu
Brn
RJ45
Plug
Rig cable mating
connector and wire
colors shown for
ref.
SP 1
Tip
Ring
Ring
Ring
Ring
Tip
Tip
Tip
Note: Return path for
audio to monitor amplifier
is made through the cable
shields to the ground
point at the PC.
Binary Phase Shift Keying - BPSK31
• Phase modulates an audio “carrier” at 31 baud
• Reverses phase 180 degrees (BPSK)
• Reduces signal level at phase shift time to
reduce spurious frequencies
• Uses variable length encoding - most used
characters are encoded into small word lengths
• Data rate consistent with that of a fast typist
• Adv: Narrow bandwidth, good performance
• Disadv: Poor performance on long path and
over the pole contacts (phase distortion)
BPSK Signal Envelope
Varicode “Space” character = 1
where 0 is a Phase Reversal and 1 is no reversal
must have at least two 0 between characters
00 0010
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