Sound Card Interfacing - Presentation
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Below is an extract of the slide presentation "Sound Card Interfacing"

Slide 1 - Introduction

Sound Card Interfacing

    Clint Hurd - kk7uq

Slide 2 - Sound Card Interfacing - Outline

bullet General Concept - SSB Rig & Sound Card Applications
bullet Sound Card Interface Requirements
bullet Evolution of Interface Design
bullet System Operation
bullet Common Problems and Solutions
bullet Example: Interfacing the FT101-E

Slide 3 - SSB and Sound Card Applications

bullet Combo of software, PC, sound card, SSB rig and Interface
bullet Software

        -  Spectrum display to 5 Hz resolution

        -  Bandpass filter for signal - 50 Hz

        -  Encode/decode of signal

bullet PC - Windows 95 or later, 100 MHz or faster
bullet Rig

        -  SSB in either USB or LSB

        -  Reasonable frequency stability

        -  Tight filters NOT needed in most cases

        -  Can NOT use ALC or Compression on Transmit

        -  Must stay within Tx bandwidth - typically 2200 Hz or less

bullet Interface - connects rig to the PC Sound Card

Slide 4 - Sound Card Interface Requirements

bullet PSK represents the "worst case" requirements

        -  "Two tone" nature demands good linearity in the system - signals

            must be clean to operate close to one another without interference

        -  Narrow bandwidth (31Hz) - can operate as close as 100 Hz apart

           unless one signal is much stronger than another, or distorted

bullet Audio from Rx to PC

        -  Signal level as high as 5v p-p, typical 1v p-p

        -  Audio frequency range from 200 to 4000 Hz, or whatever the

            transmit passband will allow

        -  Cables need to be shielded

        -  Sound card accepts max 5v p-p before saturating

                - Software detects and warns against saturated signals at

                  about 1.5v p-p

                - Several ways to control the maximum level to the sound card:

                        - Rx RF gain, Rx volume control, PC volume control,

                          Interface Rx level control

 

Slide 4 - Sound Card Interface Requirements

bullet

Audio from PC to Transmitter

        -  Sound card output up to 5v p-p at max level - may start clipping at

           around 75% level

        -  Rig expects microphone levels - at a level of a few millivolts up to a

           hundred millivolts

        -  Frequency range from 200 to 4000 Hz - maximum determined by

           Tx output filter bandwidth - typically around 2200 Hz

        -  Audio drive levels determine power output - usually rig can run at

           about 50% of CW rating or less

        -  System must operate in an RF environment

                - Shielded cables - lengths under 6 feet

                - Good grounding of all components - rig, PC and tuner

        -  Care taken to eliminate other audio sources during transmit

 

Slide 5 - Sound Card Interface Requirments

bullet

SSB Rig Control

        -  Tx On/Off methods:

                - Manual switch

                - VOX

                - PTT via Serial Port Control on PC

        -  Tx audio drive level set by:

                - Audio level from PC

                - Mike gain on rig

                - Attenuation, or level control potentiometer on interface

        -  Rx Audio to PC provided by:

                - Line out

                - External speaker or headset port

                - Accessory port

 

Slide 6 - Evolution of Interface Design

bullet

Not as simple as it first seems

bullet

Areas that affect design

        -  Linearity of all stages of Tx audio path

        -  Noise pickup in interface and cable system

                - RF

                - AC Noise (hum)

                - Other sources into sound card

 

Slide 7 - Evolution of Interface Design

bullet

Stage 1 - Shielded cable and resistor pad

        - Can work if:

                - Cable to rig is kept short, all cables shielded

                - RF environment is clean

                - No common mode noise between PC and Rig

 

Slide 8 - Evolution of Interface Design

bullet

Stage 2 - Isolating the Tx drive with a transformer

        -  Shield grounded at Sound Card End Only

        -  Reduces common mode noise injection

        -  Can filter for RF

 

 

Slide 9 - Evolution of Interface Design

bullet

Stage 3 - Complete isolation between rig and PC

        -  Transformers on Tx and Rx lines

        -  PTT Opto/Isolated

Slide 10 - Evolution of Interface Design

bullet

Adding features to improve operability

        -  Potentiometers on Tx and Rx with knobs

        -  Switch for PTT mode selection

                - Auto (PC serial port RTS or DTR line controls)

                - OFF (Disables PTT control)

                - PTT ON (Forces PTT on)

        -  Relay for PTT for older rigs

        -  Capacitor on Tx drive for DC isolation

        -  Support for either single cable Accessory port, or two

           cable mike/speaker out connection

        -  Switching for microphone / interface

        -  VOX built into interface to eliminate need for serial control

 

Slide 11 - Evolution of Interface Design

bullet Available interface - features and prices

Prices are approximate, and include ALL cables needed (rig, serial port, audio cables).  Prices do not include shipping and handling, or any applicable taxes.  See the manufacturers website for their latest pricing and products.

Ready to Go

bullet

Rascal  $49                    BuxComm                     http://www.packetradio.com/psk31.htm    

            Tx path transformer

            Rx path transformer

            Opto isolated PTT

            LED for PTT

            Supports mike/ext.spkr or single cable accessory connection

 

bullet

Nomic   $58                    West Mountain Radio    http://www.westmountainradio.com/

            Tx path transformer

            Opto isolated PTT

 

bullet

Signal Link SL-1     $60    Tigertronics                  http://www.tigertronics.com/

            Tx path transformer

            Rx path transformer

            LED for "PTT"

            May require external power

            Switch for PTT mode

            VOX built into interface

       

bullet

Rigblaster   $100            West Mountain Radio    http://www.westmountainradio.com/

            Tx path transformer

            Opto isolated PTT

            Relay for PTT

            LED for PTT

            Requires external power (included)

            Mike switching built in

            Mike PTT interrupt to software

 

bullet

Rigblaster Plus $130      West Mountain Radio    http://www.westmountainradio.com/

            Tx path transformer

            Opto isolated PTT

            Relay for PTT

            LED for PTT

            Requires external power (included)

            Mike switching built in

            Mike PTT interrupt to software

            CW/FSK keying output

            Jack for foot switch PTT

           

Home built Projects

bullet

Rascal kit  $25                    BuxComm                http://www.packetradio.com/psk31.htm

            Tx path transformer

            Tx path transformer

            Opto isolated PTT

            LED for PTT

            Supports mike/ext.spkr or single cable accessory connection

 

bullet

K8CAV Design (from QST)        estimated part cost $35

            Tx path transformer

            Tx path transformer

            Opto isolated PTT

            Potentiometers for Tx and Rx level control

            Supports mike/ext.spkr or single cable accessory connection

 

bullet

kk7uq -01   $55          Discovery Bay Computing  http://www.waypoint.com/users/~discobay/

            Tx path transformer

            Tx path transformer

            Opto isolated PTT

            Potentiometers for Tx and Rx level control

            Relay for PTT

            LED for PTT indication

            PTT mode switch

            Requires external +13.8v power

            Supports mike/ext.spkr or single cable accessory connection

 

bullet

kk7uq -02   $50          Discovery Bay Computing  http://www.waypoint.com/users/~discobay/

            Tx path transformer

            Tx path transformer

            Opto isolated PTT

            Potentiometers for Tx and Rx level control

            LED for PTT indication

            PTT mode switch

            Supports mike/ext.spkr or single cable accessory connection

 

Slide 12  Evolution of Interface Design

 

bullet

  Schematic of kk7uq Sound Card Interface

 

Slide 13 System Requirements

bullet Grounding - of computer, rig, antenna tuner is a must
bullet Transmit

        -  Absolute frequency control is not necessary

        -  Frequency stability is more important

        -  You MUST say within the Tx audio passband on transmit

        -  Be able to monitor your output level and ALC

bullet Receive

        -  Use RF gain as your primary level control for receive

        -  Tune the base frequency so the signal you want to work is in the range

            of 1000 to 2000 Hz

 

Slide 14 System Requirements

 

bullet

IMD Measuring

        -  IMD (Inter-Modulation Distortion) measurements are a part of most software

           for PSK31

        -  Measures the signal level of the fundamental signal and it's harmonic.  Represented

           in -db from fundamental level

        -  A good IMD is -24db

        -  On strong signals, reduce the RF gain, or else the IMD measurment will read low.

        -  If signals are weak, or QRN level is high, measurements will read lower than they

           really are

        -  There are some small differences in IMD readings between the popular software

           packages, maybe within a 6db spread

bullet

Dealing with Strong Local Signals

        -  Can live without a narrow filter ... but ... if you have one, use it with your passband

           tuning to reduce the signal level of the offending signal - this will reduce the effect

           of AGC pumping

 

Slide 15 System Requirements

 

Software available

Digipan     http://www.digipan.net/

    Has an internal log which supports name & qth pop on subsequent qso.

    Has waterfall display that covers 4000 Hz

    Monitors two channels

    Modes supported: PSK31 (BPSK and QPSK)

    Written by KH6TY, UT2UZ, UU9JDR

Hamscope     http://www.qsl.net/hamscope/

    Supports YPLOG

    Has both waterfall and spectrum displays that cover 2800 Hz

    Monitors two channels

    Supports PSK31 (BPSK & QPSK); MFSK16; RTTY; CW

    Written by KD5HIO

Helleschreiber     http://iz8bly.sysonline.it/

    Internal log

    Supports PSK31 (BPSK & QPSK), Hellschreiber

    Written by IZ8BLY

MMSSTV                 http://www.qsl.net/mmhamsoft/

    Internal log

    Supports SSTV

    Written by JE3HHT, who also wrote MMTTY

MMTTY     http://www.qsl.net/mmhamsoft/

    Internal log, supports name and qth pop on subsequent qso, has contest mode

    Supports RTTY

    Considered the best sound card implementation of RTTY available as freeware,

    Both Hamscope and Zakanaka use the MMTTY engine for their RTTY modes

    Written by JE3HHT

MixW       http://www.mixw.net/

    Internal log which supports name and qth pop on subsequent qso.

    Supports PSK31 (BPSK &QPSK), MFSK, RTTY, Hellschreiber, Throb, SSTV and many more

    Demo versions are available for no charge, but the registered version is a for fee product

    Written by UT2UZ, who also wrote Digipan

Stream     http://iz8bly.sysonline.it/

    Internal log

    Supports MFSK8, MFSK16 and PSK31 modes

    Written by IZ8BLY

WinPSK     http:/www.qsl.net/ae4jy/

    Supports PSK31 (BPSK & QPSK)

    Written by AE4JY.

    This was one of the first Windows supported PSK programs.  Moe, AE4JY developed

    the PSKCORE engine to provide the DSP algorithms required to implement PSK31.

    The PSKCORE engine is also used by WinPSK, WinWarbler, Hamscope and Zakanaka.

WinWarbler     http://www.qsl.net/winwarbler/

    Supports PSK31 (BPSK &QPSK)

    Monitors three channels

    Written by AA6YQ

    WinWarbler is a member of the DXLab suite of interoperating applications, which

    provide logging, QSL card/label generation, transceiver and rotor control,

    propagation prediction, DX cluster spot collection/analysis and real-time mapping

    of the solar terminator, beam headings and DX spots.  See www.qsl.net/dxlab

    for more details on this suite.

Zakanaka     http://www.qsl.net/kc4elo/

    Has excellent support of the Logger program written by the same author.

    Supports PSK31 (BPSK & QPSK), RTTY (using MMTTY engine)

    Written by K4CY

 

Slide 16 Common Problems & Solutions

 

bullet

Wide Signal

        -  Overdrive of audio on Tx

        -  ALC or Compression ON during Tx

bullet

Hum on Signal

        -  Needs shielding on cables

        -  Common mode noise, use transformers on both channels

        -  Ground all system components to a good earth ground

bullet

Harmonics of Audio Carrier

        -  ALC on, or Compression On

        -  Transmitting outside of Tx bandpass area

        -  Transmitting too low in the waterfall

bullet

Frequency Offset Between Stations

        -  RIT or XIT is ON, turn it OFF

        -  One of the transmitters has an offset in their transmitter or receiver

           one stations should turn NET OFF, and freeze their Tx frequency, the

           other should leave NET ON.

bullet

Signal Cutting In and Out

        -  CPU too slow for the processing required

        -  Too many process running on CPU while actively processing psk signals

        -  VOX is set too close to the signal level

        -  Bad connection

bullet

Strange Signals Mixed with a Good PSK Signal

        -  Mute all sources on "Playback" except WAVE and Volume Control

bullet

Sounds from the Shack Being Transmitted

        -  Sounds such as typing, phone ringing etc.

        -  Mike is active, disconnect it

        -  Mike in PC is active, mute it

 

See Sound Card Interface Manual Section 7 for setup and trouble shooting procedures

 

Slide 17 Example: Interfacing the FT 101 E

 

bullet

Classic Tube/Solid State Rig

        -  No Accessory Port available

        -  No line out

        -  Frequency accuracy is an issue

        -  Stability may be an issue

        -  No +13.8v supply available, power supply is internal to the rig

        -  PTT is at +13.8v when not activated, draws 120 ma. when activated

bullet

PC is a Laptop

        -  Only on serial port is available

        -  Mike input is a 3.5mm stereo connector on the front of the PC

        -  Headset output is a 3.5mm stereo connector on the front of the PC

        -  Serial port signal levels may be lower than standard

bullet

Solution

        -  Use 4 pin screw on mike connector for Tx audio, and PTT

        -  Use headset out for Tx audio, use a Y connector if want to monitor audio

        -  Use kk7uq -01 (with relay for PTT) design

                Dual transformers

                Opto isolated PTT drives reed relay for PTT contact closure

                Interface has level control potentiometers for tx and rx level settings

                Use Hamscope for software (ease of use, multiple modes)

                Use wall wart supply to power reed relay

                Increase drive level of opto isolator because of lower than RTS signal

bullet

Performance

        -  Frequency setting done by observing signals in 14.070 area and resetting dial on rig

        -  Transmit level of 25 to 50 watts was used

        -  Good reports on audio quality - IMD of -30db or better

        -  Some drift - about 30Hz in a one minute over

                Other station "locked" his Tx freq so could return to the starting point each time

        -  Contacts

                First contact was XE1L in Mexico City

                Second contact was VK2KUI  Yarrahapinni in New South Wales

                Made ten contacts in the TARA Rumble PSK contest

bullet

Conclusion

        -  A useable rig for PSK, some care must be taken when dealing with the drift issue.