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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
Slide 3 - SSB and Sound Card Applications
- Spectrum display to 5 Hz resolution - Bandpass filter for signal - 50 Hz - Encode/decode of signal
- 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
Slide 4 - Sound Card Interface 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
- 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
- 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
- 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
- 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
- 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
- Shield grounded at Sound Card End Only - Reduces common mode noise injection - Can filter for RF
Slide 9 - Evolution of Interface Design
- Transformers on Tx and Rx lines - PTT Opto/Isolated
Slide 10 - Evolution of Interface Design
- 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
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
Tx path transformer Rx path transformer Opto isolated PTT LED for PTT Supports mike/ext.spkr or single cable accessory connection
Tx path transformer Opto isolated PTT
Tx path transformer Rx path transformer LED for "PTT" May require external power Switch for PTT mode VOX built into interface
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
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
Tx path transformer Tx path transformer Opto isolated PTT LED for PTT Supports mike/ext.spkr or single cable accessory connection
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
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
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
Slide 13 System Requirements
- 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
- 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
- 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
- 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
- Overdrive of audio on Tx - ALC or Compression ON during Tx
- Needs shielding on cables - Common mode noise, use transformers on both channels - Ground all system components to a good earth ground
- ALC on, or Compression On - Transmitting outside of Tx bandpass area - Transmitting too low in the waterfall
- 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.
- 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
- Mute all sources on "Playback" except WAVE and Volume Control
- 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
- 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
- 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
- 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
- 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
- A useable rig for PSK, some care must be taken when dealing with the drift issue.
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