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May 4, 2013 Fulton County Amateur Radio Club

Digital Mode Workshop

Presenter: Craig Szczublewski KD8KBU

[email protected]


Today's Goals

● Homebrew Computer to Rig Interfacing● Commercial Interfaces● Software Comparison and Installation● Best Practices for Rig and PC Setup● Setting up to Receive


Introduction – Why use digital modes?

● Not New, CW has been around since the beginning, RTTY for decades

● PC Sound Card offer low start-up costs● Efficient use of bandwidth and power● Transmit text, images, and files● Usable well into the noise● Work the world on 25 watts or less


Rig Interfacing: Basic Concepts


Rig Interfacing: Acoustic Coupling

● Fast and Easy to setup and decode● Most laptops have built-in microphones● Full electrical isolation between Rig and PC● Prone to audio interference from ambient noise● Can use VOX for T/R switching


Rig Interfacing: Improved Receive

● Simple direct Rig Speaker to PC Mic Input● Rig AF Gain will impact receive quality● Can use Rig Line Out for better audio● No electrical isolation


Rig Interfacing: Improved Transmit

● Sound card Line Out/Speaker/Headphone to Rig Mic input

● When using Mic, attenuation is needed (100:1)● Line Input on Rig can bypass attenuation● Enable VOX or manual PTT● VOX enabled does not require COM Port for

PTT triggering


Rig Interfacing: Improved Transmit

● Attenuation (Voltage Divider) Circuit:


Rig Interfacing: Add Isolation and PTT

● Isolation using 1:1 600 ohm audio transformers can help solve ground loop problems

● RTS form RS232 channel used to pull down PTT with 1M914 and 4N25 photo transistor

● RS232 can be a great alternative to fussing with VOX for PTT

● Add variable resistors to attenuate xmit/receive signals


Rig Interfacing: Tone activated PTT

● Software like FLDIGI can use right audio channel to send a tone during transmit

● No USB of Serial port is required● VOX does not need to be configured


Commercial Interfacing: SignaLink USB

● Built-in sound card● Only two cables● Rig PTT provided by SignaLink● TX/RX Attenuation Controls● Requires USB 2.0 (1.1 will not work)● May need to be unplugged during Mic use● www.tigertronics.com (@ $119 w/cable)

http://www.tigertronics.com/


Commercial Interfacing: Rig Blaster

● Plug & Play/Plus/Advantage/Pro● Rig Control (CIV/CAT)● USB Control● Uses PC Sound card● True FSK for RTTY● CW keying● www.westmountainradio.com (@ $119-$299)


Commercial Interfacing: Buxcomm Rascal

● Uses PC Sound card● MK III Does not require USB or COM● GLX can use COM or USB for ● PTT or VOX● Available as Kit or Pre-Built● www.buxcomm.com (@ $69-79)

http://www.buxcomm.com/


Commercial Interfacing: MFJ 127X

● 1273B/1275/1279● COM/RS-232 PTT● Uses PC Sound card● Direct CW/FSK Keying● Optional Foot Switch PTT● Some models require 12v power● www.mfjenterprises.com (@ $59-$139)

http://www.mfjenterprises.com/


Rig and PC Settings: ALC and Mic Gain

● Keep ALC as close to 0 as possible● This will help keep IMD at a good level● IMD levels of -20 or less is ideal● If ALC meter moves during transmission, Mic

gain and audio output level from the PC may be set to high.


Rig and PC Settings: Compression and DSP

● Digital Software acts as Digital Signal Processor

● This will help keep IMD at a good level● IMD levels of -20 or less is ideal● If ALC meter moves during transmission, Mic

gain and audio output level from the PC may be set to high.


Rig and PC Settings: Output Power

● Run between 25 watts or less ● Modes like PSK are equivalent to transmitting a

CW carrier full time● Long TX cycles are close to 80% duty● Narrow signal requires very low distortion● High power produces distortion and

interference over the entire band


Rig and PC Settings: AF Gain

● Prevent Sound card Overdrive● Keeps the waterfall free of splatter● Adjust Mic input and/of Sound card output● Use variable resistors in Interface to attenuate

the output● Use Rigs line level input/output


Rig and PC Settings: Other Considerations

● Most modes will use Upper Side Band, even on traditional LSB lower bands

● If using a single sound card, disable your system sounds, close an apps that use the sound card to avoid accidental audio being transmitted

● Keep your PC clock in sync with a NTP server


Software: FLDIGI

● Open Source (Free)● Mac/Windows/Linux● Rig Control● Most Popular Digital Modes● Logging Capabilities● www.w1hjk.com


Software: Ham Radio Deluxe (HRD/DM780)

● Rig Control, Logging, Digital, Satellite Track, Rotor Control

● Commercial as of version 6 ($99)● Version 5 still available free● Windows only● www.ham-radio-deluxe.com


Software: Specialized - JT65

● WSJT – JT65A/B/C/M/ JT4– Windows and Linux (some assembly req.)– physics.princeton.edu/pulsar/K1JT

● JT65-HF– No longer developed as of 3/13/13– Still available from IZ4CZL

● MultiPSK – JT as well as other modes– f6cte.free.fr


Software: Mobile Apps

● Android:– DroidPSK– DroidRTTY– www.wolphi.com

● iPhone:– iPSK31– tunes.apple.com


My Software of Choice: FLDIGI

● 15 major digital operation modes● QSO Logbook as well as Contest Mode● RigCAT and Hamlib rig control support● RSID On transmit and receive● Spotting integration with pskreporter.info● Callsign lookup (QRZ, HamQTH, HamCall)● eQSL automatic upload


FLDIGI

● Installation● Main Screen Navigation● Signal Browser● Logging Window


Homework (things to try)

● Install FLDIGI or HRD● Try a simple rig to PC connection for receiving● Try copying a W1AW Transmission

– Monday – Friday 18:00 and 21:00 EST– Revolving schedule of PSK/MFSK/RTTY– 3.5975, 7.095, 14.095, 18.1025, 21.095, 28.095

● Listen! Watch QSO structure in various modes

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28

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