On Sun, Nov 20, 2022 at 03:30 PM, Fred Bouwman wrote:
Kenwood TM-281a r
I do not recommend the easy-digi interface.?
Isolation transformers are rarely necessary unless connecting to old vacuum tube transceivers.?
The high frequency rolloff of the isolation transformers will prevent the faster data rates.?
?
The CM108 chip on the Sabrent sound dongle is likely covered with epoxy?
and will be hard to attach a wire to pin 13 on the USB sound dongle.? ?
I used a bare CM108 USB sound dongle. Only $4.?
https://www.ebay.com/itm/203958052588?
Instructions to modify for PTT control:?
https://allstarsetup.com/how-to-modify-a-cm108-sound-fob-for-allstar/?
Skip the connection for COS, it is only necessary for the AllStar application.?
Instead of the 10k axial resistor, I reused one of the SMD microphone bias resistors removed from R6 and R7 on the dongle.
If you have no soldering skill, you can buy an assembled unit.?
https://hamprojects.info/dinah/ or?
?
fldigi, direWolf, soundmodem, ARDOP and VARA Winlink have added direct?
CM108/CM119 PTT support in their Linux and Windows versions.?
For other digital modes like WSJTx (FT8) and JS8Call use CAT7200?
to emulate the RTS interface for PTT.?
http://www.cantab.net/users/john.wiseman/Documents/CAT7200.html?
?
In direwolf.conf, comment out the other PTT methods and use?
"PTT CM108"?
See page 6 of the TM281A manual for connection info.?
https://kasc.kenwood.com/files/prod/2422/5/TM-281A_E_Instruction_Manual_V2_B62-2347-20.pdf?
?
If you suffer from common-mode "RF in the shack",?
I additionally recommend using a shielded USB extension cable, and
soldering 100pF capacitors from GND to MIC, SPKR and PTT on the dongle.?
N0YWB