Re: Digital communications with a USB sound card - dumb mistake #ubitx


For sound interfacing, I decided the best route was to keep as much inside the box as possible.  The mic and speaker jacks are wired so that if nothing is plugged in, they default to the Easy-Digi board audio transformers.  These are connected to a 6 dollar USB sound dongle plugged into a 4 port USB adapter (room for a RTLSDR panadapter later on).  A 330 ohm resistor is in parallel with the audio out to the mic-in on the sound dongle to make volume adjust less sensitive.

For heat dissipation, I used the outer shell of an old car audio amp (almost 2 pounds of solid aluminum), and mounted the PA finals directly to the case by moving them underneath the main board.  I also re-purposed one of the original heat sinks to the 7805 regulator.  That puppy gets pretty warm without a little help.

Ignore the cardboard front and back panels.  Those are temporary until I print out the permanent ones.

The 3 color LED strip also acts as a transmit light.  Only blue and green are on with power, and red turns on for transmit.

On 5/15/2018 4:18 PM, Bo Barry wrote:
Whoops, a USB sound card gives you stereo sound output. Plugged into the mike connector for digital work it activates the PTT line with the audio!
The CAT interface works find for PTT and frequency control.
It took me forever to realize the orange PTT wire needs to be disconnected for digital work.

I made a bit of progress, getting a copyable RTTY signal with fldigi on my nearby rig. I couldn't get FT8 to copy. Experimenting with proper audio levels is driving me crazy but I'll figure it out.

The receiver surprised me, with me copying PA & NY on FT8 WHILE CONNECTED TO A DUMMY LOAD. I hope my transmitted signals didn't get out too.

I happened to have a 5v fan that fit the 3d printed panels I bought. I used a 7805 to drop the voltage down. Kinda noisy, going to drop it down to 3 volts. or so.

One awkwardness - the rig runs off of 12 volts which runs thru the power switch. However the usb interface activates the LCD whenever it is plugged in. How many times have I scratched my head with it when it wouldn't transmit even tho the display said it was, because the power switch was off. A solution would be to cut the +5v lead in a USB cable I guess.

In the meantime, a simple CW QSO is in order.

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