Wednesday, July 13, 2011

VoIP Phone Patch

Below is a drawing of the VoIP phone patch configuration that I have been using for a few months. Click on the image for a full-sized view.

I'm using the phone patch audio input & output jacks of the transceiver. Modern transceivers should work in a similar manner with their line audio input & output jacks. A RIGblaster Pro forms the interface between transceiver and the PC sound card. Many other forms of audio interface can serve the same function.

The vintage SoundBlaster sound card has 4 audio jacks: line in, line out, speakers, and microphone. The line in and line out jacks connect to their corresponding jacks on the RIGblaster. My headset microphone connects to the microphone jack. I've been using the convenient headphone jack on the RIGblaster with my headset earphone(s), but I need to try the sound card speaker jack to see if its performance is any different. This setup provides ample audio levels, except for the audio from the distant phone to my earphones.

The Windows-based audio mixer associated with the sound card provides the ability to combine and adjust the level of my voice along with the distant phone voice when transmitting. I'm able to hear the distant caller's voice and my own (i.e. sidetone), but I'd like to be able to reduce the latter a bit. I can mute my own voice with a mouse click in the Windows audio mixer.

In the receive direction, I can supply as much audio as needed for the distant phone party, using the transceiver's audio gain. This tends to provide more audio than needed for my local earphone(s).

For the VoIP connection to the distant phone, which is connected to the public switched telephone network (PSTN), I've been using the Google Call Phone feature in Gmail. It is free again this year, and does not max-out the 600 MHz CPU in my ham shack PC. A PC with adequate CPU power can use Skype for the same function, but calls to PSTN phones require a paid Skype subscription. Group voice chat / calls are apparently not supported on the Google platform at this time. Skype has good capabilities for conferencing multiple participants on PC-based Skype clients or on PSTN phones.