Homebrew Phone Patch & SignaLink adapters

The first test was the GMRS radio. One of the kids was already talking to their grandparents on the phone, and several of the others and I thought it would be a hoot if we connected their call to the radio. I plugged the adapter into my GMRS base station (WQNY420; yes, in spite of my thrift, I'm one of two people in my ZIP code stupid enough to pay money so we can legally operate w/ GMRS frequencies/power) and conferenced the radio's extension in. Voila! The rest of us were listening to the conversation on a little FRS HT! Next thing you knew, kids were running around the house talking to grandpa on the things.

The quality was pretty bad, not only because there are some audio quality problems between the whole radio - phone system interface (One of these days I'll put a scope on it to see what's up where) but mostly because the sound quality of the little FRS/GMRS radios I have are downright terrible; I can't wait for my kids to get their ham licenses so I can justify buying them real radios so we can understand each other. But the whole point was that we could do it, not to make them sound better, and we were tickled.

The Net

I had an adapter ready and hooked up to my 2m rig (though not tested yet!) about 2min before the net last night. I grabbed a nearby cordless phone (I could've used my cell phone just as easily, and it would've probably sounded better than the cheap phone I did use, come to think of it!) and dialed the magic extension, and listened to Rick reading the preamble over the phone. I kept it muted so the vox didn't accidentally trigger the transmitter until it was my turn to check in. Knowing that the audio was a bit weak, I spoke fairly loudly into the phone as I checked Michele and I in. He reported me as weak but quite understandable.

Experiment over, I turned up the radio volume, shut off the SignaLink, and hung up the phone, continuing participation in a more traditional way.

What's next?

First, I need to improve the voice fidelity; it should sound better over the phone than it does. Then, improving control ability is on the hit list; right now, I have to be at the computer to manually establish a call or accept an incoming call for the radio. I plan to write some Asterisk dial plan scripts (and maybe use a different client) that will allow the SIP client to either remain connected to the PBX full-time so that it can accept coded commands from the radio, or allow a program (either the SIP client or a separate utility) to monitor the radio for DTMF tones and "pick up the phone" to make a call, and allow initiation of calls (both inside and outside my system) 100% from the radio link, while preventing unauthorized use of either phone or radio.

EmComm Application

Though I did this mostly for fun, and a little for future "casual convenience", I can see potential application under stress too. While the need for phone patches has waned with the proliferation of cell phones, there can be situations where it would be nice to plug your laptop into a phone line or Internet connection, and provide a phone link to people in the field. They can make personal phone calls, remote leadership or resource suppliers outside of radio access can talk to people in the field (everyone at once -- remember, open radio was the original "conference call"!) -- I'm sure you can think of more possibilities if you put your mind to it.