Automated Voice announcements over RF

I built this up as I wanted to have an automated way to deliver announcements to our club via the repeater network for www.fars.ca and to help drive awareness of the network and hopefully more membership.

So over the course of a few nights I built up an announcement system. Components included a modified Kenwood TK-705D, a rough clone of a Nomic interface, a Windows 7 computer not doing much around here but used occasionally, and the K1RFD EchoStation software.

The whole setup

The interface worked fine with a 4N25 I had laying around, and I added a transformer on both sides of the audio circuit for isolation. The 1:1 transformers were pulled off old laptop modem cards. The interior of the interface box is shielded with simple aluminium tape.

Inside the simple interface

The software load was easy if a bit picky in places and was last updated in 2002. K1RFD, Jon, is the same fellow that has a lot to do with Echolink and was quick to respond to my queries.

Our club received a bunch of these radios as donations and we use them for various purposes. The radio modification is well documented http://www.repeater-builder.com/kenwood/pdfs/tk-805-wiring.pdf and an intermediate level project. The TK805 and 705 are the same internally. I de-rate the power to 5W of the 25W so that the radio doesn’t heat up too much, and I also adjusted the frequency accuracy and deviation.

Once all the parts were on hand, assembly time was a few hours including modifying the radio.  I spread it out over a few nights.

Recording the announcements is done with Audacity software and saved as wave files so the announcement computer can pick them up from the network I have here.

The ad-hoc recording studio

Pro-Tip: when recording with Audacity grab a few seconds of silence before you begin speaking, say your lines and hit the stop button.  Then run a noise profile on that few seconds.  Clip out the leading few seconds, then run a small bit of compress on the clip and normalize it at -3dB.  Doing this cleans up the audio nicely and doesn’t over-deviate the FM transmitter.

All in all this was a fun build!