Hello All,
I just put together a Hi-Per-Mite CW audio filter. Would like to install it in the UBITXv6. Where to break the audio chain? I have the schematic, but no board layout. I'm thinking the top of RV4, the volume control pot.
Another idea - U1, the LM386 audio amplifier, is SOCKETED. I could pull the chip, bend out pin 3,
the positive audio input, and just solder to the pin. Of course, I would then have to sneak some little wire into the socket itself.
And then there's the challenge of turning it on & off - or at least, getting it in & out of the signal path. Front panel switches are nice. Not much space though. The whole R/H side is dedicated to the tuning knob. As it should be. Tuning is, after all, the main thing one does with a radio. There is a modicum of space on the L/H side, hiding behind the TSW Raduino card. Just about enough space for the a couple of tiny toggle switches - one for the filter, another one - later - for AGC.
Or maybe I should dig into the TSW Raduino source to add filter control to it...? Maybe CW mode wants the CW filter enabled?
One concept I have thought of - glue a tiny reed switch to the underside of the cabinet top, and enable a function by laying a magnet on it. The cabinet is aluminum, magnetism just goes through.
I don't really like piping low-level audio around the box. Can lead to hum, RF feedback, all sorts of unpleasantness. Although I did recently get a hunk of RG316 coax, just for such things. But to avoid that, I need a relay. Or diode/transistor switching. All this makes a filter in a separate box look good. What makes a separate box look bad though is AGC. I feel that AGC is best picked off the output of the filter - because otherwise strong out-of-audio-band signals can make it pump.
- Jerry KF6VB
