All,
The uBITXv6 is with the TSW Raduino is a very pleasant machine to listen on...but when I transmit, nobody hears me. Or if they do, they don't answer. Constant rejection! Almost like working in Sales!
So last night I tried out my cheap Chinese linear - just on the bench. Well, actually on the floor. I made up a quickie cord to plug it into my big 12V supply, hooked it up to the RF out of the ubitx, piped the linear's output through the Bird wattmeter into my good Narda attenuator/dummy-load, clip-leaded it into "transmit".
Started sending Dah's, and sure enough - saw 75W on the Bird. And the dummy load got pleasantly warm.
So - what's the absolute bare minimum work to get this thing operational? I have a nice oak board left over from a flooring project - I'll just cut a piece off and mount the linear on it with cable ties. With enough room on the side for the LPF. Hookup wire to power the LPF. A female Dupont header to choose the band on the LPF - one prewired header for each band.
I still need to get 12V on transmit from the uBITX. That would be signal "TX", which goes pretty much everywhere on the board. I can punt and just use pin 1 of K1, which is where it comes from.
The nice cabinet for the linear is still printing. I expect the bottom clamshell to be done by early this afternoon.
I'd like to ultimately have the linear auto-select its LPF. There are four choices: "15-10", "20-17", "40", and "80". At first, I thought I'd just have the uBITX tell the linear what band to use, but what if I want to use the linear with another radio? And another? And another?
Imagining an auto-select circuit - take a sample of input RF with a relatively high-ohm resistor. Put that into a pair of diodes, clamping it to .6V. Actually, make that TWO pairs of diodes, clamping to 1.2V... Feed the clamped RF through an appropriate-sized capacitor into an appropriately-sized resistor. As the frequency rises, the reactance of that cap falls, giving us more voltage at the resistor. Then detect it with a diode - which should give a DC voltage proportionate to the frequency. Look at the voltage with a set of comparators or maybe just pipe into an analog input on the Nano.
- Jerry KF6VB
