In 2018, I had a lot of fun with the uBITx.
Haven’t looked at them for a while, but last week got them out and decided to see what could be done with my revised aims and ideas.
3 thoughts on “uBITx”
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Last weekend I had the thought that the “problem” with the 45MHz filter could well be overloading with out of band signals.
Raj commented “Another thing that bugs me is that all BiDi stages are made DC-daylight frequency responce. Completely nonsensical to me!”
That started me thinking, so a trip to the shed in needed.
On Wednesday, I dug out another V3 I modified a couple of years ago, for a different reason then, but I have an idea that it might solve the issue that I see (I could be totally wrong with the idea anyway)
Found several resistors in the driver/final area which were incorrect values, like 75ohm instead of 2.2ohm, now the output is cleaner, and 10m is now nearly 4W, which is about as good as I would expect.
Wired in the CW side tone, with a level adjustment on the back panel, works very well.
Tried an audio CW filter, just the two stage one, and it makes a very worthwhile improvement, the 4 stage one is too narrow for easy tuning. Maybe later I will look at a PLL tone indicator to help tuning.
Looking at RX AGC next, don’t want a huge range, just enough to not have to keep adjusting the volume so often.
Today I looked at two things, the output transformer and to TX-RX RX-TX pop.
No alternative transformer was significantly better than the original.
A slight improvement was 4 bifilar turns on a binocular core, or the same as original with one turn less, which is what I settled for.
Previously I used a PIC as a TR sequencer and mute for the AF amplifier, it worked well, but not repeatable unless you had a way to programme the PIC.
Today I looked a some different options, made a couple of boards and built some of the other suggestions.
I quickly became clear that any system using the switched TX TX 12V supply would not work fully.
I ended up with a simple circuit muting the audio amps input, very similar to what some others have suggested, and what the V4 uses.
I have not decided what I will do for the CW side tone yet, there is more than one option.