I got my uBitx last week. I was surprised to get it, since it
was sent 3 days before and I paid for India Post shipment, but
it came by DHL, which was a nice surprise. I have assembled it,
and started testing and am doing a number of modifications in my
lab before moving it to its home in the shack.
Today I modified the transmitter to improve the output power at
the higher frequencies. The power out in the original state is
about 3 watts at 28 MHz. My modification brings the power at 28
MHz up to 7 watts on both the 15 and 10 meter bands. On my board
at least, there is not enough range in VR1 to increase the power
to anywhere near this level without this modification. The other
bands remain unchanged in output, which I measured at 11 watts.?
The output stage could be modified as others have done by
changing the FETs and transformer to improve it more, but I am
happy with this for now. I plan on adding a power amplifier
later, something between 50 and 100 watts.
My fix is simply to add 3 passive parts. I added:
33 uH inductor in series with R86. I lifted the resistor
mounting it on one pad standing up, and teepeeing the inductor
between the top of the resistor and the other pad.
Add a 270 pF capacitor across both R87 and R88.
The values are not very critical, I calculated that I needed 27
uH and 220 pF, but the values I tried were in the lab.
If anyone wants to try the fix and needs the parts, I have a
full reel of each, so just send me a stamped self addressed
envelope, and I will send it to you by return mail. The offer is
good until I run out of parts.
Next up is adding an AGC and S meter.
I also measured the receiver sensitivity and can confirm that
it meets specifications.?
Howard
WB2VXW
