Jerry, KF6VB
> *** I wonder if the old "audio oscillator CW" trick would work?
It was used for years on the *Bitx* transceivers, but adds opportunities for distortion,
a not quite suppressed carrier, opposite sideband leakage, spurs due to mixer products.
In short, all the various troubles one might have with SSB.
Generating the CW signal at the operating frequency avoids all of this.
It would be relatively easy to add CW envelope shaping, but nobody has yet bothered
since it isn't much of an issue at QRP levels. (You would also need envelope shaping
on your audio oscillator.) ... And CW is an afterthought for the uBitx.
> *** I ordered the amp. It uses a pair of MRF300's for 600W out.
That sounds like a fun and challenging project.
Let us know how it goes, I'll be very curious.
> I recently got a little tiny spectrum analyzer
The tinySA is a very useful tool.
However, not quite enough resolution to check for IMD.
Best Regards,
Jerry, KE7ER
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On Fri, Apr 9, 2021 at 03:23 PM, jerry@... wrote:
Name here is Jerry, KE7ER.
A ham since the early 1970's.
A pleasure, Jerry!
The uBitx is a hackers delight, a brief look at this forum will tell
you that.
*** Yes, that was the primary driver. I *love* open source software and
hardware.
It is primarily an SSB rig, CW is an afterthought.
*** I wonder if the old "audio oscillator CW" trick would work?
if you want a good cheap CW rig.)
*** My TS-590 works OK for that :).
There is no QSK for CW,
*** I'm honestly not that fond of QSK. Semi-break is fine for me.
The CW keying envelope on the stock rig is rectangular,
*** Yeah, that's bad.
there will be
key clicks which would be problematic when
driving a 600W linear.
In SSB mode, IMD and various spurs can pop up if you give it too much
mike gain,
I'd want tools to monitor signal quality if boosting to 600 Watts.
Where the uBitx shines is as a learning tool.
Many in the forum have modded it, broke it, and then fixed it.
And came out the other side quite a bit smarter.
I'd be afraid to take the covers off a $1k+ HF transceiver, on the
uBitx they come already off.
The Ebay linear amps are often, well, ebayish.
*** I ordered the amp. It uses a pair of MRF300's for 600W out. The
seller ( dxworld.e ) has a Youtube video showing it being tested, with
600W out. Drive was 10W. It comes with a bank of switchable low pass
filters. This seems to be a serious vendor.
I also ordered a 50V 20A power supply. So I need to dream
up a case and a heatsink. Seller claims 80% efficiency. On the back
of the envelope that works out to 750W input, 600W out, 150W dissipated as
heat. Maybe a copper spreader coupled to a big CPU cooler?
The linear comes without the power transistors. That's OK, I can
source them from Mouser etc, and they're AMAZINGLY cheap. I have a case
from a Heathkit "Single bander" SSB transceiver, that should be just right.
If the uBITX is too dirty, I can stil use the linear with my other rigs. The
TS590 has a"power" control, and can be turned down to 5 watts.
I recently got a
little tiny spectrum analyzer - it should work fine for checking for spurious.
- Jerry KF6VB
