On Fri, Feb 1, 2019 at 09:35 PM, Tom, wb6b wrote:
I think that would be a cool way to build a SSB transmitter. I've been doing some reading as I'm investigating the possible use of a FPGA for creating a SSB signal to drive my uBITX (in this case the signal will be feeding a linear TX chain). In the analog days it seems the results were somewhat marginal. One technique described splitting things up so the carrier was "FM" modulated (I imagine that is an over simplification) and the envelope was used to modulate the carrier with another class D audio range amplifier modulating the voltage to the class E final.
The central feature is doing half the work DSP at 16mhz (arduino uno or nano speeds) and a little analog.
Yes the carrier is sorta FM... what it is and needs to be is the mic audio signal stripped to the frequency content
and added (or subtracted) to the base frequency.? FM tends to revolve around a central frequency and has
more sidebands.? In the analog world we would hard limit the audio and mix it with a carrier the result would
have sidebands of the base plus sum (or difference).? That limiting thing in the digital realm takes processor
speed. The other half is then modulating an amplifier with a signal that represents the envelope of the audio
at audio rate and is used to re-create the power out for the driving level.? ?The simplest form of that is not
more than 100years old and known as AM save for that has carrier(largely useless save for the detector at
the other end needed it then) and both sidebands (both sum and difference of the source signal applied
to carrier).? SSB removes the carrier? and the receiver uses a BFO as replacement.? the excess
sideband can be filtered away or using Analog signal processing, we can inhibit the unwanted
sideband.? Phasing side band is more than 80 years old.? Filter mode of sideband has about the same
origin.
All of the digital techniques do that and its all math but at some point the result is RX audio or TX RF.
The fastest designs grind the numbers and drive an D/A and feed the rest directly to the antenna
without the need for frequency change and on RX grab the spectrum using a very fast A/D and
process the data down to the desired signal.? Just about all the radios with IF DSP do this but
at 12 or 30khz with conversion to user frequency as that was were the tech was 20 years ago.
>>>It would seem that in this age of DSP processors and such this should be a realizable design. In my limited searching I haven't found much on realized designs. I'm really interested if others with more experience in this, know of working designs. <<<<
If you have a MPU fast enough to do dsp (STM32F4 at 180mhz is fast enough) then the mainline techniques
can get you a very good SSB signal and also do the RX as well.
As to realized designs I give you softrock (RX), SDR2GO, Flex radio, ANAN 100, KX2, KX3, K3S, IC7300...
And just about any IF DSP radio in the last 20+ years.? However there are several ways to do it and the
EER form we are talking about has never been very successful. One amp I know of was SGC 500W,
very short market life.
Allison
