Here is my entry into the interesting project category -- A Kilowatt
transistor SSB/FM/AM/CW/etc. transmitter for 160 through 6 meters.
The transmit chain consists of:
1. A Mike preamp connected to a 16 Bit Analog to Digital converter
running at a 24 KHz sample rate -- one of the tiny ones with serial data
output.
2. A 16 Bit Digital Signal Processor chip good for about 40 mips. This
chip can perform an intelligent VOX function (no missed syllables) by
delaying the input signal 10 mS. The same buffer can be used to
implement a Hilbert transform compressor (similar in function to RF
clipping). Transmit bandwidth will be set by mode... or whim.
SSB will be generated by the Weaver (third) method & the resulting I&Q
signals will be up sampled by a factor of 32. These signals will be
delayed to compensate for the output filter delay in the envelope
re-modulator filter (part 5 below). A digital representation of the SSB
envelope will be loaded directly into the modulator at a 96 KHz rate.
For CW, this critter will also be able to create a variety of envelope
shapes... from textbook perfect to simulated chirps & clicks. :-)
FM is created directly by adding the digitized value of the mike
audio, 16 bits - up sampled to 192 KHz, scaled for the desired deviation,
to the nominal carrier setting (32 bits) and updating the DDS registers
with those results (also at a 192 KHz rate). This method gives perfect
FM with ridiculous control over the deviation: 1 LSB = .075 Hz @ 5 KHz
total deviation.
AM is made in the old way, by directly modulating the final amp.
And of course PSK, FSK, etc will be doable.
3. A combination up-sampler, Direct Digital Synthesizer & I&Q modulator
(a single IC) that can directly output on frequency up through 6 meters.
SSB is created by completing the Weaver modulation with the second mix
directly at the output frequency.
4. A limiting amp (to make Class D) followed by a two watt stage which
may operate either Class A for test or Class D for real.
5. A legal limit Class D amp modulated by a switching amplifier powered
by a power factor corrected (PFC) input circuit. Output filtering &
tuning will be by means a whole bunch of coils & capacitors switched
by... about 32 relays. An independent SWR protection circuit will
directly reduce the voltage to the finals, to prevent awful things from
happening should something screw up in the software.
The modulator, sampled at 96KHz, will be driven by a digital pulse
width generator with 11 bit resolution (ECL parts -- clocked at 200
MHz). It will implement the envelope restoration for SSB, envelope
shaping for CW, direct modulation for AM and power control for FM, CW,
AM, & SSB.
The RF amplifier and modulator stages can be line isolated by means of
RF transformers, plus optoisolators for the control signals, so no big AC
power transformer will be required.
6. and almost forgot -- An 8 bit microprocessor to handle the mode
selection, tuning, etc.driving a Vacuum Fluorescent readout for all the
words & numbers.
Finally, a 24.576 MHz master clock multiplied (by 8) to 196,608 MHz to
clock the DDS & ECL stuff; and divided as necessary to run everything
else.
******************************************
While this sounds like a lot of stuff, it will be rather compact in the
real world -- except for part 5. :-)
Comments, suggestions... anybody want to help?
73,
Marv WC6W
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