[hpsdr] The Basics (with updates)

[Philip Covington]

<snip>
> I would definitely do at least Class C, and if we can find devices which
> will not have too low a resistive component of their impedance,  Class E
> amplifier chain.  If we use PWM for the envelope,  we can get
> <<<HUGE>>>  efficiencies .  Also,  since this is DSP,  if we provide the
> correct sensing,  we can make this "envelope elimination and
> restoration"  amplifier chain automatically adaptable to changing
> loads.  Listen,  we are talking 100w  output transmitters with 120 watts
> of DC power going into them and having linearity as measured in the ARRL
> labs better than any TX ever measured there.  I am viewing HPSDR as the
> "skunk works" for the future of radio and I would love to see us push
> this envelope (pun is absolutely intended) to the limit.  We will need a
> very good switcher power supply to do the envelope restoration and
> ideally,  a softrock or lesser receiver to do a "perfect" job of sensing
> the amplifier needs dynamically.  That would be the ideal.
<snip>

Before I got interested in SDR, one of the projects I wanted to play
with was a Class E AM transmitter (<http://www.classeradio.com/>).  I
was interesting in using APT's RF MOSFETS to try to build a 10 meter
AM transmitter and then play around with feeding the PWM supply
digital audio.

One of the problems I see with using Class E amps is that the output
network seems to have to be "unique" to each band of operation.  I
don't think you can have a broadband output network in that case.  It
is ok if you are interested in covering just one band, but otherwise
it seems you would have to have plug in band modules to cover 1-30 MHz
or whatever.  Still worth it for the efficiencies...

> AD9958, AD9959
> http://www.analog.com/en/prod/0,,770_843_AD9959,00.html
>
> DO NOT be put off or fooled by the 10 bit DAC.  Analog devices has
> learned a whole lot about doing this kind of work.  This device produces
> extremely clean signals.

Good deal... I have samples of both and they are what I intended to use.

> There are several sources for the oscillators.  One that we know and
> love will require a group buy to get the several week lead time 500 MHz
> oscillator.   With the reference locking done to 1 pps, or 10 MHz, etc.
> external references,  this my be tamed to 10^-12.  I have done it with
> CNS for their clock II  (  http://www.cnssys.com ) because I needed it
> for a work project.
>
> All of this is beginning to get VERY interesting and I do like the
> multiple projects needing the same generic things.
> > 73 de Phil N8VB
> >
> 73
> Bob
> N4HY

73 de Phil C

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