[hpsdr] The Basics (with updates)

[David Woodhead]

Class E output stage is a switch, I think it is a mistake to think of it
as an amplifier. The output circuit (tank) smoothes out the on-off
pulses of the switch - it is resonant very close to the operating
frequency. I have built a 3 band (160/80/40) PWM modulated 1KW class E
transmitter. http://www.km5tz.netfirms.com/classe.htm You can certainly
achieve very high efficiencies with exceptional modulation linearity.

I am interested in the envelope restoration technique. I believe that
newer cell phones are using or developing this technique (because of its
efficiency); Class E output passes phase information (but no AM), PWM
modulates the amplitude. One of the complicating factors is the
modulation bandwidth. It is much easier to implement at lower bandwidths
than broadband - especially closed loop (demodulate transmitted signal
and pre-distort to correct for modulation non linearity). Voice
bandwidth should be easy. 


David
KM5TZ


-----Original Message-----
From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf
Of Philip Covington
Sent: Friday, May 05, 2006 5:56 AM
To: Robert McGwier
Cc: hpsdr at hpsdr.org
Subject: Re: [hpsdr] The Basics (with updates)

***** High Performance Software Defined Radio Discussion List *****

<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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