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Re: HELAPS info?

Hi Claudio,

the AMSAT-BB archive would have more goodies than I have -:)
but here is one to help you along.
          Re: [amsat-bb] AO-40 Satellite RF
          Architecture Question
          Sat, 23 Feb 2002 22:18:11 +0000
          Peter Guelzow <peter.guelzow@arcor.de>
          Joe Leikhim <jleikhim@nettally.com>
          "amsat-bb@AMSAT.Org" <amsat-bb@AMSAT.Org>

Hi Joe,

Joe Leikhim wrote:
> 1. Why is AO-40's transponder described as
having receivers and
> transmitters when nothing is apparently
demodulated? There is an IF to
> which I would assume downconvertors and
upconvertors are interfaced like
> any other bent pipe transponder..

What we usually call a receiver is not a
demodulator and a transmitter
is not a modulator. However, we convert down to
baseband, i.e. 10.7 MHz IF
with some sort of bandwidth limitation.

> 2. Why do I see little discussion of the HELAPS
(sp?) power amplifiers?
> What are these? Are they an Envelope
Elimination and Restoration
> technique? How does HELAPS work?

Probably because this is an old technology,
unfortunately not widely known.

HELAPS stands for High Efficiency Linear
Amplification by Parametric Synthesis
and this concept was the subject of a doctoral
dissertation by Dr Karl Meinzer,
DJ4ZC, past president of AMSAT-DL and P3-D
Project Leader. Karl's concept has
been proven a while ago on the Mode B and J
transponders used for OSCARs 7, 8,
10 and 13 and on AO-40 (Mode-B and Mode-S). This
technique results in a very
power  efficient, and therefore cool-running
wideband amplifier.

> 3. Did HELAPS achieve the efficiency and
linearity required for the
> mission?

Yes, with the exception that the FSK signal from
RUDAK which is feed into
the IF suffers a little bit when there is other
traffic. PSK should be fine.

One year ago Tom Clark discussed HELAPS very
detailed, better than I
could do it here, so here is Tom's email from
last year..

73s Peter, DB2OS


Subject: Re: [amsat-bb] Using Class C Amplifiers
for SSB
Date: Tue, 02 Jan 2001 22:23:56 -0500
From: "Tom Clark (W3IWI)" <tac@clark.net>

Jon Ogden wrote:

> Well, the only way I've seen it done (with a
Class C amp) is in a Dougherty
> Amplifier configuration.  This type of
amplifier uses a Class C amplifier as
> a peaking amp to amplify the signals at their
peaks.  During other parts of
> the modulation cycle a linear amplifier is
used.  The two are phased in such
> a way as to make the whole thing work.  It's a
pretty fascinating way to
> develop a more efficient linear amplifier.
I've got a paper on it somewhere
> that I should scan in someday.  The biggest
problem is that due to the
> matching/combining structure, it is inherently
relatively narrow band
> (narrow band meaning less than 10% bandwidth).

FYI -- the linear amplifier design by DJ4ZC
which has been used in most of our
satellites uses a scheme invented/patented by
Karl similar to the Doherty
amplifiers. Karl calls his scheme HELAPS,
standing for High Efficiency Linear
Amplification by Parametric Synthesis.

In essence, consider the signal you want to
amplify as consisting of a phase
component and an amplitude component; assume
that there is a 3-port black box
does the vector analysis on the input signal and
with two output ports --
A(mplitude) and P(hase).

The P component (as with any FM/PM signal) can
be amplified in a non-linear,
limiting (i.e. Class C) amplifier to achieve high

Now let's feed the A signal into a good old AM
Plate Modulator (some of us
remember that the plate is the "collector" in a
thermionic glow-FET) to vary
supply voltage feeding the hard-limiting P
amplifier, and hence re-modulating
P amplifier.

Voila -- we have a high efficiency amplifier
nearly linear where the RF power
developed by the hard limiting P amplifier and
the signal amplitude information
comes from the AM modulator.

In Karl's designs, the "plate modulator" is
actually a Class-D switching power
supply. Because the transponder bandwidths are
several hundred kHz, the
power supply operates at frequencies up to a
couple of MHz (i.e. several times
bandwidth). Transponder bandwidths have been
dictated in part by the speed of
Schottky switching diodes and power MOSFETs  and
the loses in the associated
"swinging" inductor in the Class-D modulator.

Because the P amplifier's "plate" voltage is
changing, the amplifier does not
a constant load impedance (a flaw in ordinary AM
transmitters which caused the
Doherty design to happen) and power is lost. In
Karl's design, the "Parametric
Synthesis" magic black box not only separates the
A & P components, but it
intentionally pre-distorts the A & P signals so
as to cancel the distortion
introduced by the amplifier. With this scheme,
Karl's design ends up with
distortion products that are ~30 dB down.

You certainly wouldn't want to operate next to a
station with -30 dB IMD in the
CQWW contest. But if there are many nearly equal
signals in a satellite
transponder passband, the level of IMD simply
raises the noise floor a little
for everyone. The LEILA active notch filter in
the AO-40 IF chain was designed
try to kill off alligators that hog too much of
the transponder's power and
bad IMD for all other users.

73 de Tom, W3IWI
My apologies to the original correspondents, for re-publishing without
specific permission.

I believe I have seen the original paper from Dr Karl Meinzer, it could
have been on AMSAT-DL or on one of the uni's, hth.

73 Jens    ZL2TJT
RE78nv, AMSAT-ZL #218

Claudio Martins wrote:

>   Hi folks
>   I've been using google & friends all morning, and been unable to find any
> real deep information about HELAPS (High Efficiency Linear Amplification by
> Parametric Synthesis) technology used in the Phase 3 satellite transponders.
> All references found seem to know what the HELAPS acronym means, but none
> seems to contain any implementation discussion... ;-)
> So any info or any links to a paper or similar would be apreciated.
> Thanks in advance for your attention
> Best regards, 73
> Claudio Martins

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