Re: [amsat-bb] New amateur satellite ideas

["John B. Stephensen" <kd6ozh@xxxxxxxxxxx>]

A "bent pipe" transponder is AMSAT's term for a transponder that amplifies the
received signal and retransmits it to earth without demodulation. It may be a
linear transponder, like FO-29, that will handle multiple signals as long as
they are near the same signal level at the satellite or a limiting transponder
that is captured by the strongest signal. Limiting transponders have higher
power efficiency than linear transponders.

FDM is frequency division multiplexing where each user has a independent
frequency and is each able to transmit continuously and simultaneously with
other users. The satellite must have multiple transponders or a single highly
linear transponder to minimize intermodulation.

Intermodulation - No amplifier is perfectly linear, so multiple signals will be
combined with each signal unintentionally modulating others in the passband to
some extent. The amount of distortion increases with the signal power levels.
The degree of linearity is measured by the intercept point, which is the
calculated power level at which distortion products will equal the original
signal level, and the noise factor (a simple ratio) or the noise figure (in dB),
which is the amount of power generated within the amplifier by thermal agitation
of the charge carriers in the components of the amplifier referenced to the
power generated by a resistor at the average temperature of Earth 100 years ago
(290 Kelvins). The third order intercept is most important for linear
transponders and the power level of the third-order distortion products
increases at three times the rate at which the original signal levels increase.

Passband - the frequency range over which the amplifier reproduces signals.

TDM is time division multiplexing, where multiple users can share one frequency
by transmitting short, non-overlapping bursts. The peak power required on the
uplink for each user is much more than with FDM as all of the required energy
must be compressed into a short burst. On the downlink, average power is similar
to an FDM transponder. TDM avoids the intermodulation problem entirely as each
user's signal is presented serially and the downlink transmitter can be more
power efficient than FDM.

ADC is an analog to digital converter that samples the received signal and
converts it into a series of numbers representing the time-varying amplitude of
the input.

DAC is a digital to analog converter that takes a series of numbers and converts
them into the equivalent analog signal amplitudes at the output.

MCU is a micrcontroller unit which is a processor, memory and input/output
devices combined onto one chip. The processor implements a fixed set of
arithmetic/logic operations that are executed serially as controlled by a
program stored in memory. They cost $1-100 each depending on speed and number of
I/O pins.

FPGA is a field-programmable gate array. This is an array of logic elements that
are interconnected via an array of busses. In modern FPGAs, each logic element
(LE) is a RAM-based look up table (LUT) that may be programmed to implement 3-5
term boolean equations plus a flip-flop to hold the value of the result and a
second output for implementing carry logic for arithmentic functions. The inputs
and outputs of each LE can be programmed to attach to individual busses or to
adjacent LEs in order to implement multiple aritmetic/logic operations in
parallel. The programming is stored in on-chip static RAM or anti-fuse PROM.
There may also be dedicated blocks of RAM, shift registers and/or multipliers
distributed throughout the array. The array consists of 200 to 1 million LEs and
there are 100 to 1000 I/O pins. The cost per unit is $10-1000 depending on array
size and speed.

PLD is a programmable logic device. This is similar to an FPGA but the number of
LEs is smaller (8-1024), the number of I/Os smaller (12-100), the number of
terms in each LE is larger (10-100) and LEs usually have dedicated I/O pins. The
programming is stored in an on-chip OTP PROM or EEPROM. The unit cost is
$0.10-$10.00 depending on size.

USB is the Universal Serial Bus which is a local communication network used to
connect PC I/O devices to the host PC. The host communicates with the I/O
devices by polling each device in a 1 ms (full speed) or 1/8 ms (high speed)
cycle.The communication link uses differential signalling over twisted pair wire
at 1.5 MBPS (low speed) 12 MBPS (full speed) or 480 MBPS (high speed).

RAM - random access memory. This conventionally implies sequential or
simultaneous read/write operation.

Static RAM - RAM where the information is stored permanently in flip-flops.

Dynamic RAM or DRAM - RAM where the information is stored in capacitors and the
stored value must be periodically refreshed (every 1-100 ms).

SDRAM - synchronous dynamic RAM - DRAM where access is synchronized by a clock
and cmay manipulate multiple adjacent memory locations whose values are carried
in a sequenctial stream of values at the I/O port.

ROM - read only memory. The memory may be read as in a RAM but the programming
operation is performed during manufacturing.

PROM - programmable read only memory. A ROM that may be programmed after
manufacture.

EEPROM - electrically programmable and erasable PROM using technology that
stores information by injecting charges into isolated areas in the semiconductor
substrate. The stored charge lasts 10-40 years. The number of progamming cycles
is limited to 100-10,000).

Flash ROM - EEPROM designed for fast programming.

Anti-fuse - a PROM programming technology that creates permanent links between
elements to store information.

OTP - one time programmable memory.

73,

John
KD6OZH

----- Original Message -----
From: "Emily Clarke" <w0eec@AMSAT.Org>
To: "John B. Stephensen" <kd6ozh@AMSAT.Org>; "Robert McGwier"
<rwmcgwier@comcast.net>; <amsat-bb@AMSAT.Org>
Sent: Monday, 02 August, 2004 05:11 UTC
Subject: Re: [amsat-bb] New amateur satellite ideas


> Hi John,
>
> Please. please - this is not critical.....
>
> As much as you are very close to the alphabet soup (and you shoud be)
> perhaps you should explain to the masses what a "TDM bent pipe" is, and
> what you mean by (ADC/DAC/FPGA/MSU/USB) is.  I think I know all the
> acronyms except USRP, but perhaps we can get them entered into the AMSAT
> glossary (http://www.amsat.org/amsat-new/information/glossary.php) so us
> mere mortals can figure it out?
>
> Thanks,
>
> Emily
>
> PS - Send it to me - I'll be happy to be the clerk.
>
>
>
>
>
> At 04:33 AM 8/2/2004 +0000, John B. Stephensen wrote:
> >Development projects with engineers geographically dispersed are especially
> >difficult to manage and 20 MBPS is ambitious for an amateur HEO satellite.
If
> >this is still the TDM bent pipe approach, acheiving the necessary EIRP at low
> >cost at the ground station will be a challenge. I had a few email
> >exchanges with
> >Phil a year or more ago about accomodating small earth stations and TDM vs
FDM
> >on the uplink.
> >
> >The DCP-1 is very similar to the USRP -- the main difference is a 32-bit MCU
> >rather than an 8-bit MCU. My goal was to get the cost as low as possible
> >so that
> >more people could afford to duplicate it. The sampling rate is 24.576 MBPS
> >adjustable +/-90 PPM and the maximum bandwidth of the analog front end
> >board is
> >5.8 MHz. The lower sampling rate means that the basic chip set
> >(ADC/DAC/FPGA/MCU/USB) is $50 in small quantities.
> >
> >I'll look into attending the meeting.
> >
> >73,
> >
> >John
> >KD6OZH
> >
> >----- Original Message -----
> >From: "Robert McGwier" <rwmcgwier@comcast.net>
> >To: "John B. Stephensen" <kd6ozh@amsat.org>; <amsat-bb@amsat.org>
> >Sent: Monday, 02 August, 2004 01:26 UTC
> >Subject: RE: [amsat-bb] New amateur satellite ideas
> >
> >
> > > Without going into a tremendous amount of detail why, etc., for the
> > > time being,  I am in charge of transponders for Eagle.  Others are
> > > holding positions or have positions of project technical leadership,
> > > and project management and I for one hope that all shakes out and
> > > settles down before the annual meeting.  Phil, Tom Clark, Rick
> > > Hambly, and I presented a top level view of what we might do for
> > > a useful digital transponder for C band and what it might ental.  There is
> > > a lot of work to be done on the ground elements as well as the
> > > spacecraft elements.  The reasons for my being shoved forward
> > > with a electric cattle prod in my back for the transponders will
> > > become clearer as the project leadership tells the story of where
> > > we are headed for now, and that is likely to be at the annual
> > > meeting.  Suffice it to say, it is ambitious, it is forward looking,
> > > and the team appears to be excellent with new faces, old faces,
> > > and I encourage others to become involved.  If few Mbps >= 20,
> > > then your hardware might be interesting and we would certainly
> > > look at it.  If we cannot achieve what we want at 20 Mbps,
> > > then we might drop back in speed but that is the design goal.
> > > I am using the USRP (which is remarkably similar to what you
> > > have proposed and talked about on this forum earlier) as a slower
> > > speed version to do experimentation and development.  Even the
> > > DC and AM broadcast band experiments (2m, 70cm, etc.) have a
> > > very interesting twist.  Come to the ANNUAL MEETING and if you cannot,
> > > order copies of the proceedings.
> > >
> > > Caveat:
> > > AMSAT-NA is an equal opportunity exploiter ;-) and the more warm
> > > bodies there are to exploit the better.
> > >
> > > Bob
> > > N4HY
> > >
> > >
> > > -----Original Message-----
> > > From: John B. Stephensen [mailto:kd6ozh@verizon.net]
> > > Sent: Sunday, August 01, 2004 7:04 AM
> > > To: Robert McGwier; amsat-bb@AMSAT.Org
> > > Subject: Re: [amsat-bb] New amateur satellite ideas
> > >
> > >
> > > Its good to hear that work is proceeeding. I was worried after checking
> > Phil
> > > Karn's web site and seeing that it hadn't been updated in two years.
> > >
> > > A few months ago I volunteered as the ARRL HSMM RMAN UHF project leader
and
> > > am
> > > busy with the development a DSP-based transceiver for high-speed digital
> > > communication. The design will be published in QEX starting in the
> > > November/December issue. For terrestrial links, an OFDM modem will be
> > > implemented. However the hardware is completely programmable and could be
> > > used
> > > to implement a PSK or FSK link at a few MBPS. It would be nice if hams
> > > interested in satellites and HSMM could have interoperable hardware.
> > >
> > > I let my AMSAT membership lapse so I haven't received the AMSAT Journal in
> > > the
> > > past year and I couldn't find much information on the current web site.
Who
> > > is
> > > the best person to contact to talk about coordinating efforts?
> > >
> > > 73,
> > >
> > > John
> > > KD6OZH
> >----
> >Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> >Not an AMSAT member? Join now to support the amateur satellite program!
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>
>
>
> ---------------------------------
> W0EEC - CM87tm
> AMSAT Area Coordinator - San Francisco Bay Area
> http://www.projectoscar.net    http://www.PlanetEmily.com
> http://www.emilyshouse.com/experthams/ao7/
>
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