Hi all,
Further to my earlier e-mail about the Omnibus R&O, my recommendation for now
is that AMSAT proceed with the IARU coordination process for the proposed
Eagle frequency plan, but that any out-of-the-ordinary action with FCC is
unwarranted.
The proposed orbital debris language is not now in effect, for the reasons
discussed in my earlier e-mail. It is AMSAT's position, as stated in our recon
petition, that FCC does not have the authority to adopt or enforce it.
The ITU …
[View More]notification process provided for in the R&O is just that,
notification, and is not in any sense a scheme for licensing space stations in advance.
FCC's position on that is very clear, and stated in Sec. 97.207: any amateur
station may be a space station. Full stop. We may not like that for whatever
reason, but as the shady mutual-fund operator Bernie Cornfeld once said about
the SEC, "they may be schmucks but they're the government."
The way things will work in practice is that when we file our notification
with FCC, they will in due course inform the ITU Radiocommunication Bureau. The
Bureau will, in turn, inform member states, any of which may object. If they
do, it is up to them and FCC to work it out. In such a case, our response
would be very simple: "Our uplink causes no interference, harmful or otherwise.
If you don't like it, just tell your country's amateur licensees not to use
it."
In the meantime, the fewer waves made, the better.
My 3 cents worth (before tax, that is).
73,
Ray
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Rick, Bob, Art et al,
I finally got around to reading the Report and Order, and agree that FCC is
out to lunch.
In footnote 169, they say that orbital debris matters have already been
addressed in Docket 02-54, and are therefore moot. The footnote also goes on to
state that a recon petition (ours) is pending in 02-54.
However, the revised regulation language includes all of the orbital debris
garbage (pun intended) they adopted in 02-54, which would thus become effective
30 days after …
[View More]publication in the Federal Register unless FCC takes the same
"escape hatch" that they did in 02-54, where the actual Fed Reg notice excludes
Sec. 97.207.
My suggestion, then, is that someone (Perry, Art, Paul Rinaldo??) call FCC
and ask them if, in view of the recon pending in 02-54, they plan a similar
exclusion in the Fed Reg notice of this Report & Order. If so, then we need not
do anything until action is taken on our recon petition, whenever that is. If
not, then we should file a recon petition in 04-140 that mentions the
footnote, and incorporates by reference our earlier recon petition and the associated
Reply to Oppositions. Such a new petition could also include new material as
suggested by Art.
When thinking about this, please bear in mind that the purpose of a recon
petition is not to persuade FCC to change its mind. That won't happen: their
mind is already made up and don't try to confuse them with the facts. Rather,
its purpose is to lay the groundwork for a possible future challenge in court
(as ARRL is now doing in the BPL matter), since you cannot raise in court any
issue that was not before FCC when it made the decision you are challenging.
Hope this helps.
73,
Ray
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In the October issue of the IEEE Spectrum is a review of GnuRadio and
the USRP and in the contents is a picture of Matt with his USRP and some
attachments. The article by Stephen Cass is in the "Tools and Toys"
section. It is quite favorable and points out what we all know. The
software needs to be easier to install and maintain and as always,
there needs to be better documentation.
The one software module they mention as working is the FM Stereo
demodulator I wrote so I am awfully …
[View More]glad we did it. He mentions that he
got the TV demodulator going but that its rasterization was as yet,
incomplete. We in the process of getting the digital subcarrier
demodulated and decoded (RDS) at this moment. This is being done by
someone else.
This was a thoroughly written, and very positive review for Matt and
GnuRadio, both important contributors to Eagle.
Congratulations to Matt of USRP and Eric Blossom of GnuRadio, both Eagle
team members.
Bob
N4HY
--
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
"You see, wire telegraph is a kind of a very, very long cat.
You pull his tail in New York and his head is meowing in Los
Angeles. Do you understand this? And radio operates exactly
the same way: you send signals here, they receive them there.
The only difference is that there is no cat." - Einstein
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Rick, Bob et al,
I have not read this document yet as I have been occupied with other matters.
I'll get to it in the next couple of days and make whatever recommendations
then seem appropriate.
73,
Ray
This is a note I wrote some years ago during the AO-40 project. If
people think it's useful, perhaps I could post it to Wikipedia.
Alan N1AL
-------------------------------------------------------------------
Our local PC board technical expert here at HP has done an extensive
study on power dissipation of surface-mount parts. While his report is
based on non-space applications, there are a number of conclusions that
are very interesting.
I won't include the entire report, partly because …
[View More]it is much too long,
and partly because it is HP proprietary. But here are a few highlights.
He found surprisingly little discussion of these issues in the
literature. So he performed a series of experiments using an
Inframetrics 760 infared camera system to measure component
temperatures. All measurements were taken on similar-sized PC boards
mounted horizontally with no significant airflow.
One main conclusion: "Part ratings by the vendors have little meaning
by themselves since trace width and part density have a huge impact on
heat dissipation."
For example, what is the allowable power dissipation of an 0603
resistor? The answer is somewhere between 12 mw and 526 mw, depending
on layout!
This is based on a 60 degC temperature rise. (Most resistors have a 125
degC max case temperature spec.) Temperature rise is directly
proportional to power dissipation.
The 12 mw number was measured on 112 parts packed into a 0.75 square
inch area and all dissipating the same power. The 526 mw measurement
was on a single part soldered between two half-board-sized ground planes
and tied through many vias to another ground plane on the back side of
the board.
Manufacturers rate 1206-case resistors at 125 mw, versus 62.5 mw for
0603-case resistors, a 2:1 ratio. Actually, for most reasonable trace
widths, an isolated 0603 resistor can dissipate roughly 80% as much as a
1206. When parts are packed densely together, power dissipation is
limited by the maximum watts per square inch. Note that I used a 30
degC temperature rise for the following table:
0603 1206
Isolated Resistor:
Large ground plane: 263 mw 403 mw
0.060 inch traces: 170 mw 199 mw
0.040 inch traces: 148 mw 177 mw
0.012 inch traces: 106 mw 128 mw
0.005 inch traces: 77 mw 100 mw
0.0025 bond wires: 55 mw 79 mw
High-density part layout, 0.75 square inch (4.84 cm^2) area:
Number of parts 112 32
Power per part 6 mw 20 mw
Total power 672 mw 640 mw
Number of parts 56 16
Power per part 11.5 mw 43 mw
Total power 644 mw 688 mw
Number of parts 20 8
Power per part 31 mw 80 mw
Total power 620 mw 640 mw
Since the power dissipation depends so strongly on trace width, then
clearly most of the heat must be conducted, not radiated, on SMT
resistors (and other parts). Even in the thin-trace case, much of the
heat is conducted to, and radiated from, the PC board. You can see that
on the infared photos: the PC board surrounding the part is quite hot.
Thermal resistance of isolated SOT-23 transistors was very similar to
0603 resistors up to 0.040" line widths. SOIC-8 voltage regulators had
about 1/2 the thermal resistance of SOT-23.
The above numbers are probably conservative, since they are based on
still air, even though most earth-based applications have forced-air
cooling or at least natural convection (vertical PC board). The rule of
thumb I generally use is 1 watt per square inch (155 mw/cm^2), which
gives an average temperature rise of around 35 degC in still air.
I have been told that for space applications, 15 mw/cm^2 is a more
appropriate limit. Assuming radiation cooling is only 1/10 as efficient
as convection cooling, then that seems a reasonable spec.
Conclusion:
I have heard several rules of thumb on what percentage you should derate
component power specifications for space applications. For through-hole
devices, such a rule of thumb probably makes sense. THD devices
dissipate most of their heat from the component body, and relatively
little heat is conducted out the leads. On earth, most of that heat is
conducted to the air; only a little is radiated. In space, radiation is
the only heat-dissipating mechanism, so the power must be derated by a
large factor.
But SMT devices are cooled mainly by conduction out the leads to the
copper traces on the PC board, so they are not directly affected by the
lack of air. It seems to me that as long as I keep within the 15
mw/cm^2 limit on the PC board, that allowable power dissipation of
individual components should be governed by trace width, per the above
table. If I have a hot component, I'll connect it to lots of copper and
make sure no other hot components are nearby.
<END>
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After thinking about it some more, I recommend that each device on the
power bus have a programmable I/V characteristic. This is especially
important to avoid wasteful "sloshing" of large currents between energy
storage devices.
Ideally, the storage devices would have a dead band in their I/V curves
around a nominal operating point. They'd begin discharging only when the
voltage falls below the lower edge of the dead band, and they'd begin
charging at voltages above the dead band. Also, …
[View More]the I/V slopes outside
of the dead band (i.e., their effective resistances) would be set to
balance charging and discharging currents. The controllers would act
like ballasting resistors, only they'd do it more efficiently.
You can do some useful things by reprogramming these I/V curves. For
example, if you have both supercaps and conventional batteries, you
might want to discharge the supercaps in an eclipse before the
conventional batteries. You'd do this by setting a higher discharge
kick-in voltage for the supercap modules than for the chemical batteries.
The IHU could also reprogram the I/V curves to run periodic tests on the
individual storage modules. While normally you'd want to keep the
batteries at equal charge states, you might want to intentionally charge
and deplete one battery to measure its capacity while keeping the others
full.
Some care will have to go into this to ensure that the module
controllers always come up from a power failure with reasonable default
I/V curves, but I think this is doable.
Phil
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Eagle module power dissipations as noted in my paper recently published
for the AMSAT Space Symposium, are shown below.. The allowable
dissipations presume a module temperature of 20°C in a 0°C spacecraft.
Table 1
Mean Emittance, v
Allowable Power Dissipation, Q
0.045
0.4 W
0.15
1.3 W
0.45
3.9 W
0.91
7.9 W
It would be exceptionally presumptuous on my part to assume that all
modules will be of 7.9W dissipation as the spacecraft will not have that
level of power generation (12 …
[View More]"low power" modules at 7.9W = 94.8W, plus
4 "high power" modules at 50W = 200W, totaling 295W). To achieve that
level (7.9W) of power will require the use of internal heat sinking.
On the PCB dissipation, if we are to limit the temperature rise, in a
20°C module, to 40°C or a PCB of 60°C total, then the PCB dissipation
would be 5.35W, somewhat less than the 7.9W allowed in a 20°C module.
Thus to achieve the 7.9W other heat sinking methods would need to be
used.
I fully realize that modern-day electronics are quite compact and have
significant power densities, but I personally shudder at some of these
above noted power densities in a vacuum environment. This is the basis
of my previously noted conservatism in PCB power densities. There are
some particularly critical modules that MUST be low power. These are
those involved in the commanding of the spacecraft, the command receiver
and the IHU. The noted reason for this mandate is that of the cooling
effects of the spaceframe during eclipse and the need to maintain the
command-loop equipment in suitable operating condition regardless of the
radical eclipse cooling of the spaceframe. During a 2-3hour eclipse, the
spaceframe can cool to as low as -80°C or below. These conditions have
been observed in prior P3 spacecrafts.
This whole ongoing discussion merely further reinforces my concept that
close work between the electronic designers and the thermal designer for
Eagle is sorely needed. In this environment I feel that the days of
wily-nily electronic design, damn the thermal torpedoes, are gone.
Module design must be done as a cooperative, multi-technology effort.
This is why I again emphasize that all designers should read my recently
presented paper.
Dick Jansson
---------------------------
<mailto:rjansson@cfl.rr.com> rjansson(a)cfl.rr.com
---------------------------
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I read through some of the comments on this list about lithium-ion
batteries and have a few things to add.
Lithium-ion batteries require *very* tight control of the charging
voltage. If you let it go too high, metallic lithium can be produced
inside the cell with disastrous results.
The expected lifetime of a li-ion battery depends on more than the
number of cycles and the depth of discharge. Unlike Ni- or Pb-based
batteries, li-ion batteries degrade significantly even when unused. The
…
[View More]rate depends on state of charge and temperature, with high states of
charge and high temperatures being the worst.
You may have noticed that while NiCd and NiMH batteries arrive from the
factory fully discharged, li-ion batteries usually arrive at 40-50%.
This is the level at which degradation is the slowest. This means we
should probably design our li-ion battery management algorithms to keep
them half full rather than completely full. We can still use the extra
capacity to get through an eclipse season, but when the extra capacity
is not needed the batteries should not be kept at 100%.
Like all batteries, li-ion batteries are better cold than hot. Since
they perform fairly well when cold, some thought should be given to a
spacecraft thermal design to keep them cold.
--Phil
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Team:
I learned at Symposium that some don't like some of the class names
we've been using to discuss various services.
I reaffirmed at Symposium that we need consistent names for the services
we'll provide, just like we've settled on band names.
To give us the precise nomenclature I think we need for effective
communication, I propose:
Class A for what we used to call Class 0 (A from the old "Analog",
which we need to stamp out.)
Class S for what we used to call Class 1 (S from …
[View More]SMS)
Class V for what we used to call Class 2 (small station digital Voice)
Class H for what we used to call Class 3 (High rate)
I started with A, B, . . . and decided to propose more intuitive names.
Unless one of you strongly objects in the next few hours, I'll have the
ANS announcement and AMSAT web page updated.
It was great to see many of you this weekend.
Thanks & 73,
Jim
wb4gcs(a)amsat.org
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