[eagle] Re: Module Temperatures

Juan Rivera juan-rivera at sbcglobal.net
Fri Aug 31 17:56:14 PDT 2007



I never made the WAV file since the IF output was jumping in frequency every
few seconds.  I have several .WAV files of those jumps in my log on


Once you get the SAW filters dialed in I’d like to do a temperature run and
see how they act over temperature since they seem to be so sensitive to





From: John B. Stephensen [mailto:kd6ozh at comcast.net] 
Sent: Friday, August 31, 2007 4:51 PM
To: Juan Rivera
Cc: Dick Jansson-rr; AMSAT Eagle
Subject: Re: Module Temperatures


If the first prototype behaves during the thermal testing, it will ensure
that any copy of rev. B will work. The first mixer is the hot spot and that
will remain the same. Unless anyone objects to the latest requirements
document, the power dissipation will go down by 1/2 Watt in the rest of the


I just received an assortment of 2% inductors from muRata, so I'll be able
to optimize the matching network and use a 2 pF trimmer for fine tuning.


Did you ever make a .wav file for Phil Karn? He wanted a recording of a CW
signal for evaluating phase noise. Since it's narrow band, it won't be
affected by the passband ripple.







----- Original Message ----- 

From: Juan <mailto:juan-rivera at sbcglobal.net>  Rivera 

To: John B. Stephensen <mailto:kd6ozh at comcast.net>  

Cc: Dick Jansson-rr <mailto:rjansson at cfl.rr.com>  ; AMSAT Eagle
<mailto:eagle at amsat.org>  

Sent: Wednesday, August 29, 2007 19:54 UTC

Subject: Re: Module Temperatures




We're working on a plan to get some thermal/vacuum testing in on the first
prototype.  If we can get this together in a reasonable time I'd like to do
that before you get too far into the PCB design for the next rev in case
there are some thermal surprises.  I'll keep you posted on our progress... 




On 8/28/07, John B. Stephensen <kd6ozh at comcast.net> wrote: 

If we can keep the SAW filters above -35 C there should be no problems. 


As soon as I can get the a problem with the Gerber files solved, I'll
prototype the adjustable SAW filter matching network. After that, the rev. B
PCB can be created.






----- Original Message ----- 

From: Juan Rivera  <mailto:juan-rivera at sbcglobal.net> 

To: Dick <mailto:rjansson at cfl.rr.com>  Jansson-rr 

Cc: John <mailto:kd6ozh at comcast.net>  Stephensen ; AMSAT Eagle
<mailto:eagle at amsat.org>  

Sent: Tuesday, August 28, 2007 20:05 UTC

Subject: Re: Module Temperatures




That's fantastic news and will make a huge difference in my ability to get a
sound night's sleep!  As you know, the SAW filters in the existing 70 cm
Receiver are rated at a minimum operating temperature of -35C and the
minimum storage temperature wasn't much lower.  This should mean that John
can return to a one PCB design instead of having to split the receiver into
two separate enclosures. 


73,  Juan - WA6HTP


On 8/28/07, Dick Jansson-rr <rjansson at cfl.rr.com > wrote: 

Juan & John:


I have finally been able to achieve some analytical results for projecting
the temperatures of Eagle modules after two hour and three hour eclipse
periods of no-solar heating. This has taken some time as I was struggling
with the proper use of the SINDA software and had to call for some help –
which is why we pay money for the license, it comes with help when needed.
(I should also note that with modern versions of this software and a pricey,
but fast and capable, Dell computer, these analytic runs only required 18
seconds of real run time!) 


Nevertheless, I have been able to get some believable modeling results. The
spacecraft model used is what I now call "Small Eagle", the formerly
proposed, but rejected 600x600x435mm spaceframe structure. While this is not
as large as our currently planned hexagonal structure, the equipment bays
are just about the same size as the larger spaceframe. I ran the model with
one of the E05 20, 125x180mm, modules with coatings with an effective
emittance of about 0.45, rather than 0.04, as would have to be done for the
URx module. There was essentially no power dissipations in any module, at
the most about 20mW in a few modules. This is granted to be an abnormal
situation, but I wanted to see what happens. A later run was made with only
a total spacecraft power dissipation of only 7mW were only lower by 0.1°C to
0.2°C lower temperatures.


Modules started out at temperatures of +20°C and the spaceframe core
structure at +10°C. The propellant tank was empty so it did not contribute
any large thermal mass to delaying the cool-down. After two hours of eclipse
the module temperatures were - 5.2°C to -5.4°C (with the high emittance
module being cooler), and after three hours of eclipse the module
temperatures were -15.9°C to -16.2°C. The spaceframe core structure
(equipment panels) were down to -10.2°C and -19.4°C respectively. For these
cooling periods, the spacecraft outer skin temperatures ranged from -35°C
down to -55°C. The deployed solar panels became a bit chilly, down to


A subsequent SINDA run was made with some kind of useful power dissipations
in modules – 0.5W to 1.0W – not large but supposedly enough to keep things
from getting out of hand, and with a total spacecraft dissipation of 16.5W.
The two hour eclipse temperatures ran from -3.4°C (1.0W) to -3.9°C. In three
hours of eclipse the module temperatures were at -13.3°C down to -14.0°C. In
other words, these levels of power dissipation did not significantly warm
the modules. The spaceframe core temperatures were at - 8.0°C and -16.3°C
respectively., just a few degrees warmer.


What this data tells me is that specifying the "cold" temperature of a
module does not have to be much lower than -20°C, and if it is operating at
all they can be only a little higher. Cold module temperatures certainly do
not need to be in the -60°C range. Beyond these statements, I shall not
presume to be a specification writer. 



Dick Jansson, KD1K

kd1k at amsat.org 

kd1k at arrl.net 




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