[eagle] Re: Module Temperatures

John B. Stephensen kd6ozh at comcast.net
Sat Sep 1 12:43:00 PDT 2007


I think that we're still at the stage of getting consensus on the requirements. Some have questioned whether the phase noise of the VCOs is adequate for text-mode uplinks and this needs to be resolved before finalizing the LO design for rev. B. Phil should be able to answer that question once he gets a .wav file.

As long as an external 10 MHz frequency reference is used, the existing board should be good for demonstration. No one will notice an extra 2 dB variation in signal levels across the transponder bandpass because the SDX will compensate for variations in uplink signal levels. 

73,

John
KD6OZH
  ----- Original Message ----- 
  From: Jim Sanford 
  To: John B. Stephensen 
  Cc: juan-rivera at sbcglobal.net ; 'AMSAT Eagle' 
  Sent: Saturday, September 01, 2007 09:22 UTC
  Subject: Re: [eagle] Re: Module Temperatures


  John:
  If you have a final LO design, it would seem appropriate to route (or announce posting of a paper) and convene a formal Peer Review.  We can use that to force the discussion and decision.

  Question:  Do we have a chance of getting a handle on the passband ripple in time to use the board as the downconverter for our demo at Symposium?

  Thanks & 73,
  Jim
  wb4gcs at amsat.org


  John B. Stephensen wrote: 
    Since the jumps were due to frequency corrections in the digital TCXO, you could make a recording using an external frequency reference. I'd like to make sure that everyone agrees with the current LO design before doing rev. B.

    73,

    John
    KD6OZH
      ----- Original Message ----- 
      From: Juan Rivera 
      To: 'John B. Stephensen' 
      Cc: 'Dick Jansson-rr' ; 'AMSAT Eagle' 
      Sent: Saturday, September 01, 2007 00:56 UTC
      Subject: RE: Module Temperatures


      John,



      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 EaglePedia.



      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 matching.



      Juan




--------------------------------------------------------------------------

      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 board.



      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.



      73,



      John

      KD6OZH



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

        From: Juan Rivera 

        To: John B. Stephensen 

        Cc: Dick Jansson-rr ; AMSAT Eagle 

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

        Subject: Re: Module Temperatures



        John,



        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... 



        Juan

         

        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.



        73,



        John

        KD6OZH

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

          From: Juan Rivera 

          To: Dick Jansson-rr 

          Cc: John Stephensen ; AMSAT Eagle 

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

          Subject: Re: Module Temperatures


           

          Dick,



          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 -113°C.



          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. 



          '73,

          Dick Jansson, KD1K

          kd1k at amsat.org 

          kd1k at arrl.net 







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