[time-nuts] Lassen IQ receiver APRS beacon pictures

[Mike Monett]

  Hi Robert

  "Robert Darlington" <rdarlington at gmail.com> wrote:

  > Hi Mike,  I'll  answer  the  questions  in  line  with  your email
  > message, below.

  [...]

  >> These units look interesting. Do you mind if I ask some questions?

  >> 1. What kind of non-time keeping uses have you found for them?

  > The first  project was an APRS beacon for a high  altitude balloon
  > project which  hasn't launched yet, but was tested in my  car. The
  > last project  was  for  the  local  laboratory.  They  developed a
  > sampling system which had every gadget but the kitchen sink in it,
  > and every  part was made out of unobtanium. In this  case  the gps
  > board had been discontinued for about 4 years so I had to design a
  > new one  that would be the same physical size, same  hole spacing,
  > and same pinout.

  That is very interesting. Making things fit can be fun!

  > I figured  if I was going to do this and have a minimum  run  of 5
  > boards, I was going to make 2 for me (they needed 3 total). In the
  > picture you'll  see the top half with the GPS module  has  a white
  > box around  it.  This  part I cut off  after  programming  the GPS
  > receiver modules  and installed in their gadget, the  rest  of the
  > board gave me a MAX232 (3.3 volt version if I remember  right) and
  > broke out  both  serial ports to DB9 for easy hookup  to  a  PC. I
  > should've added a PPS line but was too concerned with  keeping the
  > board working  when  I cut it in half to really  think  about more
  > than what  they  needed.  What you can't see  is  the  button cell
  > battery on the back for retaining constellation data

  Too bad  about losing the 1PPS. Maybe you can persuade  them  to get
  some spares.

  >  Here's the board: http://www.losalamostech.com/gps_board.jpg

  Thanks - that gives a good idea how bug the GPS is.

  But don't the connectors add a lot of weight?

  > Here's their gadget:

  >http://www.lanl.gov/orgs/tt/pdf/techs/hands_off_gun.pdf

  Shades of Star Trek. We can see it happening right before our eyes.

  >> 2. How  well  do  they work indoors? Do you  have  to  be  near a
  >> window? What about inside a multi-story building?

  > We only  tried  it  outside. Their  gadget  got  the  short little
  > ceramic patch  antenna.  I used the longer (5 meter  I  think) mag
  > mount version in my car when testing the APRS beacon.

  I wonder  about  the  GPS chips used in  cellphones.  Would  they be
  suitable for this project? They might save some weight.

  >> 4. Have  you ever taken the shield off and looked  inside?  If so,
  >> can you  see the crystal oscillator and tell whether it is  a bare
  >> crystal or a complete oscillator module?

  > No, but it comes off easy enough when not soldered down.  I'll try
  > to pop mine open and take some pictures of the guts for  you later
  > today.

  Thanks, I would really appreciate that.

  >> 5. How  much  do  they cost? Do you know of  any  others  that are
  >> cheaper?

  > We paid  somewhere  on the order of $50  +  the  antenna. Sparkfun
  > sells them here for $56:

  >  http://www.sparkfun.com/commerce/product_info.php?products_id=163

  Great - thanks for the link.

  > They also sell the antennas and breakout boards that  already have
  > the tiny  little surface mount sockets (I have a few  left  if you
  > end up buying one of these).

  I'm very  interested  in antennas these days. I  know  nothing about
  them, but  find they can have a lot to do with time errors.  Such as
  multipath from passing cars.

  What happens if a pigeon sits on your GPS antenna?

  > The really  interesting thing is that the manual  states  that the
  > PPS output  is  within  50ns of reality. I plan  on  using  one to
  > discipline that  Efratom  rubidium  standard  I  was  asking about
  > earlier in  the  week.  By  the  way,  the  connector  from Mouser
  > electronics came in and I'm ready to go, just waiting on  the part
  > to come in from China.

  Me too! I just got news that my rubidium has already  shipped, which
  is surprising. PayPal hasn't cleared yet, so I guess he has a lot of
  confidence in the system.

  Which Efratom do you have? And who are you dealing with in China?

  >  -Bob

  >> Thanks for your help!

  Best Regards,

  Mike Monett