wiki/ news/ 2005-06-21 - GPS redux 4: test of retuned 2m & GPS: success!

Who: Tim, Glenn and Andrew

Where: Andrew's workshop


From Tim:

1) We seek to avoid 1575.42 MHz. For convenience, it is nice if (d)
   remains 14.

  f_receive = 10.2451MHz * 187/14 + 10.7MHz = 147.545MHz

The 11 the harmonic of the 1st LO is 1505.3MHz, the 12th is 1642.14MHz.

The distance from the GPS carrier is therefore

  [-70.1221, 66.7232]MHz

I don't expect to do any better than this since my eye tells me the
SAW filter notch is a bit closer on the high end and the
notch-to-notch distance is about 112MHz.

Is this receive frequency (147.545MHz) ok for us?

According to Glenn, 147.545 MHz is fine.

2m Receiver reflash and SINAD measurement

So we reflashed the recovery node to set the 2m receiver's DPLL divisor to 187/14 (control word 0x40) and took a look at the where the LO's harmonic spikes were. They fell close to where we predicted (Tim: measurements?) and we called it good.

We then tried to get the 2m's SINAD back to the -100 dB that we originally had, and we just couldn't do it. About -88 dB was the best we could do, which was disappointing. Something happened to the 2m receiver... we wonder what.

2m/GPS/ATV test

Once again, we put the avionics module + payload module with the 2m receiver on top of a ladder in front of Andrew's house and put various laptops -- and lights, since it was of course dark by now -- on a table. We got to use Bruce's flashing red lights since the ladder was in the street - fun! We used Cantalope to turn on and off parts of the rocket, and used the Jupiter's DOS-based labmon software to monitor how the GPS satellite lock was. We turned on everything - ATV, wifi, 2m, you name it - and the GPS didn't care one bit.

So hooray, the ATV/2m/GPS interference problem has been solved.

Now we just need to figure out what happened to the 2m receiver, or replace it with the old LV1b receiver.