GRAPT/RF Validation

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GRAPT Overview

  • Turnstile antenna (or arrow)
  • USRP with TVRX
  • WXAPT example from GNU Radio

This experiment is trivial, nonetheless it validates the RF-part of the setup. It will also reveal whether additional hardware like LNA is required.


Currently, following NOAA satellites are active on 137 MHz APT and 1.7 GHz HRPT:

SAT APT Freq HRPT Freq Notes
NOAA-15 137.5000 MHz 1702.5 MHz VTX-1 / STX-2 / MSB / OMNI=RCP
NOAA-16 OFF 1702.5 MHz — / STX-2 / MSB / LCP
NOAA-17 137.6200 MHz 1698.0 MHz VTX-2 / STX-1 / LSB / RCP
NOAA-18 137.1000 MHz 1707.0 MHz VTX-1 / STX-3 / HSB / RCP
NOAA-19 137.9125 MHz 1698.0 MHz VTX-2 / STX-1 / LSB / RCP

Source: NOAASIS Satellite Status Information


Considering a time window of 24h starting at 10:00 UTC on Sat 13 June, there are many potentially useful passes.

NOAA passes occuring between 2009/06/13 10:00 – 2009/06/14 10:00 UTC

We only need a few good passes for successful experiment and they should be distributed over time in order to allow debugging and problem fixing between the passes.


  • Created this page preparing for the experiment to be carried out during the weekend 13-14 Jun 2009.
  • Need to upgrade laptops and install recent GNU Radio


  • Upgraded laptops to Ubuntu 9.04 and GNU Radio 3.2
  • Problems with example APT receiver since it uses 32k audio but my crap HW can only do 44k1 or 48k.


  • I realized that I brought a BNC male/male adapter instead of a female/female that I need to connect my antenna to the TVRX. Experiment postponed!



  • Found out that there are resampler blocks in GNU Radio - very efficient ones indeed!
  • blks2.rational_resampler_* for Python
  • gr_rational_resampler_base_* in C++ (see under filters)
  • GRC has both blocks? Have to find out about it.


  • Followed a NOAA-17 pass (max el 18°) using USRP+TVRX+Arrow. Very good SNR between 20-30 dB.

Lessons Learned

  1. Do not pack your gear in a hurry.
  2. RTFM (RE: resampling audio) — also the examples!

GRAPT Overview