Debugging RF issues with Sat and HF


  • Very little sat reception was detected at launch site
  • HF GPS did not lock at launch site

Sat Signal Investigation

Useful Digi m10 debugging commands:
66 = Get Receive Statistics
69 = Get Receiver On/Off status
86 = Get Performance Stats

Baseline Replication

Set payload up running on ground battery power in parking lot. Sat antenna boom facing west end of lot.

RESULT: Issue replicated. Received 0 syncs per hour on D-plane

Test 1

  1. Reseated sat modem coax connector
    1. May have been unseated
    2. Seated well upon reinsertion
  2. checked pins and continuity of coax jumper cable and antenna
    1. Good

RESULT: no improvement in sat RX 1 or 2 SYNC lines per hour D-plane

Test 2

  1. Reset modem to factory defaults

RESULT: Received 5-6 syncs per hour D-plane

Test 3

  1. Set sat prefs back to white star preferred

Result: Received 0 syncs per hour on D-plane
Returned to factory defaults.

Comment: Launch Director asks for clarification. If whitestar preferences did not work but factory settings did, why weren't whitestar settings considered suspect for review. They are suspect, that's why we're not using them now for further tests. Did whitestar preferences changes prior to launch but after pre-launch last tests? no.

Test 4

  1. Replaced flight antenna and jumper cable with ground test equivalent (not the highball-1 antenna)

Result: Received 0 syncs per hour on D-plane

Test 5

  1. Build new 5/8th wave whip antenna to replace old extension antenna that was our ground antenna
    1. 1176.59mm is 149Mhz
    2. Orbcomm uplinks from 148-150MHz
    3. Had to use two lengths of piano wire crimped together

COULD NOT COMPLETE - could not get antenna to match SWR properly. Could not get less than 4:1 SWR

Test 6 (LD1 suggestion)

  1. Use ground test dipole antenna and flight dipole simultaneously on two modems to get relative performance measure.
  2. Used Flight antenna on Digi Dev Kit, attached to plastic garbage can at approx same height as SB-1
  3. Used ground antenna on SB1
  4. Placed in parking lot

RESULT: Dev Kit modem receives sat signal for about 10% of each pass, slightly better, but still not enough for flight. Modest increase in performance not worth further investigation, is likely from the lack of metal payload frame next to antenna.

Test 7

  1. Rebuild broken ground station retractable whip antenna
    1. Tested at 1:1 SWR when mounted on Dan's car roof, far better than the crude handmade whips
  2. Connected to SB-1 payload modem, using flight coax jumper adapter cable
  3. Left flight antenna connected to Dev Kit modem

RESULT: 95% SYNC of actual SB-1 payload for EVERY SAT PASS. Source of problem isolated to the antenna system. This could include damage to both antennas, bad antenna location relation to the payload, 1/4 wave dipole antenna type may just has lower gain than needed, or construction may have introduced flaws that impede performance, or payload electronics may be introducing high levels of RFI.

Test 8

  1. Hang flight 1/4 wave in free space, 10 feet high on rope between trees Pic
  2. Connected to Digi Dev Kit in bushes below and to side.

RESULT: Performance worse than Car 5/8 whip yet better than flight antenna mounted on plastic garbage can from test 6. Got signal for about 40% of each sat pass.

Test 9

  1. Modify prototype non-flight duplicate of flight antenna to be a 1/2 wave dipole
  2. Raise up in free space
  3. Attach Digi dev kit to free space support (feedline on this antenna is only 1m long)
  4. Run power line to Digi dev kit

Test 10

Test Gear

  1. Modify testing antenna to 1/2 wavelength
  2. Attach testing antenna to Backup Sat Modem (Combo 1)
  3. Attach 5/8 wavelength car antenna to SpeedBall-1 Flight Modem (Combo 2)

Given Expectation

  1. Expect Combo 2 to acheive 90% sync for satellite coverage based on prior tests

Validity Requirement

  1. Combo 2 must have sync 75%

Success Criteria

  1. Combo 1 to have sync for coverage at 90% of Combo 2, (90% * Combo 2 sync) coverage overall


HF GPS Lock Investigation

Test 1

agendas/20110326.txt · Last modified: 2018/07/29 17:58 (external edit)
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