Phase 3D Frequency Conversion


Uplink Band (your transmitter)

15m 12m V U L1 L2 S1 S2 C


V 167.13 170.84


581.575 1415.275 1414.35 2546.375 2592.475 5814.575
U 456.83 460.54 581.50


1704.975 1704.05 2836.075 2882.175 6104.275
S1 2421.58 2425.29 2546.25 2836.025 3669.725 3668.80 - - 8069.025
S2 2422.58 2426.29 2547.25 2837.025 3670.725 3669.80 - - 8070.025
X 10472.38 10476.09 10597.05 10886.825 11720.525 11719.60 12851.625 12897.725 16119.825
K 24069.38 24073.09 24194.05 24483.825 25317.525 25316.60 26448.625 26494.725 29716.825

See also Phase 3D Frequency Bands.

Finding an Uplink Frequency

  1. Find the row for the downlink frequency band (your receiver's band) in the left column.
  2. Find the column for the uplink frequency band (your transmitter's band) across the top.
  3. Read the conversion constant K from the table in that row and that column.
  4. Calculate your transmitter frequency (in MHz) by subtracting your receiver frequency (in MHz) from the conversion constant from the table.

Tx = K - Rx


Suppose Phase 3D is in mode U/V, with an uplink on UHF (70cm or 435 MHz) and a downlink on VHF (2m or 145 MHz). This is the old favorite "Mode B". Suppose you hear a QSO on a downlink frequency of 145.890 MHz and wish to join in. In the "V" row of numbers, the number in the "U" column is 581.575. So you calculate 581.575 - 145.890 = 435.685 MHz, and set your transmitter to that frequency.

Doppler Shift

The calculation above ignores Doppler shift, the frequency shift caused by the motion of the satellite relative to each ground station. Doppler shift is proportional to frequency, and to the radial velocity of the satellite. Uplink Doppler is proportional to uplink frequency, and downlink Doppler is proportional to downlink frequency. Because the transponders are all inverting (Tx = C - Rx), the total Doppler shift you will observe in your receiver is proportional to the difference in frequency.

Doppler = (Rx - Tx) * Velocity/C

Much has been written about the best way to compensate for Doppler shift. Phase 3D's higher frequencies and the possibility of multiple simultaneous uplink bands translated into multiple simultaneous downlink bands make the problem more complex than ever before.   For more on Doppler compensation, see The Radio Amateur's Satellite Handbook (purchase info) or read the One True Rule article.

Preliminary Values

The numbers shown in the chart are nominal, based on design and laboratory measurements. They will be revised after the spacecraft is launched and the oscillators have stabilized in the vacuum and thermal environment of P3D in space.

Conversion table supplied by Freddy de Guchteneire, ON6UG, of AMSAT-DL, via Lou McFadin, AMSAT P3D integration manager and P3D Laboratory manager, on 21 February 2000. Formatting and text by KB5MU.