Phase 3D Frequency Conversion

P3D		Uplink Band (your transmitter)
P3D		15m	12m	V	U	L1	L2	S1	S2	C
Down Link Band	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

Finding an Uplink Frequency

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

Tx = K - Rx

Example

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.