Approximately Correcting for Doppler shifts during ISS Passes

by John Chamberlain, AC5CV, 2005

For radios with 1 kHz tuning ability

Identify max elevation of the ISS pass: Is it a High, Medium, or Low pass?
Use the right-hand columns of the table to guide WHEN to adjust the frequencies.

Hint: Store transmit and receive frequency pairs in radio memories, as indicated below.

NOTE: ISS will not perform any Doppler corrections, so YOU must do so.

Approximate Switch Times
(seconds from max elevation)

ISS Voice downlink

ISS Voice uplink

High Pass

Med Pass

Low pass

(145.800 MHz, Region 2)

(144.490 MHz, Region 2)

(>50 deg)

(25-50 deg)

(< 25 deg)

Memory location

Doppler (kHz)

ISS transmits
on

Your radio’s
receive frequency

ISS listens
on

Your radio’s
transmit frequency

Delta time
(sec)

Delta time
(sec)

Delta time
(sec)

1

+3

145.800

145.803

144.490

144.487

AOS

AOS

AOS

2

+2

145.800

145.802

144.490

144.488

-55

-70

-160

3

+1

145.800

145.801

144.490

144.489

-25

-40

-75

4

0

145.800

145.800

144.490

144.490

-7

-10

-25

5

-1

145.800

145.799

144.490

144.491

7

10

25

6

-2

145.800

145.798

144.490

144.492

25

40

75

7

-3

145.800

145.797

144.490

144.493

55

70

160

Approximate Switch Times
(seconds from max elevation)

Packet ISS downlink

Packet ISS uplink

High Pass

Med Pass

Low pass

(145.800 MHz)

(145.990 MHz)

(>50 deg)

(25-50 deg)

(< 25 deg)

Memory location

Doppler (kHz)

ISS transmits
on

Your radio’s
receive frequency

ISS listens
on

Your radio’s
transmit frequency

Delta time
(sec)

Delta time
(sec)

Delta time
(sec)

1

+3

145.800

145.803

145.990

145.987

AOS

AOS

AOS

2

+2

145.800

145.802

145.990

145.988

-55

-70

-160

3

+1

145.800

145.801

145.990

145.989

-25

-40

-75

4

0

145.800

145.800

145.990

145.990

-7

-10

-25

5

-1

145.800

145.799

145.990

145.991

7

10

25

6

-2

145.800

145.798

145.990

145.992

25

40

75

7

-3

145.800

145.797

145.990

145.993

55

70

160

Approximate Switch Times
(seconds from max elevation)

ISS Voice Cross-band downlink

ISS Voice Cross-band uplink

High Pass

Med Pass

Low pass

(145.800 MHz, Region 2)

(437.800 MHz, Region 2)

(>50 deg)

(25-50 deg)

(< 25 deg)

Memory location

Doppler (kHz)

ISS transmits
on

Your radio’s
receive frequency

ISS listens
on

Your radio’s
transmit frequency

Delta time
(sec)

Delta time
(sec)

Delta time
(sec)

1

+3

145.800

145.803

437.800

437.791

AOS

AOS

AOS

2

+2

145.800

145.802

437.800

437.794

-55

-70

-160

3

+1

145.800

145.801

437.800

437.797

-25

-40

-75

4

0

145.800

145.800

437.800

437.800

-7

-10

-25

5

-1

145.800

145.799

437.800

437.803

7

10

25

6

-2

145.800

145.798

437.800

437.806

25

40

75

7

-3

145.800

145.797

437.800

437.809

55

70

160

AOS = Acquisition of signal, i.e., when the ISS "pops" above the horizon.