Orbital Focus - International Spaceflight Facts and Figures
carousel image
Tracking the ISS

Tyneside, UK
2023 Mar 30
Thursday, Day 89

Curated by:

ISS Operations - 600 MHz

The two major Russian modules of the ISS have transmitters that operate near 600 MHz. The actual allocations are: Zarya - 628 MHz and 630 MHz, Zvezda - 632 MHz and 634 MHz. The actual transmissions consist of sidebands that can be detected 128 kHz either side of the central frequency.

Previous Russian space stations have used this frequency band, notably Mir at 636 MHz and 638 MHz. Some of the other modules that were added to Mir probably also transmitted in this band. As far as ISS modules go, these transmissions were first reported by Sven Grahn and are described at his web site.

The transmissions can be detected by tuning to one of the side bands at 128 kHz above and below the basic frequency as there is no central carrier. It is a similar structure to the 166 MHz transmissions that can be detected from Soyuz and Progress when in transit to the ISS, and during 'health checks' performed periodically while they are docked with it.

Zvezda at 630 MHz

Here is a trace of the 630 MHz transmission from Zvezda. It is the "+128 kHz" component of the signal.

ISS 630 MHz Doppler Curve

Appearance of the signal is sudden when the transmitter switches-on with the ISS several degrees above my horizon, and is the reason for the Doppler curve not being symmetrical in shape.

The aerial used was not ideal for the task in hand as it was built for use at 144 MHz. It will probably account for some of the fading. The stronger appearance of the transmission during the second half of the pass is due to the aerial having greater sensitivity towards the south-east.

The signal fades out about 30 seconds before the ISS reaches horizon. The ISS may have moved into an area of sky where the aerial sensitivity is low but there are other possibilities. There is a 200m high cliff in our local landscape in the direction where the ISS set below the horizon, and it may have blocked the signal for the last few seconds. Blocking of the signal by the ISS structure itself is also a possibility.

Copyright © Robert Christy, all rights reserved
Reproduction of this web page or any of its content without permission from the website owner is prohibited