Beginners Guide To Satellites (Part One)

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by Dee Vickers (G7BEH)

Overview

After 35 years away from the hobby, I returned to find that the world of amateur radio had changed significantly. I knew I wanted to make the most of the VHF/UHF bands and was surprised to find that what had once been very active, was now quiet and under-utilised. That is except for contest evenings!

Still, I was disappointed but looked forward to working across Europe via the satellites. I hope this guide will help you to get make the most of the satellites using very basic equipment. You don’t need that latest and greatest radio and antenna systems to enjoy using the satellites, but better gear will allow you to work more marginal situations; more on that as we go through.

Finding Satellites

It’s worth knowing a little about how to find and track satellites, before we look at the equipment needed. I would also recommend listening to a couple of satellite passes first before transmitting, just to get the hang of how to use them properly. There are a lot of resources on the internet to help and I’ll include some useful links to pages as well recommending some apps.

Types Of Satellites

There are two basic types of satellites that you’ll find, these are:

  • FM satellites
  • Linear satellites

I’d recommend starting with the FM satellites, before moving on to the linear ones. This is because the equipment and operation is simplified, yet you can still work all across Europe using them. However, there are disadvantages to them, which can be overcome by operating on the linear satellites.

At the time of writing, only the QO-100 satellite is geostationary. All the others are in Low Earth Orbit – hence, you will come across the term “LEO” satellites. We’ll take a quick look at QO-100 first, as receiving this is very simple indeed (at least initially)…

QO-100

This geostationary satellite is a great way to start listening to satellites. It’s very easy to access and only requires an internet connection (at least to start with). Be warned though, although we can receive this one via the internet, using websdr technology, you may well start looking at building your own receive station, followed by the transmit side!

You’ll find SSB, CW and various data modes on QO-100. Use the Goonhilly websdr at https://eshail.batc.org.uk/nb/ to receive stations using it. You’ll find beacons / telemetry at either end of the bandwidth used by the satellite; at the low end is the CW band, then moving up through the data band, and on to the SSB portion. Most SSB activity is clustered around the centre frequencies.

QO-100 is a fabulous satellite for hearing DX stations – being geostationary it’s orbit is much higher than the LEO satellites and consequently it has a much larger footprint. Special event stations are often on here too. It’s an excellent introduction to the satellites!

FM Satellites

FM satellites are basically repeaters, but in a Low Earth Orbit. As they are repeaters, you would use them in a similar way to ground-based repeaters, so they are simple to use. However, this is also their Achilles heel… there is only one channel that everyone has to use. This means that operating them must be done in an efficient manner to allow all to access.

As they are LEO satellites, they do not act in the same manner as a geostationary satellite. These do not occupy a ‘fixed position’ and travel around the globe, making passes over your location. These passes are typically in the region of 10-15 minutes long and occur several times a day. Sometimes the passes are directly overhead, other times they barely skim across the horizon.

Therefore, we need to be able to track their position with some degree of accuracy. Because of the speed at which they move through space, they are also subject to Doppler shift and this also needs to be taken into account. Generally speaking, you only adjust the UHF frequency to account for Doppler shift… but more on this later.

You can find out about which frequencies are used for uplink / downlink on the AMSAT FM Satellite Frequency Summary page at https://www.amsat.org/fm-satellite-frequency-summary/. Note that some FM satellites will also require the use of a transmit CTCSS tone to access them. You won’t need to set a CTCSS to receive them.

Linear Satellites

These satellites are more difficult to work, but have the distinct advantage of bandwidth. This means that many operators can be working stations at the same time and there isn’t the same ‘fight’ to get into the repeater, as there is on FM satellites.

These satellites are also Low Earth Orbiting, but are typically used for CW and SSB communications. The same rule about adjusting for Doppler on the UHF frequencies holds true here too (although you may need to slightly tune the VHF as well, the main adjustment is on UHF).

You can find out about which frequencies are used for uplink / downlink on the AMSAT Linear Satellite Frequency Summary page at https://www.amsat.org/linear-satellite-frequency-summary/.

Summary

In this article, we’ve had a quick look at geostationary and LEO satellites. We know that there are FM and linear satellites and the recommendation would be to start listening to QO-100 via the websdr and/or the FM satellites. We now where to find out about the frequencies and tones used to access these satellites too.

In Part Two we’ll look at tracking apps and equipment needed.

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