Introduction: Satellite Ground Station for the QO-100 Es'hail-2 Geostationary Bird

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About: I am an electronics engineer working in telecommunications in the UK. Generally I work on chip design for digital radio receivers. I like all things arty and consider chip design a bit arty :) Basically I h…

Hello fello Hams,

My name is Dave (G7IYK) and I am located in Bristol in the south west of the UK.

This instructable details the processes I went through in order to successfully build a satellite ground station in order to communicate through the geostationary QO-100 satellite using the SSB narrowband linear transponder.

Things I cover in this instructable are :

  • Selection of satellite dish
  • Selection of Low Noise Block (LNB) for down link receive
  • Construction of matched 2.4GHz helix antenna for uplink transmit
  • Dish alignment
  • Construction of the ground station full duplex hardware platform
  • Configuring the SDR for ethernet access
  • Configuring the SDR control software - SDR Console

Lets have a look at the QO-100 Es'hail-2 geostationary satellite ....

The satellite was launched from Kenneddy Space Center at 20:46 GMT on Noverember 15th 2018 and is now in geostationary orbit at 25.9° East and at an altitude of approximately 35,788km. This positions the satellite over central Africa and being geostationary that is where she stays. The satellite carries two amateur radio transponders operating in the 2400MHz and 10450MHz bands. A 250KHz bandwidth linear transponder intended for conventional analogue operation and an 8MHz bandwidth transponder for experimental digital modulation schemes and DVB amateur television.

This inststructable concentrates on the first of the two - the conventional analogue transponder.

Narrowband Linear transponder:

2400.050 - 2400.300 MHz uplink

10489.550 - 10489.800 MHz Downlink

The bandplan for the transponder is shown in the attached image. We can see the bandwidth is split into areas of different useage.

  • Three beacons, one at the start of the available bandwidth, one in the center and a third at the end. The central PSK beacon also contains telemetry information and other cool stuff we can decode
  • The region we are most interested in for this project is the bandwidth region of SSB (USB) either side of the central beacon

So basically the bottom line is with the right gear we can transmit SSB (USB) analogue voice on the uplink at 2.4GHz and the satellite will repeat that signal over a huge geographical area on a 10.450GHz downlink. So it is essentially a geostationary repeater in the sky - a very long way up !

So why do we want to use the satellite for amateur radio ..... easy !

  • Its technically challenging
  • It involves buying new gear
  • It's a huge amount of fun
  • We learn new stuff
  • Because it is there

It was put there for us - it would be rude not to use it !

Supplies

Here are a list of the main components I used and where I sourced them :

Pluto+ SDR

https://fr.aliexpress.com/item/1005003777029734.html?spm=a2g0o.order_list.0.0.bc195e5b73oscW&gatewayAdapt=glo2fra

Analogue devices CN0417 pre-amplifier

https://www.mouser.co.uk/ProductDetail/Analog-Devices/EVAL-CN0417-EBZ?qs=qSfuJ%252Bfl%2Fd6LxWy%2FxJy1nA%3D%3D&gclid=Cj0KCQjwuuKXBhCRARIsAC-gM0gPC81PtTWDi39eAZDaF8QxmNuXx5NKCZW_9dqXtszI_qiSWrppuPAaAmsXEALw_wcB

Bias-T network

https://www.amazon.co.uk/gp/product/B07ZQ2M8ZB/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Bullseye LNB

https://www.amazon.co.uk/gp/product/B08GJ6B1HB/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

105cm offset dish

https://www.ebay.co.uk/itm/294939561946

SG Labs 2.4GHz power amplifier

https://www.sg-lab.com/AMP2400v3/amp2400_v3.html

DC-DC conveter for 20W power amplifier

https://www.ebay.co.uk/itm/184179070285

DC-DC converter for Pluto+ and pre-amplifier

https://www.ebay.co.uk/itm/193727621572

Step 1: The Dish and Antenna

I thought we would start with the dish and antenna. The dish itself is not the antenna but a reflector that focuses the receive signal onto the antenna and radiates focused power from the antenna.

The dish I went for was an inexpensive 105cm mesh type which cost around £62 delivered in the UK and came with a mounting bracket give the dish the ability to be tilted upward to the desired angle of elevation. This dish is an offset type and came with a simple support arm to support the antenna using a plastic bracket. The advantage of a larger dish is it has a greater surface area and so provides more gain but the disadvantage is it becomes more focused and therefore more difficult to locate the satellite in the sky. With my dish the satellite is only detectable within a very narrow range of elevation and azimuth - one small nudge and you have lost the signal.

The antenna array

Probably the most tricky part of the project is building the antenna array. I say array because the antenna is actually two antennas physically located together - one forms the receive downlink antenna at 10.489GHz and the second forms the transmit antenna at 2.4GHz. There are various ways of building such an antenna and I went for using a Bullseye high stability LNB with a 3.5 turn helix antenna mounted directly in front of the LNB.

The Bullseye LNB is an off the shelve device specifically designed for the reception of analogue signals in the Ku-band. It has an integrated high stability downcoverter with an LO of 9750MHz. So for our purpose this means the LNB receives the satellite down

I must point here the design for the 2.4GHz helix transmit antenna is NOT my design but the excellent work of Patric Noelle DC8PAT. Rather than me describing the antenna it is ealier just to check out the Thingiverse parts and Patric's QRZ page:

Thingiverse page : https://www.thingiverse.com/thing:3899461

QRZ page : https://www.qrz.com/db/DC8PAT

If you have a 3D printer (as I do) you can make the antenna yourself. However you can also buy the antenna off the shelve from Patric - again check out the QRZ page.

Attached is a video of my efforts in building the combined Rx/Tx antenna:

Step 2: Pluto+ SDR Output Power

Attached are a couple of images from my spectrum analyzer showing the Pluto+ SDR output power at 1300MHz. My spectrum analyzer has a maximum frequency of 1500MHz. Although measured at 1300MHz and not 2.4GHz I suspect the Pluto+ max output power will be around +6dBm.

Further measurements with a power meter revealed :

After having used the ground station and observed my downlink with respect to the beacon I decided an output power of about 10W was best for my setup. So working backwards at 2.4GHz the SG power amplifier output is shown at 39.2dBm which is 8.3W. The corresponding output from the Analogue devices pre-amplifier is 5.9dBm and the output of the Pluto+ is -17.4dBm which corresponds to a power setting in SDR Console of 50% on the slider control.

This shows the Analogue devices pre-amplifier has a gain of 23.3dB.

Cable loses were compensated for using a known accurate source.

Step 3: The QO-100 Ground Station Main Board

Attached is an image and video description of my QO-100 ground station. The ground station consists of the following parts:

  • Pluto+ SDR transceiver
  • Bias-T network to power the LNB
  • Analogue Devices CN0417 +20dB 2.4GHz pre-amplifier
  • SG labs 2.4GHz 20W power amplifier
  • 12V to 28V power supply 3A
  • 12V to 5V x 2 power supply 1A / 2A
  • USB cables
  • SMA to F type adapters

Step 4: Pluto+ SDR Ethernet Connection to SDR Console

Attached is a series of short videos demonstrating how to set up the Pluto+ for ethernet connection to SDR Console. I chose to use a USB to Ethernet adapter - see attached image. The video covers the three main steps :

  • Configuring the USB to Ethernet adapter
  • Configuring the Pluto+
  • Configuring SDR Console


Step 5: SDR Console Converter Feature

SDR Console is a fantastic piece of software and being free is a real gift for us Hams - I take my hat off to the Authors. The software has many well thought out and useful features for anyone experimenting with satellite communications. One of the very useful features is being able to configure a Tx/Rx frequency converter. This can be thought of as a software up/down converter and in this application allows the IF output of the Bullseye LNB to be shifted back to the actual satellite downlink frequency. We can also convert the 2.4GHz uplink frequency to the same frequency as the downlink and then link the Rx and Tx together such that we Tx on whatever frequency we are Rx on. It sounds a bit confusing but I am sure will be clear if you check out the video which demonstrates the feature in practice.

Step 6: SDR Console Satellite Beacon Tracking Feature

Attached is a short video demonstrating how to use the SDR Console satellite beacon tracking feature. Unless our LNB is GPS locked it will drift with temperature and due to other factors. This drift means in practice our Rx ad Tx signals change frequency slightly over time. When listening to a station the drift will cause a frequency shift in the audio resulting in the characteristic deep voice or Mickey Mouse voice. On transmit our own audio will change in frequency slightly resulting in the same audio characteristic for anyone listening.

SDR Console has a very nice feature which allows us to lock onto and actively track the satellite central PSK beacon located at 10489.750MHz. As SDR Console knows the frequency of the beacon it can actively track the received signal and compensate for any drift.

The feature appears to work really well and I have listened to downlink stations for long periods of time and not experienced any frequency drift.

Step 7: SDR Console Transmit and Correction

Attached is a short video demonstrating how to configure SDR Console for transmit and how to correct the transmit converter feature such that the signal we receive on the downlink aligns with the signal we transmit on the uplink. In this case we transmit a 2KHz tone on the uplink and adjust the Tx converter so we hear the 2KHz tone in the correct position on the downlink. We are able to do this because the Pluto+ is a full duplex radio and SDR Console provides an independant transmit and receive frequency converter feature.

Step 8: Conclusion and Thoughts

This has been a really great, fun and enjoyable project and like all new radio projects we learn new stuff. Prior to this project I had not done anything with satellites but over the course of the project have learned many new skills both in terms of hardware and software control.

Yes, you have to spend a bit of money - well quite a bit actually but I think it is well worth the cost for the amount of fun to be had from building a satellite ground station. There is something very satisfying about using a satellite tens of kilometers up in space to speak to other like minded people. I am just very grateful to those involved in building the satellite and including amateur radio and also to the guys in producing software such as the excellent SDR Console. It is a privilege to able to use the QO-100 satellite so I would urge anyone thinking of building a ground station to use this amazing resource in a responsible manner.

Please feel free to email me if you have any questions regarding this project.

Many thanks,

Dave G7IYK