G4ELI's QO-100 Station

Antenna

The antenna is a 1.4m prime focus dish from www.satellitesuperstore.com . The ratio of focal length to aperture size (F/D Ratio) is 0.41, Gain at 10.95GHz 41.8dB. As you see, the stand is kept in place with ~ 280kg of lintel, breeze block and slab.


The dish was initially aligned using the sun on March 1st, 2019 because at 10:16 the sun's azimuth and elevation was the same as Es'Hail 2, so the shadow of the feed would be directly over the center of the dish. Afterwards the dish was further optimised by monitoring the CW beacon on the narrow band transponder and adjusting azimuth and elevation.

LNB

Frequency

The output frequency of the LNB is ~739MHz, the LNB also has considerable gain - up to 65dB!

Power

A LNB must be powered, the supply voltage determines the polarisation. Typically 13v for vertical and 18v for horizontal polarisation. Power supplies are not expensive, for example Labgear PSUFC on Amazon.

POTY from Sigi DG9BFC

October 3rd, 2021 - I now use a POTY from Sigi as my preferred feed, it is excellent! Sigi's solution has:

  • Improved TXCO which greatly reduces LNB drift due to change in temperature - don't forget the heat from the sun is reflected back on the LNB.
  • Extra insulation to reduce temperature changes as clouds pass in front of the sun.
  • N-Type connector for the 2.4 GHz transmit connection, using a good coax such as Ecoflex 16 Plus is much better than a SMA to N-Type pigtail cable.
  • A near-perfect circular polarisation and a very low SWR at the 'sweet spot'.

The image below shows what is sometimes referred to as transponder bloom - noise received at 2.4GHz and retransmitted at 10GHz. If you see this then more receive gain is not needed.

SNR on receive is improved as this feed uses the complete dish, also sidelobes are suppressed by the choke rings.

Stability

Sigi's modified LNB is very stable, even on a day when the sunshine is intermittent - typical for Cornwall in October. Just click on the image below to see the change over two hours.

Octagon 0.1db Quad High Gain

Testing with an Octagon 0.1db Quad High Gain HD Ready Universal low-noise block downconverter (LNB). This is very sensitive but drifts - for SSB / CW it must be modified, either change the crystal to a TCXO or add support for an external reference such as the Leo Bodnar GPSDO. Drift is much worse in the daylight as it is temperature dependent.

Stability

There is a special feature in SDR Console which locks the receiver to the digital beacon on the narrow-band transponder, so reception is perfect. 


From the ribbon bar select View, More Options, Geostationary Beacon.

Which SDR?

Receiver

There are many options, the most popular being:

 

  • Airspy R2,
  • RTL Dongles,
  • SDRplay RSP1A, RSP2.

 

When tuned to QO-100 the output frequency of the LNB is ~ 739MHz, so the receiver must cover this frequency.


Transceiver

The transceiver must support transmit at 2.4GHz and receive at 739MHz, preferably at the same time (full duplex).The currently supported options are:

 

 

Both work well, the recommended solution is Pluto:

 

  • Price,
  • TX output power,
  • Ease of programming.

 

Feature LimeSDR Pluto
RF chip LMS7002M AD9363 (hack to AD9364).
Frequency range 100 kHz – 3.8 GHz 325 MHz to 3.8 GHz
70 MHz to 6.0 GHz (AD9364hack)
Ext. reference Yes With modification
RX sensitivity Good Good
Stability Good Good
Bandwidth 50Mhz 6MHz (200 MB/s)
TX power -6dBm +2dBm
Case included No, eBay Plastic, metal available from eBay
Software API Good Very good
Other USB noise - needs a very good cable or metal case
USB USB3 USB2
Network No Yes (USB <=> ethernet adapter)
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