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Saturday, 10 August 2019

setting up receive for QO-100 at my QTH

The Es'hail-2 geostationary satellite, the first of its kind to carry an Amateur radio payload, designated QO-100, has been in orbit for some time now, and I listen to it now and again on the BATC WebSDR hosted at Goonhilly Earth Station in Cornwall and have got a rough idea of when it is active, I've had a look at how to receive it and it would appear it can be received with a Sky UK 60cm Minidish and LNB connected into the RTL-SDR, however the RTL-SDRs that can power accessories on the coax only can do so with 5v, a satellite LNB requires either 12v or 18v, the polarisation is selected using these two voltages, 12v for vertical, for the narrowband transponder, which I am interested in here, 18v for horizontal, this calls for a Bias-t which essentially supplies voltage to an accessory up the coax however at the same time prevents that voltage going into the receiver (or transceiver in some cases), a Bias-t simply has a capacitor to block voltage and an inductor to block RF).

LNBs generally have a LO of 9.75 GHz unless a tone is fed to them as well, which is not required for QO-100 as the 9.75 GHz LO is suitable, the downlink frequencies being around 10.4 GHz (though generally these LNBs specify a minimum frequency of 10.7 GHz), so on the RTL-SDR for me to receive the narrowband transponder requires me to take it's frequency of 10489MHz and deduct 9750MHz, this should be around 739MHz.

As I already have an LNB, which is designed for an oval shaped dish, the Sky UK Minidish, the biggest size they are in is 60cm for the north of the country is what I need, though there is a dish and LNB already on the building for my flat I cannot use this as it needs to stay set for the Astra 2 Satellites used for Sky UK and Freesat, so I need to buy another dish and this is what I had in mind as the LNB I have, a quad-output Visiblewave unit with Sky branding on the sticker, will fit this with no modification, this gives me an option to receive both transponders as the unit had a length of twin cable terminated in F male connectors, which I intend to splice and fit a Bias-T inline for each, powered at 12V and 18V respectively, however I'd need two RTL-SDRs of good quality, the NooElec NESDR SMArt is a perfect choice as it is more frequency stable than the standard stick, as reference I'll use the Goonhilly hosted WebSDR to ensure things are on frequency, LNB skew and dish alignment is obtainable from BATC.

There should be a YouTube video of my success (or failure) of receiving QO-100 with a Sky Minidish, nice to experiment with, if not I've got a portable satellite dish to take camping with me for television use.

73 de 2E0EIJ

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