OSCAR-100 - Es’hail 2 - My Approach

OSCAR-100 (Es'Hail 2) is operational and looks to be working well, very well. I'd read on the web over three years ago that a geostationary amateur called Es'hail 2 was on the cards and after several years waiting it was launched from the Kennedy Space Center at 20:46 GMT on Thursday November 15th 2018 and has now taken up its orbit at 25.9 degree East.

This orbit gives coverage from northern Europe right across to Brazil and down to Thailand as you can see from the map on the right.

I'll have some of that I thought (amongst all my other projects !) and so here are my plans and what I've found out so far .......

The ground equipment required to receive is fairly basic (as satellite equipment goes) and the satellite itself has two “Phase 4” amateur radio transponders operating in the 2400 MHz and 10450 MHz bands. A 250 kHz bandwidth linear transponder intended for conventional analogue operations (Voice,CW etc) and an 8 MHz bandwidth transponder for experimental digital modulation schemes and DVB amateur television.

The BATC (British Amatuer Television Club) have been supporting this very strongly and have deployed a ground receiving station at Goonhilly (yes Goonhilly!!) which has two receivers online - one for the linear transponder (Here) and one for the wideband transponder (Here). Thanks to them for all their efforts - simply brilliant !

The linear (narrowband) transponder receiver works really well and I've heard many stations on it right across the foot print, including Brazil, Germany, UK, Austria, Belgium, Russia to name a few and so I got to thinking that I would like to build a setup to receive and transmit through it and take part in this great experiment!

The ground equipment (for narrow band work to start with) is fairly basic

For receive (X Band - 10Ghz downlink - Vertical Polarisation) - a standard satellite dish, LNB and SDR receiver).

For transmit (S Band 2.3Ghz uplink - Right Hand Circular Polarisation) - with a 5W nominal uplink power 

Dish first -  80cm is good enough although I heard someone using a 45cm for receiving!) and these are quite low cost - offset feed is acceptable and looks more like a neighbours dish !!

Next the LNB - The Es’hail 2 Amateur transponders are at 10.5GHz most common consumer LNBs (Low Noise Blocks) can be used to receive well below 10.7GHz with a 9750MHz local oscillator, so for Es’hail 2 I'll always use the 'standard' 9750MHz local oscillator. 

Virtually any standard LNB for satellite TV will do  - BUT it needs to have a PLL rather than a DLO - so it is more stable and wont drift - Octogon LNB's seem to be quite popular (and work well by the sound of it). This will need to have suitable voltage fed to it to switch the correct polarisation (+12v for Narrowband and for Wideband +18v) via a 'T' feed. I wont bother to detail the switching of the LO in the LNB (using 22Khz tone) as for my use it wont be needed - but that's how you switch from 9750Mhz to 10600Mhz (usually!!)  

This LNB acts as a down converter and so the desired signal for receive becomes :-

10.5Ghz - 9.75Ghz = 0.75Ghz or 750Mhz

The SDR receiver needs to cover this 750Mhz frequency - there are plenty of low cost SDR's out there but I wouldn't by too low cost - look at my choice of SDR at the end which might kill two birds with one stone !

That's the receive setup.

Next for transmit.

There are multiple ways to do this but almost all involve an up converter of some sort to take a baseband frequency - such as 144 or 432Mhz for the IF - mix it with a suitable oscillator and hey presto a 13cm (2.3ghz) tx signal at low power - add an amplifier and your nearly there.

One important point to remember is that you need the system to be full duplex - ie you need to be able to listen to your transmitted signal on the downlink at the same time as transmitting, and so that is why many people I assume seem to use an SDR based setup as well as a 144 or 432Mhz IF transmitter setup - or so it seems to me!

For the antenna you can use a separate antenna  - many WiFi yagis and parabolic antennas are available that will have enough gain / bandwidth. 

Another option is a dual feed to the dish, so only one antenna is needed - less hassle to align and put up but more hassle to sort the feed out.

So what will I be doing ?

I've started to put together the building blocks 

• 80cm or preferably 100cm offset dish (to be purchased)
• Octogon Quad feed PLL LNB (so I can modify it and add an external reference for extra stability if needed - Andy Talbot G4JNT describes a modification here for an external reference feed, and here is the BATC wiki page that details how to do it for using one of the Quad inputs - this is what I will do should I need to with a suitable external GPS linked reference @ 25mhz such as Leo Bodnar's GPD reference or something similar.
• I have also got a dual feed on order when I'm ready to do the transmit side as I only want one dish and so have opted for the extra complexity on the feed side !
• Or I can build a dual feed for the LNB there are several designs around

For the SDR element I've decided to experiment and go for an LimeSDR Mini - this is a full duplex (transmit and receive) SDR transceiver which cover from 10Mhz up to 3.5Ghz and so will also produce the required transmit signal on 13cm as well as simultaneously receiving at the required IF frequency of around 750Mhz.

Class A 30w 13cm Amplifier

On the transmit side I will use the LimeSDR Mini mini and have opted for 13cm class A Amplifier  that I found that can give upto 30W output from typically 10mW input. The LimeSDR Mini outputs 0dBm at 13cm so may well need a small amplifier in front but we shall see !





I received the LimeSDR mini this week - I've already connected it to my portable, added its drivers, plugged it into a suitable USB3 socket and then updated its firmware. All worked perfectly and I've just experimented receiving on 60M and 40M and it seem to work really well - its not really designed for HF but for higher VHF/UHF and SHF - I intend to check these out soon!

The software I've been using is SDRConsole V3 from Simon Brown G4ELI - this is truly a superb piece of software which does both RX and TX and has exactly the functionality that is required to operate with a down converter and synchronise the 13cm uplink so I think I will be using this in future !

It also supports the LimeSDR Mini natively so it makes it really easy to get working :)

I've already donated £50 as a start and will donate more as I use the software more - it really is worth it - superb from my perspective - Thanks Simon !!