Friday, August 21, 2020

QO-100 Es'hail-2 ground station

It has been a while since I was busy with a ground station for the geosynchronous (geostationary) satellite Es'hail-2 also known as Qatar Oscar 100 or QO-100.

The major delay in the beginning of the project was to receive an assortment of coax adapters. Finally, those were in, now, the down-link was sorted rather quickly. There was a disused 35cm dish, which I used to analog ASTRA reception. When ASTRA satellites turned digital, I lost interest in watching those, so I never upgraded the equipment. Although, I never dumped any of that stuff either.

So, here was my down-link receiver, PLL-LNB with the old 35cm dish in a FUNcube SDR dongle. That worked perfectly. I later replaced the FUNcube dingle with an SDRplay RSP1A, so that I could receive the entire bandwidth of QO-100's narrow band transponder, allowing for locking on the mid-beacon for frequency stabilization.

Concerning the up-link, I decided to go for a DXpatrol converter. I like the possibility to select the baseband, although, I will probably stick with 432MHz.
To amplify the 2.4GHz signal, I went for the omni-present chinese 8W WiFi-PA.

Then came a long struggle of what to do about the up-link hardware.
Initially, I considered an RHCP helical antenna, something in the realm of 15 to 20 turns.
Then I found a 60cm offset dish in the trash. So, what about a 4 to 6 turn LHCP feeding helix? And yes, I wound that thing. But, the mechanical details of holding the thing in place put me off again.
Finally, I decided on a K3TX LHCP patch feed for the 60cm dish. 
I know, 60cm is rather small for a 13cm wavelengnth... 10 lambda upwards make the deal... I know. However, 60cm is what I got.

The dish I got had not LNB/feed mounting hardware, so this is what I came up with.

K3TZ LHCP patch, PCB over Al

You may wonder what the strange structure to the left is, this will be the mount to the dish.
Something not obvious from the above picture, I am using a F-connector for this feed.
Please note that this picture was taken before I filed down the edges to of the reflector to the circle seen scratched into the aluminium sheet.

The patch feed added to the up-link dish

Winds can be pretty strong over here, so I mounted the dish to a concrete parasol stand.

Up-link (grey) and down-link (white)

Note that both channels are using 75Ohms satellite cable. While for the down-link this is fine, the up-link will experience this as an attenuator, in particular over the length I am using for this experimental setup (about 20m).

Having done some experiments, I could hear my signals in both CW and SSB (USB). While CW was easy, single side band was somewhat challenging. I would not count for any SSB QSO with the attenuator in place.
However, CW should be just fine. Have a look how the signal compares to the lower beacon:

Lower beacon and pa1gsj carrier

This was my first day of bouncing signals from QO-100. I know what I need to do now, i.e. building an outdoors cabinet next to the up-link dish.

I hope to be QRV as an audible station on Es'hail-2 soon.


After further improvements, I can now provide relative signal strengths from my receive setup:

  • transponder noise about 32 dBuV
  • CW beacon 58 dBuV
  • my own signal 41 dBuV
I can also report that I made two CW contacts by now, the lower report was 589.