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Sunday, 24 February 2019

Portsdown - again?


I've been building myself another Portsdown DATV transmitter.

This is the Portsdown 2019 - instead of the Filter Modulator board in the last version, this uses a LimeSDR Mini.

I'm rather pleased with this new build, it's a lot neater than the 2018 version I made:

You can see the LimeSDR in the picture above, its in a 3D printed case - that's now got a 20mm square fan fitted.

The front panel is a lot better than the last build, if I had got the holes for the LEDs upright it would have been even better.

I wanted this second Portsdown so I can take it portable without destroying the shack to remove the 2018 version.

I'm rather pleased with this.

Sunday, 17 February 2019

Es'hail-2 - really?


I've just lashed together a first attempt at receiving the downlink from Es'hail-2.

If you have been asleep, the is the first ever Geostationary Amateur Satellite and is a bit fab 'n' groovy!

I'm just using an Amazon sourced LNB:

I've stuck it on a dish I had lying in the hedge and attached it to an Azimuth and Elevation rotatormabob - you may remember that setup from here.

There's an LVB tracker with computer driven elevation and azimuth control.

I pointed the dish in very roughly the right part of the sky and then tuned around where I expected the signals to be, with the narrow band transponder downlink at 10489.550 - 10489.800. I've subtracted the 9750 local oscillator in the LNB.

I then found some signals and used the rotator controller to peak the signals - I've ended up at 149 degrees to the south and 18 degrees elevation - there will be many, many errors in my setup at thus time.

I'm a bit off frequency, and also drifting a touch. I need to add external frequency lock to the LNB. I've also started to setup an uplink based on the system we made here.

But I've certainly found it:

So the low beacon on the narrow band transponder is sending:

5i 5i 5i de qo-100 BK dl50amsat

and I am receiving this at a constantly drifting down frequency, currently at:

739.306 MHz on my SDR. So I add the 9750 MHz Local Oscillator and we get 10489.306 MHz

If should be between 10489.550 and 10489.555 MHz so I am a bit out of bonk and drifting.

Next job - lock the LNB to a frequency reference!

Much more to follow on this topic!

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** UPDATE 1 **

I've modified my LNB to take an external 25MHz frequency - so I can feed it with a locked reference.

This has been done in accordance with the instructions here.

I'm feeding the LNB with some cheap co-ax from Amazon and I have replaced one of the "F" connectors with a BNC and attached it to my Leo Bodnar reference which I have set for 25MHz.

According to the instructions (well, read box) from the LNB:

Model: OQSLG Green HQ
Input: 10.70 GHz - 12.75 GHz
LO: 9.75 / 10.6 GHz (10.6 with 22KHz signal on coax)
0.1dB noise ratio
Gain: 60-65dB
Horizontal 18V; Vertical 12V

Now, with the 25MHz external reference, the low end beacon on the Narrow Band segment of the satellite is exactly on frequency:

I'm still worried about LNB skew as switching to horizontal doesn't null out this beacon completely = not even sure if it should, but I am definitely not seeing the DATV beacon yet so more fiddling is required.

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** UPDATE 2 **

I've fiddled and now can receive the DATV beacon:

This is really quite fantastic!

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