QO-100 A1A up-link idea

This is something I had in mind for quite some time by now. What about an A1A only up-link for QO-100?

This is an old idea. At the time, this idea was to create a CW transmitter for 70cm based of a 2m signal. I have seen similar attempts to get something transmitting on 3cm. So, why not on 13cm?

Having done some "maths", I came up with a carrier of 96MHz, which is available as a regular crystal.

With a factor of 25, this will result in a 2.4GHz frequency.

Now, why is that interesting? The multiplication of 25 can be achieved with 5 x 5 .... dahhhh. Yes, sounds simple enough. Here is the interesting thing, it should be easy with a square-wave oscillator to generate 480MHz. At this frequency, it is pretty easy to build a strip-line filter or cavity resonator to clean the signal. Now, we just have to multiply the signal again. So, we might want to use a non-linear amplifier again, in order to create all the wonderful harmonics. Again, a 2.4GHz resonator should not be to hard to build.
And here is the idea. What if we used a rather high powered amplifier at 480MHz, which is easy to build, and a non-linear element to generate all those harmonics at decent power.

With a VTCXO of 96MHz, slightly pulled by a few kHz, one should be easily creating a signal in the CW band of QO-100, using the above mentioned method.

QO-100 Up-link update

 The last few days have seen a little bit of modification and optimization to my setup. Mainly, the shortening of the helix feed. While I was monitoring my A1A signal on the downlink, I gradually cut windings of the the uplink helix. I was not sure if I could see any difference in signal strength, to be honest. Anyway, I ended up with this:

Downlink (left) and Uplink (right)

The dishes are ducked down for a reason. This is my roof deck, we often experience heavy winds in the Netherlands. With the dishes sitting low, weighted down, the positions will be stable over the course of the year.

Presently, the UL uses 10m of RG-6 cable, the original one with the hollow dielectric. This length is certainly not ideal. In the near future, I will build an outdoor unit, sitting next to the UL feed, housing the converter and the PA. This should improve my signal by some dB.

For the time being, all I heard was that my signal could be stronger, but was fine to copy... what more do you want?

73!

SDR and the DJ-Tech DJ-Mouse

Here is what you have missed, if you are not in the world of DJs.
The DJ-Tech Mouse, which employs a super-nice big wheel in the center. Have a look:
https://djtechtools.com/2009/08/20/the-dj-mouse/

Guess what this wheel can be used for in any random SDR software.... a VFO.

QO-100 ground station update

My previous post show tons of opportunities for improvement. The more I was thinking about those, the closer I came to my initial gut feel, i.e. using a helix as a feed for the up-link dish.
In fact, the helix was sitting on my desk for quite some time by now. I had doubts how to mount the helix in the first place, also matching appeared to be a big deal, without the help of any decent GHz-capable measurement equipment.

However, seen that no matter what I did, I could not really improve the performance of the up-link. Essentially, I spent two entire night to find the best position of the dish. (Night-time, so nobody is on the satellite, avoiding to disturb more senior users)

When listening to traffic on Es'hail 2, I often heard that operators switched from patch feeds to helical feeds for their up-links and reported better results with those. Was my gut feeling correct?!

So, today, I returned to trusting my gut feeling. So I removed the patch from the weird reflector / holder shown in the last post. I used a small piece of PCB to form a base, essentially a mount, for the helix. Yes, I could pretend that this was a carefully calculated matching strip for matching my 75Ohm SatTV cable to the helix, but it wasn't. I dimensioned and adjusted the PCB just such that the helix would be - more or less - in the center of the reflector.

note the remainders of glue where the patch was

Feel free to count the turns, which would result in a little of 6. My idea was, that I could always cut some off. It is much harder to cut wire on ;-)

The photo shows, it is night-time again. So, why not firing up the station and do some test transmissions?
And how right was my gut?!

lower beacon at 69dBuV

What a difference! My signal is now just 9dB weaker than the lower beacon!
Of course I had to do some side-band test. And yes, now I think I am QSO worthy.

The present setup still employs the "attenuator" made of about 10m of 70Ohm SatTV cable. So, as long as I still have not yet figured out how to build an outdoor unit (PSU,TX-converter and PA in a weather-proof box), I still will be able to do one or the other QSO.

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.

Update

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.