As you will of read in my previous post, Building the MiniTiouner V2. The reason behind building this was to enable me to receive QO-100 ‘s Wide Band transponder for DATV.
After finishing the Build of the MiniTiouner. The following day I put together a rather messy, temporary, setup so I could connect the MiniTiouner to the coax from the old sky dish on the wall. The dish wasn’t used for Sky TV, so I thought id put it to good use.
The Testing Setup
In the image above you see the 12v supply to power the MiniTiouner (bottom left), an analogue satellite receiver to provide 18v to the LNB (Top Left), On the right is the MiniTiouner itself with the USB Cable going up to the laptop sat by the open window. A power block splitter, seen in the middle, is used to prevent the 18v feeding into the MiniTiouner.
If you don’t have a spare Satellite receiver to provide the LNB Power you can use a device called a Bias-t. This is a small box you put inline with the coax which injects DC voltage up the coax to the LNB but blocks it going back into your receiver.
I will be working on fitting a switchable LNB power supply to the MiniTiouner to remove the requirement for an external source.
MiniTiouner Software Setup
To be able to align the dish to the beacon signal I wanted to pre-set as many of the parameters in the software as possible. This is so I wasn’t relying on the ‘auto’ options. Finding the needed settings is relatively easy. The frequency is found on the Band plan which is currently presented by the BATC here. On that page is all the ‘channels’ and there frequencies. To know which channel to chose you can look at the BATC Wide band Spectrum for QO-100, this is available here. From the spectrum you can see the beacon is in the first 2Msymbol channel, ‘2MS1’ on the band plan page. The spectrum also tells you the signal is 2Msymbols, DVB-S2, QPSK and 2/3 FEC. I put this information into the software as below:
Frequency, Symbol Rate, Offset, Mode & FEC
In the above image you can set the SR (Symbolrate) in kilo-symbols. You can see i have entered 2000 Kilo-symbols or 2MSymbols. I have also entered the frequency for the 2MS1 channel.
Under the frequency box there is a box to put in an offset. If you are not familiar with using an LNB then the basics are that the LNB will recieve the 10Ghz frequency from QO-100 and then convert that down to a more suitable frequency to send down the coax. This conversion is done by using a Local Oscillator built into the LNB. This basically drops the frequency by a set amount. In the case of most LNB’s this is 9750Mhz. This means if you put this figure into the offset box you can type in the actual receive frequency (The frequency actually transmitted by the satellite) in the frequency box and the software will work out what frequency will be coming out the end of the coax for you.
Below this offset box is some pre-set buttons you can program in the minitioune.ini to make switching the SR and frequency easier.
Next below that on the right is the ‘DVB mode’ as per the information from the spectrum monitor, set this to DVB-S2.
Finally ensure that the box next to 2/3 is checked under FEC. You can un-check the others to improve detecting the signal as the sofware will scan through all of the checked FEC’s until it finds the one being transmitted. Seen as we know the correct one, we can un-check the rest.
The settings in the above image are not required to be entered manually if you have ‘AutoPID’ turned on. you can enter them manually yourself to aid the decoding of the weaker signal while aligning.
For info, the PID numbers you can this of as different channels on one frequency. Each video stream will have its own PID number and one or more Audio PID’s. For example on broadcast signals you may have different audio for normal stereo, surround sound and audio description etc…
Again at the top of the image you can see some more buttons which can also be preset in the minitioune.ini file. These buttons will get replaced by PID’s found by the ‘AutoPID’ system if turned on. (Revert back to those set in the .ini on restarting of the software)
Moving outside, I had the ladder setup ready by the dish.
As per my previous post I started by aligning onto the ASTRA 2E fresat signals at 28 degrees East. Doing some checking online, with one of the many dish alignment sites, I found i needed to move the dish around 5 degrees to the south and 1 degree higher in elevation to get to where QO-100 should be.
Having the laptop on the house windowsill was not the best solution. One time when I climbed down the ladder to check the signal, I found a frozen image on the screen so had obviously received it briefly for a second or 2.
To solve this problem I found a USB extension cable, moved the laptop outside and propped it up on the boot of the car. This Allowed me to check for the signal while still up the ladder.
So first i loosened off the Azimuth clamps and moved the dish what i thought was about 5 degrees. At first I received nothing so i decided to do a VERY slow sweep from the Astra position southwards.
While I was sweeping I suddenly started getting a broken up signal. I mentally marked where this started and continued the sweep. Going until I lost the signal again.
I moved the dish back to where I thought the midpoint was between me getting the signal and losing it again. It was here I locked off the Azimuth and loosened the the elevation. Tweaking the elevation to get the best signal I could.
Understanding the Minitiouner Meters and Graphs
When aiming your dish you should be looking at the meters above. Basically to get a signal you need all of the dots / ‘Lights’ to be green to decode the video. The three on the left indicate if you have the carrier locked and whether the software is locked to the timing of the signal, This is important for digital transmission. The next two meters are the power received. In the case of the minitiouner, this is after the built in pre-amp. The second being the MER (modulation error ratio). A basic explanation of this is it is the Signal to Noise of the received digital signal. So Higher the Better.
The final graph is the constellation diagram. This is a 2D representation of the the Digital modulation of the signal. Going clockwise from vertical shows the Phase of the signal and the distance from the centre being the amplitude of the signal. Basically the better the signal you have the better ‘grouping’ or ‘clumps’ you will get. Spots all over the graph show the noise in the signal. QPSK (the QO-100 Beacon mode) would be grouping at the 0, 90, 180 & 270 degree positions.
Back to the Testing….
I would of liked to of gone back to tweaking the azimuth but light was fading and it was starting to get a bit chilly.
I locked off the Dish to go down and have a closer look at what signal I was getting. The signal was very weak with no grouping at all on the constellation graph and a MER hardly registering, Only reading 1 at best.
But I had done it. With It now being dark outside I Packed up and called it for the evening. Tweaking to be done another night.
One thing I didn’t adjust the first night was the LNB skew. This is the angle of the LNB in its clamp. This is necessary as it aligns the Vertical and Horizontal of your LNB with that of the Satellite Signal. In strong signal areas this is less critical as the intended polarisation is strong enough to not be affected by those of the other. For week signals though this can be a really critical settings. To do this I checked online and found I needed to add more skew then what the dish was currently set at for the Astra Sats. I slowly turned the LNB in its holder to achieve the best MER.
Since Adjusting the LNB Skew I have managed to get my MER up to 3 on the beacon (See the image of the meters above) and on my first decode of another amateurs signal was getting flashes of 4MER.
Receiving the Beacon
To follow on from this post I have published a Project update.