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Monday, 29 August 2016

Doppler, Frequency Inversion, What's all that then?

Well,

As I fiddle, I learn. That's the basic idea anyhow.

So, I've been making a few QSOs through these amateur satellite thingamagigs.

There are a series of Japanese birds called the XW-2 series. Their frequency allocation is as follows:

Now, the number on the far left top of that image is wrong and should read 435.000.

I just had a QSO through XW-2C, the linear transponder (the bit that receives speech on the uplink and re-transmits it on the downlink) are actualy at the following frequency ranges:

Uplink:       435,150 -> 435,170
Downlink:  145,815 -> 145,795

Now, the observant amongst you will note that the Downlink frequency I have listed goes from high to low and the Uplink from low to high. Thats because it's a linear transponder with Spectrum Inversion. So as I tune in the 20KHz passband of the satellite I have to tune +ve in the Uplink and -ve in the downlink (or the other way round).

So when the Uplink is at 435,150, the Downlink is at 145, 815 and when Up is at 435,170 Down is at 145,795. Thats all before you add in the complexity that the Uplink is in LSB and the Downlink in USB. And then theres the further complexity of Doppler.

Now, I like to think of things very simply. If you can imagine a Sine Wave shape, with the right hand end fixed and the left hand end moving left, it is quite easy to see that the frequency is being stretched and is therefore decreasing. Similarly, if the left hand end of our imaginary sine wave was being moved to the right, the wave is being squashed and the frequency is increasing.



Therefore as the fixed point (my antenna) and the satellite (moving) get closer together the frequency that I need to tune to receive the Downlink and transmit to find the Uplink are both increasing, similarly when the bird is travelling away from me, the frequency is decreasing. The effect of this change is dependent on the actual frequency itself, so the higher the frequency the more pronounced the shift needed.

Luckily the Sat32PC software calculates the Doppler for me, but I hope the rather simplified explanation above helps explain whats actually going on.


Fun egh?

Friday, 26 August 2016

QED on the Birds!

Well,

Following my last post here, I've managed to complete my first Satellite QSO.

I'm using SatPC32 to control the antennas and also the Radio:


My first QSO was with RN6MA in LN06uo - Thanks Victor!

We were using the XW-2A satellite; uplink on 435 MHz and downlink on 145 MHz.


So much to learn!

Here's a video of the antennas in action:


And here a quick video of the IC-9100 receiving the telemetary beacon from XW-2A showing the auto doppler tuning.


Here's Florrie the Ham cat enjoying some sunshine:

Local conditions.

Monday, 22 August 2016

Some More Bird Time!

Well,

Following the progress last time, today I have finished the LVB Tracker kit.

The kit is complete and the programming of the PIC done; I had some issues with this part of the project. I couldn't get the PicProg executable as supplied as part of the fileset to function - it would appear to program OK, but the verification failed. There were way too many variables involved so I dug out the PIC programmer I purchased way back when and programmed the PIC that way. Once I had figured out all the configuration bit settings I was up and running....


The image above was taken during the calibration process. Basically the rotator control box outputs two voltages which are representative of the position of the AZ (0-360) and EL (0-180). You tell the software when the rotator is at 0 in both AZ and EL and then again when in 360 and 180. It can then calculate the appropriate voltage for anything in between.

I've chosen to use SatPC32 software for tracking the birds, controlling the rotator and also handling CAT control of the radio to automatically turn the antennas (both AZ and EL) when a selected satellite is in reach, and also control the frequency setting on the radio - including the adjustment for Doppler shift as the bird is moving towards or away from my station.


Here's a quick video of my first ever reception from an Amateur satellite. This is before getting the CAT control functional - just the antennas are moving automatically to track the bird as it passes:


And here is a quick video showing the auto tuning for Doppler (no sound):


So now it's time to do some research and some listening before I decide which satellite and how to make my first QSO. Fun egh?

Here's Miss Luna Cat asleep behind one of my monitors:


Local conditions.

Sunday, 21 August 2016

Following the Birds!

Well,

For quite some time I have wanted to try my hand at Amateur Satellites. Now, I plan to utilise my IC-9100 for this task - it is a full duplex radio meaning I can TX on one band whilst RX on the other.

I decided I would build myself a "proper" satellite tracking antennamabob, and here it is up in the air:


There's 3 elements on 144Mhz and 7 elements on 70cm. The antenna has both azimuth and elevation rotation capabilities using one of these:


It's a Yaesu G-5500 rotator; unfortunately they don't supply the necessary hardware to separate the azimuth and elevation rotators - so I had to fabricate something suitable. I've mounted the azimuth rotator way down the pole and utilising these brackets from Barenco and a Yaesu thrust bearing we have a suitable working arrangement with minimum weight at the top.

The plan is to develop a means of automatically controlling the antennas such that they will auto track satellites using PC based software. I've bought one of these kits from AMSAT, here in early construction:


And here ready to wire up and start to play:


So, lots to follow on this topic!

Here are a few of the feline family members:


Good, egh? Local conditions.