Idea Box. QO-100 Downlink Reception.

For quite a while the setup for my QO-100 activity has been rudimentary:

For uplink I have used an old IC-821 as transmitter, with a lot of attenuation, followed by a low cost Chinese up-converter (BU-500) indoors, about 15m RG6 coax, with a so-called 8W WiFi booster that can deliver 2 - 2.5W without modifications, feeding a 4x patch "WiFi antenna and a 1.1m dish reflector.

This provides a decent signal on the downlink side, and certainly never overloads the transponder (triggering LEILA).

For the downlink I am using a 60cm dish, a low cost synthesizer controlled LNB, modified to be controlled by an external 25MHz reference signal.

The 25MHz reference oscillator is indoors in the shack in order to minimize the temperature drift. As this is an uncompensated DIL oscillator there is, of course some drift, up to a few kHz to each side. Actually not too bad for such a simple setup.

The LNB converts the the 10489MHz signal down to 739MHz, so for now I have used an older AOR multimode scanner receiver, the AR8600. This works, and I have made some QSOs, and often participated in the Danish-speaking net on Sundays. It is a bit inconvenient with the drift, as I have to compensate by manually checking the AR8600 frequency for the beacon, and then remember to calculate the offset.

Further, the IF filters in the AR8600 are low cost ceramic filters, so for SSB and CW the selectivity is not what I am used to from my HF/VHF transceivers.

Here comes the idea: The AR8600 has an IF output on 10.7MHz, with a bandwidth of 4MHz. Why not use that to feed one of my HF radios? That way I can use the better filters of the HF radio. On top of that, a quick manual compensation of the LNB frequency drift can be made by switching to one of the beacon frequencies and retune the AR8600 so the beacon is in the pass band of the IF receiver. Then the recalculation of the offset becomes unnecessary.

This is the simplest way to improve the downlink receive system with the equipment I have at hand.

It does require using two radios, as the AR8600 is simply used as a second down converter.

If I want to eliminate the AR8600 from this there is another idea. This requires more construction, so I think I will use the AR8600 in the first instance.

I have some older TV tuner modules with synthesized local oscillators. With a bit of programming of the synthesizer chip using a microcontroller, the Arduino or the like, this can function as a down converter to an IF of 28-40MHz. One little disadvantage is that the TV tuner as-is inverts the IF band. 

This can be eliminated in two ways:

1) a second down converter inverting the band once more. This adds complexity to the system, but can be done without too much building.

2) retuning the RF filters of the tuner, so the LO moves below the signal input frequency. This is the simple way, but requires more test equipment. I do have enough test equipment to do this, so if I go the TV tuner way, this is the likely way to do it.

For now, the AR8600 with HF receiver will be the way, after all the Christmas activities. I am looking forward to improving my QO100 setup.

I am still looking into what next year's "challenge" will be. It should require some activities from my side, on the other hand it should also be fun.

I do think that a part of this will be running the most used parts of my station on solar (with battery backup, of course) hopefully on solar power, even through the winter. I may have to switch parts of it on mains power in the poorest sunlight conditions. The really power hungry parts, like big linear amplifiers will be running on mains power in any case, but they will not be running a lot in any case.

Using only the IC705 in December I have been able to get the battery up to 80%, but that has been with saving the time I was using it.