Wednesday, 26 December 2018

Persistent cough

Whatever the bug is, it is persistent. It just won’t clear. It seems to be very common, as well. I hear a number of people reporting a similar problem.
Hopefully, not too much longer.....three weeks is long enough.......

I have managed to do a bit more observing of the Es’Hail-2 satellite and further optimised my receiver. I still can’t get a good comparison with the beacon reception by other amateurs as each seems to have a different set up and hence way of making measurements on the 10706MHz engineering (broadcast) beacon. The problem seems to relate to making a measurement in the beacon centre carrier level in a known resolution bandwidth. Simple  you’d think? A number of levels have been given for signal level, but without resolution bandwidth these are meaningless.

This morning I decided to have another look. The engineering beacon centre frequency has always sounded ‘rough’ and showed several ‘carriers’ within the narrow passband I was looking at. This is with the LNB I had modified for external 25MHz reference input. It just didn’t ‘feel’ right. That radio engineer’s feeling for a signal? Not knowing whether the engineering beacon actually had some form of data modulation, close to the carrier, it was difficult to tell what was going on. 
As a test I set my RF Explorer signal generator to 10706/4MHz and connected it to a WA5VJB LPY antenna. The resulting forth harmonic showed quite strongly on the SDRUno display and with the same ‘data modulation. It was now clear that the external locking on the LNB was not working as intended.  As an aside, the TCXO in the RF Explorer showed within a few hundred Hz of the beacon centre frequency. 
I have a spare,  unmodified, Octagon LNB (27MHz reference version), so I substituted it for the modified one and looked again at the beacon. Now the beacon  centre frequency was clean and sounded it on the headphones. 
I’ll waterproof the system again, later, and remeasure signal levels.

I have a spare high performance 10GHz LNA and horn feed system. I am going to look carefully at using that for the satellite in preference to the LNB. Although that is a cheap approach, I am beginning to wonder if the noise figure will turn out to be too high, down at 10489MHz?
I’ll need to use my spare DB6NT transverter and the feed/LNA and an IF at 265MHz
The Minitouner will tune into the required frequency range, so no need to worry about that.

Happy New Year

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