2019-02-26

Receiving Es'hail QO 100 With Own Equipment, Stage One.

The Octagon PLL LNB has arrived and the set-up is beginning.
Today I got my initial setup for receiving OSCAR 100 up and running :
This is how I did it:

Assembling 60cm dish
Mounting dish on the"main" mast
Cable from shack to LNB
Feeding DC from the sat receiver through a two "output" signal splitter, so the next RX can be safely connected.
Trial and error alignment to maximize signal from Hotbird at 13deg E
Setting azimuth for Astra1 at 19deg E
Optimizing elevation for Astra, and adjust the elevation a tiny bit down.
IC-R7100 would not start up, so got the older AOR8200 down from the upper "shack".
S meter showed full, so inserted an attenuator.
LO deviation from standard frequency was unknown, so initially tried to tune RX +/- 50kHz. It turned out to need 200kHz, meaning that the reference XO was about  500Hz too low.
Optimized azimuth for OSCAR 100, the transponder noise is audible and the beacon (and other signals) quite strong. Maybe more attenuation needed.
Frequency stability is sufficient to be able to make a QSO, but too much for comfortable operation. Frequency was seen to vary about 20kHz with the current, relatively stable weather.
Not bad for a day's work.

Better frequency stabilization is needed. For the moment I will not modify the only LNB of mine that I know is a PLL type. Two new low cost ones are on the way from a "low cost" shop, known to be PLL types.

One day later :

I went to the shop, anyway, could not wait for the cheap LNBs to arrive :
Purchased cheap LNBs at Harald Nyborg, a low price shopping chain nearby.
The price for a single LNB was DKK 58, a TwinLNB was 139, and the Quad was 199.
Tested those and others I have purchased lately.
All single LNBs were PLL types Octagon OSLO and the locally purchased - branded Maximum ST-11, as expected, because others have tested them. All were relatively stable and with a clean tone reception from Es'hail, albeit at different down converted frequencies.
A cheap Twin LNB branded "Goobay" was stable, but the tone of the received/down converted signal was not clean. Phase jitter, maybe.

The other Twin LNB, Maximum ST-12 sounded clean.

The quad LNB from Maximum turned out to be a DRO controlled model, though not extremely unstable, and not suitable for narrow band operation.
Same is the case (as expected) for an octo LNB from Octagon.

The quad LNB from Maximum and the Twin LNB from Goobay are hereby relegated to use for satellite TV only.
Two more Maximum single LNBs and one Twin LNB are on the way, still, so I decided to start taking the Twin version apart. The sealing of the shielded box turned out to require  quite a bit of work, so not finished yet.

Finally finished disassembly of the Twin LNB, and things look good for a simple modification.
This simple modifications sacrifices one of the IF outputs for use to connect the external reference in the simplest possible way, and requires two cables to be connected to the LNB for just one down conversion. The "reference input" will be completely disconnected from the IF output/DC input, cutting the PCB tracks to the F connector. Ole, OZ2OE mentioned that the DC input circuitry may be the source of attenuation of the reference signal in the single LNB versions, where it is connected to the DC regulator through a low pass filter with a cut-off frequency suitable for the IF, and not to the reference frequency.

For the experimentation I needed a sufficiently stable signal source for approximately 10GHz. The initially useable solution turned out to be a cheap Baofeng transceiver transmitting on 432.000MHz. This provides a decent, if drifting, drifting signal, enough to check if the LNB is locked to the reference.

A better 10GHz signal source is planned, and probably involves a relatively stable crystal oscillator, or possibly a stabilized DDS generator with a simple multiplier made with a Schottky diode. The housing and antenna could be a now discarded LNB - it had lost its protective sealed cover for the horn, and is useless anyway, and the horn antenna has not rusted or anything, so after a bit of cleaning the feed horn should work nicely, at least for indoor work.

Stage 2 will involve doing the modification for using an external reference, and making that reference source. I still have to decide how to proceed, exactly. When it is done I should make a description of the modification I use.

No comments: