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Saturday, 4 November 2017

Hacking the Schwaiger SPG101 into an analogue satellite modulator


Last year I posted about a curious device, the Schwaiger SPG101 "LNB tester":

I finished my review with the thought that it should be easy to hack this device, to show a composite image instead of the test image with a grid.

Well, today I had some free time and so I finally looked at how to hack this device. I found the trace that transports the video signal from the generator and I interrupted it. Three wires were quickly soldered: one with the generated grid video signal before the trace interruption, one wire from a chinch connector I fitted to the case and a third soldered right after the trace interruption.

The idea is to switch between the external composite video input on the chinch connector and the internal video generator.

The results are promising, but not perfect:

There is a nice spot on the case, where a CHINCH connector fits in nicely!

Just place the modified SPG101 somewhere near the LNB.

 Tune the Satlook Digital Color to 11.288MHz.

And look at the video in analogue mode.
This is the original test pattern produced by the internal ZNZ234E.

Changing the jumpers and feeding some composite video on the CHINCH connector, we get a "real" satellite transponder on 11.228MHz. Best of all: it is in colour!

The problem is that the video signal from the generator is still visible over the external composite video signal. Just interrupting the trace is not enough. Because there is no space left for better shielding, I decided to cut another trace: the trace that powers the ZNA234E video pattern generator. Vcc is on pin 7, but naturally I got it wrong in the first attempt and cut the trace of the CROSS HATCH output on pin 14...

So I had to retrace that one, first. No harm done, as I am considering getting a switchable knob with 5 positions, since this video pattern generator can actually produce horizontal lines, vertical lines, grid, dots and a gray scale!

Because I did not have any switches at hand, for now I used two jumpers: one is to select between external or internal video, the other powers the pattern generator on or off.

Hopefully I can find a suitable switch to replace these two jumpers.

Now I can not only test if an LNB is working, I can actually broadcast video on 11.288MHz!

This is useful to test analogue SAT receivers, prior to modding them for ATV use. Another application is to test and/or review satellite field meters which still have an analogue mode, like my Satlook Digital Color.


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