Notizbl0g.

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Opticum Quad LQP 04H Mod

After Octagon is currently not able to provide more PLL based LNBs to be used for SAT mode I decided to have a look at Opticum LQP 04H types. Those are also sold modified by AMSAT-DL for use with their down converter v3 (see [1]). My portable setup is also based on such a unit so I wanted to try a mod of the quad model in order to also connect an SDR stick in parallel (or a DATV SAT RX or whatever).

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This type of LNB uses the same case as the twin variant. Only the PCB seems to differ slightly. The 25MHz crystal sits right in the center on the PCB under a metal shield that can be removed by unscrewing 4 torx screws. Removing the crytal is a little tricky because it is glued to the PCB. I did this by using two soldering irons in combination with a sharp knife to lift the crystal while heating.

Anyway the crystal came off including the pads. Not sure if that would have work properly without heat as there are two traces nearby that could easily be damaged from hard mechanical force. The picture above shows the opened LNB with crystal removed.

In this variant I did not cut off one of the IF outputs to feed the reference but instead built a low pass filter into one of the outputs in order to be able to use all 4 outputs. In this case I chose the connector at the very back of the LNB. The printed inductance was cut as a 2u2 coil inserted. This is the component at the bottom on the following picture.

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Above the IF trace feeding the output at the very back there seem to be a “patch panel” of unused pads. So I did mount a 120pF capacitor and a 330nH coil from the IF trace to those pads. The reference frequency is then using a short thin wire connected to one of the pins of the RT340 where the original 25 MHz crystal was connected. It is the third pin counted from the corner of the chip. The wire is soldered to a small via located just in front of that pin. You may need to remove some of the solder stop paint before.

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Now you can feed a 25Mhz (or other arbitrary offsets) into the back most connector while using it as an output. I.e. connect the WB port of the AMSAT-DL down converter here. The other 3 ports can be used as normal outputs (H/V depending on the voltage fed).

References

[1] https://shop.amsat-dl.org/produkt/qo-100-modifizierter-lnb/