For beacon needs at AMSAT-DL groundstation for QO-100 in Bochum there was the need to have a LNB with separate V/H outputs of the IF as well as 12V and 25MHz input. Ideally it would only need 12V for both polarizations instead of 18V which is normally required to switch a Quad LNB to H polarization. A look inside a LQP 04H revealed that a “hard switch” to H pol cannot be done by simply putting a pin high or low. In addition to that a Quad LNB required a DC input on all ports that need to provide an IF output.
So a Quattro LNB Opticum LRP 04H was ordered which seems to be of the same series as the LQP 04H. Cracking the case open reveals a 25 MHz crystal for the LO as well as just one DC regulator instead of four. Also there are four larger black components with a marker that look like diodes on the first glance. The 25 MHz crystal and its caps are already removed on the following picture.
As the outputs of a Quattro LNB are fixed we need to keep the L/V and L/H ports intact and modify the other two that are normally used for the upper band (i.e. LO of 10.6 GHz). For the pictured Opticum LRP 04H the port configuration is High/V, Low/V, High/H, Low/H (from left to right). Low/V and Low/H will be used for IF output. The other are modified for Vcc input and 25 HHz reference input.
First of all three of the four diode-like components are removed from the ports 1, 2 and 4. Marked by larger red Xes in the image below (one of them yet to be removed). Also seven 0402 SMD components are removed from the High/V port and the IF output line from the central ship is cut. The cut is marked by a vertical blue line and the components by smaller red Xes. The green circle shows the 25 MHz crystal and its caps removed.
The result looks like the next picture. All components are removed and the IF line is cut shortly before the via and pin at the chip. (Some solder spillings yet to be removed as well as the black resisitor or inductor at the top left)
The 25 MHz input port is then refactored with 2x 10nF capacitors and a 100R resistor. The two 10nF caps (0402 size) are soldered across the two free pads in the IF path (marked with green circles). The 100R is connecting the IF path to GND (marked by the blue line). And finally a thin threading wire is soldered where the red marker is and connects to the former upper pad of the removed 25MHz crystal. The complete mod is shown in the following picture.
And a detailed view of the 25 MHz path and the three inserted components:
So after this modification the ports have to be used as follows:
- Number 1 (leftmost): Used for feeding 25 MHz (or other frequencies) into the LNB to stabilize the LO
- Number 2 (2nd from left): Vertical output for RX of the narrow band QO-100 tpx
- Number 3 (2nd from right): 12V DC input for powering the LNB and preamps
- Number 4 (rightmost): Horizontal output for RX of the wide band QO-100 tpx
As these technical functions are now fixed of course it needs a proper labeling on the case. So label all the things…
And the other side:
This mod has a few differences (aka advantages and disadvantages). You may use this one or the Quad mod to suit your needs.
Pro:
- No bias-T needed to feed DC into the port that IF is picked up from
- No 18V input needed to receive in hoizontal polarization
- IF from the H/V ports can directly be feed into a receiver (no DC on wire)
- Quattro LNB a few bucks cheaper than Quad LNB
Con:
- Only two ports (one H / one V) available for reception
- Separate 12V line required (may be combined with 25MHz input by removing the corresponding components in the first step)
So this may be a valid option for the scenario described and a few bucks less than the Quad mod. YMMV …