SETI uses for old Satellite LNBs

Any second-hand LNB will contain at least three HEMT-FET devices, but the older LNBs offer much more! For instance, the original 'bullet' and 'Blue-cap' LNBs (see photo) both contain 5 HEMT-FET, two 15-20dB MMIC devices and a dual schottky mixer package - not bad for 2 to 3, for which these can be picked up for both in surplus magazines or radio rallies. Newer LNBs now tend to use an integrated mixer/lo/if amp package, which is much less useful really.

The easiest part of these LNBs to use without removing components is the two stage MMIC IF pre-amp (see link).

To retrieve components, just drill out the 4 rivets (same on each type of LNB). Then unscrew the half dozen or taptites that sandwitch the pcb. Before this can be completely removed, even though the inner casting has been removed, there is still one additional taptite securing the regulator IC. Also unsolder the connection to the 'F' connector. In the case of the bullet LNB, the pcb will look as follows:

The lighter coloured side of this multilayer, composite board is ptfe. This side contains the five HEMT-FETs and the mixer. It is easy enough to follow the signal path from the pcb track, where starting at the horizontal and vertical antennas at the bottom of the board, each signal passes through a switched HEMT-FET before joining going through a further two stages (LH side of board as shown above) before passing through the band pass filter at the top, till finally reaching the mixer just below the top rh corner. This mixer is also fed from the fifth HEMT-FET, which acts as the local oscillator controlled by the circular ceramic puck, clearly seen just high and to the right of centre.

On the other, darker coloured side (ordinary fibreglass board material) is all the regulation and switching ciruitry. However, at the top left above, you can see the two 15dB gain MMIC devices, which feed to the output 'F' connector, which was disconnected when the board was removed from the housing.

As an example of usage, see link, which makes use of both MMIC devices and the single schottky mixer package.

[The boards shown are actually from bullet LNBs. However, the bluecap circuitry is virtually identicle, though on a larger pcb]