Es’hail-2 receive system

Since the successful launch of Es’hail-2 satellite I have brought my Ku band LNB out of its hidey hole  and proceeded to check out the modifications I had done previously. I had previously opened the Octagon PLL LNB and performed the G4FRE  version of the external reference modification.

Dave used one of the two F connector IF outputs as an external 25 or 27MHz reference input. This IF output can no longer be used as an IF output, of course. The remaining IF output being the only one now available.

Dave’s modification is described in the September 2018 BATC magazine (well worth the membership fee).

The modification involves opening up the LNB and cutting a track. A 1nF ceramic capacitor is then soldered between the pad where the IF connector a appears and the nearer of the two crystal pads. A short wire is required if a 0805 SMD capacitor is used. I elected to use a bigger 1206 size capacitor and cut the track further up so that I could bridge the gap between the required pads with the capacitor. In the event I still needed a very, very, short wire to complete the gap. Why do it this way? Dave had commented that he had observed some instability and had to reroute the wire. I haven’t observed any instability doing it this way.  I may just have been lucky.  One other comment is that I did seem to require a little more 25MHz drive, at -4dBm, but that might be due to using a longer RG58 coaxial cable to get from the external 25MHz source to the LNB.

Two versions of the Octagon PLL LNB seem to be available. One uses 27MHz reference, and may be an older version. The other one uses a 25MHz reference.

As my stable reference source I used a Leo Bodnar GPSMini. This can produce too much output. I used mine at 8ma drive (the lowest setting) and then a 3dB attenuator before connecting to the coax cable at -4dBm.

Replacing a standard DRO LNB, that had come with my 45cm dish and tripod (described as a caravan system on eBay), with the Octagon PLL LNB, the Sky and Freesat digital satellite TV signals were indicating about the same signal level on the MiniTouner receiver. A weak 10.4896GHz signal from my sweeper, radiated by an WA5VJB LPY antenna connected to the sweeper output, produced a very respectable signal on my spectrum analyser connected to the LNB, and tuned to 739.5MHz,  as the IF.

My  next stage is to ‘plant’ a 3inch pole in the garden and then mount my 90cm Channel Master offset dish on the top of it. The CM dish mount is designed for this size pole. The LNB will attach to the dish 40mm clamp.

739MHz IF output on my analyser