LNB cables

I had an interesting problem with the Es’Hail-2 satellite LNB. Actually, not so much the LNB as the cables.

I have been running the LNB IF over the supplied 75R ‘white’ cable. This is not quite long enough to reach to the selected position of the Minitoiuner. On the other the 25MHz reference runs over a much longer RG58 cable, but only to the rack position of the Leo Bodnar Mini GPS source.

In order to close the shack door and generally tidy up the cable runs, the cables have now been brought into the shack through the wall gland cable entry. Because of the incompatible cable lengths decided to swap over the functions of the two cables. The shorter 75 R IF  cable now being used for the 25MHz reference and the longer RG58 now the IF and LNB power cable.

Although the Minitoiune display showed a strong signal, it was clear from the phase constellation that the software was struggling to obtain lock. I couldn’t get a picture from Freesat.

Swap the cables back, temporarily, and all was well again.

With the high gain of the LNB the Minitoiuner should be OK with the much longer IF lead. I changed the reference drive level over quite a large range with no success, just in case. 

Could the reference be objecting to 75R cable or was something else happening? I decided to reset the 25MHz reference drive level and use another  50R coax  cable reference  able connection to the LNB. This worked absolutely fine. 

I really am not sure whether the problem was down to impedance or to cable loss (at 25MHz?). However, I will replace the crappy white 75R stuff with a length of RG58 tomorrow and see if all is still OK.

Entertaining times!

Sam

LNB received

Second Octagon LNB received. Now to open it and check which reference it uses. 25 or 27MHz. 25MHz I hope!

Note that this one has 1301 rather than 1309 on the label, as was expected.......opening it is the only option to if I want to be sure.

And, very disappointed. 27MHz reference. Apparently I misread the online data on LNBs and it was actually another 1609 that I needed.

I won’t be able to try the tests I wanted on this one and as the ordering process seems to be pretty random, I don’t feel inclined to order yet another one unless I can specify it as a 1609.

I did try to use my FT817 to listen to whether the reference was 25 or 27MHz. Even with the antenna on the 817 very close to the LNB I could not detect any carrier at either frequency. There was a tremendous amount of digital ‘hash’ however.

I eventually opened the LNB (carefully) to check that it did, indeed, have a 27MHz crystal (in fact two) and the 3560 PLL chip.

Sam

LNB info

DG0OPK.darc.de has details of the Octagon LNB with the 25MHz single crystal that I use in my LNB for Es’Hail-2 satellite system. This is supposedly the low cost LNB using the RT320m PLL chip in the OTSLO twin LNB. It looks like there is lots of info on this LNB and others on the uhf-satcom.com web page links. 

I did notice that a lot of the published info, on modifying these LNBs, refers to the version with the 27MHz crystal. Apparently, several of these have two  crystals and two PLLs. The Octagon PLL LNB i have only has the one crystal (25MHz) and it easy to modify. The first visible difference, inside, is that the ones with the 25MHz crystal has red solder resist, whilst the 27MHz version has green resist. Of course, this doesn’t help from the outside!

I haven’t checked but the 25MHz ones (which might be the ones you can drive with a 24MHz reference for a better (higher) IF) have a code 1609 instead of the 1306

It’s all a bit of a minefield when ordering!!!!!!!,

Further Progress on Es’Hail-2 system

As mention on my Twitter (DXing) account, I have planted a 3inch diameter, 6 foot, galvanised pole in a 2 foot deep hole near the shack. The hole was back filled with 10mm gravel (from Homebase at £2.50 bag) and then top soil on the top of that.

My 90cm Channel Master offset dish is attached to its original az/el non-motorised mount. I’m glad I didn’t through that out!

I had to fabricate a new saddle top to hold the LNB as I’d lost the original and besides the 40mm diameter LNB would not quite fit the original clamp.

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Currently I can easily swing the dish between 28E and 26E. The Freesat TV at 28E is very strong here in East Anglian, using the 90cm dish. The 26E signals I can see might be from BADAR, but I need to check this.

I need to connect my SDRPlay RSP2Pro to the LNB output and check what the noise is like at 739MHz (The IF from the LNB when receiving the Es’Hail-2 amateur narrowband (voice/data) signals. G8DKK has suggested an attenuator will be required. This will cause a problem as I intended to use the RSP2Pro internal bias tee to drive the LNB. As it happens, the 4.7V output from the RspPro2 is too low for the LNB, anyway, so an external bias tee and 12v supply for the LNB are required.

Sam

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

Preamp builds

The last few days have seen a flurry of preamp building. Following The DX Shop decision not to supply built VLNAs I have had a number of (nice!) requests to build kits for those who either felt unable to cope with building an SMD kit with 0603 size parts, or who don’t have the equipment to align the VLNA for lowest noise. As I am not set up for production of built preamps, it has taken a while to get round to clearing my backlog. I still have a few ‘specials’ to build, but these should be done soon.

I have a new batch of solder paste and this is producing nice results with my BetaFlow reflow oven system. The results have been consistent and little rework has been necessary.

The picture below shows the results of measurement on the most recent VLNA23.

I might even get round to building one for myself.......

Sam

G4DCV

I was able to briefly visit with Paul and his lovely partner,  Miranda, on my way back from Heathrow, earlier this evening.

I had a video item to drop off. Some of you may recall does a lot of the RSGB video work.

Paul and I had a nice chat about our earlier days in amateur radio.

A most enjoyable visit to the Berkshire/Surrey borderlands.

Sam

Building preamps

I was asked to build another 1694MHz range VLNA for a customer who wanted a more weatherproof version of the  VLNA. I am in the process of mounting the VLNA in a small ABS plasic box (box within a box) with the input connector accessed through a hole in the box and the output connector cabled to the VLNA from a bulkhead SMA. This has been an interesting exercise in weatherproofing......

Sam