Dish Feeds

Latest News and Discussion about the use of the DATV transponder on Es'hailsat 2
g8gtz
Posts: 1034
Joined: Wed Apr 07, 2010 6:26 pm

Re: Dish Feeds

Post by g8gtz » Mon Feb 11, 2019 8:35 am

Hi Gareth,

That's right - allow about 15mm above the top plate and whatever is needed behind the back plate.

Common method of mounting LNB seems to mill / file down the o/s diameter so its fits in to a 22m compression back to back coupler - and you use that joint to adjust the LNB skew rather than twist the hole plate.

Just heating up the soldering iron to do mine :-)

73
Noel

radiogareth
Posts: 210
Joined: Wed Jan 06, 2016 9:46 am

Re: Dish Feeds

Post by radiogareth » Mon Feb 11, 2019 6:01 pm

Progress on two projects today, one of them DATV. Using a new Octagon OSL SO I opened the case (tabbed, two down each side) and then carefully filed off the two die-cast tabs just behind the horn. Then I hacksawed off the concentric horn unit and cleaned up the edge.
This is a very loose fit in a 22mm compression coupler, in fact it passes through the stop-ring in the centre of the coupling. This is helpful as its not a bad fit in there. To make the 22mm olive grip the LNB it needed sectioning and about 4-5 mm removing equally (2.5 each) from the two halves. With some careful assembly the whole assembly can then be tightened up and securely grips the LNB outer body.
Pictures show the outcome.
2019-02-11 17.00.51.jpg
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2019-02-11 17.02.28.jpg
2019-02-11 17.02.28.jpg (66.4 KiB) Viewed 186 times
Waiting for the 'Rocket' LNB nose-cone to finally size the copper pipe length, in the meantime making up an adaptor ring from HEX central nut to 40mm OD for fitting it all into the LNB holder.
Gas torch at the ready for the soldering job, just a bit beyond my 50 watt Weller ;-)
Gareth

radiogareth
Posts: 210
Joined: Wed Jan 06, 2016 9:46 am

Re: Dish Feeds

Post by radiogareth » Mon Feb 11, 2019 6:17 pm

That was fun :-)
Capture.PNG
Capture.PNG (19.66 KiB) Viewed 182 times
30 mins to print.
Gareth

G7JTT
Posts: 63
Joined: Fri Jun 10, 2016 5:05 pm

Re: Dish Feeds

Post by G7JTT » Mon Feb 11, 2019 7:21 pm

Well took the plunge and cut off the horn on my Goobay LNB and fitted it to the dual band feed lost 4MER on the received signal from QO-100 but I don't have the rocket LNB lens/cap yet hopefully it'll improve the signal again.
https://ibb.co/92ByfPL

g8gtz
Posts: 1034
Joined: Wed Apr 07, 2010 6:26 pm

Re: Dish Feeds

Post by g8gtz » Mon Feb 11, 2019 8:03 pm

Maybe you've put the feed point too far in to the dish past the feed point - presume the end of the 22mm needs to be at the same point as the end of the LNB horn?

Noel

gi7ugv
Posts: 22
Joined: Tue Oct 31, 2017 2:47 pm

Re: Dish Feeds

Post by gi7ugv » Mon Feb 11, 2019 8:04 pm

I had 4/5dB MER with the chopped Venton LNB on my dual feed including the cap then a solid 6dB when swapped to the Octagon.

The positioning of the dual feed was a little too far forward and there was a slight tilt upwards with the weight of the pipe/fitting I was using so there's hopefully a little improvement to be had when I sort out the LNB holder.

G7JTT
Posts: 63
Joined: Fri Jun 10, 2016 5:05 pm

Re: Dish Feeds

Post by G7JTT » Mon Feb 11, 2019 8:42 pm

I tried moving the feed back and fourth but no real difference, I held the cut off horn in front of the 22mm copper and the MER improved to around 6. Will have to experiment some more tomorrow in the light.

John

radiogareth
Posts: 210
Joined: Wed Jan 06, 2016 9:46 am

Re: Dish Feeds

Post by radiogareth » Tue Feb 12, 2019 12:26 pm

My rocket LNB arrived today, the cone 'feels' like polythene or polypropylene and is quite a complex internal shape which I don't fancy reverse-engineering at this point. The tiny sliver I removed and burned also pointed to one of the two plastics. Neither are 'last forever' outdoors in sunlight unless possessed of UV additives, but for under a tenner delivered its the easiest source of a lens at this point.
Its a 'tight snap-over' fit on the end of the LNB and its a LOT easier to remove if you soak the red bit it in a mug of boiling water then apply a 'twist and lean to one side' motion to get it off.
Its a two piece mounding so if remote mounting some form of retaining method would be a good idea for the outer part. This will make sense when you have one in your hand. The inner is a snug fit inside the 22mm copper.
Gareth

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