Dish Feeds

Latest News and Discussion about the use of the DATV transponder on Es'hailsat 2
g0mjw
Posts: 668
Joined: Sat Sep 20, 2014 9:15 am

Re: Dish Feeds

Post by g0mjw » Tue Dec 18, 2018 5:03 pm

It's a little bit worse a dB or so, than my Chaperal feed horn for MER, I suspect the sidelobes are worse.

Mike

m0eyt
Posts: 4
Joined: Wed Nov 14, 2018 3:30 pm

Re: Dish Feeds

Post by m0eyt » Tue Feb 05, 2019 9:23 am

Hi all, had a few requests for the CAD dimensions for the patch that Mike worked on to design, so here it is.

From tests it certainly appears to be a good LHCP.

regards,

Paul M0EYT.
Attachments
patchdims.png
patchdims.png (46.77 KiB) Viewed 369 times
esh2_feed.jpg
esh2_feed.jpg (346.73 KiB) Viewed 369 times

g0mjw
Posts: 668
Joined: Sat Sep 20, 2014 9:15 am

Re: Dish Feeds

Post by g0mjw » Tue Feb 05, 2019 10:06 am

Simulations indicate this will work well but it may not immediately match as it is sensitive to getting the dimensions right. Working to 0.5mm tolerances is difficult with hand tools. A good match can be achieved with a little tweaking once built if you have a VSWR meter for 2.4 GHz.

I am currently working on an update to this design to include 10 GHz lens being developed by Remco, PA3FYM and also looking at a design with a 40mm horn made from plumbing fittings. While doing that I will see it's possible to broaden the match so it is easier for those without test gear to reproduce. There are some recent tweets showing initial work on these.

If you have power to spare, there is a much simpler design but it's polarisation is not very LHCP so you lose a couple of dB. If you don't need 10 GHz, G3RUH sells a very nice 2.4 GHz LHCP patch feed. Finally, Peter DJ7GP has a dual band feed in production, I don't know what it's performance is like but will try to simulate it. It looks very nicely made.

See https://forum.amsat-dl.org/index.php?bo ... /&pageNo=1 for more info.

Eventually this will go into the Wiki.

Mike

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

Re: Dish Feeds

Post by radiogareth » Tue Feb 05, 2019 12:46 pm

Paul, could you post a drawing with location dimensions for the feed on the patch? Scaling off a scaled print does not match with what's shown. I can then 3-D print a guide template and give it a go with a file.
BTW, if anyone can design a plastic lens for the LNB (dimensioned sketch will do, I can CAD it for 3-D printing) its feasible to make our own lenses.
I can print in PLA, PETG, Fillamentum CPE (co-polyester) made from modified PETG material, additional monomer improves all the properties when compared with PETG filament. ABS (although its evil stuff and warps so I wouldn't bother) and nylon although at the moment its of chinese origin so finding out WHICH nylon blend might be tricky.
Possibly easier to machine known grade rod. I have a HUGE stock of PTFE rod that I acquired a long time ago and also some black nylon stuff which if I recall might have something printed on it (brand/grade??). But it was from 1986!! (It MIGHT come in useful one day!!).
I'm assuming the two sets of holes are for SMA or N-Type.
All good stuff :-)
Gareth

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

Re: Dish Feeds

Post by radiogareth » Fri Feb 08, 2019 4:04 pm

In seeking a Octagon PLL OSL SO to build into the dual feed, I just browsed eBay and bought the cheapest I found, £12 odd. To my surprise it arrived in an Amazon box, sold and shipped by amazon, where its available for just £8. So eBay may be wonderful for cheap electronics from China, but if its a UK seller its worth looking elsewhere before clicking 'buy'. Same applies to Orchid compost as I found out recently, I should have remembered ;-)
Having extracted the LNB from its case, the external barrell is coming up as 20.45 with my 22mm copper measuring very close to that - a simple stretching tool may assist here.
Is there any definitive distance the LNB should be mounted behind, I've seen one using a compression fitting and another using a brass adaptor.
https://forum.amsat-dl.org/index.php?th ... -2-4g-10g/
Some form of simple clamping collar is clearly going to help mount this enlarged assembly in a standard dish mount.
Happy to design and print up something just as soon as I have the mechanical recommendations to hand.
Found the nylon rod I mentioned, 11/4 diameter, 'nylon 6' I think it shows, about 2 metres of it. That would make a lot of 'rocket' caps if someone could design one. I still have a Bob Platts designed/made waveguide lens thats a piece of copper pipe transitioning from the rectangle down to the nylon cone. No idea where to start with this, other than google. I can design and make but my maths is naff....
Gareth

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

Re: Dish Feeds

Post by g8gtz » Fri Feb 08, 2019 4:37 pm

Hi Gareth,

I took the easy way out and bought a red pocket rocket!

https://www.ebay.co.uk/itm/UNIVERSAL-TW ... 2749.l2649

Haven't got it yet but should be OK as it was recommended by Paul M0EYT.

Re copper tube length it is acting as relatively low loss wave guide but as short as makes sense in your installation.

73
Noel

g0mjw
Posts: 668
Joined: Sat Sep 20, 2014 9:15 am

Re: Dish Feeds

Post by g0mjw » Fri Feb 08, 2019 4:54 pm

g8gtz wrote:
Fri Feb 08, 2019 4:37 pm
Hi Gareth,

I took the easy way out and bought a red pocket rocket!

https://www.ebay.co.uk/itm/UNIVERSAL-TW ... 2749.l2649

Haven't got it yet but should be OK as it was recommended by Paul M0EYT.

Re copper tube length it is acting as relatively low loss wave guide but as short as makes sense in your installation.

73
Noel
I ordered one of those, turned out to be a DRO. However the lens is useful and sits nicely on the 22mm water pipe.

Mike

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

Re: Dish Feeds

Post by radiogareth » Fri Feb 08, 2019 5:12 pm

Well if it fits its barely worth the effort calculating/making it at all. I do recall that the old BSB DISH LNB had a nylon insert that did the same job. Actually got 3 of those dishes BNIB for something 'one day'. They were very cheap.....
Gareth

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

Re: Dish Feeds

Post by radiogareth » Sun Feb 10, 2019 8:27 am

Interesting how its a different shape from the older style BSB conical ones. Maybe its not made of nylon (costly compared to polyethylene etc). I've ordered one and will sample a tiny sliver and attempt to ID the plastic.
I don't expect it to be a rare one... https://www.boedeker.com/Technical-Reso ... tification
Without software modelling I'd expect different shapes and materials could be tried in pursuit of stronger (or weaker) signals based on dish illumination.
Gareth

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

Re: Dish Feeds

Post by radiogareth » Mon Feb 11, 2019 7:39 am

From what I have gleaned on building this feed, the patch spacing is 3mm above the 105mm diameter ground plane and enought 22mm pipe needs to protrude out in front of the patch to allow securing the Rocket LNB red cone.
Behind the ground plane if doesn't matter much how far the LNB is mounted, but like anything RF, the shorter the better?
So planning just enough to fit a mounting collar around it....
I plan on mounting the amp directly underneath on the underside of the LNB arm with a short link of SMA-solid coax-SMA.
Any thoughts or guidance before I commit soldering?
Thanks
Gareth

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