POTY Location

Latest News and Discussion about the use of the DATV transponder on Es'hail-2
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radiogareth
Posts: 1215
Joined: Wed Jan 06, 2016 9:46 am

POTY Location

Post by radiogareth » Sat Nov 07, 2020 8:19 pm

At last I have set up a dish (after unusual direction winds bent the K bracket in a tricky place). This time I've mounted the dish upside down and in a very slight bit of shelter, on my garage roof. Its a 105x115 (actual parabolic part) Offset.
Using a stock 2-port PLL Octagon and SDR CONsole, I was getting the NB beacon at about 38-40 snr.
Today I changed to a POTY with rocket lens, but the LNB mounting arm does not let me locate the round reflector where the original LNB lens would have been. The snr is now about 34, but as I can see the noise floor, is it worth pursuing?
If yes, I can either cut away a little of the inside support arm where the POTY disc is touching, or cut a flat on the edge of the POTY. The sellotape is holding in the Rocket LNB lens, which replaced a 3-D printed one (which was -3dB).
Which, if any, should I bother with?
Suggestions welcome.
Gareth G4XAT
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g0mjw
Posts: 2330
Joined: Sat Sep 20, 2014 9:15 am

Re: POTY Location

Post by g0mjw » Sat Nov 07, 2020 8:43 pm

The lens needs to be in the right place or it won't work. You should be seeing much greater noise floor than that. It's easy to do.

See this diagram from Hans http://www.hybridpretender.nl/poty_mount.JPG

Ideally you should modify the feed arm to move it down (or in your case I suppose up) a bit to allow you to put a spacer in the plastic bit to allow the larger antenna move back to the right place without hitting the feed arm. Just needs a bit of simple metalwork.

I used a plumbing fitting and a bit of aluminium plate mounted on top of the bottom half of the original LNB mount.
Mount.jpg
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Mike

radiogareth
Posts: 1215
Joined: Wed Jan 06, 2016 9:46 am

Re: POTY Location

Post by radiogareth » Thu Nov 12, 2020 4:30 pm

Thanks Mike, as I had decent wx today I applied myself to the problem, retaining a degree of adjustment prior to final fixing. Around 1pm I had the beacon making 41dB S/N in SDR COnsole so I'm happy with that. There was a fair bit of wind last night but the reduced windage meant nothing shifted. I've upgraded the LNB with a 10Mz TXCO I salvaged from some 3.5GHz gear. This drives a SI5351 to produce the required 25MHz. All wrapped in sponge its very steady and drift-free. I'll post the gen on my 'surplus' thread.....
Gareth
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2020-11-12 14.50.42.jpg
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g0mjw
Posts: 2330
Joined: Sat Sep 20, 2014 9:15 am

Re: POTY Location

Post by g0mjw » Thu Nov 12, 2020 4:45 pm

radiogareth wrote:
Thu Nov 12, 2020 4:30 pm
Thanks Mike, as I had decent wx today I applied myself to the problem, retaining a degree of adjustment prior to final fixing. Around 1pm I had the beacon making 41dB S/N in SDR COnsole so I'm happy with that. There was a fair bit of wind last night but the reduced windage meant nothing shifted. I've upgraded the LNB with a 10Mz TXCO I salvaged from some 3.5GHz gear. This drives a SI5351 to produce the required 25MHz. All wrapped in sponge its very steady and drift-free. I'll post the gen on my 'surplus' thread.....
Gareth
2020-11-12 15.10.35.jpg2020-11-12 15.10.19.jpg2020-11-12 14.50.42.jpg
That looks good - so how did you modify the feed arm? Might be useful for others.

Mike

radiogareth
Posts: 1215
Joined: Wed Jan 06, 2016 9:46 am

Re: POTY Location

Post by radiogareth » Thu Nov 12, 2020 5:08 pm

On the basis that if it failed, I wanted to go back to the original mount, i.e. I wanted to keep the original 'datum' if required.....
I cut away the obstructing bottom part of my support tube to give clearance on the POTY disc. Before I did that I used my Lidl angle finder to measure the offset angle (Boom to LNB mounting collar flange, 32 degrees on mine). I cut a piece of aluminum sheet (16g/1.6mm), drilled mounting holes for the LNB collar and then bent it to 32 degrees. This allowed me to find the sweet-spot by clamping the alloy plate to the boom and sliding the LNB assembly in/out/left/right. Once maxed out I drilled a single hole through the plate and outer boom skin, it's secured with a single 3mm nut and bolt.
The waterproofing (water bottle) lasts well in UV, the green collar (3-D printed) will keep most of the rain out of the patch area.
Gareth

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