1.8 metre cheap and nasty segmented dish from Ebay

Latest News and Discussion about the use of the DATV transponder on Es'hail-2
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g7ntg
Posts: 24
Joined: Sat Feb 17, 2018 7:07 pm

1.8 metre cheap and nasty segmented dish from Ebay

Post by g7ntg » Fri Aug 16, 2019 2:09 pm

I bought one of these dishes from Ebay because I figured that it would be OK fror 2.4ghz TX.
I assembled it but ignored most of the segment joining holes and drilled fresh ones, making sure the front faces lined up which they don't if you use their holes!
I have mounted it on the front of my i.2 metre prime focus dish and after initial alignment it gives about the same RX performance as the 1,2 metre dish - maybe 1dB more - but on TX i now find that it only needs half the transmit power of the 1.2m dish.
This is 3db better which is about right.
I have still to fine tune the pointing but the results are not bad. I can equal the beacon at 2M/S with only 80 watts transmit power and to equal the beacon at 250K/S I only need 14 watts
There is now less risk of overheating my PA.
Receive MER of the beacon is only 9dB so the accuracy of the dish pressing for 10ghz is very poor and around 2dB down on what id should be.

g0mjw
Posts: 912
Joined: Sat Sep 20, 2014 9:15 am

Re: 1.8 metre cheap and nasty segmented dish from Ebay

Post by g0mjw » Fri Aug 16, 2019 2:29 pm

Did I read this correctly? You need 80W to equal the beacon at 2MS/S with a 1.8m dish? That seems a lot, but perhaps not. Does anyone know the EIRP of the beacon uplink?

My beacon MER was only 10 dB yesterday with my 2.4m dish. However I am seeing the transponder noise floor at 5 dB above the receiver noise floor. It might not be as bad as you think. The beacon MER is not a good indicator for larger dishes.

Mike

Nick
Posts: 69
Joined: Sat Oct 03, 2015 10:09 am

Re: 1.8 metre cheap and nasty segmented dish from Ebay

Post by Nick » Fri Aug 16, 2019 3:05 pm

I also have one of those 1.8Mtr dishes.

It arrived somewhat worse for wear - dented from poor packaging - so got a partial refund for that.

Assembling was a nightmare - holes for the segments did not match up and also required much drilling and filing to get segments to line up. I used the supplied mounting stand and there were a number of bolts missing so a trip down the road to the local builders merchants was required.

The LNB mounting arms were twisted and required bending to get them to fit - I will probably replace those soon.

As for receive I found my 1Mtr dish gives a better signal, so for time being I am using that.

It's probably not aligned quite correctly yet, but I have found that 6W works well, at 125 K/S, 12W at 250 K/S, and around 24W for 500 K/S, so seem to be getting the same performance at 2.4GHz transmit. Based on that 80W seems about right for 2 M/S.

Until I get a bigger amplifier can't do much more.

Nick - G4NKV

EBay 1.8Mtr Dish.jpg
E-Bay 1.8Mtr Dish
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g0mjw
Posts: 912
Joined: Sat Sep 20, 2014 9:15 am

Re: 1.8 metre cheap and nasty segmented dish from Ebay

Post by g0mjw » Fri Aug 16, 2019 3:24 pm

I checked - I need about 50W in the shack, ~40W at the feed, to equal the beacon with a 2.4m dish. The gain difference is 2.4dB in theory so it adds up and those 1.8m dishes are good for 2.4 GHz. If they are poor on 10GHz but equivalent to 1.2m it will probably do well enough to not bother trying to improve further. So, a bargain despite everything.

Mike

RimaNTSS
Posts: 21
Joined: Fri Apr 12, 2019 9:29 am

Re: 1.8 metre cheap and nasty segmented dish from Ebay

Post by RimaNTSS » Fri Aug 16, 2019 4:22 pm

Nick wrote:
Fri Aug 16, 2019 3:05 pm
The LNB mounting arms were twisted and required bending to get them to fit - I will probably replace those soon
I have set of extendable feedarms (from 70 to 90 cm ). Those would last much longer than antenna you got, as they are INOX made. :D PM if interested.
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IMG_20190803_130122 (Large).jpg
IMG_20190803_130122 (Large).jpg (740.87 KiB) Viewed 674 times

g8lce
Posts: 74
Joined: Sun Dec 06, 2015 10:26 am

Re: 1.8 metre cheap and nasty segmented dish from Ebay

Post by g8lce » Sun Aug 18, 2019 8:37 am

If this dish is only being used for TX could a different aerial or feed be used? Maybe a helix? There is a design for one that could be mounted from the centre hole of the dish without support arms. see http://g8haj.uk/?page_id=477

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