Does anyone have C-band reception?

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G4EWJ
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Joined: Wed Feb 17, 2010 10:11 am

Does anyone have C-band reception?

Post by G4EWJ » Sat Nov 10, 2018 11:37 pm

I'm setting up a 2.4m dish on C-band that will eventually be used for the uplink. I don't have anything to compare it with, so I wonder if someone could look at 10E, 3689L, SR1083, DVB-S2 and see what they get please.

Brian

M0DTS
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Joined: Sun Feb 24, 2008 9:03 pm

Re: Does anyone have C-band reception?

Post by M0DTS » Sun Nov 11, 2018 7:03 pm

Hi Brian,

I can have a look but it won't be until next weekend.
An easy check of performance is sun noise but does involve panning the dish about, should be in the region of 10dB i guess, think i got 9dB last time i had the feed on the 3m dish which does not work that well above 23cm.
With a 3cm LNB on it i can get BADR sat but only just.

Rob

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

Re: Does anyone have C-band reception?

Post by g0mjw » Sun Nov 11, 2018 7:23 pm

Hi Brian,

Why are you pointing it there? I don't have C-band but I see there are C-band transponders at 26E. I am trying to do the same thing with a 2.4m dish for 10 GHz and have been looking at the Ku band BADR transponders. My dish is not yet optimised, I don't know exactly where the focus is, and I am seeing an MER of only 10dB on those transponders so I have some more work to do.

https://www.lyngsat.com/Eutelsat-10A.html claims a 40 dBW EIRP on that transponder for London. Here is the coverage plot https://www.telesatellite.com/images/sa ... frique.jpg which shows similar EIRP where you are. That should be a strong signal on a 2.4m dish - probably why you are looking for it.

Mike

G4EWJ
Posts: 1358
Joined: Wed Feb 17, 2010 10:11 am

Re: Does anyone have C-band reception?

Post by G4EWJ » Sun Nov 11, 2018 11:51 pm

Thanks both.

The dish isn't very movable and pointing it is a bit hit and miss, so the stronger the transponder the better. There's only one transponder at 26E and it looks like it's a lot weaker.

It's just getting the hang of several new things: lower frequency, big dish, prime focus, big LNB, scalar rings, circular polarisation. If it looks optimum at 3.7GHz then it should be fine for 2.4GHz with a helical feed or patch.

Lyngsat shows C/N figures for each transponder, but I don't have a feel for how that might translate to MER values.

The 2.4m will be for uplink only. We'll be using a 1.2m for receive.

Brian

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

Re: Does anyone have C-band reception?

Post by g0mjw » Mon Nov 12, 2018 7:48 am

The good thing about aligning on Ku band at 26E is you can align at 28.2E instead, the signal is so strong you can't really miss it, even from quite far off and looking at TV dishes gives you a good idea for initial pointing. After peaking at 28E your system is calibrated fairly well and you can replace the Ku LNB with a C-band one in the same place and be fairly sure where you are pointed. To get to 26E, move a couple of degrees to the right and 1 degree more elevation. I did that with my 2.4m dish by noting the length of the feed arm and a bit of trigonometry. Taking the sine of the angular offset and multiplying by the boom length to the right was accurate enough for 1 or 2 degrees. Would need to be a bit more complex for larger offsets but not a lot more.

I think I will use a dual band feed - To be Constructed.

Mike

G4EWJ
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Joined: Wed Feb 17, 2010 10:11 am

Re: Does anyone have C-band reception?

Post by G4EWJ » Tue Nov 13, 2018 4:59 pm

I used that method to try out the 1.2m Channelmaster that will be used for receive. It's hard to miss Astra.

The 6 petal Fortec Star dish that we're using at G3NWR doesn't have a very good reputation: poor geometry, fragile and rust prone, to name a few. It's particularly not recommended for 10GHz, but people are getting reasonable results from them on 3.7GHz, so 2.4GHz should be even better.

The main attraction is that they cost one tenth of the price of a 'good' one, if you can still get them. There's a 2.4m version of the Channelmaster going for £2300 second hand on Ebay.

The dish still has the strings across it to check the geometry. It's within a few mm. It should be fairly well shielded from the wind and the takeoff to 26E is good.

Brian
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G4EWJ
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Re: Does anyone have C-band reception?

Post by G4EWJ » Tue Nov 13, 2018 4:59 pm

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G4EWJ
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Re: Does anyone have C-band reception?

Post by G4EWJ » Tue Nov 13, 2018 5:00 pm

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