Channel Master 1.2m Dish

Latest News and Discussion about the use of the DATV transponder on Es'hail-2
RimaNTSS
Posts: 16
Joined: Fri Apr 12, 2019 9:29 am

Re: Channel Master 1.2m Dish

Post by RimaNTSS » Wed Apr 17, 2019 9:04 pm

Thanks @G4WIM
Aim of my experiment is to find out whether feedarms are not obstructing 105mm disc when phase center of the LNB is co-located with antenna's focal point.
By any chance, do you know how far from 105mm disc phase center is located? Something like 50mm?

g0mjw
Posts: 789
Joined: Sat Sep 20, 2014 9:15 am

Re: Channel Master 1.2m Dish

Post by g0mjw » Wed Apr 17, 2019 9:20 pm

Phase centre for 10 GHz is in the middle of the polymer lens more or less. That is the lens taken off a rocket style LNB. I do not recommend the PTFE bi-conical lens as it is several dB worse. Better to go with the notch patch and small horn if you cannot get a proper lens feed. Not sure why people are using that PTFE or Nylon cone when donor rocket LNBs are so cheap. People don't like to break things up, even when they only cost 6 Euro.

For 2.4 GHz the phase centre is just above the patch so approximately in the same place if you follow the instructions. The 10 GHz is most critical, you can tolerate a large error at 2.4 GHz because the wavelength is four time greater. I would aim to make the distance adjustable in any case.

Mike

RimaNTSS
Posts: 16
Joined: Fri Apr 12, 2019 9:29 am

Re: Channel Master 1.2m Dish

Post by RimaNTSS » Wed Apr 17, 2019 9:28 pm

g0mjw wrote:
Wed Apr 17, 2019 9:20 pm
I would aim to make the distance adjustable in any case.
Thanks Mike! Adjustable in which limits? Can I assume that phase center can be located between 50 and 100mm from 105mm disc? Between green lines Image

g0mjw
Posts: 789
Joined: Sat Sep 20, 2014 9:15 am

Re: Channel Master 1.2m Dish

Post by g0mjw » Thu Apr 18, 2019 12:11 pm

Nothing like that. Have a look at the article. It should be quite clear.

https://uhf-satcom.com/blog/patch_antenna there are pictures too. The typical distance from the reflector is 8mm as the phase centre is just above the patch. Your picture below has no patch and has far far too much waveguide coming out in front.

Make it as in the instructions, then make sure your feed holder allows you to adjust the the focus.

Mike

RimaNTSS
Posts: 16
Joined: Fri Apr 12, 2019 9:29 am

Re: Channel Master 1.2m Dish

Post by RimaNTSS » Thu Apr 18, 2019 8:58 pm

I see. No problem, I can simply turn around the disc Will do experiments during the holidays.

G4WIM
Posts: 202
Joined: Thu Jan 29, 2015 8:36 pm

Re: Channel Master 1.2m Dish

Post by G4WIM » Thu Apr 18, 2019 9:11 pm

Hi Rima,

given your obvious mechanical skills, why not make a dual feed as exactly as drawn in the article ?

When you're done testing with it I'm sure a forum member would take it off your hands !

Good luck and have a great holiday.

Regards Tim

RimaNTSS
Posts: 16
Joined: Fri Apr 12, 2019 9:29 am

Re: Channel Master 1.2m Dish

Post by RimaNTSS » Sat Apr 20, 2019 4:04 pm

Tim! Perhaps you are expecting too much from me :( To do real testing I need to be very deep inside the topic most of you guys are dealing with. I am not ready for that...IMHO.
But what I can be pretty sure is the hardware side of the issue, IMHO again, that original CM feedarms are no providing perfect solution, even if LNB-holder is changed. The best option is to change feedarms and LNB-holder, then you will have possibility to adjust the feed exactly in the focus of the antenna. Adjustable feedarms and LNB-holder give this possibility. Image Image Image

G4WIM
Posts: 202
Joined: Thu Jan 29, 2015 8:36 pm

Re: Channel Master 1.2m Dish

Post by G4WIM » Sat Apr 20, 2019 9:00 pm

Looks good, I may have to finger out a way to get / make some longer support arms.

satdxer
Posts: 20
Joined: Sat Jan 26, 2019 6:10 pm

Re: Channel Master 1.2m Dish

Post by satdxer » Wed Apr 24, 2019 4:55 pm

make some longer support arms.

Hi to be honest there is no reason to make longer arms and no reason to over complicate a very simple modification, its as simple as this.
DSC_0117.jpg
DSC_0117.jpg (265.36 KiB) Viewed 321 times
All my reports here are with the above setup 1.2 channel master dish.

Code: Select all

https://www.techwatch.co.uk/forums/forum/fringe-reception-ku-band/

RimaNTSS
Posts: 16
Joined: Fri Apr 12, 2019 9:29 am

Re: Channel Master 1.2m Dish

Post by RimaNTSS » Thu Apr 25, 2019 7:29 pm

satdxer wrote:
Wed Apr 24, 2019 4:55 pm
Hi to be honest there is no reason to make longer arms and no reason to over complicate a very simple modification, its as simple as this.
Yes, it is quite simple and well camouflaged (little bit rusted holder though :twisted: )but I do not think this solution can provide best performance of the system. Seems that LNB is located too close to the surface of the dish, so LNB's phase center could not be co-located with antenna's focal point. Reception is, of course, possible, but, again it will never be best as it could be.
P.S. looked in your link but did not find your name and any pictures of your dish. But, I am pretty sure, if you were placing LNB in proper position you would certainly have even more astonishing reception results whatever good/bad they are right now. :D

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