CM 1.2m beats Fortec 1.8m on C band

[PopcornNMore]

Last weekend I tried out my new Fortec 1.8m prime focus dish on C band and was very happy with the results. Most signals received were between 65% and 70% on my Coolsat 4000 receiver.

Last night, I decided to try using a DMS International BSC621 on my CM 1.2m motorized offset dish using brackets designed by another member on this forum. Without doing any fine tuning to get the highest possible signal (it was getting dark outside) I started to scan in some C band satellites and was very impressed. In fact, signal quality was better than on my Fortec 1.8m dish with signals ranging from 68% to 82%. Signals on AnikF1R were the strongest. Plus I wasn't even using a coned scalar ring.

People often say that C band on a 4' dish is ok for experimenting, but not too good if you want to actually watch C band programming. After my results last night I tend to disagree. I must have received 90% of everything up there with no picture breakups and it was even clearer than KU band signals on the same dish.

I even received scrambled programming on Galaxy 14, AMC 11 and Galaxy 15 with signals in the mid 70's.

Now I am wondering if my 1.2m offset dish works as good as my 1.8m prime focus dish would my 1.8m offset dish work as good as a 10' prime focus dish. I just may drag out my CM 1.8m offset dish out of the garage this weekend to find out.

I wasn't able to receive KU band signals for some reason using the BSC 621 LNBF. There were signals, but not strong enough. Perhaps I need to perform some adjustments tonight. With the KU feed being deep inside the BSC 621 maybe the focal distance needs to be adjusted. Or perhaps the feed isn't dead center and needs adjustment.

Attached are some pictures:

 

[Anole]

C-band on 4' dish

That orange sky in the pictures is certainly majestic!

Now I am wondering . . .
. . . if my 1.2m offset dish works as good as my 1.8m prime focus dish . . .
. . . would my 1.8m offset dish work as good as a 10' prime focus dish. [?]

Are you implying that a smaller offset beats a bigger prime-focus?
I don't think so.

Go find the 7/8 FEC channels Iceberg has mentioned, and try to receive those.
I think the wider beam width of the 4' dish will get you signal spill-over from adjacent birds, killing your reception.

I just may drag out my CM 1.8m offset dish out of the garage this weekend to find out.

By all means, do that.
I might have a 6' offset in my future, and I'd like a preview! :

 

[Mr Tony]

something isnt aimed right. I can get almost everything on C-Band that I should. The 7/8 stuff is a bugger but everything else I get on the 6 footer just fine

 

[Corrado]

This started me thinking...I wonder if I put a BSC621 on my 1m Primestar dish if I could get anything on C band? I think I'll try it when I have time to experiment.

 

[Anole]

Anything?
I would think so.
Give it a go, take some pictures, and let us know! - :up

From previous reports, it's no longer a signal strength issue given todays LNBs and transmitter power levels.
It's more of an adjacent-bird rejection problem, that the bigger dishes solve.


well, that's 2000 posts. have I said anything funny, yet?

 

[PopcornNMore]

Ok, perhaps a 6' prime focus dish would work better on 7/8 FEC channels. However for 3/4 FEC channels my 4' offset outperformed my 6' prime focus. Plus for an added bonus my 4' is motorized so I can get every satellite and not just one.

I will be posting pictures with signal strengths for those non-believers.

 

[tvropro]

Just a thought... What is the efficiency of the Fortec dish? Could the Channel Master be performing better because of a better surface accuracy ? A prime focus antenna usually has a lower efficiency than an offset. I know my Primestar 90cm can out perform most 10 ft prime focus antenna's on Ku.

In theory the 6 foot should work better on C band. Was everything assembled correctly? is the reflector warped? (try stringing the dish) Make sure the focal distance and F/D ratio are set right. The feed could be skewed. A six foot as well as a four foot will run into sidelobe problems from adjacent satellites no matter how well it's made or aligned. A very high quality 8.5 foot just starts to get away from the 2 degrees spacing issue. A 10 foot or larger works the best.

 

[ftarock]

Don't take this offended but the statement "you can get 90% of what up there" is not accurate...at least with the offset 1.2m dish.
the 1.2m dish should not outperform the 1.8m prime focus in terms of C-band receiption.
I think you don't have the 1.8m tunned correctly yet.
Even with a 1.8m prime focus, you will not get 90% up there...maybe 80%.

Last weekend I tried out my new Fortec 1.8m prime focus dish on C band and was very happy with the results. Most signals received were between 65% and 70% on my Coolsat 4000 receiver.

Last night, I decided to try using a DMS International BSC621 on my CM 1.2m motorized offset dish using brackets designed by another member on this forum. Without doing any fine tuning to get the highest possible signal (it was getting dark outside) I started to scan in some C band satellites and was very impressed. In fact, signal quality was better than on my Fortec 1.8m dish with signals ranging from 68% to 82%. Signals on AnikF1R were the strongest. Plus I wasn't even using a coned scalar ring.

People often say that C band on a 4' dish is ok for experimenting, but not too good if you want to actually watch C band programming. After my results last night I tend to disagree. I must have received 90% of everything up there with no picture breakups and it was even clearer than KU band signals on the same dish.

I even received scrambled programming on Galaxy 14, AMC 11 and Galaxy 15 with signals in the mid 70's.

Now I am wondering if my 1.2m offset dish works as good as my 1.8m prime focus dish would my 1.8m offset dish work as good as a 10' prime focus dish. I just may drag out my CM 1.8m offset dish out of the garage this weekend to find out.

I wasn't able to receive KU band signals for some reason using the BSC 621 LNBF. There were signals, but not strong enough. Perhaps I need to perform some adjustments tonight. With the KU feed being deep inside the BSC 621 maybe the focal distance needs to be adjusted. Or perhaps the feed isn't dead center and needs adjustment.

Attached are some pictures:

 

[tdti1]

Fortec is not one of the best dishes, I do think it would do a bit better, are you sure the reflector did not get warped.

 

[Anole]

Popcorn -

I don't know if your 4' CM is transmit-certified, but I'll wager your 6' CM is.
I've got to think those are the Mercedes/Cadillac class dishes of their size.
So, if they perform well, which I have no doubt, then I think their quality is the winning factor, not whether they are offset or prime focus.
(not that you were necessarily arguing that position)

I know my Primestar 90cm can out perform most 10 ft prime focus antenna's on Ku.

This seems to be commonly reported, and I just saw Iceberg say it in another thread today.
I think the reasons are a combination:
- F/D of LNB is not matched to dish
- BUD surface is not really Ku-efficient
- BUD surface could be warped a little and C would be fine; Ku would be stuffed

 

[Mr Tony]

Even with a 1.8m prime focus, you will not get 90% up there...maybe 80%.

other than Equity mux and G10 to 133 due to a tree I can get everything that Lyngsat shows with my 6 footer

 

[Sadoun]

Iceberg,

Are you using a motor on your 6' dish? which motor are you using?

 

[tvropro]

Sadoun, Do you know what the efficiency is of the 6 foot Fortec at c band frequencys?

 

[tvropro]

Popcorn -

I don't know if your 4' CM is transmit-certified, but I'll wager your 6' CM is.
I've got to think those are the Mercedes/Cadillac class dishes of their size.
So, if they perform well, which I have no doubt, then I think their quality is the winning factor, not whether they are offset or prime focus.
(not that you were necessarily arguing that position)



This seems to be commonly reported, and I just saw Iceberg say it in another thread today.
I think the reasons are a combination:
- F/D of LNB is not matched to dish
- BUD surface is not really Ku-efficient
- BUD surface could be warped a little and C would be fine; Ku would be stuffed

From what I understand the Primestar / Channel Master fiberglass dishes are really made by Andrews. You can't beat Andrews dishes, commercial quality. This may be why his CM is performing so well for him. The Fortec on the other hand is a cheaper so so dish so even though it has more surface area if the tolerances aren't there performance will suffer. If the thing is warped or not set up right this will hurt it more.

 

[caddata]

....Perhaps I need to perform some adjustments....

Hey Popcorn:

Great photos. What a beautiful sunset. Excellent job on fabricating the support clamps. The nice thing is your can reinstall the original bracket later if you want. Bottom support strut makes a good conduit for the coax also.

I believe, once you've peaked the feed location, you'll see good Ku performance also. May require dual coax. I found I was losing signal strength thru the switch.

Keep up the good work. I and others are glad to see your success and it's nice to know that we're getting some repeatability in our adaption of the 1.2M dish.

Harold

 

[PopcornNMore]

It's more of an adjacent-bird rejection problem, that the bigger dishes solve.

You are exactly right! Most satellites are received very well on the 1.2m, but a few like Galaxy 25 are a bugger to tune in due to adjacent satellites interfering. I want to buy a coned scalar ring from Sadoun someday to help reduce this problem.

 

[PopcornNMore]

Just a thought... What is the efficiency of the Fortec dish? Could the Channel Master be performing better because of a better surface accuracy ? A prime focus antenna usually has a lower efficiency than an offset. I know my Primestar 90cm can out perform most 10 ft prime focus antenna's on Ku.

In theory the 6 foot should work better on C band. Was everything assembled correctly? is the reflector warped? (try stringing the dish) Make sure the focal distance and F/D ratio are set right. The feed could be skewed. A six foot as well as a four foot will run into sidelobe problems from adjacent satellites no matter how well it's made or aligned. A very high quality 8.5 foot just starts to get away from the 2 degrees spacing issue. A 10 foot or larger works the best.

I read on another forum that the focal distance on the Fortec 1.8m dish is actually incorrect and should be moved out more to take full advantage of the entire dish. I have not had the time to confirm this.

Also, you are right offset antennas are more efficient than prime focus dishes and with the CM dish being one piece this helps too.

 

[PopcornNMore]

Don't take this offended but the statement "you can get 90% of what up there" is not accurate...at least with the offset 1.2m dish.
the 1.2m dish should not outperform the 1.8m prime focus in terms of C-band receiption.
I think you don't have the 1.8m tunned correctly yet.
Even with a 1.8m prime focus, you will not get 90% up there...maybe 80%.

I am not offended at all and before trying the CM 1.2m on C band I would have agreed 100% with your statement. However, I have since received almost every C band signal out there (digital, analog, digital digicipher, etc) and they are locking in very well and the picture is amazing. I even found some C band signals with signal strengh in the 80's using the 1.2m dish.

I am going to try tweaking the Fortec 1.8m dish this weekend, but from what I have gotten so far the CM 1.2m beats it every time once the channel is scanned in.

I even would go as far to say that the video looks better on the CM 1.2m offset dish than it did on my 10.5' mesh C band dish back in the early 80's. Technology has really come a long way.

 

[PopcornNMore]

Hey Popcorn:

Great photos. What a beautiful sunset. Excellent job on fabricating the support clamps. The nice thing is your can reinstall the original bracket later if you want. Bottom support strut makes a good conduit for the coax also.

I believe, once you've peaked the feed location, you'll see good Ku performance also. May require dual coax. I found I was losing signal strength thru the switch.

Keep up the good work. I and others are glad to see your success and it's nice to know that we're getting some repeatability in our adaption of the 1.2M dish.

Harold

So, it was you who I got the bracket design from. I knew it was from somebody here.

I discovered last night that the DMS International BSC621 does NOT use DiSEqC as per the instructions. It actually uses a 22KHz switch which is written on the box. Odd thing, when set as DiSEqC #2 and LO 10750 it actually scanned in C band channels. In fact, it didn't matter if the DiSEqC was set to 1,2,3 or 4 a signal was always present. I thought I was going out of my mind. This is when I realized that it uses 22KHz and not DiSEqC.

The KU band doesn't scan in very well and I only can receive the highest KU signals. I believe this is due to the focal distance now since the KU feed is way in the back. I might also need to adjust the brackets in order to center the feed better.

Iceberg once said that with the DMS International BSC621 LNBF you might need to move the dish slightly for KU band. I found this to be true.

If I bypass the 22KHz switch could I use a DiSEqC switch instead? Are your C band signals as good as mine? There is some adjacent satellite interferance, but not too much. I am very impressed so far.

 

[caddata]

....Are your C band signals as good as mine?....

Similar C Band results. Found my Ku probes were off angle. The Ku section of the feedhorn can be rotated independent from the C Band section for tweaking.

I'm still not sure the C Band resonate cavity is the proper size. This may be causing a slight missmatch. A Corotor2 is slightly different in size and seems to be more efficient in allowing the Ku signal to locate the Ku probe. The Corotor Ku probe is also closer to the mouth of the feed than the BSC621.

I believe if the cavity was properly sized, it wouldn't matter where the Ku probe was located, front to back.

Harold