Would a gregorian CM180 make any difference in H/V fringe reception?

[archive10]

Hi everyone,

have been thinking for some month on ways to improve 2D reception here.
In Scandinavia (disregarding the west of Denmark), the verticals are the problem.
Even with a decent dish, the verticals still are prone to pixellation and the occasional drop-out due to rain or whatever it is.
It would (to the optimistic eye) seem that clarification of verticals would be good.

I have read with great interest that Gregorians have the beneficial trait of rectifying some of the muddling of polaristaion on a dish.
Which makes them especially good for Tx/Rx dishes.

But would that be of benefit to us vertically challenged people (polaristion-wise, that is)

Had a chat with the folks at Skyware recently. it turns out that CM180 comes in a gregorian version too.
I could make one out of one my CM180s by getting a new mount and feed assembly.
(Which would turn it from a type 180 to a type 184, I have learned!)

Would this make any difference to verticals reception on 2D, do you think?

 

[ralphmagno]

hello,
yes it will be better.
there a several types of dishes.
prime focus has 55% to 60% efficiency
offset has 62%
cassegrain has 65 % to70%
and gregorian has 70%
this is due to the fact that less is blocking the signal, the feed and support arms.
and there is more reflector surface.
but it is unknown if this will solve your problem 100%.
using the best LNB and better dish will make a big improvement for sure.
ralph

 

[iceman]

Hi everyone,

have been thinking for some month on ways to improve 2D reception here.
In Scandinavia (disregarding the west of Denmark), the verticals are the problem.
Even with a decent dish, the verticals still are prone to pixellation and the occasional drop-out due to rain or whatever it is.
It would (to the optimistic eye) seem that clarification of verticals would be good.

I have read with great interest that Gregorians have the beneficial trait of rectifying some of the muddling of polaristaion on a dish.
Which makes them especially good for Tx/Rx dishes.

But would that be of benefit to us vertically challenged people (polaristion-wise, that is)

Had a chat with the folks at Skyware recently. it turns out that CM180 comes in a gregorian version too.
I could make one out of one my CM180s by getting a new mount and feed assembly.
(Which would turn it from a type 180 to a type 184, I have learned!)

Would this make any difference to verticals reception on 2D, do you think?

My guess is that it would make a difference, but negative instead of positive.
I dont know what type of LNB or feed you use on your 180CM dish but you are likely to get the best result on this dish with an original Channel Master (Andrews) feed horn + invacom C120 Quad LNB...

 

[Robbo]

I don't agree with the logic of the above, as the type 184 would be using be using an original feed.

_www.atrexx.com/images/aktuelles/File/AN-C180.pdf

so, that is no justification to say it would perform worse.

 

[satkingno]

In Scandinavia (disregarding the west of Denmark), the verticals are the problem.

Hmmm...certainly not here in Southeast Norway...where the horizontals are much weaker.

 

[timo_w2s]

Hmmm...certainly not here in Southeast Norway...where the horizontals are much weaker.

Yeah, verticals are much stronger in Helsinki too. Can't get the horizontals at all on a 1.8m dish.

 

[Analoguesat]

Before you spend loads of money remember Astra2D (and 2A / 2 will be coming out of service in a couple of years and replaced by new satellites. At this point all the 2D reception maps can be screwed up and thrown away and we will be starting again with the fringe reception reports.

 

[Huevos]

remember Astra2D [...] will be coming out of service in a couple of years

Or the next couple of days for all we know.

 

[Analoguesat]

Personally I dont think that will be just yet.

 

[archive10]

Hi Ralph,

hello,
yes it will be better.
there a several types of dishes.
prime focus has 55% to 60% efficiency
offset has 62%
cassegrain has 65 % to70%
and gregorian has 70%
this is due to the fact that less is blocking the signal, the feed and support arms.
and there is more reflector surface.

as the mod would make an offset into a gregorian, sadly I'd get no more reflector, and I'd actually have more things blocking the signal (the LN.
They main (only) improvement would be the re-aligning of the polarisation.

but it is unknown if this will solve your problem 100%.
using the best LNB and better dish will make a big improvement for sure.
ralph

Not sure how I can get better LNB - only potential improvement would be a C120 with a CM feed horn (which seem mightily hard to get these days).
Better dish... not sure I can get a better 180 cm dish. Next step up would be a 2.4 meter CM, but really, I have strong signal on almost all transponders (incl all 2D), it's the quality measure that fails.

 

[archive10]

My guess is that it would make a difference, but negative instead of positive.
I dont know what type of LNB or feed you use on your 180CM dish but you are likely to get the best result on this dish with an original Channel Master (Andrews) feed horn + invacom C120 Quad LNB...

I have an Inverto Black Ultra Quad. I have an Invacom, but no Andrew feedhorn. Not sure how much difference we would be talking about; and it will probably be difficult to predict.

 

[archive10]

Hmmm...certainly not here in Southeast Norway...where the horizontals are much weaker.

Hmm, let me rephrase that, then:
In Denmark where I live, the verticals is the problem (quality wise).
I have about the same strength on H and V, but the first TPs to go when atmospheric phenoma sets in.
Perhaps we can start talking about polarisation hot spots as we do with the Stockholm anomaly for strenght

 

[archive10]

Before you spend loads of money remember Astra2D (and 2A / 2 will be coming out of service in a couple of years and replaced by new satellites. At this point all the 2D reception maps can be screwed up and thrown away and we will be starting again with the fringe reception reports.

You are right, AS. (which is why my CMs are second hand )

I have actually been considering getting a secondary reflector from some other mfg, and then adapt the mount to see if it would be made to work.
(Probably not for the faint-hearted, but that's where the sport is in this hobby, isn't it??)