Bullseye II

[Comptech]

My invacom quad on my 1.2 meter finally died.I am thinking of putting a dual orthomode like the bullseye II on my 12 foot unimesh.Do you guys think it is worth it or should I stick with a separate Ku dish.I already have a pair of norsat Ku's and am running a dual c-band feed now with a pair of CalAmp mini mags so all I have to do is buy one of those "gold plated" Bullseyes.

 

[pendragon]

My invacom quad on my 1.2 meter finally died.I am thinking of putting a dual orthomode like the bullseye II on my 12 foot unimesh.Do you guys think it is worth it or should I stick with a separate Ku dish.I already have a pair of norsat Ku's and am running a dual c-band feed now with a pair of CalAmp mini mags so all I have to do is buy one of those "gold plated" Bullseyes.

I would be very hesitant about doing this. I started with a dual ortho on my 3m perf and after trying it on all my BUDs, it got relegated to my 1.8m solid and modified at that.

The best news I can report is there is only a 0.25-0.5 dB loss in CNR on C-band vs. a single orthomode using the identical Norsat 8115 LNBs (I moved them out of thoroughness). Ku performance has never outstanding even with Norsat 2707 LNBs. The Ku feed appears to suffer from not having something like a scalar, and it also forms a very narrow beam. Thus the Ku side only illuminates the center of the dish. This last part might be ok if your BUD has a f/D of around 0.5, which virtually none of them do. You have the further problem that a 12' mesh is not likely to match a perfect paraboloid as well at Ku frequencies as it does in C-band. No doubt you'll get Ku, but your SQs may very well be lower than on your 1.2m.

Once I gave up on the bigger dishes, I had some success with the dual ortho on the solid. I attribute this to a more consistent surface, which is easier to keep in tolerance as compared to much larger BUDs. However on the 1.8m it did not stand out over my 1.2m offset that has a circular/linear Invacom quad. Ultimately I ripped out the Ku waveguide on the back of the dual ortho and fashioned a Superdish feed flange to adapt an Invacom quatro Ku universal LNB. I finally had something worth keeping. The 1.2m often still beats the 1.8m combo on SQ, except for very weak signals and under more extreme conditions such as rain fade. I haven't spent a lot of time looking into this, but my pet theory is there is more cross-polarization on the 1.8m.

I haven't yet given up on the dual ortho and am considering a 2.4m solid with a f/D around 0.48. But I have another Invacom quatro Ku universal with a real scalar feed looking for a home, too. Based on past history, I suspect the dual ortho faces long odds against that. Replacing the Invacom is less expensive than a dual ortho and has a pretty good chance of outperforming it.

 

[Anole]

From a practical point of view, if you want Ku on the BUD, it might not be any worse than your 1.2m dish.
Very dish-dependent.
The old saying of putting all your eggs... comes to mind.
But, for some (or spouses, or neighbors) who don't relish multiple dishes the single BUD may be desirable.

As for the Ku being improperly illuminated, that's disappointing to hear.
I thought the orthos worked better because they illuminated better than the dual-band voltage-controlled LNBFs on Ku.
Maybe you should invest in a Ck-1 or DMX741, and try that first?

The other thing I was going to bring up is the price.
I first found the Chaparrals for around $500.
But, upon further research, they and their competitor were down in the $200-300 range.
Then, sometimes they pop up on eBay or . . . ?
I've seen the ADL go for $50 - 100, used.

So, if money and convenience ARE considerations, you might not want to slam the door on the idea.
If performance is your only goal, then I think Pendragons comments above may be more appropriate.

 

[pendragon]

As for the Ku being improperly illuminated, that's disappointing to hear.
I thought the orthos worked better because they illuminated better than the dual-band voltage-controlled LNBFs on Ku.
Maybe you should invest in a Ck-1 or DMX741, and try that first?

I'm only speculating because I haven't tried to model this, but if you look at any dual band C/Ku feed, one has some control of the C-band illumination pattern via scalar ring adjustment, but this is completely ineffectual for controlling the Ku-band pattern. For most intents and purposes there is no compensation for f/D for Ku, and these types of feeds seem to have a fixed f/D on Ku that is on the high side for a BUD. Hence the poor illumination that is often seen.

Furthermore, the Ku side on such a feed has no real scalar tuned for that band. Scalars provide more benefits that just pattern control, and this forum has ample demonstrations of the detriment of running a C-band feed without one. Recently I did a comparison of a Superdish 121 feed (no scalar) to a 105 feed (abbreviated scalar) to a Dish Pro feed (normal Ku scalar). The DP beat the 121 by more than 2 dB in CNR across the board. I would not be surprised if that was also happening here.

The above applies fairly similarly to any dual band feed. When putting any Ku feed on a BUD, it's important to realize that Ku is going to be about 3X more exacting than C-band on the quality of the dish surface. If one takes a 1/10 wavelength rule-of-thumb, we would want to keep the reflector surface within 2.5 mm for Ku-band, but only 7.5 mm for C-band. The latter is well within most BUD designs, but mesh dishes will have a hard time with the former. When one stretches mesh with ribs and considers local convexities or concavities plus the inevitable minor blemishes and damages, this will all exact a price in performance as the focal cloud will be large.

 

[1ADAM12]

I'm only speculating because I haven't tried to model this, but if you look at any dual band C/Ku feed, one has some control of the C-band illumination pattern via scalar ring adjustment, but this is completely ineffectual for controlling the Ku-band pattern. For most intents and purposes there is no compensation for f/D for Ku, and these types of feeds seem to have a fixed f/D on Ku that is on the high side for a BUD. Hence the poor illumination that is often seen.

Furthermore, the Ku side on such a feed has no real scalar tuned for that band. Scalars provide more benefits that just pattern control, and this forum has ample demonstrations of the detriment of running a C-band feed without one. Recently I did a comparison of a Superdish 121 feed (no scalar) to a 105 feed (abbreviated scalar) to a Dish Pro feed (normal Ku scalar). The DP beat the 121 by more than 2 dB in CNR across the board. I would not be surprised if that was also happening here.

The above applies fairly similarly to any dual band feed. When putting any Ku feed on a BUD, it's important to realize that Ku is going to be about 3X more exacting than C-band on the quality of the dish surface. If one takes a 1/10 wavelength rule-of-thumb, we would want to keep the reflector surface within 2.5 mm for Ku-band, but only 7.5 mm for C-band. The latter is well within most BUD designs, but mesh dishes will have a hard time with the former. When one stretches mesh with ribs and considers local convexities or concavities plus the inevitable minor blemishes and damages, this will all exact a price in performance as the focal cloud will be large.

Not sure what you mean here, The BSC-621 Ku LNBF does have a conical scalar behind the C Band section. Don't remember on the DMX-741 but think it was a copy.

 

[pendragon]

Not sure what you mean here, The BSC-621 Ku LNBF does have a conical scalar behind the C Band section. Don't remember on the DMX-741 but think it was a copy.

Could you post a photo looking down the feedhorn? It would see to me that a proper Ku scalar for a prime focus dish would completely block the C-band waveguide.

 

[1ADAM12]

C/Ku LNBF

Could you post a photo looking down the feedhorn? It would see to me that a proper Ku scalar for a prime focus dish would completely block the C-band waveguide.

Found two pictures.

First picture is from BSC-621 post on this site in 2008 and it shows the Ku scalar but it is not conical it is a flat ku scalar.

Second picture is from another site and shows a Ku circular lnbf bugerd to a C Band LNBF.

 

[pendragon]

Found two pictures.

First picture is from BSC-621 post on this site in 2008 and it shows the Ku scalar but it is not conical it is a flat ku scalar.

Second picture is from another site and shows a Ku circular lnbf bugerd to a C Band LNBF.

Thanks, but I'm not entirely sure what I'm looking at. Does the first picture show what is at the back of C-band waveguide, ie. removed from the tube? If so this seems way too far from the focal point to have any real effect as a Ku-band scalar and that might explain why this unit didn't win any prizes in the Ku department. I'm sorry if I'm not getting it.

 

[madmadworld]

My invacom quad on my 1.2 meter finally died..Do you guys think it is worth it or should I stick with a separate Ku dish.

buy a new invacom quad $60
it's all good again
how long did you have the invacom quad ?
good luck

 

[Anole]

buy a new invacom quad $60
it's all good again
how long did you have the invacom quad ?
good luck

. . . hrmmmm . . .
That may be the best answer yet! - :up -

Say, don't they come with a 5-year warranty?
Maybe your unit is still covered...

 

[madmadworld]

. . . hrmmmm . . .
That may be the best answer yet! - :up -

Say, don't they come with a 5-year warranty?
Maybe your unit is still covered...

thus the ?

how long did you have the invacom quad ?

 

[Comptech]

Sorry guys back to work so I have limited internet time.The LNBF is probally pushing the 4 or 5 year mark.Problem is I do not even remember were I bought it.The plastic cover over the end fell apart then a driving rain and then no worky anymore.The main reason I was thinking of the dual orthomode was a single reciever to control one dish.It is a pain to go to the back bedroom to move the Ku disk with my CS8000.To run it from my living room would make a cable run of about 300 feet,then back 75 or so to the multi switch.

 

[Tron]

This thread reminds me... The feedhorn cover on my QPH has deteriorated, and I need to contact Invacom for a replacement LNBF before the five years is up. I've still got a few more months, but I don't know if I have my original receipt (I purchased from PSB)...