Anyone use a deep dish bud

[chuckinnc]

I have a 7.5 ft "deep" dish solid spun aluminum dish, it uses a button hook type
feed horn support, I have read these deep dish types don't work very well so I
would like to hear from anyone who has used one. I am thinking it should be sutable for single band C or maybe Ku if I can find the proper feedhorn/scaler rings.

 

[phlatwound]

I have a 7.5 ft "deep" dish solid spun aluminum dish, it uses a button hook type
feed horn support, I have read these deep dish types don't work very well so I
would like to hear from anyone who has used one. I am thinking it should be sutable for single band C or maybe Ku if I can find the proper feedhorn/scaler rings.

You may have to use some guy wires to center your feed/focal point, but unless your dish is damaged or warped there is no reason why it shouldn't perform on C or Ku-bands.

Please post some pics if possible.

 

[pendragon]

Properly set up a deep dish should outperform a shallow dish because they tend to deliver better SNR. Shallow dishes tend to deliver better gain. The problem is getting deep dishes set up properly.

Because of their shorter focal length, adjustments are usually more critical. If you have a particularly deep dish (say f/D < 0.3) you need to make sure your feed can accommodate it. Otherwise the feed will only be seeing part of the dish. I have a couple of deep dishes with modified feeds (not originally designed for low f/Ds) and get excellent results.

 

[chuckinnc]

Fine, now where to find info on mods

I have several lathes and a milling maching so moding a scaler ring or feed wouldnt be a problem, that is if it can be done at all in the home shop. Pendragon
can you direct me to a website or where to find info on what needs to be made or modified to work with my very deep .25 f/d dish.

 

[pendragon]

It sounds like you have all the right equipment for doing mods. Normally the main problem is being able to slide the scalar rings far enough back on the feedhorn. If they're too close to the feedhorn opening, they will restrict the angle the feed can see and you will be only using the center portion of your dish.

Corotors are normally decent in this respect because they have a very long feedhorn, but they generally have higher losses than a good ortho feed. Ortho feeds can be very nasty as they have projections out of the feedhorn for one or both polarizations. These normally block the rings from going back far enough.

I've published one thread here on a mod I did to a dual orthomode feed. Basically I cut notches out of the mounting ring and good-sized chunks out of the scalar rings themselves to make room for the feed to slide through more. I've also modified a single ortho feed recently and that was easier and delivered a better result.

I would say a f/D of 0.25 is extremely low. Did you measure/calculate it? For that the feedhorn should project beyond the scalar rings by at least 1.5". If the f/D is really that small there may not be any point to using a scalar at all. As a start you could just try mounting the feed to the buttonhook without any scalar.

 

[truckracer]

my ortho feed horn out performs my corotor II and previous c band lnbf's

 

[chuckinnc]

I tried adjusting the scaler rings but

It didnt seem to have any effect so I would say your right, with a dish this shallow it may not help. I had a adl (I think) c/ku feedhorn on it before, c band was good but ku never worked very well, I even milled out a circle in the scaler ring & placed a seperate ku lnb but no luck that way either.
I would really like to use this as a ku only dish but haven't figured out how to
place a modified feed horn to capture the main dish area. This was a old commercial or military dish and I did not get the origional feel/lnb so I don't know
how it looked.-

 

[pendragon]

my ortho feed horn out performs my corotor II and previous c band lnbf's

The orthos are definitely the way to go if you have spare change. My dual ortho feed smokes my corotor on all my buds, currently f/Ds from 0.278 to 0.38. But I'm largely converting over to single orthos (C-band only) because they smoke my dual ortho. Admittedly the latter difference is smaller than the former, but very measurable.

 

[pendragon]

It didnt seem to have any effect so I would say your right, with a dish this shallow it may not help. I had a adl (I think) c/ku feedhorn on it before, c band was good but ku never worked very well, I even milled out a circle in the scaler ring & placed a seperate ku lnb but no luck that way either.
I would really like to use this as a ku only dish but haven't figured out how to
place a modified feed horn to capture the main dish area. This was a old commercial or military dish and I did not get the origional feel/lnb so I don't know
how it looked.-

Ku on a 0.25 f/D is going to be a tough nut to crack. Any LNBFs designed for offset dishes are intended for f/Ds around 0.6 and will be terrible matches. I imagine that's what went wrong with your milling experiment.

I picked up an Invacom Ku LNB with a C120 flange recently to try on my prime focus dishes. I also picked up one of their adjustable ADF-120 feedhorns. It's specified for f/Ds from 0.32-0.43, but you could likely modify it to go lower. I modified mine to go the other way because I have a low f/D offset dish (0.5) that I believe might do better with it. At the moment no one in the US has these feeds in stock and there is no ETA to boot. I ordered one from Europe and had it within a few days, however. At the same time I was going to see how it worked on my prime focus dishes, but I've been tied up by other matters.

Another possibility might be to get a Dish Network Superdish 105 LNB and feed (cheap on eBay when available). It also has a C120 flange and you could simply cut off the scalar. I suppose you could do this with just about any Ku LNBF. But don't try to mount it at the same time with any C-band feed.

There is the question whether your problems are caused by a f/D mismatch or an imperfect parabolic surface. Most of my C-band dishes don't do as well on Ku as one would hope, and the evidence so far seems to be pointing toward the latter. You may have a different case, however. Regardless a 1.2m offset dish will get almost anything up there on Ku.