How Well Does Your Orthomode Feed Perform?

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Pixl

Pixl

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Feb 27, 2010
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Traverse City, Michigan
I currently using a C/Ku combo lnbf on my 8ft Andrew. The C works pretty good, the Ku is just ok at best. I would like to improve the C band even if it means skipping the Ku. Some of you guys have worked with C/Ku lnbf, C orthomode, and C/Ku orthomodes. How do they compare? Does the C/Ku ortho compromise over the C only ortho?

Jim
 
Pix, I changed out my c/ku Chaparral corotor II to a Chaparral Bullseye II Orthomode last spring and put in a modified zinwell switch (see Pendragon's mod on this forum), best thing I have done to improve signal and ease of connecting rcvrs. Signal strength improved about 2 to 5 % on the birddog meter. Quality improved also. There is some added expense for the additional lnbs, but the overall improvements made it well worth it. Thats My two cents worth, I'm sure others will have opinions too. The Bull
 
I recently changed from a Geosatpro C2 LNB on my 6' WSI dish to a Chaparral ortho feed with dual Norsat 8115 LNBs. The improvement was very noticeable. I don't get the picture pixalization on high FEC transponders (like DW on 103W) like I did with the Geosatpro LNB and can now lock and watch many S2 signals (including some 9/10 FEC) that I could not receive previously. The upgrade was expensive, but I wanted the best performance possible out of my small dish. Ironically, I haven't had the opportunity to totally tweak my dish since I installed it last fall (still waiting for the weather to improve). So there are probably some other gains (pun intended :) ) to be had once it is tweaked.

For ku, I have a dedicated 1 meter dish for that -- so I can't provide any feedback on a dual ortho setup.

An ortho upgrade to good dish like an 8' Andrew dish should provide excellent results. I would like to hear your results if you do make the change.
 
bullseye II ortho c/ku here-way better performance than the dmx-741. slightly better performance than my corotor.

any c and ku feed will be a compromise at best but my results have shown the ortho does best.
 
A dual-ortho with quality LNBs should easily outperform inexpensive C-band LNBFs and corotors. However Ku performance on a dual ortho is generally nothing to write home about. I have a project bubbling to the surface to try to improve this, but it will take time. If all you want is C-band, go with a single ortho. They're a lot cheaper and will outperform a dual-ortho by a noticeable margin.
 
Ok, this sounds inviting. And how about choice of lnb's? I see Norsat 8115 mentioned. What else is working good? And what about noise figure or other specs.
 
I have 2 Chaparral Bulls-Eye II Quad, and one ADL Quad Ortho-mode feeds.

Perhaps it is the quality of the dishes that I have used them on, but I have had great success with both C-Band, and Ku-Band.

I have used them on my perforated Birdview, my solid Birdview, my 10 foot standard Uni-mesh dish, and on my perforated 10 foot Uni-mesh dish.

I can say that all have performed on Ku as well as a 1 M Primestar dish for Ku, and outstanding C-Band reception too.

They are definitely the way to go if you are looking for superior signal quality numbers.

The next best route is to separate the signals with a dual orthomode or a C2 LNBF for C-Band , and a 1 M Primestar dish for Ku.
 
i have to say ku band is super on my dual band ortho on 10' mesh. it honestly outperforms my 90cm solid patriot ku dish with an invacom quad lnbf.

some signal percentages are very close yey others are higher on the 10' with dual ortho.

my 10' is very well tuned with no dings or dents and very straight.
 
Others have unwittingly confirmed my claim that a dual ortho on Ku provides very marginal performance. For comparison purposes, a 1m dish should provide about 10 dB more gain than a 12" dish. A 10' dish should provide nearly 10 dB more gain than a 1m dish, all things being equal. But they're not. It seems for the most part a 1m offset on Ku is roughly equivalent to a 10' with a dual ortho on Ku. I can handle something less than theoretical, but this is way over the top.

My dual ortho is currently sitting on a 1.8m dish. It works well on C-band, but not quite as well as a single ortho had before. On Ku, this dual ortho does at best 1 dB better than my 1.2m offset, but usually about the same. Both have comparable Invacom LNBs.

The 1.8m should do about 3.5 dB better than the 1.2m; the actual 0-1 dB is lousy. That led to my 1.8m Prodelin offset acquisition. With a nice feed and an Invacom LNB, it averages 4 dB better than the 1.2m. (Note to studious readers - this makes some sense as the 1.2m f/D is 0.5, which causes some loss with a 0.6 f/D feed)

When and if I can get the dual ortho Ku performance up to 2-3 dB better than the 1.2m, I will be happy. It cannot do this as stock. If you can only put up one dish, a dual ortho on a 10' prime-focus is a decent option. I believe I can do better than this, either with feed mods or a slightly different approach. But that remains only conjecture. If you can put up more than one dish, the cost and lackluster performance of a dual ortho (about 0.5 dB less than a single on C-band, many dB worse than theoretical on Ku) should be cause for careful consideration.
 
Pendragon,

I am fortunate to have plenty of room in my yard for dishes,I have 12. So far from what I have read from you and the others I'm going to want to do a C only ortho. Which brings me to another project that has to be done first. This C/Ku combo is my only movable dish for Ku. I have a couple of 1.2 m Prodlins I could try to motorize, or should I try to find a 1.8m? I'm a little mixed up from your post if the 1.8 is better or not all that great. I also have a 6ft solid aluminum microwave dish prime focus that I tried to make my main Ku last summer. You even gave me some advice on getting the Invacom feed fd set on it. I could never get it to work all that good and a 1m offset out performed it. I know I'm getting off topic with this Ku stuff but need to be done before I take apart my Cband dish.

Jim
 
Pixl - your dish farm sounds like a lot of fun. I'm at 15 myself and wouldn't want to give up a single one. Sorry for the confusion about the 1.8m dishes. I have two - a 1.8m solid petal Fortec prime-focus and a 1.8m Prodelin offset.

The 1.8m Fortec is a flimsy dish, but it performs pretty well on C-band when tweaked. In fact with a single ortho and Norsat 8115s it could lock almost every C-band FEC 9/10 high rate DVB-S2 up there. It ended up with my dual ortho after I decided I preferred the better performance of single orthos for my bigger prime-focus dishes. I had hoped this would provide better Ku performance than my 1.2m GeoSatPro offsets (3), but this has yet to happen. Some of the Ku performance loss may be caused by the Fortec itself, but a lot is from the dual ortho.

Over time I started doing a lot more low-horizon and out-of-footprint work, particularly on Ku. The 1.2m dishes just weren't sensitive enough, and they are highly vulnerable to the high winds we can get. Only one of the 1.2m dishes has a USALS motor, which can't keep the dish from flopping back and forth in the gusts. I put a C-band HH motor on a second 1.2m, but that didn't entirely cure the problem because the 1.2m's mount isn't stiff enough. The third 1.2m works fine in any wind, but it is fixed and anchored both at the back and at the LNB. I love and hate these dishes.

My extreme Ku solution was to find a used 1.8m Prodelin offset. It slams the 1.2m dishes on sensitivity and doesn't budge at all in the wind. It stopped my dual ortho Ku research on the 1.8m Fortec for at least a year, because I don't really need it any more. For curiosity reasons I would like to improve the dual ortho performance on Ku, but that isn't my highest priority.

In terms of your Ku motor project, you have some interesting decisions to make. The 1.2m Prodelins should have impressive performance, but I expect they are way too heavy for an ordinary USALS motor. A friend of mine is planning to build a polar mount for his 1.2m Prodelin so he can use an actuator. He says Prodelin doesn't even make polar mounts for that size dish. If you have or can locate even a lightweight C-band style HH motor, that would probably work fine, too.

My 1.8m Prodelin came with a dual-axis mount, which I converted to a polar mount using a heavy duty HH motor. Prodelin makes a polar mount for this size of reflector, but they want a lot for it. It's an incredible dish and highly recommended for power users. I see unused ones everywhere I go, but almost all of them have only AZ/EL mounts. They're often available for free, but they would require some work to motorize.

In your case I think your best option is to look into motorizing your 1.2m Prodelins. The 1.8m Prodelin is a nicer dish, but motorizing it isn't any easier unless you want to pay Prodelin for the luxury. I would stay away from a prime-focus dish for Ku-only unless it's truly designed for that purpose. Few are.
 
A single ortho costs about $60 new, and I've seen new Norsat 8515s in the neighborhood of $45 each. So that option is about $150 at best, but well worth it. A dual costs between $200 (very lucky score) to $450. With LNBs, you'll be lucky to be much south of $400. Unless you have only one large prime-focus dish, stick with the single ortho. It performs better.
 
Ok, I think I have it now, a 1.2m offset is good, a 1.8 is even better as long as it too is offset. You confirm an thought I've had about mounting one of these on a C-band frame and use a actuator arm. As for an H-H motor I wonder where you could buy a decent one and what they cost. I did buy a used H-H made for the FTA hobby. I took it apart, decided not to use it, the motor is pitifully small like something in a kids toy. I want something manly!
 
Just an FYI.

My Birdview dishes are not 10 foot.

The perforated measures 8 foot 3 inches, and the solid measures 8 foot 6 inches, and both perform as well as a 1 M Primestar dish on Ku with a quad orthomode feed-horn, while still performing as well as most 10 foot dishes on C-Band using the same feed-horn.
 
I'm using norsat 4106a's on the ku side of my bullseye II. It out performs my 1.2m offset Channel Master equipped with Ivacom QPF 031 lnb
My bullseye is on a 10ft Andrews solid alm dish. If you can find one the Ajax 180 H to H dish mover is the best I've found, they are for sure manly =), kinda like hens teeth to find though. The Bull
 
Linuxman - there's nothing unexpected about a 8.5' dish with a dual ortho performing on Ku like a 1m offset. However it does mean around 8 dB of gain is being thrown away. That seems excessive to me, as I'm often fighting to get 0.1 dB improvements in my tweaking.

Maybe I'm cracked, but I'd like to figure out what is causing this loss. Is it the dish surface's departure from a pure paraboloid, is it poor cross-polarization, is it a poor illumination pattern, is the lack of a scalar preventing symmetric field patterns (amplitude and phase)? A little bit of knowledge could go a long way to getting back some of the missing 8-10 dB we lose on big prime-focus dishes, even with dual ortho feeds.

I will say if a 8.5' dish performs like a 10' dish, there is something wrong with the 10' or its alignment. There's nothing complicated about reflector theory, and a 10' should get around 1.5 dB more gain than a 8.5'. All of my prime-focus dishes have different diameters (1.8 - 3.2m) and cover a fairly broad range of f/D (0.278 - 0.38). With some attention to each dish's need, I can get them to perform within about 0.2 dB of their relative gains.

Pixl - if you can find a C-band frame and use an actuator arm, that might work. However you will have to be able to lower the dish quite a bit with respect to the polar axis because of the dish offset angle. Most declination adjustments won't allow anything close to what is required.

Madbull's suggestion to look for an Ajax HH180 is a good one if you can find one. The motors in these things are not giant, but the torque they can generate through the gear reductions is staggering. I wouldn't try to arm wrestle one, even on a good day. In Colorado where these things were made, you can spot them everywhere. I didn't want another dish, so I ended up going to a junkyard where I had a choice from about a dozen.
 
I've seen Norsat 8525s and 8515s on fleabay for about $50 plus shipping from the same seller. I understand that those two LNBs provide 500kHz stability and 25k and 15k noise temps, respectively.

If one were to get themselves set up with either a single or dual ortho, just what does the 100kHz, 250 kHz, or 500kHz stability mean for us? I understand that the 100khz provides "better" LO stability but I'm not sure I know what that means. Is it just a matter of an IF frequency being within 100, 250, or 500 kHz of the frequency you thought it should be when looking on an spectrum analyzer?

From pricing I've seen on the net the 100kHz LNBs also cost almost twice as much as the 85XXs.
 
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cracklincrotch - all other things being equal, a lower frequency stability number on a LNB will likely be of little practical benefit for most FTAers. If you're looking on a SA as you say, it will give you a more accurate frequency measurement. It would also have a some value for extremely low SR signals that are closely spaced. Nothing that would be of any meaning to FTA, though. In my recollection the phase noise and noise temperatures of the Norsat 8515s are the same as for the 8115s, meaning you can save some money and still get good locks on high FEC/SR DVB-S2 signals.
 
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