Pendragon vs. the Birdview

[Lone Cloud]

LC, it is not a matter of conjecture that increasing your focal length on a BV will improve your signal, it has been proven time and again.

I do agree that it is weird that BV built them like that. If they had a reason for it I would like to know what it was.

In those days, just as today, the mathematics of parabolas was known with precision. I don't think you could have designed the Birdview dish so well without knowing exactly where to put the scalar.

I can only say that I get extremely strong signals on all DVB transmissions - I mean well over 70. It makes no sense to me that I would get a consistent zero on the vast majority of S-2 transmissions. I could be wrong. Maybe I am.

I guess we will see what Pendragon discovers. I wish there were a better way. Like some kind of a photographic plate that you could put over the front of the scalar that was sensitive to DVB, and left an image on there. You'd know if you were focused and centered.

So we will see. If I am wrong, my stubbornness will ultimately give way to football and I'll change the struts.

 

[Anole]

it's only a stupid idea if it doesn't work...

I don't think you could have designed the Birdview dish so well without knowing exactly where to put the scalar.

... some kind of a photographic plate that you could put over the front of the scalar that was sensitive to DVB, and left an image on there.
You'd know if you were focused and centered.

Roll out some aluminum foil.
Use spray adhesive, and put a big cross (+) of it on the dish.
(yes, two 8' strips, one up 'n down, other side to side)
Get an old net you dip up fish with, and remove the netting.
Put wax paper over the open loop where the net was located.
Hold the wax paper near the focal point, while aiming the dish at the sun, and note the (+) pattern.
Adjust distance from the dish 'till you find the sharpest image.

 

[Lone Cloud]

Roll out some aluminum foil.
Use spray adhesive, and put a big cross (+) of it on the dish.
(yes, two 8' strips, one up 'n down, other side to side)
Get an old net you dip up fish with, and remove the netting.
Put wax paper over the open loop where the net was located.
Hold the wax paper near the focal point, while aiming the dish at the sun, and note the (+) pattern.
Adjust distance from the dish 'till you find the sharpest image.

And then I will have a dish that is aimed perfectly at the sun? I would have to be assuming that DVB waves act exactly like solar photons

Anyway, I appreciate creative stuff. Unless there is a medium that will register visual patterns for satellite signals reflected off the dish, I don't think the aluminum foil thing will help me out.

I suppose I could use the foil for a hat. My old one is wearing out

 

[linuxman]

And then I will have a dish that is aimed perfectly at the sun? I would have to be assuming that DVB waves act exactly like solar photons

Anyway, I appreciate creative stuff. Unless there is a medium that will register visual patterns for satellite signals reflected off the dish, I don't think the aluminum foil thing will help me out.

I suppose I could use the foil for a hat. My old one is wearing out

Reflectivity is the same whether light or microwaves.

The point is to find the focal point of that reflectivity, and yes, you would have to re-aim the dish at the arc again, but you would have the precise focal point to set the scalar.

If you want to do the research, I did prove the focal length on the Birdview dishes to be extended out about an inch further than the factory set it as. I don't remember which thread, nor the exact post where I gave the focal length, but I'm sure Pendragon will tell us in just a few days.

I'd look for it myself, but some of my threads were a little long winded, and it might be buried somewhere 10 pages deep.

 

[ynnedibanez]

if i were to venture a guess, i would theorize that the reason for the difference in focal length was because the original lna is quite different from a modern lnbf.

 

[pendragon]

I think it's fair to point out that the original Birdview scalar/waveguide/feed all have significant design differences from 'modern' FTA feeds that we all know and love. I'm not wasting any time on analyzing the original Birdview designs, but they may work best when the focal point is placed deeper in the throat. Maybe, maybe not. I have been doing a little math on mating the Birdview scalar to a modern feed, and am a little concerned about under-illumination. Hopefully this will be resolved in testing along with the optimal focal length.

Today, with a little help from friends, I cut a hole in the roof, dropped in a 13.5' pole, crunched it against a recently reinforced wall with some giant U-bolts and installed the Birdview. Per my conformance to city code, I retired my 1.8m Fortec petal and one of my three 1.2m GeosatPro offset dishes. I'll see if anyone wants the Fortec for free, but otherwise it will be scrapped. I'm keeping the 1.2m in the shed as a backup for my other 1.2m dishes.

It was after dark, but we got the dish tracking pretty well and the dual ortho Frankenstein feed perfectly centered on the adjustable struts. I'm starting out with a focal length of 1.028m, but that will be tweaked. I'm testing version 1 of the scalar/dual ortho optimization plan, but I may need to get a hacksaw out because the feed is already bottoming out on the clamp. The rotary encoder seems to be working fine, but I haven't put it to the acid test. Sorry, no pictures yet. Installations are always such a rush that the picture taking has to wait until it's done. Lots more to do.

 

[Lone Cloud]

Reflectivity is the same whether light or microwaves.

The point is to find the focal point of that reflectivity, and yes, you would have to re-aim the dish at the arc again, but you would have the precise focal point to set the scalar.

If you want to do the research, I did prove the focal length on the Birdview dishes to be extended out about an inch further than the factory set it as. I don't remember which thread, nor the exact post where I gave the focal length, but I'm sure Pendragon will tell us in just a few days.

I'd look for it myself, but some of my threads were a little long winded, and it might be buried somewhere 10 pages deep.

OK, I'm listening. But isn't the focal length technically from the dish surface to the actual receiving wire ( or rod as in the case of the dual ortho) inside the feedhorn? What in the end does the
scalar distance have to do with focal length?

I have been assuming all this time that you just pull the feedhorn away from the dish surface and lock it in "deeper in the throat" as pendragon describes - at about the same distance as the original Birdview lnb was. Is this the wrong notion also?

 

[pendragon]

OK, I'm listening. But isn't the focal length technically from the dish surface to the actual receiving wire ( or rod as in the case of the dual ortho) inside the feedhorn? What in the end does the
scalar distance have to do with focal length?

I have been assuming all this time that you just pull the feedhorn away from the dish surface and lock it in at about the same distance as the original Birdview lnb was. Is this the wrong notion also?

No, the LNB probe is positioned in a waveguide, and is almost never at the focal point. 'Coupling' the focal point to the waveguide depends on a number of factors and compromises. Many 'modern' feeds like the focal point a bit inside the feed mouth, but this will depend on the dish, scalar and what taper and sidelobe suppression you want. There is no perfect setting, because each will have positives and negatives. Fortunately these choices are normally only of concern to crazy people like me.

 

[Lone Cloud]

OK, I guess I don't really grasp the purpose of the scalar plate.

If someone would be kind, perhaps they will explain what a scalar does in a general sense, and why the scalar distance is important to the focal length question.

Thanks in advance.

 

[FaT Air]

You all have to remember that the BV dish was designed when the satellite spacing was 10°. And also, during this time, terrestrial microwave WAS a big issue. Just guessing, as I don't personally know any BV engineers, but maybe they compromised on gain in order to lessen T.I. at a greater rate. Just a guess. I had, BITD, taken part in taking a couple of 4Ghz terrestrial sites (AT&T) down as authorization was not being renewed because the increasing popularity of space based 4Ghz.(from the mouth of an AT&T engineer, at that time) If I remember some physics right, Max efficiency of power transfer occurs approximately 1/4 wavelength inside the wave guide.(throat of the feed, as it's, essentially, a waveguide) so you'd want the focal point 1/4 wavelength from the front of the feed. >>scalar distance<< Huh? Don't know what your referencing. The scalar is actually a low Q, wide bandwidth, 1/4 wave choke. Any waves traveling across it's face will essentially,(to some degree), get trapped(choked), and not show up in the feed. This is mainly for T.I. and earth noise attenuation. But miss-adjustment can also cause it to attenuate, more than desired, the signal of interest reflected from the outer edges of the dish.

 

[Lone Cloud]

So I've been all over the internet, trying to find an explanation like "Scalar Plates for Dummies", so I can understand what the darn thing does, and its relationship to focal length.

Coming up dry

 

[turbosat]

So, you have to give up 2 dishes, every time you put up 1 new one? The HOA out-foxed you on that arrangement, lol.
j/k
Looking forward to the squeaky clean new Birdview pictures.

 

[pendragon]

Lone Cloud - I doubt you'll find much on the Internet about scalar theory, especially something that is correct. There are some highly technical books, but that may not what you are looking for.

turbosat - outfoxing may depend on one's perspective I believe the city thought they had me boxed in with the ordinance they passed last year - grandfathered, but effectively frozen from making any changes since I have more than the allowed number of dishes under the new rules. I could have tried to get a variance, but I would have had to give the city a healthy escrow account and dealt with months of hearings. Probably not a lot of chance for success there. However I found a neat little clause from 1970 that allows ANY changes without city approval as long as the result is closer to compliance. I actually set up my spare 1.2m as a potential sacrificial lamb just before the ordinance passed. I really didn't need it and it only cost $30 for the pole. That paid off and it's back to being a backup dish. I could still put a 1m or less dish on the pole, but I can't think of any reason to do that at the moment.

In other news, the Birdview wiring is done and I did a thorough alignment this evening. I can see slight effects of a declination error at the extremes because the Birdview only has a fixed declination. If I can get more range on the motor angles I might do the washer trick to tweak this up.

The rotary encoder is working perfectly. I have 6771 counts from 43W to 139W, that works out to about 64 counts per motor angle degree (0.016 degrees per tick). No apparent backlash. On Ku this actually translates to better pointing accuracy as I can measure the difference with a 1-2 count offset. The Birdview has a laser mainlobe on Ku. My Birdview mount is very nice and can be adjusted with fine and repeatable accuracy. I found setting the elevation a cinch by myself, so I'm sorry but I won't be making any mods there for the time being.

I spent a LOT of time tweaking the focal point and the taper. At the moment my best overall setting has the front of the scalar rings 1.030m from the dish center and the dual ortho feed mouth projects 8mm in front of the scalar rings. This is within a couple of mm of my final estimates, and I tested over a range of +/- 5mm from the final setting. Both C and Ku perform best with this adjustment.

I was never happy with the dual ortho in the past as its Ku performance was generally horrible compared to theoretical. With all the planets aligned and some luck I could get it to perform within about 4 dB of theoretical, but most of the time it was more like 6-8 dB off. Its cross-polarization performance seemed particularly lousy. I'm not jumping up and down with joy, but with the Birdview I'm consistently getting around 3 dB from theoretical with none of the dreadful stuff. My 1.8m Prodelin offset still beats the 2.6m Birdview usually by 0.5 dB on Ku, but the Prodelin is a commercial-grade fibreglass dish. I'm actually fairly satisfied with the Birdview Ku performance so far, and I haven't had to go exotic, yet. It certainly outperforms the 1.2m I sacrificed.

I haven't done as much comparison on C-band. It performs fine, but nothing special. It's my third biggest dish and looks like it will stay in third place. Still, much better than the 1.8m Fortec it replaced on C and dramatically better on Ku.

I'm completely tied up tomorrow and probably will have to paint the house on Sunday. Pictures will come when I can find some spare time.

 

[linuxman]

I spent a LOT of time tweaking the focal point and the taper. At the moment my best overall setting has the front of the scalar rings 1.030m from the dish center and the dual ortho feed mouth projects 8mm in front of the scalar rings. This is within a couple of mm of my final estimates, and I tested over a range of +/- 5mm from the final setting. Both C and Ku perform best with this adjustment.

The following is for those of us who didn't have to learn the Metric system in school.

"I spent a LOT of time tweaking the focal point and the taper. At the moment my best overall setting has the front of the scalar rings" 40.5511 inches "from the dish center and the dual ortho feed mouth projects" 0.3149606299216 inches "in front of the scalar rings. This is within a couple of mm of my final estimates, and I tested over a range of +/-" 0.196850393701 inches "from the final setting. Both C and Ku perform best with this adjustment."

This is for Lone Cloud:
That's why I mentioned the distance for the scalar rings in a post above, because as you can see, the feed throat just barely peeks out from the scalar about a 1/4 inch, so if you set the scalar at the correct distance, setting the feed is relatively simple.

 

[Lone Cloud]

...

This is for Lone Cloud:
That's why I mentioned the distance for the scalar rings in a post above, because as you can see, the feed throat just barely peeks out from the scalar about a 1/4 inch, so if you set the scalar at the correct distance, setting the feed is relatively simple.

If I go that way, I think I have a simple way of doing it: The coupler nuts you get at Home Depot are an inch long. Assuming, with the help of a propane torch and some penetrating oil, I can get the strut nuts off, putting the coupler nuts on the ends should move the scalar away by about the distance recommended.

I have been working all day on my USALS skew project for the dual orthomode. It's together. I will be trying to get it going tomorrow. I have the motor mounted and the drive nut connected to the mounting plate the ortho is attached to. I have three little rubber wheels on that for resistance free turning. We will see

 

[pendragon]

Here's a handful of pictures of the current project state. The front view shows the dual orthomode Frankenstein feed with an Invacom quatro universal Ku LNB. You can see my three toroids in the background.

I attached this to an outside wall (on both sides) underneath the house's overhang and have a couple of views of the wall mounting. I first took off the siding and the sheathing, and nailed and glued a bunch of studs back-to-back to reinforce the wall. After putting the sheathing back on, I bolted on some redwood 2x8s to both sides of the wall. I had some custom U-bolts made by my friends at Stengel Brothers from grade 8, 7/8" steel rods. They are 6.75" across and 18" long. Pretty neat. Nothing moves and I was able to tweak the tightening to get the pole absolutely plumb.

The rear view shows the usual wiring I do. There are three dual inline amps for the six LNB outputs that feed six taps. That way I can simply plug in a meter without disconnecting any cables or interfering with the operation. There is also a jack with constant +18V power to run the meter if necessary. The control cables use 8-pin watertight connectors so I can plug in a GBOX on the roof without having to open anything up.

The GBOX was modified to have a 5-pin locking connector on the back to avoid dealing with the stock cheapo speaker wire clamps. This allowed me to use the GBOX's internal +5V supply to drive the rotary encoder and the driver circuitry mounted in the Birdview motor enclosure. Sorry I didn't take pictures of this before putting on the cover. It's pretty simple: just an XOR gate taking the quadrature outputs of the encoder and feeding an high voltage open collector buffer.

Everything is well grounded and you can see my ugly roof patch. I was able to find flashing that perfectly fit the 6" schedule 40 steel pipe on the bottom (6.625" OD) and also a cover that adapts 6" schedule 40 to the 6" OD of the Birdview.

The dish as shown is parked on 58W. For maintenance I simply drive it to the western extreme, allowing me to work on the feeds standing on the flat roof. The precision offered by the rotary encoder is great and I can run the dish back and forth knowing that it's going to stop on a dime.

I'm expecting to play with this some over the next few weeks before doing anything drastic. I'll be doing comparisons with my other dishes on both C and Ku-band. I'll also verify the gain and equalization levels going into my switch matrix.

When I have some time I plan to work a little more on the scalar to see if I'm getting full illumination, especially on Ku. I'm also contemplating setting up a temporary Ku-only feed using my Invacom ADF-120 with the quatro LNB. That should give me a clue as to the viability of the Ku side of the dual ortho. If the Invacom feed does better, I'll consider some further mods to the dual ortho. Otherwise I could drill out an access port in the Birdview scalar for the ADF-120 and go back to a single ortho on C-band. More to come.

 

[pendragon]

NB: It was with a bit of nostalgia that I took apart the 1.8m Fortec petal dish this afternoon. I absolutely hate the mount, but the dish has served us well for the past few years, getting nearly every high FEC DVB-S2 feed out there. I didn't see any future for this on our property because of the city ordinances, and I didn't expect to find a caring owner. After all the Craigslist FTA dishes stay posted for months at a time in Denver.

It would be awful to send it to the scrap heap. So on a lark I thought perhaps somebody might be more attracted to it if they didn't have to rescue it off the pole and didn't need a truck to pick it up. I posted an ad on Craigslist as a freebie and within 20 minutes I got a response. The guy drove over immediately and hopefully the dish has many more years of service ahead

 

[Anole]

You can see my three toroids in the background.

The Birdview looks a lot less white than your torroidal dishes.
I like it. - :up

I had some custom U-bolts made by my friends at Stengel Brothers from grade 8, 7/8" steel rods.
They are 6.75" across and 18" long.

Outstanding!
Good looking pipe-work, as well.

The precision offered by the rotary encoder is great and I can run the dish back and forth knowing that it's going to stop on a dime.

You cured the overshoot? How so? Lower the count?

The front view shows the dual orthomode Frankenstein feed with an Invacom quatro universal Ku LNB....
When I have some time I plan to work a little more on the scalar to see if I'm getting full illumination, especially on Ku.
I'm also contemplating setting up a temporary Ku-only feed using my Invacom ADF-120 with the quatro LNB.
That should give me a clue as to the viability of the Ku side of the dual ortho.
If the Invacom feed does better, I'll consider some further mods to the dual ortho.

That would be very telling. Good test.
Even though the Ku sounded pretty good in your previous comments.

Otherwise I could drill out an access port in the Birdview scalar for the ADF-120 and go back to a single ortho on C-band.

Then offset move to get Ku?
I suppose.

 

[phlatwound]

Wow, that's a first class install, well done.

I am quite sorry you found the elevation so easy to adjust that you will not be designing an adjuster for me to ape (yet).

I have some pics of a very nice one that 1captain did on one of his BVs if you want them.

Have you determined how much declination was built into your mount from the factory?

I remember you mentioning that you might use some washers if you needed to adjust the dec. Here is what I did:

http://www.satelliteguys.us/166422-phlats-birdview-2-a-7.html#post2005588

 

[pendragon]

Anole - I didn't do anything about the overshoot, but with the dish on the motor it tends to be less. Perhaps the motor is running slower or there's more friction compared to my original tests with the motor assembly resting on a bench. Regardless this doesn't matter for C-band, and for Ku I can always move it back manually.

In terms of Ku reception, I'm happy with it as it's the best I've seen on a BUD. In fact the Birdview is now the #2 Ku dish in my stable. However that doesn't satisfy my curiosity - is the ~3 dB loss because of the (1) poor coupling because of feed/scalar compromises, (2) incomplete illumination, (3) dish surface, (4) waveguide losses, (5) combinations, (6) etc? The downside to my curiosity is satisfying it will be a lot of work and will temporarily disrupt a perfectly working setup. I may take the lazy route because my 1.8m Prodelin has always sufficed for tough Ku feeds.

phlatwound - I've haven't measured the declination on the pole, yet. Before I put the motor assembly up, I measured 5.8 degrees between the top plate's two surfaces. I then measured the polar axis as 5.4 degrees from level when resting the assembly on a level surface. Something in the middle would be ideal, but it looks like the actual declination is on the high side. It would only take a few minutes to determine this, but I've not gotten around to it yet. Your adjustable declination approach is a good idea.