Does this make sense.

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truckracer

truckracer

Thread Starter
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Sep 17, 2004
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Charleston wv
I was outside today playing with my corotor II with a norsat 8000 lnb(that's all it says) It does not specify temperature. It looks old.

my scalar is centered on the dish. I think it comes out to be 63 3/8" from the edge of the scalar to edge of the dish all the way around.

My focal length according to SAMI is 45 5/8" to 1/4" inside the feedhorn throat.

Simple enough..... Tape measure it and tighten the set screw and I'm done right?

OK.....I did it like that and My signal went down! My feedhorn works better closer in to the dish than specified.

Strange. I would think the formula should be pretty exact according to antenna specs.

Best signal is obtained at about 45 1/8" to 1/4" inside feedhorn.
 
L

Lak7

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Feb 28, 2008
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Near Chicago, Illinois
Did you move Feedhorn and Scalar Ring as one, keeping the f/d set properly?
I believe that you should set the Feedhorns f/d to the Scalar Ring first. Then as a whole, mount and adjust for proper focal length, keeping the f/d set. The measurement from the edge does not matter, as long as they are the same. Also, the recommended focal length is only a recommendation. An 1/8" or more either way wouldn't be surprising.
 
starman345

starman345

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Nov 25, 2004
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New Brunswick, Canada
Lak7 is right, make sure the f/d is set properly with the feedhorn/scaler ring, set that to the right number and forget it. Then adjust the focal length of the whole feedhorn/scaler ring unit, you might have to shim to get the right distance. The forumla gives me a focal distance of 44.5" for my particular dish but I find it works better around 45" so I guess a little playing around is probably more accurate than the formula.....where ever you get the most signal is the best spot.
 
truckracer

truckracer

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Sep 17, 2004
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Yes, My feedhorn is dead on the .38 mark. I just slightly twisted the whole thing on the feed struts like one of the members suggested. When the struts slightly turn it draws the whole feedhorn into the dish. Of course the struts are not at perfect right angles to the Chaparall scalar ring.

I have the best signal at around 45 1/4". Signal drops quite noticeably at 45 5/8".

Bummer.........One of my used Norsat 8000's died this morning.
I woke up after leaving my tv on to find "No signal" on the C-band side.

I put my other cheap lnb on and my signal came back strong.
 
spyder

spyder

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Jan 2, 2004
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Contrary to what most people think, unless you live in an area with very high terestrial interference, the scaler ring is really a non important device. I never bother with adjusting the actual scaler ring itself. I've even ran a 10ft setup with no scaler ring (flat plate and collar mount) and shown absolutely no reception difference. In most situations you could mount the thing backwars and it wouldn't matter. The signal is focused at the feedhorn throat and not the scaler ring. If someone has signal focused on the scaler ring then they are getting very little or no siganl at the feedhorn.

As for the f/d calculations, they are usually pretty close, but I've found on almost every system I have set up that the numbers vary slightly from the calculated numbers. Pretty much normal. :)

I uaually set it initially at the calculated value, then do some fine tune adjustments for best reception quality accross the arc. (never minding the scaler ring)
 
qwert1515

qwert1515

SatelliteGuys TheList
Sep 26, 2005
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Spyder that is quite interesting, I am using a C-Band LNB on a 1.2 Meter dish and I see a huge difference with the scaler ring, I would have expected the same with a larger dish.
 
spyder

spyder

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Jan 2, 2004
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upstate SC
Spyder that is quite interesting, I am using a C-Band LNB on a 1.2 Meter dish and I see a huge difference with the scaler ring, I would have expected the same with a larger dish.



Yes, but you have to remeber, a 1.2 meter dish never has, and never will be compliant with the laws of physics concerning c band reception. In other words, it may work ok in some situations, but it just aint meant to be used for c band recption. :)

I would imagine you would have to have some assistance in focusing the signal on a reflector that small receiving a signal with that wide of a distribution pattern.
 
truckracer

truckracer

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Sep 17, 2004
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Charleston wv
I noticed a difference adjusting the scalar ring. If I set my scalar setting to .38 for my big dish (specified f/d) ratio and then adjust the whole assembly (scalar ring and all) I get better signal quality than if I just set the scalar wherever it falls on the struts and do the feedhorn in and out.

For instance, If i just mount the scalar ring on the struts I have to set my f/d on the scale at .32. to get acceptable signal.

But doing the above adjusting the whole assembly set at .38, I get the best signal.
 
spyder

spyder

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Jan 2, 2004
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upstate SC
If it works out that way then that's the way you should keep it then. :)

The scaler ring was designed to block signals, not receive them.

If you'll take a look at and think about the scaler ring construction, there's no way it can help to focus the reflected signal from the dish into the feedhorn throat. For one thing it's flat, and the signal coming into the feedorn is doing so at a reflected angle. If the signal were to be reflected into the scaler ring surface area it would be blocked or dispersed by the surrounding ring structure.

"would be blocked or dispersed by the surrounding ring structure" : That's what the scaler ring is all about. Used to be, and still is in some instances in few areas, that much of the microwave communication (telephone/data etc) systems could and did emit frequencies that were in interference with the satellite signal being recieved. The scaler ring when adjusted to the proper location helped to inhibit those stray unwanted signals from entering the feedhorn throat and causing interference, or at least keeping it to a minimum.
 
truckracer

truckracer

Thread Starter
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Sep 17, 2004
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So basically helps to eliminate sidelobes from a prime focus dish.
 
Hermitman

Hermitman

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Jul 2, 2006
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Limestone, Mi
When you adjust the position of the lnb in the scalar ring, you are adjusting the angle of received signals that the lnb will see. The farther the lnb is extended through the scalar ring, the wider the angle the lnb will see. The less the lnb is extended through the scalar ring, the narrower the angle the lnb will see. This is necessary since all dish designs aren’t the same. You want the lnb to see the maximum signals reflected off the dish but nothing more or you'll start picking up background signals bad for reception. Example: I want the lnb on my 10 foot orbitron to see 140 degrees for maximum signal reception without picking up background noise. However on my shallower, 12 foot dish, I want the lnb to see only 120 degrees for maximum reception. Then you look at an 18 inch pizza dish. There you only want a lnb to pick up 90 degrees of signal. That's where the f/d ratio comes in handy. Based on calculations, the f/d ratio is an indicator of the appropriate angle the lnb should see for best reception on that particular dish, i.e. the maximum reflected signal without picking up signals outside the dish rim. Prime focus f/d ratios run in the .30-.40 range while offset dishes run around .60-.70. The flat scalar ring is only at its best down to about .45. That’s why you need a conical scalar ring for the best reception on a smaller, offset dish. If you don’t have a conical scalar ring for the offset dish, you should try to set the lnb with the least amount extended through the flat scalar ring. A deep, prime focus dish may get by without a scalar ring since the sides of the lnb will block the extraneous signals. But the smaller the angle you want the lnb to see, the more you need a scalar ring to prevent unwanted signals outside the dish rim from entering the lnb. Also please remember, we’re dealing with microwave radiation and waveguides. The normal line-of-sight rules and energy traveling in a straight line may or may not apply depending on the situation. Bottom line: you should calculate the f/d ratio based on the dish’s dimensions and set your lnb in the scalar ring to that setting. That should set the lnb to see the correct angle of reflected signals off the dish without the background noise. Then adjust the lnb to put the dish’s focal point just inside the opening of the lnb. I hope I haven’t confused you too much. Good luck.
 
truckracer

truckracer

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Sep 17, 2004
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Charleston wv
Makes sense. So how much of the dish does the recommended f/d ratios see?

For example does a 10' dish with a f/d of .38 see 9 feet? or 8 feet?
 
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