LNB in Correct Location?

[cyberham]

I have been pushing a 1m Star Choice dish back and forth for days to find 87W. This is usually a simple task here at 64 west longitude since the satellite is 33 degrees elevation here. But I can't find the sat. This dish is a good quality commercial dish similar to a Winegard.

So yesterday in the late afternoon when signals are often strongest, I pointed the dish using my best guesstimate where it should be. I then removed the Geosatpro PLL LNB and physically moved it around the dish surface. Sure enough I received the Patient channel. And the SQ was briefly quite good. But it was difficult to hold the LNB long enough to get a good sense where the best position was.

It seemed the best location was higher than the LNB holder. And maybe slightly closer to the dish. Yet I am using the original holder where it is designed to be mounted. Also, the LNB arm appears to be in original location. The arm has 2 struts holding it.

Today I tried fixing the LNB in different locations using an offset bracket. No results from this so far.

I really want to fix this dish on 87W for LPB for the winter. And to test the second tuner and PIP on the Edision OS Mio+.






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[comfortably_numb]

Any photos?

 

[cyberham]

I've temporarily removed the LNB arm holders. Also, elevation is high in these pics. I'm moving it up and down.

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[a33]

A paraboloid (offset) dish has only one focal point. The location of that can be calculated; if it is a dish with a flat dish face with only three input measures: e.g. height, width, and depth at the center of the paraboloid surface (so measured without the rim!).

When you change the LNB position without changing the elevation, and then get a better reception, it might also be the case that your elevation was not right. So I don't know how you tested your variable LNB position?

Greetz,
A33

 

[cyberham]

Agreed. I assumed the dish elevation must have been off when I held the LNB above the holder. But merely receiving any signal proved line-of-sight to the sat, the LNB, cabling, receiver were functioning and signal from the sat tp was good. And I found signal within minutes while holding the LNB.

Yet after days with the LNB in the correct position I've not received any signal.

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[cyberham]

SQ45% on a data transponder with LNB in this position.

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[a33]

So... is it time for a not-warped check (is it indeed a flat dishface dish?), and some measures...?

Greetz,
A33

 

[cyberham]

That won't be necessary. I decided if the LNB wants to be higher, then I'd accommodate it. I braced the dish with my body and yanked upward on the end of the LNB arm to place the LNB about 8 inches higher. Bang! The data transponder was SQ 70%.

After some final dish tuning and lock down of the bolts, I have the CNN Newsource tp at 71% and dead flat on the microHD signal bar graph. I know from past when you have that on 87W, then you're done. Everything else scans in perfectly. Job finished.

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[a33]

That won't be necessary. I decided if the LNB wants to be higher, then I'd accommodate it. I braced the dish with my body and yanked upward on the end of the LNB arm to place the LNB about 8 inches higher. Bang!

Bang! It's a nice hobby, isn't it?

The LNB now looks dangerously low at the dish, but Bang! Who cares?
That's the spirit!


I had a really good laugh, there. In fact, third time today on satellite forums (I visited about 8, today). Thank you, really appreciate it!

Greetz,
A33

 

[cyberham]

It's great fun...when things go right. The dish is right on the ground but it's OK. We have no pets or kids to run into it. Could bother the raccoons and we had a wild beaver one time. It's much easier working on a dish at ground level. You can sit down while you tinker.

With hindsight, I should have realized earlier something was amiss. When everything is working correctly, and on a clear day, it is simple work to find a satellite high in the sky with a 1m dish and a good receiver.

31 TV channels scanned in.

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[RimaNTSS]

Bang! The data transponder was SQ 70%....the CNN Newsource tp at 71%

It only means that you have got the lock and some kind of reception, nothing more, nothing less. To be sure you have LNB in correct location (as it was questioned in the topic) , you have to make sure that phase center of the LNB and focal point of the antenna are co-located. Do you know where those 2 points are? In addition, you have to point LNB to the right direction toward the face of the dish. Do you know where this point on the surface of the dish is?
So, IMHO, if you do all correctly, you would have better reception performance of your satellite system.

 

[Larry1]

A long time ago I had posted the measurements of the LNBF placement that Winegard faxed to me for the Starchoice 1m dish. Should still be in an old post if I can find it again.

 

[cyberham]

It's possible the LNB arm was bent down in the course of handling and I just returned it to the correct original location. This dish is years old and I don't know its history. Or, it's possible the LNB arm was always in the wrong position since it was used to receive pay TV. Pay TV signals are powerful and LNB location is less critical than for FTA.

Bottom line is the LNB is definitely at the dish focal point now. The results I am obtaining from it confirms this. I have used other dishes to receive 87W and these results are as good as it gets at this location.


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[Larry1]

Here is the fax...
I have penciled in the measurements for the other size Winegard dishes.

 

[cyberham]

I'll take some measurements of my dish tomorrow and compare with these specs.

 

[a33]

Bottom line is the LNB is definitely at the dish focal point now. The results I am obtaining from it confirms this. I have used other dishes to receive 87W and these results are as good as it gets at this location.

Even if you are about at the focal point, the LNB is looking too low on the dish, as I wrote.
So I'll be curious to your measuring results.

(Offset angle of the 1 m dish would be about 23.2 to 23.4 degrees ~ the data from Larry1 are not fully congruent to the two digits behind the decimal point...)

Greetz,
A33

 

[cyberham]

Before going out to take the measurements on my 1m dish, I have recorded 1m C/N values on 87W versus 1.2m values for comparison. See below. These readings were taken on the indicated channels at the same time.

Patient channel
1m: 9.7 dB
1.2 m: 10.6 dB

LPB
1m: 6.7 dB
1.2m: 7.4 dB

Newsource
1m: 6.2 dB
1.2m: 6.7 dB

Florida channel
1m: 10.0 dB
1.2m: 11.5 dB

For this reason, I won't be changing anything on the 1m dish regardless what the measurements indicate since I believe the dish is performing well against the larger 1.2m dish.

 

[cyberham]

Here are measurements taken on the 1m dish.

Dish top to LNB: 37 to 38"
Dish centre to LNB: 24.5 to 26"
Dish bottom to LNB: 24 to 25.5"

The variation is due to where on the LNB you measure.

The distance measured from dish top to LNB suggests I pulled the LNB arm too high. But I pulled the arm up and then tweaked the exact position while watching the SQ on the receiver. So I was effectively tuning the LNB's position.

I'm satisfied I am hitting the dish sweet spot. The PLL LNB may also make up for any small discrepancy for where the LNB is. I'm using the original LNB holder, therefore the LNB is pointing where that holder points it.

In attached pics, you can see original LNB, the fact the dish installation shows the dish is slightly rotated clockwise and the view the LNB sees looking at the dish.

Added: I have another identical dish I used this summer to try to receive PBS on 125W. I failed thinking leaves were blocking the signal. Perhaps I need to try tuning its LNB arm. I will give this another go later after the autumn leaves have fallen.

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