Help Required Av-Comm C Band Waveguide Polariser and a Zinwell Dual Polarity C Band LNBF,

Spiff

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Good afternoon gentlemen the sun is out : )

I have just replaced my C Band LNB which had a dielectric plate.

The replacement is an Av-Comm C Band Waveguide Polariser and a Zinwell Dual Polarity C Band LNBF.

I have done every adjustment, but the results are about the same.

One very odd thing is that the raised points inside the polarizer are not as the images on this forum in image one, but as image two.

In the position I have been told is correct as image one, there are no results,, there are however results as image two ?

I have tried all the sats and stations I had logged before, they are similar or worse but then the signals vary quite a bit.

I checked and the station we were using to set up has circular polorization.

Another question does the orientation skew of the LNB in relation to the sats matter, I thought not with circular polarization ?

One other thing moving the waveguide in relation to the dish peaks the signal, but moving the LNB in and out of the waveguide makes no difference ?

God Bless Spiff
 

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moonbase

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Spiff,

Moving the waveguide in relation to the dish impacts the signal as it is the feed throat aperture of the waveguide that the signal travels into.
Moving the LNB inside the waveguide has no impact on the feed throat aperture distance from the dish and would not be expected to impact signal levels.

It looks like you are using a Precision 1.5m dish with focal length of 546mm?
The opening edge of the AV-COMM polariser barrel nearest to the dish needs to be less distance than the focal length for maximum signal level.
Try it at 541mm and 536mm to see what impact that has on signal levels.

Also, try moving the scalar to different positions on the polariser barrel.
Start it off at 15mm from the end and move it back in 5mm steps to se what impact it has on signal level.

There is quite a bit of trial and error with C-Band to optimise the signal.

Added Note:
I forgot to say that I had better results with the polo pipe using a cheapo skimpy little scalar rather than the meatier chunky scalar that came with the polo pipe.
If you have a skinny wimpy scalar try that and see if it makes any difference.
 

Spiff

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Spiff,

Moving the waveguide in relation to the dish impacts the signal as it is the feed throat aperture of the waveguide that the signal travels into.
Moving the LNB inside the waveguide has no impact on the feed throat aperture distance from the dish and would not be expected to impact signal levels.

It looks like you are using a Precision 1.5m dish with focal length of 546mm?
The opening edge of the AV-COMM polariser barrel nearest to the dish needs to be less distance than the focal length for maximum signal level.
Try it at 541mm and 536mm to see what impact that has on signal levels.

Also, try moving the scalar to different positions on the polariser barrel.
Start it off at 15mm from the end and move it back in 5mm steps to se what impact it has on signal level.

There is quite a bit of trial and error with C-Band to optimise the signal.

Added Note:
I forgot to say that I had better results with the polo pipe using a cheapo skimpy little scalar rather than the meatier chunky scalar that came with the polo pipe.
If you have a skinny wimpy scalar try that and see if it makes any difference.
Hallo Moonbase,

Thank you for your reply : )

I found that the scalar ring position was critical.

I do have a thin one so will try that as well.

Should I reset the orientation of the waveguide to the position in the first image, in relation to the LNBs dipoles and try again from there ?

As it is it only produces a signal when set as in the second image.

From what I have seen and read, the way I have it though it produces a signal is incorrect ?

541mm is the front of the scalar ring at the moment, the polarizer is about half inch further back.

I started with the polarizer at 560mm which was the distance the previous LNB had been at.

I then peaked this polarizer added the scalar ring and peaked that.
 

moonbase

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Spiff,

At 560mm you are 14mm further away from the dish than the focal length.

From my limited knowledge of dish geometry and feed alignment you need the opening rim of the polo pipe to be at a distance that is less than the focal length.
The logic is to get the focal length of the dish to a point inside the polo pipe at a depth whereby the polo pipe is at a distance to be fully illuminated by the dish but close enough not to be gathering noise from ouside the surface of the dish.

My general starting point settings are to secure the polo pipe so that the opening rim nearest to the dish is 5mm less than the focal length of the dish and place the scalar so that the edge of scalar concentric rings is 20mm from the opening rim of the polo pipe. This gives 20mm of polo pipe protruding from the scalar.

You might find that you are restricted in how far back you can slie the scalar along the polo pipe due to the amount the polo pipe has been turned down at the scalar end.
I had my polo pipe modified by getting an additional length turned down on the scalar end to provide more backward adjustment with the scalar.
 

moonbase

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Spiff,

'ere cop for this picture, dont say you never got owt for nowt from moonbase.
Feed Focal Point Depth and Feed Aperture Distances are theoretical and in practice will probably have a +/- variance.

.
Precision 1.5m.jpg
 
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Spiff

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Spiff,

'ere cop for this picture, dont say you never got owt for nowt from moonbase.
Feed Focal Point Depth and Feed Aperture Distances are theoretical and in practice will probably have a +/- variance.

.
View attachment 138398
Thank you Moodbase I have saved and printed that list. : )
 

scopus

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Spiff,

At 560mm you are 14mm further away from the dish than the focal length.

From my limited knowledge of dish geometry and feed alignment you need the opening rim of the polo pipe to be at a distance that is less than the focal length.
The logic is to get the focal length of the dish to a point inside the polo pipe at a depth whereby the polo pipe is at a distance to be fully illuminated by the dish but close enough not to be gathering noise from ouside the surface of the dish.

My general starting point settings are to secure the polo pipe so that the opening rim nearest to the dish is 5mm less than the focal length of the dish and place the scalar so that the edge of scalar concentric rings is 20mm from the opening rim of the polo pipe. This gives 20mm of polo pipe protruding from the scalar.

You might find that you are restricted in how far back you can slie the scalar along the polo pipe due to the amount the polo pipe has been turned down at the scalar end.
I had my polo pipe modified by getting an additional length turned down on the scalar end to provide more backward adjustment with the scalar.
I had to do the same with my polo pipe get some milled off where the scalar goes to get best results. The position of the scalar is critical..My pipe protrudes about a half an inch from the ftont of the plate.20210821_091300.jpg
 

Spiff

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Good evening Scopus,

On mine I do not have to use the scalar rings to mount as in your image.

I made a bracket that has an opening large enough to take the full diameter of the un-turned part of the pipe.

I also have a skimpy scalar ring that has small protrusions on its inside diameter, the part that slides over the pipe.

These could be filled off making the entry large enough to slide back over the un-turned part of the pipe if required.

Will give all these things a try. : )

Still no answer to the polo pipe working in the wrong orientation see my first post.

Is this due to the incorrect focal point ?
 

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Spiff,

At 560mm you are 14mm further away from the dish than the focal length.

From my limited knowledge of dish geometry and feed alignment you need the opening rim of the polo pipe to be at a distance that is less than the focal length.
The logic is to get the focal length of the dish to a point inside the polo pipe at a depth whereby the polo pipe is at a distance to be fully illuminated by the dish but close enough not to be gathering noise from ouside the surface of the dish.

My general starting point settings are to secure the polo pipe so that the opening rim nearest to the dish is 5mm less than the focal length of the dish and place the scalar so that the edge of scalar concentric rings is 20mm from the opening rim of the polo pipe. This gives 20mm of polo pipe protruding from the scalar.

You might find that you are restricted in how far back you can slie the scalar along the polo pipe due to the amount the polo pipe has been turned down at the scalar end.
I had my polo pipe modified by getting an additional length turned down on the scalar end to provide more backward adjustment with the scalar.

.. :Y - some nice set-up guidance given out here MB :Y. Btw, when i ran my Cband set up using the same components my Poloriser tube had the steps positioned on the sides. It can be a bit confusing sometimes if you select the wrong probe H or V when using a twin probe lnbf's such as the Zinwell or TiT types and also the fact that you will be able to have all polarities available to use L/R/H/V depending where the lnbf position within the pol pipe is - after following MB's advice, select a known channel on a satellite with a known polarity, say Vertical, select 13v onto the Zin to activate the V probe, poloriser internal steps located to the sides, rotate the Zinwell until the signal peaks - using a meter with spectrum display will make it easier. Good luck.
 

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I had to do the same with my polo pipe get some milled off where the scalar goes to get best results. The position of the scalar is critical..My pipe protrudes about a half an inch from the ftont of the plate.View attachment 138399



>> "My pipe protrudes about a half an inch" - - yep that's what iv'e heard also :eek:
 

Spiff

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.. :Y - some nice set-up guidance given out here MB :Y. Btw, when i ran my Cband set up using the same components my Poloriser tube had the steps positioned on the sides. It can be a bit confusing sometimes if you select the wrong probe H or V when using a twin probe lnbf's such as the Zinwell or TiT types and also the fact that you will be able to have all polarities available to use L/R/H/V depending where the lnbf position within the pol pipe is - after following MB's advice, select a known channel on a satellite with a known polarity, say Vertical, select 13v onto the Zin to activate the V probe, poloriser internal steps located to the sides, rotate the Zinwell until the signal peaks - using a meter with spectrum display will make it easier. Good luck.
I get the idea thank you John.
 

Spiff

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Thank you all that has answered all my questions. : )

I will start again tomorrow from scratch and follow all of the directions kindly submitted.

God Bless Spiff
 

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Spiff,

At 560mm you are 14mm further away from the dish than the focal length.
Unless it was a parallel universe, Spiff was the owner of a Precision 1.3m reflector which would be quite a lot less for the focal point.
 

Spiff

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Unless it was a parallel universe, Spiff was the owner of a Precision 1.3m reflector which would be quite a lot less for the focal point.
Good evening Channel Hopper,

You are correct I do own a 1.3, but it is used for KU band.

I have a 1.5 for C band as well now.

Bit tight for anything much large, maybe a 1.8 some day could be squeezed in, there is always a way : ).
 

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Thank you all that has answered all my questions. : )

I will start again tomorrow from scratch and follow all of the directions kindly submitted.

God Bless Spiff
Spiff,

Here is a better picture of my pipe and scalar. The Scalar I use is a Chapparal one, I found this the best for my setup..20210904_085326.jpg
 

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Unless it was a parallel universe, Spiff was the owner of a Precision 1.3m reflector which would be quite a lot less for the focal point.


Spiff purchased a Precision 1.5m dish from me and painted it green.
I noticed the dish used by Spiff with the polo pipe was green and looked like it had Precision feed support arm locating points on the dish face.
From these obeservations I made the correct assumption that Spiff was using a Precision 1.5m dish for his C-Band tests.

Welcome to my universe where the focal length of a Precision 1.5m dish is 546mm.
 

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Spiff,

To give you an idea of how the signal levels can vary with feed distance from the dish and scalar position I have attached a table below.
The table was compiled some time ago from 40.5W so the signal levels and frequencies nowadays might have changed, however, the table illustrates the logic.


Table Notes:
1. Precision 2.0m dish with focal length of 755mm was used.
2. Scalar positioned at eight different locations along the polo pipe.
3. Feed positioned at three different distances from the dish at 745mm, 750mm and 755mm

As you can see, the signal levels varied, possibly due to the polo pipe introducing some artefacts.
From my tests, I concluded that the feed and scalar position can be frequency specific, the optimum parameters for one frequency do not always apply globally to all frequencies on a satellite

I think there is a similar table from me for another satellite somewhere in the C-Band section of the forum which ilustrates a similar trend.

.
Feed-Scalar Pairs - 40.5W.jpg
 

Spiff

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Good morning gentleman,

Results so far better than standard dielectric strip, but no better than T piece.

This is an old webpage, about the development of multi polarization LNBs

God Bless Spiff

Hope for new LNBs
 

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Good morning gentleman,

Results so far better than standard dielectric strip, but no better than T piece.

This is an old webpage, about the development of multi polarization LNBs

God Bless Spiff

Hope for new LNBs
I did ask if you wanted the old one back.

I have the short mechanical Prodelin here, (the short r/o one).
It will do a better job than the pipe options but you will need to work out the feedhorn illumination, create a motor drive, and find a 229 flange LNB.
 
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